A 1.5-V, 4-MHz CMOS Continuous-Time Filter with a Single-Integrator Based Tuning

A 4-MHz, fifth-order elliptic low-pass Gm-C filter is described whose characteristics are tuned by an on-chip automatic tuning circuit. The tuning circuit uses only one integrator as the master of tuning instead of problematic voltage controlled oscillator (VCO) and voltage controlled filter (VCF). MOS transistors in linear operation region perform the voltage-tocurrent conversion in an operational transconductance amplifier, and thereby we achieved 1.5 V operation. A prototype filter was implemented in a 0.8m double-poly, double-metal CMOS process. The filter exhibits the dynamic range of 57.6 dB and dissipates 10 mW with 1.5-V supply. The stopband attenuation is better than 45.0 dB and the passband ripple is smaller than 1.0 dB.