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Voltage Controlled Oscillator

IP.com Disclosure Number: IPCOM000085120D
Original Publication Date: 1976-Feb-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Wang, LC: AUTHOR

Abstract

A voltage-controlled oscillator (VCO) employs a transistor network (T1-T4) and a current source Is to charge and discharge a timing capacitor C. The rate of discharge and hence the frequency of oscillation is controlled by the input current Ic. Transistors T1 and T2 are alternately switched ON and OFF by the differential interlock circuit which acts regeneratively to effect the switching, whenever the currently OFF transistor becomes conductive as a result of discharge of capacitor C. Opposite phase outputs appear at Phi 1 and Phi 2.

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Voltage Controlled Oscillator

A voltage-controlled oscillator (VCO) employs a transistor network (T1-T4) and a current source Is to charge and discharge a timing capacitor C. The rate of discharge and hence the frequency of oscillation is controlled by the input current Ic. Transistors T1 and T2 are alternately switched ON and OFF by the differential interlock circuit which acts regeneratively to effect the switching, whenever the currently OFF transistor becomes conductive as a result of discharge of capacitor C. Opposite phase outputs appear at Phi 1 and Phi 2.

Transistors T3 and T4 form a dual-current switch for alternately connecting T1 and T2 to current source Is. The bases of transistors T3 and T4 are tied to the bases of T2 and T1, respectively, so that T3 is OFF when T1 is ON and T4 is OFF when T2 is ON. By means of this switch the current IE, drawn by whichever of T1 and T2 is ON, is kept equal to Ic and the frequency f of the oscillator is given by: f = Ic over 2.Delta V.C = Ie over 2.DeltaV.C where Delta V is the differential voltage across capacitor C.

In prior circuits, two current sources were employed and IE was twice Ic. Thus, for the same emitter current, the frequency of the VCO is doubled. Alternatively, the power consumption of the VCO may be reduced. Furthermore, the voltage-to-frequency linear conversion region is extended.

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