Circuit and method of controlling a VCO with capacitive loads
First Claim
1. A circuit for controlling an output signal frequency of a voltage controlled oscillator (VCO), comprising:
- first means operating in response to the output signal frequency of the VCO for providing a first control signal having a first logic state upon detecting the VCO operating above a predetermined frequency;
a shift register operating in response to said first state of the first control signal for rotating a first logic state between a plurality of outputs;
a first control circuit responsive to said first logic state from a first one of said plurality of outputs of said shift register and said first logic state of said first control signal for providing a first enable signal;
a first counter having an enable input and a plurality of outputs, said enable input receiving said first enable signal, said plurality of outputs providing a first digital value which increments at each first enable signal; and
a load circuit having a first output coupled to an output of the VCO and operating in response to said first digital value applied at a first control input for slowing the output signal frequency of the VCO.
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Accused Products
Abstract
A phase lock loop operates independent of temperature and process variation by digitally loading a VCO until reaching the desired operating frequency. The VCO reaches a high output frequency even under worst case processing by controlling multiple current mirrors to increase inverter switching current without slowing the response of the VCO to changes in loop node voltage. An Initialize-to-VDD circuit sets the loop node voltage to VDD so that the load control circuit need only increase loading to slow down the VCO to the desired operating frequency. A frequency range detector monitors the output frequency of the VCO and passes control signals to a load control circuit to activate digital loads and slow down the VCO to the desired operating frequency.
72 Citations
17 Claims
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1. A circuit for controlling an output signal frequency of a voltage controlled oscillator (VCO), comprising:
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first means operating in response to the output signal frequency of the VCO for providing a first control signal having a first logic state upon detecting the VCO operating above a predetermined frequency; a shift register operating in response to said first state of the first control signal for rotating a first logic state between a plurality of outputs; a first control circuit responsive to said first logic state from a first one of said plurality of outputs of said shift register and said first logic state of said first control signal for providing a first enable signal; a first counter having an enable input and a plurality of outputs, said enable input receiving said first enable signal, said plurality of outputs providing a first digital value which increments at each first enable signal; and a load circuit having a first output coupled to an output of the VCO and operating in response to said first digital value applied at a first control input for slowing the output signal frequency of the VCO. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method of controlling an output signal frequency of a voltage controlled oscillator (VCO), comprising the steps of:
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providing a first control signal having a first logic state upon detecting the VCO operating above a predetermined frequency; rotating a first logic state between a plurality of outputs of a shift register in response to said first state of said first control signal; providing a first enable signal in response to said first logic state from a first one of said plurality of outputs of said shift register and said first logic state of said first control signal; incrementing a first digital value at a plurality of outputs of a first counter upon receiving said first enable signal; and loading an output of the VCO in response to said first digital value for slowing the output signal frequency of the VCO.
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10. An integrated phase lock loop, comprising:
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first means for comparing a phase difference of first and second input signals and generating an output signal to charge and discharge a loop node; second means having an output coupled to said loop node and operating in response to the first input signal for initializing said loop node to a predetermined voltage; a VCO having an input coupled for receiving said output signal of said first means and having an output for providing an oscillator signal; third means for dividing down said oscillator signal into first and second divided oscillator signals, sa-;
d first divided oscillator signal operating as said second input signal of said first means;fourth means coupled for receiving said second divided oscillator signal and said first input, signal and generating a first control signal when said second, divided oscillator signal changes logic state more than a predetermined number of times during a first logic state of said first input signal; a shift register operating in response to said first state of said first control signal for rotating a first logic state between a plurality of outputs; a first control circuit responsive to said first logic state from a first one of said plurality of outputs of said shift register and said first logic state of said first control signal for providing a first enable signal; a first counter having an enable input and a plurality of outputs, said enable input receiving said first enable signal, said plurality of outputs providing a first digital value which increments at each first enable signal; and a load circuit having a first output coupled to said output of said VCO and operating in response to said first digital value applied at a first control input to increase loading at said output of said VCO. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17)
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Specification