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background-position: left; width: 550px; min-height: 105px; _height: 105px; background-repeat: no-repeat; '> <div class='titlewrapper' style='background: transparent'> <h1 class='title' style='background: transparent; border-width: 0px'> <a href='http://www.righto.com/'> Ken Shirriff's blog </a> </h1> </div> <div class='descriptionwrapper'> <p class='description'><span>Computer history, restoring vintage computers, IC reverse engineering, and whatever</span></p> </div> </div> </div></div> </div> </div> <div class='header-cap-bottom cap-bottom'> <div class='cap-left'></div> <div class='cap-right'></div> </div> </div> </header> <div class='tabs-outer'> <div class='tabs-cap-top cap-top'> <div class='cap-left'></div> <div class='cap-right'></div> </div> <div class='fauxborder-left tabs-fauxborder-left'> <div class='fauxborder-right tabs-fauxborder-right'></div> <div class='region-inner tabs-inner'> <div class='tabs no-items section' id='crosscol'></div> <div class='tabs no-items section' id='crosscol-overflow'></div> </div> </div> <div class='tabs-cap-bottom cap-bottom'> <div class='cap-left'></div> <div class='cap-right'></div> </div> </div> <div class='main-outer'> <div class='main-cap-top cap-top'> <div class='cap-left'></div> <div class='cap-right'></div> </div> <div class='fauxborder-left main-fauxborder-left'> <div class='fauxborder-right main-fauxborder-right'></div> <div class='region-inner main-inner'> <div class='columns fauxcolumns'> <div class='fauxcolumn-outer fauxcolumn-center-outer'> <div class='cap-top'> <div class='cap-left'></div> <div class='cap-right'></div> </div> <div class='fauxborder-left'> <div class='fauxborder-right'></div> <div class='fauxcolumn-inner'> </div> </div> <div class='cap-bottom'> <div class='cap-left'></div> <div class='cap-right'></div> </div> </div> <div class='fauxcolumn-outer fauxcolumn-left-outer'> <div class='cap-top'> <div class='cap-left'></div> <div class='cap-right'></div> </div> <div class='fauxborder-left'> <div class='fauxborder-right'></div> <div class='fauxcolumn-inner'> </div> </div> <div class='cap-bottom'> <div class='cap-left'></div> <div class='cap-right'></div> </div> </div> <div class='fauxcolumn-outer fauxcolumn-right-outer'> <div class='cap-top'> <div class='cap-left'></div> <div class='cap-right'></div> </div> <div class='fauxborder-left'> <div class='fauxborder-right'></div> <div class='fauxcolumn-inner'> </div> </div> <div class='cap-bottom'> <div class='cap-left'></div> <div class='cap-right'></div> </div> </div>  <div class='columns-inner'> <div class='column-center-outer'> <div class='column-center-inner'> <div class='main section' id='main'><div class='widget Blog' data-version='1' id='Blog1'> <div class='blog-posts hfeed'> <div class="date-outer"> <div class="date-posts"> <div class='post-outer'> <div class='post hentry' itemprop='blogPost' itemscope='itemscope' itemtype='http://schema.org/BlogPosting'> <meta content='https://static.righto.com/images/oq-ecl/die-w700.jpg' itemprop='image_url'/> <meta content='6264947694886887540' itemprop='blogId'/> <meta content='7703953794742767286' itemprop='postId'/> <a name='7703953794742767286'></a> <h3 class='post-title entry-title' itemprop='name'> <a href='http://www.righto.com/2021/04/reverse-engineering-vintage-ornor-chip.html'>Reverse-engineering a vintage OR/NOR chip</a> </h3> <div class='post-header'> <div class='post-header-line-1'></div> </div> <div class='post-body entry-content' id='post-body-7703953794742767286' itemprop='description articleBody'> <style type="text/css"> .hilite {cursor:zoom-in} a:link img.hilite, a:visited img.hilite { color: #fff;} span.wm {text-decoration: underline; text-decoration-skip-ink: none}; </style> <p>Recently, I received a die photo of a mystery integrated circuit, the OQ100,<span id="fnref:philips"><a class="ref" href="#fn:philips">1</a></span> from <a href="https://www.instagram.com/evilmonkeyzdesignz">EvilMonkeyDesignz</a>. I analyzed the die photo and found that it is a logic chip implemented with fast ECL (Emitter-Coupled Logic) circuitry, probably from the early 1970s. The chip contains three logic gates, two with 2 inputs and one with 4 inputs. Each gate has non-inverted and inverted outputs, acting as both an OR gate and a NOR gate. This blog post summarizes my investigation. (I also recently analyzed the <a href="https://www.righto.com/2021/04/reverse-engineering-vintage-comparator.html">OQ104</a>, a different chip in this series.)</p> <p><a href="https://static.righto.com/images/oq-ecl/die.jpg"><img alt="Die photo of the Philips QC100 chip. Click this photo (or any other) for a larger version. Photo courtesy of EvilMonkeyDesignz." class="hilite" height="543" src="https://static.righto.com/images/oq-ecl/die-w700.jpg" title="Die photo of the Philips QC100 chip. Click this photo (or any other) for a larger version. Photo courtesy of EvilMonkeyDesignz." width="700" /></a><div class="cite">Die photo of the Philips QC100 chip. Click this photo (or any other) for a larger version. Photo courtesy of <a href="https://www.instagram.com/evilmonkeyzdesignz">EvilMonkeyDesignz</a>.