DCO gain calibration technique in fractional-N Delta-Sigma PLL based two-point phase modulators

This paper proposes a digital-controlled oscillator (DCO) gain calibration technique for fractional-N Delta-Sigma phase-lock loop (PLL) based two-point phase modulators. The technique is verified in a 400 MHz/2.4 GHz dual-band combo transceiver. Two-point modulated signal of the 2.4-GHz transmitter is divieded by six and then processed in the 400-MHz receiver. Frequency measurement is realized with coordinate rotation digital computer (CORDIC) algorithm in the 400-MHz digital baseband. By reusing the 400-MHz receiver, hardware cost is reduced compared to existing gain calibration techniques. High calibration speed and accuracy is achieved with the aid of the CORDIC algorithm. Simulation results show that the error vector magnitude (EVM) improves from 3.4% to 1.5% in the 2.4-GHz transmitter with the aid of the proposed technique.