Design and compensation of high-frequency, narrow-band, bandpass MOSFET-C filters.

Abstract

Circuit designs that employ only CMOS technology are becoming more desirable than those using traditional bipolar integrated circuit technology. This technology offers a high density of MOS circuitry, good capacitor accuracy and high stability. The availability of techniques for the design and realization of precision filters in fully integrated form has many applications in signal processing VLSI circuits. The design, simulation and compensation of MOS transistor filters are presented. The MOS transistor is used as a voltage controlled resistor. The resulting "MOSFET-C" filters can then be built of MOS transistors, capacitors and operational amplifiers fabricated in MOS technology. The advantages of MOSFET-C filters over other integrated filters are discussed. Desirable MOS transistor circuit configurations for use in these filter designs are also presented. High-order, high-frequency, narrow-band bandpass filters are designed and simulated to give a systematic step-by-step design procedure for realizing MOSFET-C filters. These steps include modifying existing well established and studied filter building blocks for use in this method. The nonidealities associated with MOS transistors, especially at high frequencies, are studied and modeled for simulation. Compensation techniques for these nonidealities, together with those of operational amplifiers are presented and applied to both RC and MOSFET-C filters. A compensation scheme is developed which cancels the op amp effects in second-order filter building blocks.