Self-contained charge-coupled split-electrode filters using a novel sensing technique

Self-contained single-chip charge-coupled split-electrode filters with 55 taps and a novel channel structure have been built with a double-level polysilicon NMOS process. Operating at a sample rate of 32 kHz, these devices provide a low-pass filter function with a passband from 0 to 3.2 kHz and a stopband above 4 kHz. The image charge on the sense electrodes is detected with a novel sensing circuit employing two on-chip operational amplifiers, one of which suppresses the common-mode signal on the two sense buses while the other one integrates the difference signal. In addition, the chips carry antialiasing prefilters, a correlated double sample-and-hold circuit to minimize reset noise and to restore the output signal, and all the necessary peripheral logic and biasing circuitry so that the devices can be operated from a single master clock and two power supplies of +12 and -5 V, respectively.