Browse Prior Art Database

Emitter Coupled Logic, Controlled Oscillator

IP.com Disclosure Number: IPCOM000083896D
Original Publication Date: 1975-Aug-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

McCarthy, WF: AUTHOR [+3]

Abstract

The circuit shown is a wide-range, voltage-controlled oscillator (VCO) that is simple to construct and operates in an emitter-coupled logic (ECL) environment, without the need for special power supplies or level conversion circuits.

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Emitter Coupled Logic, Controlled Oscillator

The circuit shown is a wide-range, voltage-controlled oscillator (VCO) that is simple to construct and operates in an emitter-coupled logic (ECL) environment, without the need for special power supplies or level conversion circuits.

The output frequency of the circuit is determined by the switching delay of gate 1, and the charge/discharge time constant of R2 and the capacitance of the voltage variable-capacitance diode VC1. Capacitors C1 and C2 provide DC isolation to allow the control voltage to impress an average voltage on VC1, and thereby control the time constant. Resistors R1 and R3 provide AC isolation for this diode bias voltage. R4, R5 and R6 are emitter pull-down resistors for the ECL gates. Gate 2 is used for isolation of the output from the oscillator, gate 1.

In operation, with gate 1 inverted output at a downlevel, R2 discharges VC1 until gate 1 input drops below threshold. At this time, the inverted output switches to an uplevel and the noninverted output switches to a downlevel, holding the gate 1 in that state by further decreasing the gate input voltage through VC1. R2 now starts charging VC1 until the gate input again crosses the threshold, switching the gate back to the original state and completing the cycle.

The advantage of using an RC oscillator as a VCO is that frequency varies as 1/C, instead of 1/ square root of c as in an LC oscillator. This provides a wider tuning range. In addition, since...