Application of Monolithic CMOS Switched-Capacitor Filters and Amplifiers for Signal Processing

A custom monolithic CMOS array was designed and integrated for use in meeting the analog conditioning requirements for microsignal processors. These processors are used in "smart" sensors for the purposes of detection and classification. Constrained by very low power dissipation requirements, this array provides a variety of bandpass and low-pass filter functions and programmable CMOS operational amplifiers for AGC amplification for signals in the audio region. Specifically, the custom chip contains 12 poles based on switchedcapacitor techniques partitioned into a 6-pole low-pass filter ladder configuration, and three 2-pole bandpass and low-pass state variable filter configurations. The amplifiers were used in conjunction with an associated microprocessor for software-controlled AGC. A mask change can provide for different capacitor ratios, and hence, frequency responses. Also, the switch clock rates can be used to vary the filter characteristics. Operating from a single +5 V supply, this standard process chip dissipates about 2 mW, and meets all predicted performance characteristics.