Electronics 1

Lecture 6

Multistage Amplifiers, Interstage Coupling, Feedback Tuned Amplifiers

Literature1. Tietze U, Schenk Ch: Electronic Circuits – Handbook for Design and Applications,

Springer, 2008, ISBN: 35400042972. Horowitz, Hill W: The Art of Electronics, Cambridge University Press, 1989,

ISBN: 0521370957

Coupling of amplifier stages

Direct coupling- both DC and AC components of the input signal are amplified- biasing of individual stages influence each other

Capacitive- only the AC components of the input signal are amplified- biasing of individual stages are independent

Inductive (via signal transformer)- only the AC components of the input signal are amplified- biasing design must take into account the fact that coils have very low DC resistance

Coupling of amplifier stages

Direct coupling- both DC and AC components of the input signal are amplified- biasing of individual stages influence each other

Differential common emitter common collectorinput stage voltage amplifier power stage

Multistage DC amplifier with direct coupling

Coupling of amplifier stages

Inductive (via signal transformer)- only the AC components of the input signal are amplified- biasing design must take into account the fact that coils have very low DC resistance

Class B push-pull amplifier with induvtive coupling

Class A amplifier with capacitive input and inductive output coupling

The principle of feedback

Negative series voltage feedback

Negative series voltage feedback

Two-stage common emitter amplifier with negative series voltage feedback

Negative series current feedback

Negative series current feedback

Common emitter amplifier without emitter resistance bypass

Tuned amplifiers Applied at high frequencies. Gain is strongly reduced out of the vicinity of the resonance frequency.Bandwidth: the limit of 3dB gain decrease.

Real oscillator circuit. Series-parallel equivalence

00 ps QQ

sp Cr

LR

Tuned amplifiersIn case of common emitter tuned amplifier the collector impedance is an oscillator circuit, therefore the gain is strongly frequency dependent.

gm 10…500 mS : transistor transconductance (DiC /DuB h21 / h11)1/h22 10…100 k : transistor output resistance1/h22 >> Rt

Coupling of tuned amplifier stages

Sinchronous tuning Staggered tuning

Coupling of tuned amplifier stages

Effect of coupling constant on a two-stage tuned amplifier

Oscillator circuit coupling

Coupling of tuned amplifier stages

The first mass production transistor radio receiver (1954)

Common base radiofrequency amplifier