Oscillators – Automatic frequency stabilization using a phase or frequency... – Particular frequency control means
Patent
1996-12-12
1998-05-05
Grimm, Siegfried H.
Oscillators
Automatic frequency stabilization using a phase or frequency...
Particular frequency control means
331 57, 331177R, H03B 504, H03L 7099
Patent
active
057480486
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 V.sub.control. 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 V.sub.control increases beyond a predetermined level, the transistors conduct, and carry a current that is proportional to the square of the input control voltage V.sub.control. 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.
REFERENCES:
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"AX.TM. ATM-SONET/SDH Transceiver;" Cypress Semiconductor Corporation; Feb. 1994-Revised Nov. 1996; 1-80.
"MOS Oscillators with Multi-Decade Tuning Range and Gigahertz Maximum Speed", Banu, M., IEEE Jour. of Solid-State Circuits, vol. SC-23, pp. 474-479, Apr. 1988.
Cypress Semiconductor Corporation
Grimm Siegfried H.
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