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Operational Amplifier
Chapter No. 3
Differential Amplifiers
Operational Amplifiers:
The operational amplifier is a direct-coupled high gain amplifier usable from 0 to over 1MH Z to which feedback is added to control its overall response characteristic i.e. gain and bandwidth. The op-amp exhibits the gain down to zero frequency.
Such direct coupled (dc) amplifiers do not use blocking (coupling and by pass) capacitors since these would reduce the amplification to zero at zero frequency. Large by pass capacitors may be used but it is not possible to fabricate large capacitors on a IC chip. The capacitors fabricated are usually less than 20 pf. Transistor, diodes and resistors are also fabricated on the same chip.
Differential Amplifiers:
Differential amplifier is a basic building block of an op-amp. The function of a differential amplifier is to amplify the difference between two input signals.
How the differential amplifier is developed? Let us consider two emitter-biased circuits as shown in fig. 1.
Fig. 1
The two transistors Q1 and Q2 have identical characteristics. The resistances of the circuits are equal, i.e. RE1 =
R E2, RC1 = R C2 and the magnitude of +VCC is equal to the magnitude of ?VEE. These voltages are measured with respect to ground.
To make a differential amplifier, the two circuits are connected as shown in fig. 1. The two +VCC and ?VEE supply terminals are made common because they are same. The two emitters are also connected and the parallel combination of RE1 and RE2 is replaced by a resistance RE. The two input signals v1 & v2 are applied at the base of Q1 and at the base of Q2. The output voltage is taken between two collectors. The collector
Notes prepared by Mrs. Sejal Shah
1
Operational Amplifier resistances are equal and therefore denoted by RC = RC1 = RC2.
Ideally, the output voltage is zero when the two inputs are equal. When v1 is greater then v2 the output voltage with the polarity shown appears. When
Chapter No. 3
Differential Amplifiers
Operational Amplifiers:
The operational amplifier is a direct-coupled high gain amplifier usable from 0 to over 1MH Z to which feedback is added to control its overall response characteristic i.e. gain and bandwidth. The op-amp exhibits the gain down to zero frequency.
Such direct coupled (dc) amplifiers do not use blocking (coupling and by pass) capacitors since these would reduce the amplification to zero at zero frequency. Large by pass capacitors may be used but it is not possible to fabricate large capacitors on a IC chip. The capacitors fabricated are usually less than 20 pf. Transistor, diodes and resistors are also fabricated on the same chip.
Differential Amplifiers:
Differential amplifier is a basic building block of an op-amp. The function of a differential amplifier is to amplify the difference between two input signals.
How the differential amplifier is developed? Let us consider two emitter-biased circuits as shown in fig. 1.
Fig. 1
The two transistors Q1 and Q2 have identical characteristics. The resistances of the circuits are equal, i.e. RE1 =
R E2, RC1 = R C2 and the magnitude of +VCC is equal to the magnitude of ?VEE. These voltages are measured with respect to ground.
To make a differential amplifier, the two circuits are connected as shown in fig. 1. The two +VCC and ?VEE supply terminals are made common because they are same. The two emitters are also connected and the parallel combination of RE1 and RE2 is replaced by a resistance RE. The two input signals v1 & v2 are applied at the base of Q1 and at the base of Q2. The output voltage is taken between two collectors. The collector
Notes prepared by Mrs. Sejal Shah
1
Operational Amplifier resistances are equal and therefore denoted by RC = RC1 = RC2.
Ideally, the output voltage is zero when the two inputs are equal. When v1 is greater then v2 the output voltage with the polarity shown appears. When