∆Σ PLL Transmitter With a Loop-Bandwidth Calibration System

We developed a DeltaSigma 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 DeltaSigma PLL transmitter for GSM phones, the calibration system keeps the loop bandwidth within 2% and the calibration time is about 25 mus. 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 DeltaSigma 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.