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ADR-0042 - Revision history
2026-09-04T12:34:46Z
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Ronald: add breadcrumb navigation
2026-09-04T09:17:58Z
<p>add breadcrumb navigation</p>
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<tr><td colspan="2" class="diff-side-deleted"></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;"></ins></div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>== ADR-0042: Ahuja over Miller compensation for the ramp-generator OTA ==</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>== ADR-0042: Ahuja over Miller compensation for the ramp-generator OTA ==</div></td></tr>
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Ronald
https://wiki3.rohmega.com/index.php?title=ADR-0042&diff=19&oldid=prev
Ronald: showcase seed
2026-09-04T09:13:17Z
<p>showcase seed</p>
<p><b>New page</b></p><div>== ADR-0042: Ahuja over Miller compensation for the ramp-generator OTA ==<br />
<br />
{| class="wikitable"<br />
|-<br />
| '''ID''' || ADR-0042<br />
|-<br />
| '''Status''' || accepted<br />
|-<br />
| '''Date''' || 2026-05-20<br />
|-<br />
| '''Chips''' || RC2.0<br />
|-<br />
| '''Blocks''' || ramp-generator, OTA<br />
|-<br />
| '''Sources''' || [[Timeline|timeline/weekly/2026-W20.md]]<br />
|}<br />
<br />
=== Context ===<br />
The ramp-generator OTA needed frequency compensation. Two candidates: classic Miller compensation, and Ahuja (cascode) compensation.<br />
<br />
=== Decision ===<br />
Use '''Ahuja compensation'''. It gives better power-supply rejection and removes the feedforward zero that Miller introduces, at the cost of an extra bias branch.<br />
<br />
=== Rejected alternatives and why ===<br />
* '''Miller compensation''' โ simpler, but the feedforward zero degrades phase margin at the ramp speeds required, and PSRR is worse on the noisy 28nm supply.<br />
<br />
=== Consequences ===<br />
* Extra current in the cascode branch within power budget.<br />
* PSRR improved enough to sit on the dirty supply without a dedicated LDO for this block.<br />
<br />
=== What would make us revisit this ===<br />
A move to a cleaner supply rail for the ramp generator, or a power budget cut that makes the extra branch unacceptable.</div>
Ronald