Frequency-to-voltage converter for temperature compensation of CMOS RC relaxation oscillator

RC oscillator is often used in CMOS mixed-signal integrated circuits where lower power dissipation and/or lower cost are required while precision requirements for the oscillation frequency are moderate. One of the challenges in RC oscillator in CMOS integrated circuits is frequency compensation for variations of process parameters and temperature because the time constant depends on absolute values of resistors and capacitors which are not stable against such variations. This paper describes an on-chip RC relaxation oscillator and a feedback control to stabilize the oscillation frequency by using a reference voltage, and proposes a simple frequency-to-voltage converter based on switched-capacitor technique. Simulation results show that the compensation circuit improves the frequency stability against temperature variation.