Differential amplifier with gain compensation

• US 4,929,909 A
• Filed: 03/27/1989
• Issued: 05/29/1990
• Est. Priority Date: 03/27/1989
• Status: Expired due to Term

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Gilbert, Barrie
• Primary Examiner(s): Mullins, James B.
• Application Number:
  US07/328,946
• Time in Patent Office: 428 Days
• Field of Search: 330/256, 330/261, 330/289
• US Class Current: 330/256
• CPC Class Codes: H03F 1/302 in bipolar transistor amplifiers H03F1/303, H03F1/305, H03F1/307 take precedence
• CPC Class Codes: H03F 2203/45508 the CSC comprising a voltage generating circuit as bias circuit for the CSC
• CPC Class Codes: H03F 3/45479 characterised by the way of common mode signal rejection

Abstract

A differential amplifier including circuit means for generating a tail current which is not only porportional to absolute temperature, but also is adjusted to compensate for the non-ideal transistor geometries and properties, including finite beta and non-zero, temperature-dependent intrinsic resistances, so as to result in an amplification ratio which is substantially independent of all component variations.

Claims

1. A gain-compensated differential amplifier circuit comprising:

(a) a transistor differential amplifier, with reasonably matched current gains, operating at a tail current I_tail ;

(b) a transistor current source responsive to a control voltage for generating said tail current as a function of the control voltage;

(c) control voltage generating means for generating, as the control voltage, a voltage which varies proportionately to absolute temperature; and

(d) the control voltage generating means including means for functionally relating the control voltage to the intrinsic emitter resistance of the current source.

2. The amplifier of claim 1 wherein the control voltage generating means is adapted to generate, as the control voltage, a voltage which generates a tail current having a component that is functionally related to and tracks the ohmic resistances associated with the geometries and current gain characteristics of the differential amplifier transistors and the transistor current source.

3. The amplifier of either claim 1 or claim 2 wherein the current source comprises a common-emitter transistor whose collector is connected to receive the emitter currents of the transistors of the differential amplifier and the control voltage generating means includes a Δ

V_BE cell for supplying to the base of the common-emitter transistor a control voltage which produces in the collector of the common-emitter transistor a current which is a function of the current gain of the differential amplifier transistors.

4. The amplifier of claim 3 wherein the control voltage produces in the emitter of the common-emitter transistor a current 2I(1+2/beta) and a tail current of 2I(1+1/beta), where beta is the current gain of the differential amplifier transistors, over a selected temperature range.

5. The amplifier of claim 3 wherein the current source further includes an emitter resistor connected between the emitter of the common-emitter transistor and a voltage reference, and wherein the differential amplifier transistors have finite intrinsic emitter resistance and the control voltage is a function of the emitter resistance, the finite intrinsic emitter resistance of the common-emitter transistor and the current gains of the differential amplifier transistors.

6. A gain-compensated differential amplifier circuit comprising:

(a) a transistor differential amplifier, with reasonably matched current gains, operating at a tail current I_tail ;

(b) a current source responsive to a control voltage for generating said tail current as a function of the control voltage;

(c) control voltage generating means for generating, as the control voltage, a voltage which varies proportionately to absolute temperature, and which is provided by a Δ

V_BE cell; and

(d) the Δ

V_BE cell including means for functionally relating the control voltage to the intrinsic emitter resistance of the current source.

7. The amplifer of claim 6 wherein the control voltage generating means is adapted to generate, as the control voltage, a voltage which generates a tail current having a component that is functionally related to and tracks the resistances associated with the transistor geometries and current gain characteristics of the transistors of the differential amplifier and the current source.

8. The amplifier of either claim 6 or claim 7 wherein the current source comprises a common-emitter transistor whose collector is connected to receive the emitter currents of the transistors of the differential amplifier and the Δ

V_BE cell supplies to the base of the common-emitter transistor a control voltage which produces in the collector of the common-emitter transistor a current which is a function of the current gain of the differential amplifier transistors.

9. The amplifier of claim 8 wherein the control voltage produces in the emitter of the common-emitter transistor a current 2I(1+2/beta) and a tail current of 2I(1+1/beta), where beta is the current gain of the differential amplifier transistors, over a selected temperature range.

10. The amplifier of claim 8 wherein the current source further includes an emitter resistor connected between the emitter of the common-emitter transistor and a voltage reference, and wherein the differential amplifier transistors have finite intrinsic emitter resistance and the control voltage is a function of the emitter resistance, the finite intrinsic emitter resistance of the common-emitter transistor and the current gains of the differential amplifier transistors.