Browse Prior Art Database

Amplifier With Gain and Frequency Response Independent of Operating Point

IP.com Disclosure Number: IPCOM000052967D
Original Publication Date: 1981-Aug-01
Included in the Prior Art Database: 2005-Feb-12
Document File: 2 page(s) / 26K

Publishing Venue

IBM

Related People

Driscoll, CD: AUTHOR [+2]

Abstract

The gain and frequency response of an amplifier in a feedback system is made independent of its operating point by using a second amplifier to buffer the reference voltage for the first amplifier.

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 79% of the total text.

Page 1 of 2

Amplifier With Gain and Frequency Response Independent of Operating Point

The gain and frequency response of an amplifier in a feedback system is made independent of its operating point by using a second amplifier to buffer the reference voltage for the first amplifier.

Operational amplifiers are used to establish loop gain and add frequency compensation in feedback systems, e.g., switching regulators. In a switching regulator application, the DC operating point of the operational amplifier must be adjusted to vary the output voltage of the regulator. Conventionally, the operating point of such an amplifier is varied by adjusting either a feedback resistor or an input resistor in the reference voltage circuit for the amplifier. Changing either resistor has the undesirable effect of changing the loop gain and frequency response.

The circuit shown in the drawing allows the operating point of an operational amplifier 10 to be adjusted without changing the loop gain or frequency response. The feedback resistor 12, input resistors 14 and 16 and input capacitor 18 have fixed values.

The DC operating point of amplifier 10 is adjusted by a circuit including a DC amplifier 20 having an adjustable feedback resistor 22 and an input resistor 24 connected to ground. A reference voltage is applied to the non-inverting input of amplifier 20. The output impedance of amplifier 20 is very low and is essentially constant with the operating point. The impedances of the resistors 14...