</div></p> <p>The die photo above shows the chip under the microscope. Most of the silicon appears bright pink in this image. Regions of silicon with different doping appear green or yellowish and form the transistors and resistors of the chip. The speckled regions are the metal layer on top of the silicon, wiring the circuitry together. Around the edges, the black bond wires connect the chip to the external pins.</p> <h2>The chip's components</h2> <p>Transistors are the key components in a chip. This chip uses a type of transistor called an NPN transistor. The photo below shows a transistor as it appears on the chip. Underneath the photo is a cross-section drawing showing approximately how the transistor is constructed. The transistor is more complicated than the N-P-N sandwich you see in books, but if you look carefully at the vertical cross-section below the 'E', you can find the N-P-N layers that form the transistor. The emitter (E) wire is connected to N+ silicon. Below that is a P layer connected to the base contact (B). And below that is an N layer connected to the collector (C).</p> <p><a href="https://static.righto.com/images/oq-ecl/transistor-structure-npn.jpg"><img alt="Structure of an NPN transistor. Top: transistor as it appears on the die. Bottom: cross-section diagram." class="hilite" height="328" src="https://static.righto.com/images/oq-ecl/transistor-structure-npn-w350.jpg" title="Structure of an NPN transistor. Top: transistor as it appears on the die. Bottom: cross-section diagram." width="350" /></a><div class="cite">Structure of an NPN transistor. Top: transistor as it appears on the die. Bottom: cross-section diagram.</div></p> <p>The chip also uses a few PNP transistors. Although you might expect a PNP transistor to simply be the reverse of an NPN transistor, it has a different structure, with the regions arranged laterally instead of vertically. The collector and base form concentric square rings around the emitter. The base wire is not connected to the base region directly. Instead, the wire is at a distance, and the base signal travels underneath through the N layer.</p> <p><a href="https://static.righto.com/images/oq-ecl/transistor-structure-pnp.jpg"><img alt="Structure of a PNP transistor. Top: transistor as it appears on the die. Bottom: cross-section diagram." class="hilite" height="376" src="https://static.righto.com/images/oq-ecl/transistor-structure-pnp-w350.jpg" title="Structure of a PNP transistor. Top: transistor as it appears on the die. Bottom: cross-section diagram." width="350" /></a><div class="cite">Structure of a PNP transistor. Top: transistor as it appears on the die. Bottom: cross-section diagram.</div></p> <p>The PNP transistors in this chip have another complication. The collector is split, so the transistor has two collectors. Moreover, one of the collectors is wired directly to the base. In the photo above, you can see how the collector region is split vertically, so there is one collector on the left and one on the right, with collector on the right connected to the base. This construction may seem bizarre, but it is common in integrated circuits. The motivation is to build a current mirror, where both collectors pass the same current.</p> <p>The other key components of this chip are the resistors. The photo below shows two resistors as they appear on the die. The resistors are formed from strips of higher-resistance P silicon, which appears pink in the die photos. Each end of a resistor is connected to the metal layer; the metal in the middle connects the two resistors together in series. (A metal wire also passes over the resistor but is not connected.) A resistor has higher resistance if it is longer and narrower, so these resistors have relatively high resistance.<span id="fnref:ratio"><a class="ref" href="#fn:ratio">2</a></span> Resistors are relatively large on an integrated circuit and fairly inaccurate.</p> <p><a href="https://static.righto.com/images/oq-ecl/resistors.jpg"><img alt="Two resistors as they appear on the die." class="hilite" height="158" src="https://static.righto.com/images/oq-ecl/resistors-w600.jpg" title="Two resistors as they appear on the die." width="600" /></a><div class="cite">Two resistors as they appear on the die.</div></p> <h2>The circuitry</h2> <p>Once the components can be recognized on the die, the circuit can be traced out and reverse-engineered. But before I describe the complete circuit, I'll explain how ECL (Emitter-Coupled Logic) works.<span id="fnref:ecl"><a class="ref" href="#fn:ecl">3</a></span> The schematic below shows a differential pair, or long-tailed pair, which amplifies the difference between its two inputs. (This circuit is also common in analog circuits, forming the heart of an op-amp.) The basic idea is that a current sink (the circle at the bottom) generates a fixed current <em>I</em>. This current gets split between the left path (<em>I1</em>) and the right path (<em>I2</em>). If the transistor on the left has a higher input voltage than the transistor on the right, most of the current will go to the left. But if the transistor on the right has a higher input, most of the current will go to the right. This circuit amplifies the voltage difference: even a small difference between the two inputs will switch most of the current from one side to the other.