A low power monolithic AGC with automatic DC offset cancellation for direct conversion CDMA receiver

There is an increasing interest in monolithic integration for wireless transceivers. This integration can be made possible with the advantages of direct conversion techniques. However, DC offset and flicker noise become critical to the system. In this paper, we propose a wide tuning range and high gain AGC with an effective automatic DC offset cancellation. The proposed AGC and transceiver architecture is specifically designed for direct conversion wideband CDMA system or hybrid FH/DS CDMA system operating at 2.4GHz used in telemetering applications. The AGC was fabricated using TSMC 0.35μm double poly Nwell process. The AGC’s performance will not be affected by the DC offset of the previous stages. Due to the large signal bandwidth, the effect of flicker noise can be neglected. The large and the continuous gain tuning range increase the dynamic range of the receiver. The circuit achieves an 80dB continuous gain tuning range, [-30dB, 50dB], with 40 dB dynamic range for differential output voltage set to 500mVpp and a THD better than 30dBc. The AGC is powered by 3V with 7mW power consumption.