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Differential Amplifier

IP.com Disclosure Number: IPCOM000095842D
Original Publication Date: 1964-Aug-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Related People

Sumilas, JW: AUTHOR

Abstract

This differential amplifier has good common mode noise rejection and a stable gain. The amplifier includes common base amplifier T1 and series feedback amplifier T2 with resistor R4 serving as the feedback resistor. Resistors R1 and R2 reference input terminals 1 and 2 to ground. Resistor R6 sets the bias voltage at the collectors of T1 and T2. At the frequencies at which the amplifier is operated, inductor L1 causes resistor R6 and the positive supply voltage to act as a current source. Resistor R3 allows the input signal at 1 to appear as a current source at the emitter of T1. Input voltages can be in the order of 100 millivolts.

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Differential Amplifier

This differential amplifier has good common mode noise rejection and a stable gain. The amplifier includes common base amplifier T1 and series feedback amplifier T2 with resistor R4 serving as the feedback resistor. Resistors R1 and R2 reference input terminals 1 and 2 to ground. Resistor R6 sets the bias voltage at the collectors of T1 and T2. At the frequencies at which the amplifier is operated, inductor L1 causes resistor R6 and the positive supply voltage to act as a current source. Resistor R3 allows the input signal at 1 to appear as a current source at the emitter of T1. Input voltages can be in the order of 100 millivolts.

Assuming the input voltages are equal at 1 and 2, T1 and T2 conduct to produce an output of predetermined value at the terminal 3. If the input signals at 1 and 2 both increase positively the same amount (a common mode signal), the current through T1 decreases and the current through T2 increases substantially in the same amount to maintain the signal level at 3 relatively constant.

However, when one of the input terminals, e.g., 1, goes negative or positive, and 2 remains constant, the current through T1 increases or decreases to produce a corresponding increase or decrease in the signal level at output terminal 3. Similarly, if the input signal at 2 goes more positive or negative while the input at 1 remains constant, current through T2 increases or decreases, respectively. Such produces a correspondingly more...