</p> <p><a href="https://static.righto.com/images/oq-ecl/differential-pair.jpg"><img alt="Schematic of a simple differential pair circuit. The current sink sends a fixed current I through the differential pair. If the two inputs are equal, the current is split equally between the two branches. Otherwise, the branch with the higher input voltage gets most of the current." class="hilite" height="303" src="https://static.righto.com/images/oq-ecl/differential-pair-w250.jpg" title="Schematic of a simple differential pair circuit. The current sink sends a fixed current I through the differential pair. If the two inputs are equal, the current is split equally between the two branches. Otherwise, the branch with the higher input voltage gets most of the current." width="250" /></a><div class="cite">Schematic of a simple differential pair circuit. The current sink sends a fixed current I through the differential pair. If the two inputs are equal, the current is split equally between the two branches. Otherwise, the branch with the higher input voltage gets most of the current.</div></p> <p>To make this into an OR gate, we can put multiple transistors on the left. If any input is high, the current will be switched to the left, otherwise the current will be switched to the right. Since the current pulls that side low, the left branch will be the NOR output while the right branch will be the OR output. (With ECL, you get both the complemented and uncomplemented outputs "for free".) The schematic below shows how one logic gate is implemented; this is a two-input gate. The gate uses a second differential pair to buffer and amplify the outputs. The current sink circuit is discussed in a footnote.<span id="fnref:sink"><a class="ref" href="#fn:sink">4</a></span></p> <p><a href="https://static.righto.com/images/oq-ecl/gate-schematic.jpg"><img alt="Schematic of one logic gate." class="hilite" height="390" src="https://static.righto.com/images/oq-ecl/gate-schematic-w500.jpg" title="Schematic of one logic gate." width="500" /></a><div class="cite">Schematic of one logic gate.</div></p> <p>The diagram below shows how the four-input gate is implemented on the die. The majority of the area is occupied by the current sink and the associated resistors. The NPN and PNP transistors are relatively compact, but the resistors occupy a lot of space. At the bottom, the four input transistors implement the OR function, along with the reference transistor on the other branch. The output transistors are larger so they can provide more current.</p> <p><a href="https://static.righto.com/images/oq-ecl/gate-labeled.jpg"><img alt="One gate with functional blocks labeled." class="hilite" height="631" src="https://static.righto.com/images/oq-ecl/gate-labeled-w400.jpg" title="One gate with functional blocks labeled." width="400" /></a><div class="cite">One gate with functional blocks labeled.</div></p> <p>The diagram below shows how the three gates are arranged on the die. (The gate described above is at the right.) The voltage divider resistors provide a voltage reference for the current sources.</p> <p><a href="https://static.righto.com/images/oq-ecl/die-labeled.jpg"><img alt="The die with major functional blocks labeled." class="hilite" height="475" src="https://static.righto.com/images/oq-ecl/die-labeled-w600.jpg" title="The die with major functional blocks labeled." width="600" /></a><div class="cite">The die with major functional blocks labeled.</div></p> <p>Putting everything together, the diagram below shows how the circuitry of the chip maps onto its 16 pins. The three OR gates are represented by the OR symbols; the gate on the right has four inputs. Each gate has a non-inverted output and an inverted output, which is indicated by a bubble. I don't know what voltages the chip takes, so I've indicated the power pins with + and -.</p> <p><a href="https://static.righto.com/images/oq-ecl/pinout.jpg"><img alt="Reverse-engineered pinout of the chip." class="hilite" height="198" src="https://static.righto.com/images/oq-ecl/pinout-w350.jpg" title="Reverse-engineered pinout of the chip." width="350" /></a><div class="cite">Reverse-engineered pinout of the chip.</div></p> <p>I announce my latest blog posts on Twitter, so follow me <a href="https://twitter.com/kenshirriff">@kenshirriff</a>. Many thanks to EvilMonkeyz Designs for providing the photos; follow on <a href="https://www.instagram.com/evilmonkeyzdesignz">Instagram</a> or <a href="https://twitter.com/EvilMnkyzDsignz">Twitter</a> for more interesting die photos.