1 /spl mu/m CMOS programmable surface acoustic wave filter integrated circuit

Abstract

In this paper a 8-bit 1 /spl mu/m CMOS programmable surface acoustic wave filter integrated circuit is introduced and fabricated. It can be used for sampling, weighting, controlling and summing of both SAW delay lines and SAW IDTs in multi-chip module (MCM) programmable SAW filters. The circuit of each bit consists of two sampling capacitances, which are constructed in a sandwich structure of two layers of Al and one layer of polysilicon, and two high transconductance MOSFETs with a high W/L ratio. Its programmability arises from the change of on-resistance of the output MOSFET with weighting voltage in its gate. The summing function is realized by the connection of the output terminals of each bit. After testing, an 18.68 dB insertion loss and a 16.31 dB on/off ratio are obtained at 35.5 MHz. This IC can realize sampling, weighting, controlling and summing of the SAW signal within the frequency range from 15 MHz to 200 MHz with an acceptable insertion loss (-7.94 dB /spl sim/-20 dB) and on/off ratio (7 dB /spl sim/18 dB).