An image rejection type Ku-band direct RF undersampling CMOS receiver

Abstract

We propose an image rejection type direct RF undersampling receiver. By using a direct RF I/Q sample and hold (S/H) circuits, and 90 degree power combiners in the digital domain, upper side band (USB) and lower side band (LSB) signals can be separated into two different (USB and LSB) output ports, therefore the image rejection functionality can be realized with half of the clock frequency of the conventional RF undersampling receivers. The proposed IC is designed for Ku-band (12.25-12.80 GHz, system bandwidth = 550MHz) very small aperture terminal (VSAT) application and is fabricated in 90 nm CMOS process. The fabricated IC performs a signal-to-noise ratio (SNR) of higher than 27.4 dB and an image rejection ratio (IRR) of higher than 19.5 dB with a 610 MHz sampling clock.