</p> <h2>Notes</h2> <div class="footnote"> <ol> <li id="fn:philips"> <p>A reader said that Philips used the OQ designation for their custom integrated circuits. That would explain why I was unable to find these chips in a databook. <a class="footnote-backref" href="#fnref:philips" title="Jump back to footnote 1 in the text">↩</a></p> </li> <li id="fn:ratio"> <p>The resistance of a resistor is proportional to the length divided by the width. To understand this, note that a region twice as long is the same as two resistors in series, so it has twice the resistance. A region twice as wide is the same as two resistors in parallel, so it has half the resistance. <a class="footnote-backref" href="#fnref:ratio" title="Jump back to footnote 2 in the text">↩</a></p> </li> <li id="fn:ecl"> <p>The logic circuit on this chip has a couple of differences from standard ECL gates. A typical ECL gate has inputs on one branch and a reference voltage connected to the transistor on the other branch. Thus, an input higher than the reference voltage is a logic 1, and an input lower than the reference voltage in a logic 0. This gate, however, uses the output of the first branch as the input to the second branch. If an input is high, it pulls this output low, shutting off the other branch. Conversely, if the input is low, the output goes high, turning on the other branch.</p> <p>I'm not sure what the motivation is for this design. It looks a bit like NTL (Non-Threshold Logic), since there isn't a threshold set by a reference voltage. One possibility is that the circuit implements a Schmitt-trigger, a circuit with hysteresis, where once it turns on, the input must drop significantly lower to turn it off.</p> <p>The second difference between this circuit and a typical ECL gate is the output buffer. ECL gates typically use an emitter follower, rather than a second differential pair. <a class="footnote-backref" href="#fnref:ecl" title="Jump back to footnote 3 in the text">↩</a></p> </li> <li id="fn:sink"> <p>I'll just briefly describe the current sink circuit, shown below. Two large resistors form a voltage divider that produces a reference voltage midway between the two supply voltages (maybe 0 volts). Due to the behavior of transistors, V<sub>BE</sub> will be one diode drop (~0.7 V). The rest of the circuit generates the "correct" current through the lower-right resistor to achieve this voltage drop. On the chip, the two PNP transistors at the top are one transistor with two collectors. They implement a current mirror, where the current through the right transistor matches the current through the left transistor.</p> <p><a href="https://static.righto.com/images/oq-ecl/current-schematic.jpg"><img alt="The current sink circuit used in the chip. The divider is shared by all the current sinks on the chip." class="hilite" height="304" src="https://static.righto.com/images/oq-ecl/current-schematic-w300.jpg" title="The current sink circuit used in the chip. The divider is shared by all the current sinks on the chip." width="300" /></a><div class="cite">The current sink circuit used in the chip. The divider is shared by all the current sinks on the chip.</div></p> <p> <a class="footnote-backref" href="#fnref:sink" title="Jump back to footnote 4 in the text">↩</a></p> </li> </ol> </div> <div style='clear: both;'></div> </div> <div class='post-footer'> <div class='post-footer-line post-footer-line-1'><span class='post-comment-link'> <a class='comment-link' href='https://www.blogger.com/comment/fullpage/post/6264947694886887540/7703953794742767286' onclick=''> 4 comments: </a> </span> <span class='post-icons'> <span class='item-action'> <a href='https://www.blogger.com/email-post.g?blogID=6264947694886887540&postID=7703953794742767286' title='Email Post'> <img alt='' class='icon-action' height='13' src='http://img1.blogblog.com/img/icon18_email.gif' width='18'/> </a> </span> <span class='item-control blog-admin pid-1138732533'> <a href='https://www.blogger.com/post-edit.g?blogID=6264947694886887540&postID=7703953794742767286&from=pencil' title='Edit Post'> <img alt='' class='icon-action' height='18' src='https://resources.blogblog.com/img/icon18_edit_allbkg.gif' width='18'/> </a> </span> </span> <span class='post-backlinks post-comment-link'> </span> <div class='post-share-buttons goog-inline-block'> <a class='goog-inline-block share-button sb-email' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=7703953794742767286&target=email' target='_blank' title='Email This'><span class='share-button-link-text'>Email This</span></a><a class='goog-inline-block share-button sb-blog' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=7703953794742767286&target=blog' onclick='window.open(this.href, "_blank", "height=270,width=475"); return false;' target='_blank' title='BlogThis!'><span class='share-button-link-text'>BlogThis!