Self tuned fully integrated high image rejection low IF receivers: architecture and performance

Two new architectures of fully integrated low inter-mediate frequency (IF) receiver with high image rejection ratio (IRR) are proposed in this paper. Image rejection is realized by following an in-phase and a quadrature (I/Q) mixers with a complex filter which is tuned to the desired IF signal passband. To eliminate the phase mismatch of I/Q local oscillators and the gain mismatch of I/Q mixers, two new compensation techniques are developed. One is with a feedback loop and two variable gain amplifiers (VGA). The gains of two VGAs are self tuned through a feedback loop so that both the I/Q amplitude and phase mismatches in the forward receiver can be eliminated. The other employs two tuning loops, which are designed to automatically compensate the I/Q amplitude and phase mismatches separately. After the compensation, the IRRs of these two architectures both can be significantly improved (to ∼70 dB). The proposed low IF receivers are self tuned image rejection systems with very fast settling time and high adjusting precision. They can be fully integrated and applied in most of wireless receiver systems including GSM, DECT, WCDMA, Bluetooth and wireless LAN etc. Simulation results for a Bluetooth receiver as well as a GSM receiver are presented.