A tunable gm-C filter with low variation across process, voltage and temperature

A tunable g_m-C filter with cutoff frequency insensitive to Process, Voltage and Temperature is proposed. An external clock frequency is used to generate a current using a switched capacitor circuit. The proposed filter is ideally suited for applications where a tight control on cutoff frequency is desired across different operating conditions of the chip. The circuit was designed in 3.3 V BiCMOS technology and simulations were carried out using SPICE. The simulation results show that the total variation in the cutoff frequency is 1% as compared to the 27% variation in conventional g_m-C filter over the temperature range of -40 to 120 degC. The variation across process corners is 2.4% and is almost independent of the capacitor variation due to process and temperature.