Design of Switched Capacitor Filter with Transmission Gate Switches

Abstract

A filter is a circuit that allows some frequencies to pass through it, while attenuating others frequencies. Generally, Filter can be designed using components like resistors and capacitors. In VLSI Technology Resistors with large values cannot be inserted on to a chip so easily. An alternate circuit can be replaced in place of resistor (i.e., Switched capacitor). In this paper we are designing a low pass filter using the switched capacitor and comparator, the switched capacitor constitutes two switches and a capacitor, op-amp is been used as comparator. The switches can be either Nmos or Pmos Transistors or Transmission gate, they perform the switching action when clock driver o/p signal is given to gate terminal of these transistors. Frequency response of low pass filter using Pass Transistors and Transmission gate is observed and cutoff frequency is been calculated in each case, it may be either by pass transistors or transmission gates in tool named cadence virtuoso. Designing of low pass filter is done by 180nm technology in cadence Virtuoso. By Observing the frequency response of pass transistor and transmission gates, the transmission gates frequency response provides good roll-off compared to pass transistor frequency response. The combination of both an PMOS and NMOS in transmission gate arrangement avoids the problem of reduced noise margin. If the same designing of low pass filter done by 45nm Technology in cadence virtuoso then we can achieve more accurate results.

Keywords: : Resistor, Switched capacitor, Pass Transistor, Transmission Gate, Comparator, Cut-Off frequency