A 0.13 μm CMOS transmitter with 72-dB RF gain control for mobile WiMAX/WiBro applications

Abstract

A direct conversion transmitter for Mobile WiMAX/WiBro applications is developed. It is composed of a reconstruction filter, an I/Q modulator, a four-stage RF programmable gain amplifier (PGA), and a power amplifier (PA) driver. A 7-bit digital-to-analog converter (DAC) is also implemented to compensate the DC offset in the modulator due to device mismatch. A 72-dB gain control range in 1-dB step is available by the RF PGA and the maximum relative gain error is less than 0.5dB. The transmitter has a maximum voltage gain of 4.3dB and OP1dB of 9.6dBm. For a WiMAX OFDMA 64QAM-3/4 modulated signal, the best measured error vector magnitude (EVM) is 1.5% with — 5dBm output power. A 1.2Vsupply voltage is used for the transmitter except that 2.5V is used for the PA driver. The chip is fabricated in a 0.13μm 1P8M CMOS process and consumes 164mW DC power.