Self-calibrating controllable oscillator
AssigneeTelefonaktiebolaget LM Ericsson (publ)
InventorsLars B. Nord, Erik Bengtsson
Life of this patent
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Abstract
The controllable oscillator in a phase-locked loop (PLL) can self-calibrate by tapping the PLL's feedback path with a suitable circuit or logic block. The logic block may include a counter. This enables the self-calibration/trimming to be handled completely within a product, such as a radio telephone, and no external instruments or software are needed for trimming.
Claims18
A method of calibrating a controllable oscillator in an electronic phase-locked loop circuit, comprising the steps of:
- initializing the circuit by resetting a counter and setting at least one oscillator control signal to tune said controllable oscillator to an initial level;
- and
- calibrating the oscillator by:
- opening and tapping a feedback path in the loop circuit;
- in response to a gating signal, counting pulses at a the tapped position in the feedback path in the loop circuit;
- stopping the counting upon occurrence of a predetermined event determined by the gating signal;
- comparing a result of the counting to a trim window;
- and
- if the result is outside the trim window, adjusting the at least one oscillator control signal and repeating the counting, stopping, and comparing steps.
A self-calibrating electronic circuit, comprising:
- a phase-locked loop (PLL), wherein the PLL comprises:
- a phase detector that produces a first output signal based on a frequency or phase difference between a reference signal and a feedback path signal,
- a charge pump that produces a second output signal based on the first output signal,
- a loop filter that produces a shaped second output signal, and
- a controllable oscillator that produces a third output signal based on the shaped second output signal, and
- a feedback path that produces the feedback path signal based on the third output signal;
- and
- calibration logic that opens and taps the feedback path through at least one switch and provides control signals to the controllable oscillator;
- wherein the calibration logic includes a counter that is gated by a gating signal and that counts pulses in the feedback path signal.
A fractional-N frequency synthesizer electronic circuit, comprising:
- a reference oscillator;
- a phase-locked loop (PLL) driven by a reference signal generated by the reference oscillator, wherein the PLL comprises:
- a phase detector that receives the reference signal and a first output signal from a sigma-delta modulator and that produces a second output signal that is related to a frequency or phase difference between the reference signal and the first output signal,
- a charge pump that receives the second output signal and produces a third output signal based thereon that is shaped by a loop filter, and
- a controllable oscillator that receives the shaped third output signal and produces a fourth output signal based thereon that is an output of the synthesizer electronic circuit and that is provided to a feedback path that includes a pre-scaler that produces a fifth output signal that is provided to the sigma-delta modulator;
- and
- calibration logic that opens and taps the feedback path through at least one switch and provides output signals to the controllable oscillator.
Dependencies are inferred from the claim text.