An image-rejecting mixer and vector filter with 55-dB imagerejection over process, temperature, and transistor mismatch

摘要

This paper describes an image-rejecting mixer and vector filternfor use in radio systems with channel bandwidths in the range of 1 MHz.nThe circuit replaces the SAW filter and second downconverter commonlynused in this style of radio. Because the output of the circuit is at annIF of 5 MHz, traditional demodulation methods including limiting and FMndiscrimination can still be used. The circuit is based on a quadraturenmixer that guarantees good performance despite device mismatches andnprocess variation. The circuit consumes 29 mA at 3.3 V,and achievesnbetter than 55-dB image rejection despite device mismatches and processnvariation and is implemented in a single-poly triple metal 0.5 ΜmnCMOS process with linear capacitor implants. The circuit is designed forninput signals from 125 to 250 MHz. Input referred voltage noise is 900nΜVrms. The in-band IP3 is 18 dBm. By changing an external referencenfrequency, the passband width of the filter can be varied from 3 to 0.5nMHz