Browse Prior Art Database

Highly-Stabilized Voltage-Controlled Oscillator

IP.com Disclosure Number: IPCOM000035874D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 5 page(s) / 110K

Publishing Venue

IBM

Related People

Bailey, JA: AUTHOR

Abstract

Prior art in voltage-controlled oscillators contains many attempts at providing an accurate nominal frequency (sometimes called the free- running frequency) that is also stable with varying circuit temperature and power supply conditions. While this circuit provided good temperature and power supply stability, the free-running frequency accuracy was inadequate, unless an expensive pontentiometer adjustment was included to calibrate the initial free-running frequency.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 50% of the total text.

Page 1 of 5

Highly-Stabilized Voltage-Controlled Oscillator

Prior art in voltage-controlled oscillators contains many attempts at providing an accurate nominal frequency (sometimes called the free- running frequency) that is also stable with varying circuit temperature and power supply conditions. While this circuit provided good temperature and power supply stability, the free- running frequency accuracy was inadequate, unless an expensive pontentiometer adjustment was included to calibrate the initial free-running frequency.

The invention described herein provides improved power supply and temperature stability as well as providing an accurate free-running frequency without the need of external adjustments.

The circuit is composed of two parts: (1) a stable current reference, the output of which is proportional to a control voltage; and (2) a current-controlled oscillator which uses as a current control, the output of the current reference as shown in Fig. 1.

Referring to Fig. 1, the current reference uses as a reference, a fixed external resistor. The control voltage input serves to change the control current output in a well-controlled linear fashion. The current-controlled oscillator uses as a reference, the external timing capacitor. The control current input serves to change the oscillator output frequency also in a well controlled linear fashion. These two blocks are described in the following pages.

(Image Omitted)

Refer to Fig. 2 for the following explanation of operation of the current source referenced. Transistors T3 and T4 form matching current sources; also T7 and T12 for matching current sinks having output magnitude proportional to the current output of T3 and T4. T5 and T6 form a differential amplifier with both inputs tied to the bandgap reference output. This differential amplifier along with T7 and T3 form a reference circuit which is a replica of the differential amplifier formed by T10 and T11 and the current source T4 and the current sink T12. Because both T5 and T6 bases are connected to the bandgap reference voltage and because R3 and R4 are equal, the collector currents of T5 and T6 are equal. This condition is analogous to the control voltage input being equal to the bandgap voltage. Because of the matching currents of T7 and T12, as well as T3 and T4, when the control voltage input is equal to the bandgap reference, the output control current is equal to the current being fed to external reference resistor R1. Operational amplifier OA1 has a large voltage gain and serves to amplify the difference between the voltage across R1 and the bandgap reference. This voltage, in turn, controls magnitude of all the current sources in the circuit.

Because the gain of OA1 is very large, the voltage across R

(Image Omitted)

1

Page 2 of 5

is controlled to be equal to the bandgap voltage reference. This means that the current through R, and the control current are both: Ic = VBG V control = VBG

R1

As the control voltage input dev...