Voltage controlled oscillator (VCO) frequency gain compensation circuit
First Claim
1. A signal generator comprising:
- means for generating an output signal having a value responsive to a control signal applied thereto; and
,means for generating said control signal including means for modulating a control current signal between a first state and a second state as a function of an input signal, said control signal corresponding to said control current signal;
wherein when in said first state said modulating means is configured to increase said control current signal at a first rate substantially proportional to a rate of increase of said input signal, and when in said second state said modulating means is operable to increase said control current signal at a second rate that is substantially non-linear relative to said rate of increase of said input signal to thereby reduce a variation in a gain characteristic of said signal generator.
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Accused Products
Abstract
A voltage controlled oscillator (VCO) having a current gain compensation circuit includes a control circuit portion for generating a frequency control signal, and a ring oscillator responsive to the frequency control signal for outputting the VCO output signal. The control circuit includes a control transistor responsive to input control voltage Vcontrol. Connected between the source terminal of the control transistor and ground is a resistive element in parallel with an N-channel field effect transistor and a P-channel field effect transistor, each configured to operate in saturation. The resistor, and the N-channel, and P-channel transistors provide parallel current paths which, collectively, form a control current that corresponds to the frequency control signal. As the voltage control signal Vcontrol increases beyond a predetermined level, the transistors conduct, and carry a current that is proportional to the square of the input control voltage Vcontrol. Accordingly, the magnitude of total control current is dominated by the transistor-provided component, and assumes a square relationship, with respect to the input control voltage. This square-law current-voltage gain characteristic compensates for the inversely mirrored frequency gain characteristic of the ring oscillator in order to attain a reduced frequency gain variation for the overall VCO, with respect to control voltage variations. This reduction in variation translates to a reduced variation in the frequency gain of the VCO with respect to temperature variations when the VCO is used in a phase locked loop (PLL) circuit.
79 Citations
18 Claims
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1. A signal generator comprising:
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means for generating an output signal having a value responsive to a control signal applied thereto; and
,means for generating said control signal including means for modulating a control current signal between a first state and a second state as a function of an input signal, said control signal corresponding to said control current signal; wherein when in said first state said modulating means is configured to increase said control current signal at a first rate substantially proportional to a rate of increase of said input signal, and when in said second state said modulating means is operable to increase said control current signal at a second rate that is substantially non-linear relative to said rate of increase of said input signal to thereby reduce a variation in a gain characteristic of said signal generator. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A signal generator comprising:
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an output circuit configured to generate an output signal having a value responsive to a control signal applied thereto; a control circuit having an output for generating said control signal as a function of an input signal, said control circuit further including a control transistor having a first channel region for carrying a control current signal and a gate terminal coupled to receive said input signal, said control circuit further including a resistive element coupled between one end of said first channel and a reference node, said control circuit further including an active device having a second channel region coupled between said one end and said reference node; wherein a magnitude of said control current signal comprises the sum of the respective currents through said resistive element and said active device as a function of said input signal. - View Dependent Claims (15)
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16. A method of operating a signal generator, said method comprising the steps of:
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(A) generating an output signal having a value responsive to a biasing current signal; (B) converting an input signal to a control current signal in a first state wherein a first rate of increase of said control current signal is substantially proportional to a rate of increase of said input signal; and
,(C) converting said input signal to said control current signal in a second state wherein a second rate of increase of said control current signal is substantially non-linear relative to said rate of increase of said input signal to thereby reduce a variation in a gain characteristic of said generator. - View Dependent Claims (17, 18)
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Specification