Offset-compensated switched-capacitor filter for TDM multichannel analog signals

Abstract

For adaptive line equalization of a time-division multiplexed analog signal, an offset-compensated filter circuit comprises a timing circuit for generating channel-switching signals respectively synchronized with the time slots of the TDM signal. A switched-capacitor filter comprising an operational amplifier and a switched-capacitor circuit is responsive to the channel-switching signals for sequentially establishing transfer functions specific to the time slots of the TDM signal. A plurality of switched-capacitor DC decoupling circuits are connected to the output of the switched-capacitor filter. These DC decoupling circuits are respectively associated with the channel-switching signals for coupling a respective one of the filtered components to an input terminal of a summing amplifier. Each of the DC decoupling circuits has a first and a second capacitor and switches responsive to the presence of the associated channel-switching signal for charging the first capacitor with a voltage developed at the output terminal of the switched capacitor filter and charging the second capacitor with a voltage developed between the output of the switched capacitor filter and the input terminal of the summing amplifier and discharging the first and second capacitors in response to the absence of the associated channel-switching signal. The operational amplifier offset voltage and clock feedthrough of the switched-capacitor filter are eliminated.

Dependencies are inferred from the claim text.