two/three stage comparator

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gggould

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Hi,
Sometimes I see people add a preamp before comparator. Does anyone know what’s the pros/cons for doing so?
I know it is good for reducing kickback noise and metastability. But how about bandwidth?
Also can someone recommend any good newer architecture? I only know of strongarm.

Thanks.
 

hi,
One reason for adding a pre-amp is to isolate the input impedance of the comparator from the source impedance.
eg: if the source output impedance is 'high', connecting that directly to a 'lower' impedance comparator input, will load the source

Another reason is to amplify a low level signal so that the comparator will have a wider more easily 'settable' threshold.
eg: if the source signal was say, a +/-10mV signal, setting the comparator thresholds and possible hysteresis would be difficult, amplifying by say, 10 times would give a 100mV signal input to the comparator, which would allow a wider more stable threshold/hysteresis setting.
E
 

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