A superheterodyne receiver front-end with on-chip automatically Q-tuned notch filters

Abstract

A superheterodyne receiver front-end with on-chip automatically Q-tuned notch filters is proposed. The front-end includes a differential LNA and a Gilbert down-converter, where each block is coupled with an on-chip image-rejection notch filter to get high image-rejection ratio. Each notch filter is formed by one on-chip LC network and one negative-resistance cross-coupled pair to compensate for the loss of the LC network. The current through the cross-coupled pairs is automatically adjusted by an automatic Q tuning circuit so that the loss of the notch filter is perfectly compensated to achieve a deepest notch. The automatic Q tuning circuit is an analog---digital mixed signal circuit, and successive approximation register algorithm is used to search for the optimum current value. The superheterodyne receiver front-end has been implemented in 0.18 µm CMOS. Experimental results show that the circuit could achieve an image rejection ratio of 75 dB with 105 MHz IF Frequency. The LNA draws 5.86 mA current, and the down-converter draws 1.27 mA current while two image-rejection filters and the master VCO totally draw 363 µA current, all from a 1.8 V power supply.