An analog-digital adaptive image-reject technique for quadrature receivers

In this paper, an analog-digital adaptive image-reject (IR) technique for quadrature receivers is presented. In these receivers, I/Q mismatches degrade the image rejection performance. To compensate the mismatches, a complex error signal is generated digitally of which the real and imaginary parts are proportional to the I/Q amplitude and phase mismatches. This error signal is applied to Digitally-Controlled Multiplier-Adder (DCMA) blocks to correct the phase and amplitude mismatches. Simulations show that the image-rejection ratio is improved to more than 57 dB for a low-IF cable modem receiver. This performance is independent of the synchronization and equalization of the receiver.