NOTCH FILTER FOR RIPPLE REDUCTION

摘要

A notch filter is controlled synchronously with a chopper to filter out chopping ripple. In one embodiment, the notch filter is coupled to the differential output of the chopper and includes a sampling capacitor, a hold capacitor, and a second set of switches between the sampling capacitor and the hold capacitor. The second set of switches is temporarily closed once per chopper switching cycle to transfer charge from the sampling capacitor to the hold capacitor such that the ripple from the chopper is not transferred to the hold capacitor. The voltage across the hold capacitor may be coupled to any other circuit, such as to the differential inputs of an amplifier.

主权项

1. A circuit comprising:
an input chopper receiving an input signal; an amplifier receiving a first signal corresponding to an output of the input chopper; an output chopper, synchronized with the input chopper, receiving a second signal corresponding to an output of the amplifier, the output chopper comprising a first set of switches controlled by at least clocked phase 1 and phase 2 control signals at a chopping frequency, the output chopper outputting a third signal containing chopping ripple at the chopping frequency; and a notch filter coupled to receive the output of the output chopper, the notch filter comprising a sampling capacitor, a hold capacitor, and a second set of switches between the sampling capacitor and the hold capacitor, wherein the second set of switches is temporarily closed during each output chopper switch cycle to connect the sampling capacitor to the hold capacitor, pursuant to a phase 3 control signal at the chopper frequency, to transfer charge from the sampling capacitor to the hold capacitor at least once per switching cycle of the output chopper, wherein the hold capacitor is isolated from the output chopper during times when the second set of switches is open such that the chopping ripple from the output chopper is not transferred to the hold capacitor.