# Swamped Amplifier

# Swamped Amplifier

Fig. 1 shows the circuit of a swamped amplifier.

#### Note that d.c. emitter resistance R_{E} is divide into two parts viz. R_{E1} and R_{E2}. Only resistance R_{E2} is bypassed by the capacitor CE while resistance R_{E1} is not.

This method swamps or minimises the effect of

r′_{e} on the voltage gain without reducing the

voltage gain too much. Now the total a.c. emitter resistance is (r_{′e}+ R_{E1}) instead of

r′_{e} as in a standard

CE amplifier. Therefore, the voltage gain of a amplifier at no-load becomes :

If R_{E1} ≥ 10 e

r′_{e} , then the effect of e

r′_{e} is almost negligible and the voltage gain is give by ;

A_{v} =R_{c}/R_{E1}

Therefore, the voltage gain is essentially independent of e

r′ or it is reasonably stabilised.

Effect of swamping on Z_{in} (base)

. The Zin (base) with R_{E} completely bypassed is Z_{in} (base)= β _{e}r′_{e} .

When the emitter resistance is partially bypass, the portion of the resistance that is unbypass (i.e.

R_{E1}) is seen by the a.c. signal and appears in series with e

r′ . Therefore, for swamped amplifier,

Z_{in} (base) = β ( r′_{e} + R_{E1})

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