</span></a><a class='goog-inline-block share-button sb-twitter' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=7703953794742767286&target=twitter' target='_blank' title='Share to X'><span class='share-button-link-text'>Share to X</span></a><a class='goog-inline-block share-button sb-facebook' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=7703953794742767286&target=facebook' onclick='window.open(this.href, "_blank", "height=430,width=640"); return false;' target='_blank' title='Share to Facebook'><span class='share-button-link-text'>Share to Facebook</span></a><a class='goog-inline-block share-button sb-pinterest' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=7703953794742767286&target=pinterest' target='_blank' title='Share to Pinterest'><span class='share-button-link-text'>Share to Pinterest</span></a> </div> </div> <div class='post-footer-line post-footer-line-2'><span class='post-labels'> Labels: <a href='http://www.righto.com/search/label/chips' rel='tag'>chips</a>, <a href='http://www.righto.com/search/label/electronics' rel='tag'>electronics</a>, <a href='http://www.righto.com/search/label/reverse-engineering' rel='tag'>reverse-engineering</a> </span> </div> <div class='post-footer-line post-footer-line-3'></div> </div> </div> </div> </div></div> <div class="date-outer"> <div class="date-posts"> <div class='post-outer'> <div class='post hentry' itemprop='blogPost' itemscope='itemscope' itemtype='http://schema.org/BlogPosting'> <meta content='https://static.righto.com/images/comparator/die-labeled2-w600.jpg' itemprop='image_url'/> <meta content='6264947694886887540' itemprop='blogId'/> <meta content='3536366513333877606' itemprop='postId'/> <a name='3536366513333877606'></a> <h3 class='post-title entry-title' itemprop='name'> <a href='http://www.righto.com/2021/04/reverse-engineering-vintage-comparator.html'>Reverse-engineering a vintage comparator chip</a> </h3> <div class='post-header'> <div class='post-header-line-1'></div> </div> <div class='post-body entry-content' id='post-body-3536366513333877606' itemprop='description articleBody'> <style type="text/css"> .hilite {cursor:zoom-in} a:link img.hilite, a:visited img.hilite { color: #fff;} span.wm {text-decoration: underline; text-decoration-skip-ink: none}; </style> <p>I recently saw an interesting die photo of an unknown chip <a href="https://twitter.com/EvilMnkyzDsignz/status/1381991092929761284">on Twitter</a>, so I did some analysis of it. Looking at the circuitry inside, the chip appears to be four comparators, probably in the ECL (Emitter Coupled Logic) family. This is a quick blog post to summarize my investigation.</p> <p>The die photo below shows the chip under the microscope. Regions of the silicon appear pink, blue, or yellow, depending on how the silicon was doped. The speckled regions are the metal layer on top of the silicon, wiring the circuitry together. Around the edges, the black bond wires connect the chip to the external pins. These wires are attached to the square bond pads. The die has four blocks of circuitry, one for each of its four comparators. Much of the die is unused, especially the large metal area in the middle. Because this chip's circuitry is relatively simple, it only uses a fraction of the available space.</p> <p><a href="https://static.righto.com/images/comparator/die-labeled2.jpg"><img alt="The chip with pins labeled. Click this photo (or any other) for a larger version. Photo courtesy of EvilMonkeyDesignz." class="hilite" height="431" src="https://static.righto.com/images/comparator/die-labeled2-w600.jpg" title="The chip with pins labeled. Click this photo (or any other) for a larger version. Photo courtesy of EvilMonkeyDesignz." width="600" /></a><div class="cite">The chip with pins labeled. Click this photo (or any other) for a larger version. Photo courtesy of <a href="https://www.instagram.com/evilmonkeyzdesignz">EvilMonkeyDesignz</a>.</div></p> <p>The photo below shows the chip with its metal lid removed. Modern chips are usually in a black epoxy package, but this chip has a white ceramic package. The tiny silicon die is visible in the middle, with bond wires connecting the die to the lead frame, the metal connections to the chip's gold-plated pins. The metal layer on top of the die is visible, and can be matched with the die photo above. The semi-circular notch on the left indicates the orientation of the chip; the "P" is pin 1.</p> <p><a href="https://static.righto.com/images/comparator/chip.jpg"><img alt="The chip with the metal lid removed, showing the tiny silicon die inside. Photo courtesy of EvilMonkeyDesignz." class="hilite" height="300" src="https://static.righto.com/images/comparator/chip-w300.jpg" title="The chip with the metal lid removed, showing the tiny silicon die inside. Photo courtesy of EvilMonkeyDesignz." width="300" /></a><div class="cite">The chip with the metal lid removed, showing the tiny silicon die inside. Photo courtesy of <a href="https://www.instagram.com/evilmonkeyzdesignz">EvilMonkeyDesignz</a>.</div></p> <h2>The chip's components</h2> <p>Transistors are the key components in a chip. This chip uses a type of transistor called the NPN transistor. The photo below shows a transistor as it appears on the chip. The orange and blue colors are regions of silicon that have been doped differently, forming N and P regions. The speckled areas are the metal layer of the chip on top of the silicon—these form the wires connecting to the transistor's collector, emitter, and base.