A configurable active-RC filter for half-duplex transceiver

A configurable active-RC filter for a half-duplex transceiver is presented. The filter is primarily composed of two low-pass filters (LPF), which are shared between transmitter mode and receiver mode of the half-duplex transceiver. When in transmitter mode, the filter is simply used as I/Q LPF, and in receiver mode, the filter is configured as a complex filter, with the help of a configurable switching network. The LPF bandwidth is configurable at 125kHz and 250kHz. The complex filter has a bandwidth of 500kHz, centered at 1MHz. An automatic frequency tuning circuit is introduced in the filter to compensate RC variations. The experimental transceiver chip is implemented in UMC 0.18μm CMOS process. Measurement results show the filter achieves image rejection ratio of 31dB, passband gain of -1dB, output 1-dB compression voltage of 0.32V, and power of 4.8mW.