Amplification Factor 𝝁

Another parameter of importance is called the Amplification factor and is represented by the symbol 𝝁

This is obtained from the plot drawn between the VDS and VGS(negative value) keeping the value of the Drain current ID constant.

Figure 10: Amplification Characteristic

The Amplification factor 𝝁 represents the maximum amount of amplification the JFET can produce.

Relationship between the Amplification Factor 𝝁, Transconductance gm and Drain Resistance rd:

From equation (1), it may be noted that i_{D} is the instantaneous value of the Drain current, v_{DS} is the instantaneous value of Drain - Source Voltage and v_{GS} is the instantaneous value of the Gate - Source voltage.

It may be noted here that the word instantaneous value represents the variable DC value.

It may also be observed from the equation (1) that the total variation in the value of the Drain current i_{D} is the sum of the variations in v_{DS} and v_{GS}.

Ilustration:

For this look at the equation (2).

Here

v_{DS} → Variable DC

V_{DS} → Pure DC

v_{ds} → Pure AC

Expand the equation (1) using Taylor's expansion, we get

From (3) note the following:

∆v_{DS} → Small change in v_{DS}

∆v_{GS} → Small change in v_{GS}

∆ i_{D} → The corresponding change in i_{D}

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