Neutralization technique in Electron Devices and Circuits(EDC)

1. Neutralization

2. • Technique used for the elimination of
potential oscillation is called neutralization
• BJT and FET are potentially unstable over
some frequency range due to feedback
parameter(YN ) present in them.
• Feedback can be cancelled by an additional
feedback signal
• That is equal in amplitude and opposite in
sign.

3. Equivalent circuit of a neutralization
transistor

4. • Yre
‘ = Ib / Vce by making Vbe = 0
• Ib = Yre Vce- YN Vce
• Yre
‘= Yre - YN
• For perfect neutralization, Yre
‘ = 0
• Therefore Yre = YN
• desired component used for neutralization is
Negative capacitor

5. Tuned RF amplifier with Hazeltine
Neutralization

6. • Hazeltine technique is used to maintain
Stability
• Undesire effect of collector to base
capacitance is neutralize by introducing a
signal which cancels the signal.
• CN - Variable capacitor
• CN - connected from bottom of the coil
• It introduces a signal to base of transistor
such that it cancels the signal Cbc.

7. Modified Hazeltine -Neutrodyne

8. • Modified version of hazeltine
neutralization called Neutrodyne
neutralization technique.
• CN is connected to the lower end of
secondary coil of next stage.
• Hence it is connected with VCC, It is
insesitive to any variation in supply
voltage
• It provides higher stabilization for the
tuned amplifier

9. Advantages
• Amplify defined frequencies
• Signal to noise at output is good
• Suited for radio transmitter and receiver

10. Disadvantages
• Circuit is bulky because of inductors and
capacitors
• Circuit is Costly
• Design become complex if band frequency
increases
• Not suitable to amplify audio frequency