Calibration arrangement for frequency synthesizers

摘要

An electronic device has a calibration arrangement for controlling a frequency characteristic of a PLL circuit having a phase comparator having an output for generating a phase difference signal, a voltage controlled oscillator and a divider. The divisor of the divider is programmable, and the oscillator is also directly modulated by an oscillator modulation signal. A modulation unit has a modulation input for receiving a modulation signal and generates the oscillator modulation signal and the divisor such that modulation generates a predefined change of the output frequency and a change of the divisor proportional to said predefined change. The calibration arrangement receives the phase difference signal, and has a ripple detector for providing a detector output signal by detecting a ripple on the phase difference signal correlated to edges in the modulation signal. A calibration control unit adjusts the oscillator modulation signal based on the detector output signal such that the ripple is reduced.

主权项

1. An electronic device, the device comprising a calibration arrangement for controlling a frequency characteristic of a circuit, the circuit comprising:
a phase comparator having a first input for receiving a feedback signal and a second input for receiving a reference frequency and a phase comparator output for generating a phase difference signal; a voltage controlled oscillator having a first control input coupled to receive the phase difference signal and a second control input for receiving a second control signal, and an oscillator output for outputting an oscillator signal at an oscillation frequency controlled by the first and second control inputs; a divider having a first input coupled to receive the oscillation signal and an output for generating the feedback signal by dividing the oscillation signal by a divisor, the divisor of the divider being programmed based on a divisor control signal received via a divisor input; and a modulation unit having a modulation input for receiving a modulation signal, a first modulation output to provide the second control signal, and a second modulation output to provide the divisor control signal, and a change of the modulation signal generates a predefined change of the second control signal and a change of the divisor via the divisor control signal that is proportional to said predefined change; and the calibration arrangement comprising:
a calibration input for receiving the phase difference signal;a ripple detector for providing a ripple detector output signal by detecting a ripple on the phase difference signal correlated to edges in the modulation signal; anda calibration control unit for generating a calibration control signal based on the ripple detector output signal,wherein the second control signal is adjusted based on the calibration control signal such that the detected ripple is reduced.