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Open Loop Small Signal Gain

The open loop gain of this circuit (without feedback resistors) is given by the product of the gain of the individual stages.

Av=Av1Av2Av3

The gain of stage 1 (Av1) is given by equation ([6.23]). However, the load resistor RL now become the input resistance of stage 2, which is $R_{TB7}= r_{\pi 7}+\beta R_{E7}$ (Note that $ R_{E7}=470\Omega$in the figure.

The gain of stage 2 (Av2) is that of a CE amp with an active load.

 

Where the Rin3 is the input resistance of stage 3, $R_{in3}=100K\vert\vert 100K\vert\vert R_{TB9}\vert\vert R_{TB10}\approx 100K\vert\vert 100K=50K$|RTB9,  RTB10 are the input resistances of Q9 and Q10, which for open loop and no load are almost infinity.

Stage 3 is a push-pull amp so $A_{v3}\approx 1$.


Bassel Al-Annouf
12/7/1998