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Voltage Controlled Oscillator

IP.com Disclosure Number: IPCOM000078436D
Original Publication Date: 1973-Jan-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Buckley, F: AUTHOR [+2]

Abstract

The voltage-controlled oscillator (VCO) 10 has a capacitor C, which is charged and discharged by gated current switch A1 and a Schmidt trigger 2A.

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Voltage Controlled Oscillator

The voltage-controlled oscillator (VCO) 10 has a capacitor C, which is charged and discharged by gated current switch A1 and a Schmidt trigger 2A.

The gated current switch A1 provides a drive current I which is programmable by the application of a voltage Vb to an input pin 1a in the biasing network 1, associated with differential amplifier pair 1A, 1B of switch A1. The gated current switch A1 provides a current drive of +/- I/2 to the capacitor C.

With the noninverting input 2 of amplifier M2 connected to a reference voltage Vref, the output voltage Vo is Vref + Vd, where Vd is the forward drop of the shunt feedback diodes D1, D2 of differential amplifier M2.

In operation, at time t0, assume Vo equals Vref + Vd. Vp will be at some voltage level v3 dependent upon the ratio of the resistive divider formed by potentiometer R, and Vc is = v2. With Vo applied to terminal 3 of A1, current I/2 is driven into capacitor C, cf. solid line arrow. The capacitor voltage Vc rises at the rate I/2C until it reaches level v3 at time t1.

At time t1, comparator M1 switches forcing output voltage Vo to the voltage level Vref - Vd = v1. Switch A1 now pulls or sinks current I/2 out of capacitor C, cf. dash line arrow, until it reaches v2 at time t2, whereafter the cycle repeats.

The output frequency I/T is proportional to I which in turn is controlled by the input biasing voltage Vb to A1. The gain of VCO 10, which is defined as the change in output freq...