</p> <p>Underneath the photo is a cross-section drawing showing approximately how the transistor is constructed. There's a lot more than just the N-P-N sandwich you see in books, but if you look carefully at the vertical cross-section below the 'E', you can find the N-P-N that forms the transistor. The emitter (E) wire is connected to N+ silicon. Below that is a P layer connected to the base contact (B). And below that is an N+ layer connected (indirectly) to the collector (C). The emitter, base, and collector can be distinguished on the die with careful examination. The base's region surrounds the emitter, forming a blue rectangle. The collector contact is larger and off to the side.</p> <p><a href="https://static.righto.com/images/comparator/transistor-structure.jpg"><img alt="Structure of an NPN transistor. Top: transistor as it appears on the die. Bottom: cross-section diagram." class="hilite" height="440" src="https://static.righto.com/images/comparator/transistor-structure-w350.jpg" title="Structure of an NPN transistor. Top: transistor as it appears on the die. Bottom: cross-section diagram." width="350" /></a><div class="cite">Structure of an NPN transistor. Top: transistor as it appears on the die. Bottom: cross-section diagram.</div></p> <p>The other key components of this chip are the resistors. The photo below shows two resistors as they appear on the die. The resistors are formed from strips of higher-resistance P silicon, which appears blue in the die photos. The two ends of each resistor are connected to the metal layer. A resistor has higher resistance if it is longer and narrower. While one resistor below is a simple rectangle, the other has a complex zig-zag shape to fit more length into the available space. (The blue rectangle in the lower right is a transistor, not a resistor. To distinguish it from a resistor, note that it has three contacts, and the two contacts on the rectangle are not symmetrical.)</p> <p><a href="https://static.righto.com/images/comparator/resistors.jpg"><img alt="Two resistors as they appear on the die." class="hilite" height="308" src="https://static.righto.com/images/comparator/resistors-w400.jpg" title="Two resistors as they appear on the die." width="400" /></a><div class="cite">Two resistors as they appear on the die.</div></p> <h2>The circuitry</h2> <p>Once the components can be recognized on the die, the circuit can be traced out and reverse-engineered. But before I describe the complete circuit, I'll explain one important functional block.</p> <p>The schematic below shows a differential pair, or long-tailed pair, which amplifies the difference between its two inputs. This circuit is common in analog circuits, forming the heart of an op-amp. It is also the basis of Emitter-Coupled Logic (ECL). The basic idea is that a current sink (the two circles at the bottom) generates a fixed current <em>I</em>. This current gets split between the left path (<em>I1</em>) and the right path (<em>I2</em>). If the transistor on the left has a higher input voltage than the transistor on the right, most of the current will go to the left. But if the transistor on the right has a higher input, most of the current will go to the right. This circuit amplifies the voltage difference: even a small difference between the two inputs will switch most of the current from one side to the other.</p> <p><a href="https://static.righto.com/images/comparator/differential-pair.png"><img alt="Schematic of a simple differential pair circuit. The current sink sends a fixed current I through the differential pair. If the two inputs are equal, the current is split equally between the two branches. Otherwise, the branch with the higher input voltage gets most of the current." class="hilite" height="299" src="https://static.righto.com/images/comparator/differential-pair-w250.png" title="Schematic of a simple differential pair circuit. The current sink sends a fixed current I through the differential pair. If the two inputs are equal, the current is split equally between the two branches. Otherwise, the branch with the higher input voltage gets most of the current." width="250" /></a><div class="cite">Schematic of a simple differential pair circuit. The current sink sends a fixed current I through the differential pair. If the two inputs are equal, the current is split equally between the two branches. Otherwise, the branch with the higher input voltage gets most of the current.</div></p> <p>In this chip, the circuit is used as a comparator, a circuit that compares the two inputs and generates a logic output that indicates which input is higher. The side with the current will get pulled low, while the other side is pulled high by the resistor. Thus, the output can be treated as a logic signal.</p> <p>The schematic below shows the circuitry for one of the four comparators on the chip. Note that the differential amplifier circuit above is used twice. For better performance, the output from the first differential amplifier is fed into a second differential amplifier. This sharpens the output: if the inputs are close together, the outputs from the first stage may not be fully "0" or "1". The second stage amplifies this difference, providing solid "0" and "1" outputs. The current sinks provide a relatively constant current for the amplifiers, but I won't explain them in detail.