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2nd order sigma-delta opamp criteria

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mitrobge

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Sigma delta opamp choise

Which are some criteria to choose appropriately the type of an amplifier in a 2nd order sigma-delta modulator beside tha gain and the cut-off frequency?
I am actually new in this topic and i do not really understand in deep the differences between folded,folded-cascoded,AB class amplifiers etc.
Please give me some advices.
 

Re: Sigma delta opamp choise

Very High gain is not really that critical in Sigma delta. One thing you should take care of is very high gain bandwidth. Another thing is that it should be mostly having a single dominant pole. In 2-stage sigma delta, the first stage will take care of low frequency errors and the second stage of high frequency errors......
 

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    mitrobge

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Sigma delta opamp choise

As usually, there's no "one-size-fits-all" answer..
The algorithm for choosing OTA structure is as follows:

1. Choose IC technology - Vdd & Vt values are important

2. Make the behavioral simulation of the SD ADC and specify the requirements for OTA: gain & bandwidth with the required load, output swing, slew rate.

3. Choose an OTA structure that fits these requirements with best power consumption
 

Re: Sigma delta opamp choise

i think i also relate with noise, the amplifer must be LNA. right?
 

Sigma delta opamp choise

In sigma delta modulators, high gain of opamp is not required, but usually high bandwidth is necessary, and also high slew rate, for more detailed discussion, you can refer to boser's paper and others
 

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