2nd Order Sallen Key Switched Capacitor LPF with N-type Transistors

摘要

This paper presents active low pass RC and switched capacitor filters with only N-type transistors. Two different high-gain OpAmp configurations with positive feedback are explored in this paper: One circuit based on cascaded inverters and the other based on capacitor bootstrapping. While the cascaded inverter configuration gives a gain of more than 50 dB and bandwidth of 48 MHz with 210 μw of power consumption, OpAmp with capacitor bootstrapping gives a gain around 40 dB and bandwidth of 2 MHz consuming 70 μw power. Circuit simulations were carried out in standard 180 nm technology. With these OpAmps, RC and SC filter implementations are presented. SC filter using OpAmp with cascaded inverter gives a THD of 5.36 % with 946.6 μw of power consumption, while SC filter with capacitive bootstrapped OpAmp give THD of 7.47 % with 351.7 μw of power consumption.