</p> <p><a href="https://static.righto.com/images/comparator/schematic-labeled2.jpg"><img alt="Schematic of one comparator." class="hilite" height="547" src="https://static.righto.com/images/comparator/schematic-labeled2-w500.jpg" title="Schematic of one comparator." width="500" /></a><div class="cite">Schematic of one comparator.</div></p> <p>The diagram below shows the circuitry on the die, corresponding to the schematic above. The red boxes indicate the transistors for the two amplifier stages and their associated current sinks. The other components are the resistors, which appear as blue rectangles. The wiring in the metal layer connects the components together, as well as the inputs on the left and the output at the top.</p> <p><a href="https://static.righto.com/images/comparator/circuit-labeled.jpg"><img alt="One comparator, as it appears on the die." class="hilite" height="504" src="https://static.righto.com/images/comparator/circuit-labeled-w500.jpg" title="One comparator, as it appears on the die." width="500" /></a><div class="cite">One comparator, as it appears on the die.</div></p> <p>The diagram below shows how the circuitry of the chip maps onto its 16 pins. Each triangle represents a comparator with its positive and negative inputs. Two of the comparators have a single output, while two also have an inverted output (indicated by a bubble).</p> <p><a href="https://static.righto.com/images/comparator/pinout.jpg"><img alt="Reverse-engineered pinout of the chip." class="hilite" height="224" src="https://static.righto.com/images/comparator/pinout-w400.jpg" title="Reverse-engineered pinout of the chip." width="400" /></a><div class="cite">Reverse-engineered pinout of the chip.</div></p> <h2>Conclusion</h2> <p>So what is this chip? Maybe it's simply four comparators, but they could have a specific purpose. The chip could be a converter for four differential input signals, e.g. DCS (Differential Current Switch) logic. Another chip in the family seems to be Emitter-Coupled Logic, so this chip could be four ECL inverters (but it doesn't make sense to have four pins for the reference voltage). It's a bit puzzling that two comparators have inverted and noninverted outputs, while two have single outputs.</p> <p>Based on the circuitry and ceramic packaging of this chip, I estimate that it is from around 1970. The chip is labeled "OQ104", so I did a bunch of searching through old databooks, but I couldn't find anything that matches it. Since the chip looks like ECL and has the part number 104, it's tempting to think that the chip might be the 10,104 part in the <a href="http://www.bitsavers.org/components/motorola/_dataBooks/1974_MECL_Integrated_Circuits_Series_A_Vol4.pdf">MECL 10,000 series</a>. Unfortunately, the 10,104 is a quad AND gate, and the internal circuitry is different. The "P" on the chip might indicate Philips, but I couldn't find any matching Philips components. For now, the exact identity of this chip is a mystery.</p> <p>I announce my latest blog posts on Twitter, so follow me <a href="https://twitter.com/kenshirriff">@kenshirriff</a>. Many thanks to EvilMonkeyz Designs for providing the photos; follow on <a href="https://www.instagram.com/evilmonkeyzdesignz">Instagram</a> or <a href="https://twitter.com/EvilMnkyzDsignz">Twitter</a> for more interesting die photos.</p> <div style='clear: both;'></div> </div> <div class='post-footer'> <div class='post-footer-line post-footer-line-1'><span class='post-comment-link'> <a class='comment-link' href='https://www.blogger.com/comment/fullpage/post/6264947694886887540/3536366513333877606' onclick=''> 7 comments: </a> </span> <span class='post-icons'> <span class='item-action'> <a href='https://www.blogger.com/email-post.g?blogID=6264947694886887540&postID=3536366513333877606' title='Email Post'> <img alt='' class='icon-action' height='13' src='http://img1.blogblog.com/img/icon18_email.gif' width='18'/> </a> </span> <span class='item-control blog-admin pid-1138732533'> <a 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class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2022/08/'> August </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2022/07/'> July </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2022/06/'> June </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2022/05/'> May </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2022/04/'> April </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2022/03/'> March </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2022/02/'> February </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2022/01/'> January </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate expanded'> <a class='toggle' href='javascript:void(0)'> <span class='zippy toggle-open'> ▼  </span> </a> <a class='post-count-link' href='http://www.righto.com/2021/'> 2021 </a> <span