Sampled-and-Hold Based Automatic Calibration Modulator for WLAN Transmitter

This paper presents an automatic calibration circuit to correct the I/Q imbalance and DC offset in the modulator of a WLAN transmitter. The impairments are estimated and compensated by a sampled-and-hold negative feedback circuits. The circuit architecture is controlled by an on chip 12 steps state machine. After the calibration, the LO leakage at the modulator output can be suppressed more than 50dB. The side band unwanted signal also can be eliminated 45dB at least. The proposed self-calibrated modulator with quadrature LO generator is implemented in 0.25 mum 1P5M mixed-mode CMOS process. The chip area is 1.2mm times 1.7mm. The total power dissipates 17 mW at 1.1~1.3 GHz from a single 2.5V supply voltage