[sdiy] OTA diodes

Ian Fritz ijfritz at comcast.net
Sat Jun 14 22:11:51 CEST 2014


I'm a bit rusty on this, but I believe keeping the top of the current 
mirrors at ~2V reduces the Early effect and reduces the common mode voltage 
into the opamp I/V converter.

Ian

At 01:01 PM 6/14/2014, Justin Owen wrote:
>In Electronotes EN62 pg12 (one of the pages that is publicly available 
>AFAIK...) there is a schematic of a basic OTA where the top current mirror 
>hangs off a 680R resistor with 3 diodes to GND. I remember seeing this in 
>another discrete OTA schem but never in the simplified schematics of the 
>major production OTA's.
>
>Recently I noticed that the simplified 2164 schematic uses a similar 
>config - but in a different way (I think...).
>
>What are these doing, what purpose do they serve, what are they improving? 
>I'd be particularly interested in answers from an OTA POV.
>
>Thanks!
>
>- Justin
>
>
>
>
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