Output stage with fast feedback for driving ADC

摘要

A driver for an analog-to-digital converter (ADC) has an overall feedback loop between its input and its output for maintaining overall accuracy, and a much faster feedback loop in its output stage that quickly compensates for output transients before the overall feedback loop can substantially react to the transients. Output voltage transients are created by the intermittent capacitive load of the ADC. The fast feedback loop can be made very fast since there are only a few components in the fast feedback path. The fast reduction of the output transients enables a shorter sampling time, leading to more accurate analog-to-digital conversion. The overall gain of the driver can be set to be greater than unity while still providing good output transient suppression.

主权项

1. A circuit comprising:
a driver comprising:
an input amplifier including a differential input amplifier having a first input terminal for receiving an input voltage;an output stage coupled to receive a signal from the input amplifier and providing an output voltage at an output terminal;an overall feedback loop feeding back a first voltage, corresponding to the output voltage of the driver, to a second input terminal of the differential input amplifier, the overall feedback loop having a first time constant,wherein the input amplifier further comprises a high gain amplifier having a capacitor connected between its output and its input to set a time constant of the overall feedback loop; anda fast feedback loop within the output stage, the fast feedback loop having a second time constant smaller than the first time constant, the fast feedback loop reducing transients in the output voltage so as to reduce effects of the transients on the overall feedback loop.