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Electronic Circuits Laboratory EE462G Simulation Lab #9

Electronic Circuits Laboratory EE462G Simulation Lab #9. The BJT Differential Amplifier. Differential Amplifier. The object of the differential amplifier is to amplify the difference between V in1 and V in2 for output V out . V CC. R C1. R C2.

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Electronic Circuits Laboratory EE462G Simulation Lab #9

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  1. Electronic Circuits LaboratoryEE462GSimulation Lab #9 The BJT Differential Amplifier

  2. Differential Amplifier The object of the differential amplifier is to amplify the difference between Vin1 and Vin2 for output Vout. VCC RC1 RC2 In many applications VEE = -VCC. This can be obtained in the lab by setting the one negative and positive terminals of the dual power supply to earth ground and then set the power supply for the positive connection to the circuit to VCC and the negative connection to VEE. + Vout - + Vout1 _ + Vout2 _ Q1 Q2 Vin2 Vin1 RE VEE

  3. Differential Amplifier Inputs The ideal differential amplifier suppresses the common mode input given by: VCC RC1 RC2 + Vout - + Vout1 _ + Vout2 _ and amplifies differential mode input given by: Q1 Q2 Note that the input to this system is uniquely determined by the (Vin1, Vin2) pair or the (Vicm, Vidm) pair. There are several types of gain that can now be described for this amplifier. Vin2 Vin1 RE VEE

  4. Differential Amplifier Gain The gain between Vidm and Vout1 is described as the single-ended ideal differential gain given by: VCC RC1 RC2 + Vout - + Vout1 _ + Vout2 _ A similar gain is described for Vout2: Q1 Q2 Vin2 Similar gains can be described for the common mode input: Vin1 RE VEE

  5. Differential Amplifier Gain The single ended output can be computed from the previously defined gains using superposition given by: An important performance measure for differential amplifiers is the common-mode rejection ratio (CMRR) given by:

  6. Small Signal Model vout1 vout2 Circuits I analysis methods can be applied to compute the previously described gains and CMRR in terms of circuit parameters. RC1 RC2 ib2 ib1 r r ib1 ib2 vin2 vin1 RE Where are the Q1 and Q2 transistor nodes on this model?

  7. RC2 RC1 - Vout1 + + Vout2 - VCC Ib1 Ib2 VBE VBE VEE Ib1 Ib2 Vin1 RE Vin2 Large Signal Model Circuits I analysis methods can be applied to compute the quiescent points in terms of circuit parameters. Where are the Q1 and Q2 transistor nodes on this model?

  8. Crude Op Amp • A simple Op Amp can be create from the differential amp. Most Op Amps have additional stages to buffer the output (See http://www.williamson-labs.com/480_opam.htm ).

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