class='post-count' dir='ltr'>(26)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2021/12/'> December </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2021/11/'> November </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2021/09/'> September </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2021/08/'> August </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2021/07/'> July </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2021/06/'> June </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2021/05/'> May </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate expanded'> <a class='toggle' href='javascript:void(0)'> <span class='zippy toggle-open'> ▼  </span> </a> <a class='post-count-link' href='http://www.righto.com/2021/04/'> April </a> <span class='post-count' dir='ltr'>(2)</span> <ul class='posts'> <li><a href='http://www.righto.com/2021/04/reverse-engineering-vintage-ornor-chip.html'>Reverse-engineering a vintage OR/NOR chip</a></li> <li><a href='http://www.righto.com/2021/04/reverse-engineering-vintage-comparator.html'>Reverse-engineering a vintage comparator chip</a></li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2021/03/'> March </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2021/02/'> February </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2021/01/'> January </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/'> 2020 </a> <span class='post-count' dir='ltr'>(33)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/12/'> December </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/11/'> November </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/10/'> October </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/09/'> September </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/08/'> August </a> <span class='post-count' dir='ltr'>(5)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/07/'> July </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/06/'> June </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/05/'> May </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/04/'> April </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/03/'> March </a> <span class='post-count' dir='ltr'>(5)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/01/'> January </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2019/'> 2019 </a> <span class='post-count' dir='ltr'>(18)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2019/11/'> November </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2019/10/'> October </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2019/09/'> September </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2019/08/'> August </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2019/07/'> July </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2019/04/'> April </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2019/02/'> February </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2019/01/'> January </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/'> 2018 </a> <span class='post-count' dir='ltr'>(17)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/12/'> December </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/09/'> September </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/08/'> August </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/06/'> June </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/05/'> May </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/04/'> April </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/03/'> March </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/02/'> February </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/01/'> January </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/'> 2017 </a> <span class='post-count' dir='ltr'>(21)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/12/'> December </a> <span class='post-count' dir='ltr'>(5)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/11/'> November </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/10/'> October </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/08/'> August </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/07/'> July </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/06/'> June </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/04/'> April </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/03/'> March </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/02/'> February </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/01/'> January </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2016/'> 2016 </a> <span class='post-count' dir='ltr'>(34)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2016/12/'> December </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2016/10/'> October </a> <span class='post-count' dir='ltr'>(5)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2016/09/'> September </a> <span class='post-count' dir='ltr'>(8)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2016/08/'> August </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> 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