Design Of Multiplier For EDGE Polar Transmitter

EDGE stands for Enhanced Data Rates for GSM Evolution. It triples the gross transmit data rate offered by GSM through introducing a 3π/8 rotated 8-Phase Shift Keying modulation and coding schemes. Besides, it provides a transitional solution between GPRS and the 3rd generation mobile communication system, thus maximizes the compatibility with existing GSM networks.The high peak to average ratio character of 8PSK causes a higher linearity requirement on RF power amplifier which makes the efficiency relatively low. To solve this problem, we can use polar modulation to realize high efficiency and low power consumption. For the reason that it can employ RF circuits in saturation mode to modulate non-constant envelop linear signals which can reduce the current and raise the efficiency.A 900MHz low-noise high-linearity polar transmitter front-end for EDGE system is presented, which includes a multiplier and a succeeding driver amplifier. The whole circuit is implemented in 0.18μm CMOS process. The multiplier and DA provide output power ranging from -30dBm to 4.5dBm, an ACPR of -63dBc at 400KHz offset and output noise of -163dBc/Hz at 20MHz offset. The spurious around 2nd and 3rd harmonics are -46dBc and -39dBc respectively. The carrier suppression is -45dBc. The whole circuit consumes 23~56mA from a 1.8V supply voltage according to different gain levels.