Method for measuring the response of a voltage controlled oscillator
AssigneeXerox Corporation
InventorMichael B. Neary
Life of this patent
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Abstract
A method for calibrating a VCO within a phase locked loop circuit is disclosed. First, a DAC output voltage is set to its minimum, and a counter M is adjusted until a comparator is its threshold voltage. Next, the DAC is set to another voltage, and counter M is again adjusted to the comparator threshold. This process is repeated for as many steps as desired. When the phase locked loop circuit requests an instantaneous frequency, an interpolation of the requested frequency against the curve created by the above-described method gives the value required by the DAC.
Claims14
A method for measuring the response of a voltage controlled oscillator within a phase locked loop comprising the steps of:
- a) setting a voltage output of an integrator near a threshold voltage of a comparator;
- b) holding a time period between a start of scan pulse and an end of scan pulse constant;
- c) setting a digital to analog converter output voltage to its minimum value;
- d) adjusting a counter M until said comparator equals said threshold voltage,
- e) setting the digital to analog converter output voltage to another output voltage;
- f) repeating steps (d) through (e) for as many intervals to meet precision requirements, and
- g) returning said counter M to its nominal value which returns said voltage output of said integrator near said threshold voltage of said comparator.
A phase locked loop circuit comprising:
- an integrator having a voltage set near a threshold voltage of a comparator;
- a digital to analog converter output set to a minimum value;
- a counter M continuously adjusted until said comparator equals said threshold voltage, wherein said digital to analog converter output voltage is changed in stepwise fashion to another output voltage in association with said counter M for as many intervals needed to meet precision requirements
A phase locked loop system comprising the steps of:
- means for setting a voltage output of an integrator near a threshold voltage of a comparator;
- means for holding a time period between a start of scan pulse and an end of scan pulse constant;
- means for setting a digital to analog converter output voltage to its minimum value;
- means for adjusting a counter M until said comparator equals said threshold voltage;
- means for setting the digital to analog converter output voltage to another output voltage wherein said means for adjusting and setting are repeated for as many intervals as necessary to meet precision requirements;
- returning said counter M to its nominal value which returns said voltage output of said integrator near said threshold voltage of said comparator;
- and
- calculating an exact frequency for any voltage output of said digital to analog output.
Dependencies are inferred from the claim text.