Browse Prior Art Database

Simple Precision RC Oscillator

IP.com Disclosure Number: IPCOM000080921D
Original Publication Date: 1974-Mar-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Kovach, PS: AUTHOR [+2]

Abstract

The present circuit uses fewer components to make an accurate RC oscillator. The frequency of this oscillator is set by resistor R1 and capacitor C1. Resistors R2, R3 and capacitor C2 set a reference for the threshold levels. 11 charges and discharges capacitor C1. I2, R1 changes the threshold value of differential amplifier A2 and switches the differential amplifiers A1 and A3. Currents 11 and 12 are matched within +/-3% and a relationship between R1 and C1 can be made.

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 85% of the total text.

Page 1 of 2

Simple Precision RC Oscillator

The present circuit uses fewer components to make an accurate RC oscillator. The frequency of this oscillator is set by resistor R1 and capacitor C1. Resistors R2, R3 and capacitor C2 set a reference for the threshold levels. 11 charges and discharges capacitor C1. I2, R1 changes the threshold value of differential amplifier A2 and switches the differential amplifiers A1 and A3. Currents 11 and 12 are matched within +/-3% and a relationship between R1 and C1 can be made.

Referring to Fig. 2, there is shown the voltage window produced by I2, R1. I2, R1 produce a voltage about the reference voltage point c. This sets a positive VT threshold and a negative VT threshold. Capacitor C1 will charge to +VT and discharge to -VT. The +VT voltage level is produced by the positive 12 current from the y output of amplifier A2, and the -VT voltage level is produced by the negative 12 current into the y output of amplifier A2. The positive 12 current equals the negative I2 current. Hence, point c is the center point between +VT and -VT. The 12 current also supplies input bias currents which will be considered negligible, since they are much smaller than 12.

With the voltage window defined, a direct relationship can be made between the charging and discharging of capacitor C1 and the voltage window dV, as shown in Fig. 3.

Currents I1 and I2 are matched within +/-3% and they track with the supply and temperature. Therefore, change in supply and temp...