Offset-insensitive switched-capacitor gain stage

Analog-to-digital conversion means for use as part of signal-processing means incorporated in a system having a signal common and comprising an IC chip for converting analog input signals to corresponding digital signals to be directed to a digital signal processing and/or storage device of said system;

• said IC chip including:
• an input signal selection circuit having a plurality of input lines respectively connectible to different input signal sources;
• at least one buffer amplifier having an output signal line;
• switch means for coupling any one of said input signals to the input of said buffer amplifier;
• a reference signal line;
• a switched-capacitor circuit having two input terminals, one of said terminals being connected to said output signal line and the other being connected to said reference signal line;
• and
• a capacitor fixedly connected through a non-switched connection between said reference signal line and signal common.

An a-c gain circuit for use as part of signal-processing means to be incorporated in a system having a signal common and comprising:

• (1) an IC chip including:
• an input signal selection circuit having a plurality of input lines respectively connectible to different input signal sources;
• an input signal line;
• a reference signal line;
• switched-capacitor circuitry having an input signal circuit and an output signal circuit, said input signal circuit including two input terminals;
• means coupling said two input terminals to said input signal line and to said reference signal line respectively;
• amplifier means coupled between said input signal circuit and said output signal circuit to provide amplification of the signals passing through said switched-capacitor circuitry;
• and
• (2) a capacitor fixedly connected through non-switched circuitry between said reference signal line and signal common.

In an a-c gain circuit for use as part of signal-processing means to be incorporated in a system having a signal common, and wherein the gain circuit comprises an IC chip providing an input signal line and a reference signal line to direct an input signal carried on an input signal line and a reference signal line to the input signal circuit of switched-capacitor gain circuitry having first and second input terminals to be connected to said input signal line and reference signal line respectively, said switched-capacitor gain circuitry having an output signal circuit, the a-c gain circuit including amplifier means connected to one of said signal circuits;

• the method of reducing the effect of unwanted d-c signals on the performance of the a-c gain circuit comprising the steps of:
• developing on a capacitor a voltage corresponding to said unwanted d-c signals;
• and
• coupling said capacitor between said reference signal line and said system common to prevent introducing said unwanted d-c signals into the gain of said a-c gain circuit.