Voltage controlled oscillator (VCO) frequency gain compensation circuit
First Claim
1. A voltage controlled oscillator (VCO) comprising:
- means for generating a VCO output signal having a frequency value responsive to a frequency control signal applied thereto;
means for generating said frequency control signal including means for modulating a control current signal between a first state and a second state as a function of an input control signal, said frequency 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 control 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 control signal to thereby reduce a variation in a frequency gain characteristic of said VCO with respect to variations in temperature.
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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.
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Citations
18 Claims
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1. A voltage controlled oscillator (VCO) comprising:
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means for generating a VCO output signal having a frequency value responsive to a frequency control signal applied thereto; means for generating said frequency control signal including means for modulating a control current signal between a first state and a second state as a function of an input control signal, said frequency 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 control 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 control signal to thereby reduce a variation in a frequency gain characteristic of said VCO with respect to variations in temperature. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A voltage controlled oscillator (VCO) comprising:
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an output circuit configured to generate a VCO output signal having a frequency value responsive to a frequency control signal applied thereto; a control circuit having an output for generating said frequency control signal as a function of an input control 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 control 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 control signal. - View Dependent Claims (15)
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16. A method of operating a voltage controlled oscillator (VCO), said method comprising the steps of:
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(A) generating a VCO output signal having a frequency value responsive to a biasing current signal; (B) converting an input control 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 control signal; and
,(C) converting said input control 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 control signal to thereby reduce a variation in a frequency gain characteristic of said VCO with respect to variations in temperature. - View Dependent Claims (17, 18)
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Specification