Clock generator circuit with low current frequency divider

Abstract

A clock generator circuit for producing a clock signal while drawing reduced current drain is disclosed. The clock generator circuit includes a crystal oscillator which produces a periodic signal having a relatively small voltage swing, controlled by one or more reference voltages; the reference voltages are preferably produced by a sub-threshold biased voltage reference circuit. The small signal output of the crystal oscillator is applied to the first of a series of frequency divider stages, prior to amplification by a level shift circuit. Each divider stage includes a current switch which switches the current drawn through current divider legs to produce output signals to latches in the divider stage. Each divider stage also includes one or more current source switched latches, each controlled by current sources that are switched by the current switch. As a result, each divider stage divides the frequency of the oscillator output signal without requiring amplification of the signal, thus reducing the active current. The output of the last divider stage is applied to a level shift circuit to provide the large voltage swing clock signal.