Simple switched-capacitor voltage-controlled oscillator

A novel switched-capacitor VCO circuit is presented. The charge-balancing principle and bucket-brigade charge-transfer device concepts are used. The resulting circuit is very simple and requires only single-channel enhancement-mode MOS transistors and MOS capacitors. The VCO frequency range is determined by the ratio of two internal capacitors and may be made electrically programmable, if desired. The voltage/frequency relationship is linear. The circuit has been theoretically analysed and a prototype has been built and tested. The circuit required only two nonoverlapping clocks and was operated up to 1 MHz.