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Stable Symmetrical Gateable VCO

IP.com Disclosure Number: IPCOM000075061D
Original Publication Date: 1971-Jul-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Johnson, HW: AUTHOR

Abstract

This voltage controlled oscillator comprises two identical current sources alternately charging and discharging a capacitor under the control of two cross-coupled Schmitt triggers. The two current sources are composed of Q5 and Q6 along with their associated biasing resistors and diodes. Control current applied through input A may be varied to control the frequency of oscillation. The uniqueness of the configuration lies in the use of emitter-coupled complimentary Schmitt triggers, which also comprise constant-current source elements.

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Stable Symmetrical Gateable VCO

This voltage controlled oscillator comprises two identical current sources alternately charging and discharging a capacitor under the control of two cross- coupled Schmitt triggers. The two current sources are composed of Q5 and Q6 along with their associated biasing resistors and diodes. Control current applied through input A may be varied to control the frequency of oscillation. The uniqueness of the configuration lies in the use of emitter-coupled complimentary Schmitt triggers, which also comprise constant-current source elements.

In operation, assuming that Q1 and Q3 are conducting, the base potential of Q1 depends upon the values of zener diode CR1, temperature compensating diode CR2 and the current through R2. However, the current through R2 results substantially from the constant-current sources comprising Q5 and Q6. Hence, the base potential of Q1 is constant with respect to +V, whereby Q1 is effectively a constant-current source. Moreover, as long as Q3 conducts, output D is maintained at a constant voltage relative to ground due to the constant current through R4. Thus the lefthand node of capacitor C1 is fixed.

The current from current source Q6 causes the righthand node of C1 to move negative until Q4 conducts, thus initiating regenerative switching of Q2 to the conducting state, whereby Q1 and Q3 are turned off. In this condition, Q2 is conducting constant current and the lefthand node of C1 begins charging negativel...