Automatic Adjustment of Phase Locked Loop Transfer Function

Abstract

This paper presents an automatic adjustment of the transfer function of phase locked loop (PLL). The time constants and the gain factor of the transfer function are adjusted without opening the loop of PLL. The time constant adjustment is performed using a replica of the 1st order RC low pass filter and the gain factor is adjusted by detecting the open loop gain at the unity gain frequency. These adjustments are automatically carried out using a digitally controlled capacitance array and a digitally controlled charge pump. The proposed calibration can reduce the bandwidth error of ±30% to ±5% and the gain error of 7dB to 1dB.