A programmable clock generator that uses noise shaping and its application in switched-capacitor filters

A programmable digital clock generator that produces a wide range of clock frequencies with fine resolution is described. The clock generator consists of a noise-shaping control loop and a number-controlled oscillator. The generated clock has a time-varying period. When this clock is used as the sampling clock in a switched-capacitor filter (SCF) to set its frequency response, the time-varying period causes nonuniform sampling, which is acceptable under certain conditions that are described. Measured performance of a 2-μm CMOS implementation of the clock generator is presented. Also, measured data for the clock generator driving two SCF´s are reported