PROGRAMMABLE VCO, METHOD OF CALIBRATING THE VCO, PLL CIRCUIT WITH PROGRAMMABLE VCO, AND SETUP METHOD FOR THE PLL CIRCUIT

摘要

The PLL circuit comprises a phase/frequency detector (302), a loop filter (304, 306), a VCO (308) and a feedback loop (320).The VCO can be electrically disconnected from the PLL and comprises a programmable trimming circuit (316) and a current-controlled oscillator (318). For calibration the VCO is electrically disconnected from the loop filter and from the feedback loop, a constant reference voltage is applied to the voltage input (IN), a center frequency programming code (L) is applied to the trimming circuit,the center frequency programming code is iteratively adjusted until a desired centre frequency is obtained,a gain programming code (K) is applied to the trimming circuit while the adjusted code is still applied, and the gain programming code is iteratively adjusted until a desired gain is obtained. Then the VCO is connected to the PLL, which is then ready for normal operation.