question about OPAMP offset

[iexplorer]

pipelined adc opamp offset

In p Gray's book ,he said in sc circuit like sc filter,opamp's input offset voltage can be dismissed by charge storaged in cap.,I can't get how does that happen?Does that mean in pipeline ADC offset have liittle effect?

 

[hr_rezaee]

Hi
Yes, offset can be very important.
for example gain error can be appeared as offset and has very important effect on total error in pipeline adc.
regards

 

[safwatonline]

u have two phases , one u sample the offset using unity feedback on the OTA, then in the next phase u put the cap in a way that the input has two components : one the normal offset and the second is the negative of sampled offset saved on the cap. , in this way u remove DC offset and low frequency noise are also filtered

Added after 51 seconds:

BTW this is called CDS

 

[iexplorer]

dear safwatonline , I get it,but does that mean the offset or common voltage shifting will not be a serious problem?

 

[A.Anand Srinivasan]

the inputs are charged to a constant voltage with a capacitor connected at both input terminals. now the one of the capacitor would be charged to the input voltage plus the offset voltage and if it used after this charging then offset is considerably reduced....

 

[neter]

Can to reduce offset in input terminal ?

 

[songjunjian]

offset is important , so some pipeline adc use calibration tech to decrease the offset of adc .