Self-calibrating voltage-controlled oscillator for asynchronous

Details Self-calibrating voltage-controlled oscillator for asynchronous Self-calibrating voltage-controlled oscillator for asynchronous

1998-08-06

2000-09-05

Mis, David

Oscillators

With frequency adjusting means

Step-frequency change

331 17, 331 34, 331 57, 331143, H03B 520, H03L 7099

Patent

active

061149209

ABSTRACT:
A circuit, such as a phase-lock loop (PLL), has an oscillator having a plurality of operating curves. During circuit auto-trim operations, the oscillator is automatically trimmed to an appropriate oscillator operating curve for use during normal circuit operations. In particular PLL embodiments, the PLL is a charge-pump PLL having a phase/frequency detector (PFD) that generates error signals based on comparing an input signal and a PLL feedback signal; a charge pump that generates amounts of charge corresponding to the error signals; a loop filter that accumulates the amounts of charge to generate a loop-filter voltage; and a voltage-controlled oscillator (VCO), where the VCO output signal is used to generate the PLL feedback signal. During normal PLL operations, the loop-filter voltage is applied to the voltage input of the VCO. During the PLL auto-trim operations, a state machine applies a sequence of digital control input values to the VCO to select different VCO operating curves until an appropriate operating curve for the present PLL application is found. In different embodiments, the state machine uses different signals to determine whether the center frequency of each operating curve in the sequence is above or below the desired nominal operating frequency for the VCO, and select one such operating curve for use in normal operations. The present invention can also be implemented in circuits having self-calibrating oscillators, other than PLLs.

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