ΔΣ PLL transmitter with a loop-bandwidth calibration system

We developed a PLL transmitter with a linear charge pump and a new loop-bandwidth calibration system that can calibrate loop bandwidth accurately in a very short time. The calibration system uses a double integration technique that integrates the transient signal at the voltage-controlled oscillator output during the response to a step wave input to the divider. In our PLL transmitter for GSM phones, the calibration system keeps the loop bandwidth within 2% and the calibration time is about 25 s. To improve the GSM spectrum, we developed a charge pump that reduces a spike noise and the asymmetry of the charge and discharge characteristics. The phase error of modulation in the PLL transmitter with the charge pump and calibration system was kept within 2 degrees rms, and after calibration the 400-kHz offset noise level of the spectrum mask was 64 dBc.