the drive ability of the AFE

[Alice Lee]

Hi,all. I want to know how to decide the drive ability of the AFE in front of ADC. Actually, I'd like to understand it from the perspective of current that the ADC needs(e.g. dynamic switching current）instead of impedance. Is the largest current or average current dominate?

 

[nitishn5]

Basically the AFE will have to drive the Sampling Capacitor of the ADC.
One of the specification would be to ensure that the Sampled signal settles to the required accuracy within the specified sampling time.
Depending on your architecture/use case, you might have to charge the sampling cap from zero it could just be a delta change in the charge.
Based on that you will have to check whether you need to just drive the average current or do you need to worry about the instantaneous peaks.
Although, if you can have a big capacitor at the output of the AFE (other than the sampling cap), that reservoir cap can provide the instantaneous charge.

 

[Alice Lee]

Basically the AFE will have to drive the Sampling Capacitor of the ADC.
One of the specification would be to ensure that the Sampled signal settles to the required accuracy within the specified sampling time.
Depending on your architecture/use case, you might have to charge the sampling cap from zero it could just be a delta change in the charge.
Based on that you will have to check whether you need to just drive the average current or do you need to worry about the instantaneous peaks.
Although, if you can have a big capacitor at the output of the AFE (other than the sampling cap), that reservoir cap can provide the instantaneous charge.

Thanks for the advice.
it's indeed important to care about the settling time of adc.
and in my opinion, the peak current may be dominate. if the AFE driver can provide the average current that the ADC needs but can't provide the peak current, does it work?
(i'm a junior designer and haven't taped out. maybe my understanding of this problem is too simple)
btw, thanks a lot.

--- Updated Mar 30, 2023 ---

Thanks for the advice.
it's indeed important to care about the settling time of adc.
and in my opinion, the peak current may be dominate. if the AFE driver can provide the average current that the ADC needs but can't provide the peak current, does it work?
(i'm a junior designer and haven't taped out. maybe my understanding of this problem is too simple)
btw, thanks a lot.

Basically the AFE will have to drive the Sampling Capacitor of the ADC.
One of the specification would be to ensure that the Sampled signal settles to the required accuracy within the specified sampling time.
Depending on your architecture/use case, you might have to charge the sampling cap from zero it could just be a delta change in the charge.
Based on that you will have to check whether you need to just drive the average current or do you need to worry about the instantaneous peaks.
Although, if you can have a big capacitor at the output of the AFE (other than the sampling cap), that reservoir cap can provide the instantaneous charge.

i'm wrong. i'm agree with u. it depends on the specific use case.Thanks a lot