A fully on-chip VGA-based load-independent linear amplitude modulator for GSM/EDGE polar transmitters

A fully on-chip CMOS VGA-based load- independent linear amplitude modulator is implemented for class E1, E2 power amplifiers of GSM/EDGE polar transmitter. By utilizing VGA-based 3-path architecture based on capacitor-free low-dropout linear regulator (LDO), the proposed circuit provides fast and stable operation at all-load conditions including open load when the battery varies from 3.4 V to 5.5 V. The small-signal bandwidth is wider than 5 MHz and the phase margin is bigger than 64deg at the worst-case-simulation condition. The circuit can stably drive output load-current of 0 to 1.6 A at a static bias-current of under 1 mA. The output voltage varies from 0.43 V to 3.2 V when the input reference-voltage V_RAMP varies from 0.2 V to 1.5 V. The chip is fabricated in a TSMC 0.35 mum mixed-mode CMOS 2P 4M process and the size of pass transistor is 1.6 mm times 1 mm.