Increasing the clock frequency of switched-capacitor filters

The time constant ¿ of a switched-capacitor (s.c.) integrator is C/(fcCR), where CR is the value of the s.c., C the integrating capacitor and fc the clock frequency. For a given ¿, if fc is to increase, C/CR must increase proportionately. Since a large capacitor ratio C/CR is inconvenient to implement in an integrated circuit, most s.c. filters are clocked at the Nyquist rate. Since higher clock rates reduce switching delays, a technique of enabling higher clock frequencies without the need for large capacitor ratios has been developed.