d.c. Block capacitor circuit for rejection of d.c. offset

Abstract

A d.c. block capacitor circuit suitable as an integrated circuit in that it requires only one pin for the connection of an external capacitor. The circuit has particular, but not exclusive, application to direct conversion receivers. The circuit comprises an operational amplifier (10) having an inverting and a non-inverting input and an output. A pair of resistors (12, 14) having values R1, R1', respectively, connect the respective amplifier inputs to a signal input (16). The amplifier has a feedback resistor (18) having a value R2 connected between the inverting input and the output. Another resistor (20) having a value R2'and a capacitor (22) are connected between the non-inverting input and either and same or different voltage reference point(s). The values of the resistors (12, 14, 18, 20) are selected so that the ratio of R2':R1' equals the ratio R2:R1. Any d.c. offset present in the input signal is rejected by the circuit so that the output therefrom comprises the signal centered on the reference voltage.

Dependencies are inferred from the claim text.