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 0.5 dB. The transmitter has a maximum voltage gain of 4.3 dB and OP1dB of 9.6 dBm. For a WiMAX OFDMA 64QAM-3/4 modulated signal, the best measured error vector magnitude (EVM) is 1.5% with -5 dBm output power. A 1.2 Vsupply voltage is used for the transmitter except that 2.5 V is used for the PA driver. The chip is fabricated in a 0.13 mum 1P8M CMOS process and consumes 164 mW DC power.
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