In this thesis, a simple on-chip automatic frequency tuning circuit is presented. The tuning circuit is improved from voltage-controlled filter (VCF) frequency tuning circuit. We use a single time constant (STC) circuit to substitute the voltage-controlled filter. The STC circuit can produce a controllable delay time clock. The tuning circuit uses the constant delay time to tune the frequency of the filter. The design of a STC circuit is easy. Because the circuit is simple, the tuning circuit has less chip area and less power consumption. The circuit has been fabricated with 0.35£gm CMOS technology. It operates with supply voltages ¡Ó1.5 V. The filter operates at a 3-dB frequency of 10MHz. In simulation, the frequency tuning circuit has a 3-dB frequency tuning error of less than 12% and the power consumption less than 9.05mW over a range of supply voltages (¡Ó10%), operating temperatures (-20¢J to 70¢J) and five models of SPICE model.