A 1.25 GHz Q-enhanced filter with image rejection

A 1.25 GHz two-stage band-pass filter fabricated in TSMC 90 nm CMOS process is presented. The Q-compensate technique is used for better filtering performance, and a notch circuit is added to achieve the desired image rejection of 40 dB. Measured gain of this filter is 16.3 dB at 1.25 GHz with the pass band width of 20 MHz. The out-of-band suppression at 100 MHz offset and image rejection at 1.1 GHz are 26 dB and 42 dB, respectively. The power consumption is 22mA from a 1.2 V supply.

Introduction

Superheterodyne receiver has been widely used in modem wireless systems. Band selection and image rejection are both important for this architecture, especially in a noisy environment. In order to ensure the quality of the received signal, a filter with high performance is required before downconversion mixing. The traditional off-chip SAW filter exhibits excellent performance, with the sacrifice of cost and integration. Compared with that, the on-chip active filter is more efficient for highly integrated RF front-end.