Digital self-aware charge pump calibration technique for frequency synthesizers

Abstract

As radio design complexity increases and features sizes decrease, more innovative solutions are explored to ensure analog circuit designs meet specifications. Digital calibration is an inexpensive and effective solution. A novel digital calibration technique to improve charge pump current mismatch in frequency synthesizers is presented. This method detects the charge pump error by measuring the low pass filter voltage of the system forced to operate at a fixed phase error. A reference table developed from a mathematical model of the system uses the measurement result to produce a digital control word. The digital control word acts on a charge pump array to correct the error. The technique is implemented and tested in Matlab/Simulink for a case study frequency synthesizer. The calibration technique corrects the charge pump current absolute error to within 1.4% of the nominal value. Additionally, the technique is exceptionally effective for correcting the charge pump current mismatch to within 1%.