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Preamp design in flash ADC

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akbarza

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hi
please answer to my question:
considering that a pre-amplifier compares the input voltage with a special voltage obtained from resistive ladder in flash adc, I would like to know whether the design of pre-amplifiers is different from each other?/every pre-amplifier is different from another one?
thanks
 

Haven't we been here before?

What has a pre-amplifier got to do with 'special voltage' or a flash ADC?

Pre-amplifiers are for 'pre' amplifying, increasing a signal level before main amplification, it has nothing to do with ADC whatsoever.

Brian.
 

Preamps are used to relax the constraints on the regeneration circuits, especially to lower the input referred mismatch of the latch. All the comparators will should have same kind of preamp and the amplification need not be linear.
 

Hi
i want express my question explicity
In flash ADC, taking into account reference voltages built by resistor ladder are different from each other as well as reference voltage actually determines bias point of preamp, is the design of a pramp different from others?
thanks
 

akbarza said:
considering that a pre-amplifier compares the input voltage with a special voltage obtained from resistive ladder
Click to expand...
Those are comparators, not amplifiers. Design is easier if you design 1 comparator which can handle the full range and replicate that for every tap point of the ladder. The main specifications are the speed, offset and the comparator has to ensure those in the full range. If it is not possible you can divide the range and you can use more different comparators to ensure the speed and offset specifications in the sub-ranges of course.
 

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