A fully integrated feedback AGC loop for ZigBee (IEEE 802.15.4) RF transceiver applications

Abstract

This work presents an efficient solution for automatic gain control (AGC) loop in ZigBee transceiver compatible to IEEE 802.15.4 standard. The design is based on a RF (Radio Frequency) and linear IF (Intermediate Frequency) chain where the signal amplification is done in the RF front-end blocks and analog VGAs (variable gain amplifiers). The gains of the RF block and VGA are digitally controlled by the DAGC (Digital AGC) block to ensure that the ADC (Analog-to-Digital Converter) operates inside its dynamic range. Feedback loop architecture is employed for the advantage of high linearity due to its inherent characteristic. The whole AGC loop has been integrated in the ZigBee transceiver which was fabricated in a 0.18μm CMOS technology. The AGC loop achieves a dynamic range of about 95dB with the gain error of less than ±0.5dB. The two-channel VGAs and peak detectors occupy an area of 1.5mm×0.4mm and dissipate 1.71mW from a single 1.8V power supply. The DAGC has been integrated in the digital baseband processor and occupies an area of about 0.4mm×0.4mm. The max gain lock time of the AGC loop is about 1.25μs.