Autozero opamp

[metuo_abeo]

Hi,

Why this autozero opamp uses 4 capacitors instead of 2? I also attached the schematic of these opamps.

Thanks!

 

[crutschow]

Why this autozero opamp uses 4 capacitors instead of 2? I also attached the schematic of these opamps.

Likely the designers who designed the one requiring 4 capacitors weren't as sharp as the one's who designed the one using 2 capacitors.

 

[frankrose]

2 cap AZ needs a clock cycle when the main OPAmp cannot buffer/amplify the desired signal (nulling period), and the 4 cap circuit can.
Thus, 4 cap AZ is a continuous offset canceling method like choppering but doesn't require high frequency clock, so this is why it is advantageous.

In both version the number of caps is even because it is better to store the control voltages differentially, it reduces effect of ground/supply noise and charge injection, charge feedthrough of switches.