An image-rejecting mixer and vector filter with 55-dB image rejection overprocess, temperature, and transistor mismatch

This paper describes an image-rejecting mixer and vector filter for use in radio systems with channel bandwidths in the range of I MHz. The circuit re places the SAW filter and second downconverter commonly used in this style of radio. Because the output of the circuit is at an 1 F of 5 MHz, traditio nal demodulation methods including limiting and FM discrimination can still be used. The circuit is based on a quadrature miser that guarantees good p erformance despite device mismatches and process variation. The circuit con sumes 29 mA at 3.3 V, and achieves better than 55-dB image rejection despit e device mismatches and process variation and is implemented in a single-po ly triple metal 0.5 mum CMOS process with linear capacitor implants. The ci rcuit is designed for input signals from 125 to 250 MHz. Input referred vol tage noise is 900 mu Vrms. The in-hand IP3 is 18 dBm, By changing an extern al reference frequency, the passband width of the filter can be varied from 3 to 0.5 MHz.