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 2 added 29 characters in body edited Dec 27 '17 at 21:20 G36 5,76111 gold badge55 silver badges1111 bronze badges Well, the equation for the Zin and voltage gain looks for the emitter follower with the bootstrap (positive feedback) at the input simulate this circuit – Schematic created using CircuitLab looks like this: $$Z_{IN} = \frac{(r_eR_E + R_3(r_e + R_E))\cdot (1 + \beta)}{R_3 + (\beta+1)r_e }\approx \frac{R_3}{1 - A_V}||(r_e+R_E)(\beta+1)$$ $$A_V = \frac{(R_3+r_e) R_E}{r_e R_E + R_3r_e + R_3R_E} \approx \frac{R_E}{r_e+R_E}$$$$A_V = \frac{(R_3+r_e) R_E}{r_e R_E + R_3r_e + R_3R_E} = \frac{R_E}{R_3||r_e + R_E} \approx \frac{R_E}{r_e+R_E}$$ Of course $$\R_E\$$ is for your circuit equal to $$R_E = R1||R2||R4$$ So, in conclusion, your reasoning is correct Well, the equation for the Zin and voltage gain looks for the emitter follower with the bootstrap (positive feedback) at the input simulate this circuit – Schematic created using CircuitLab looks like this: $$Z_{IN} = \frac{(r_eR_E + R_3(r_e + R_E))\cdot (1 + \beta)}{R_3 + (\beta+1)r_e }\approx \frac{R_3}{1 - A_V}||(r_e+R_E)(\beta+1)$$ $$A_V = \frac{(R_3+r_e) R_E}{r_e R_E + R_3r_e + R_3R_E} \approx \frac{R_E}{r_e+R_E}$$ Of course $$\R_E\$$ is for your circuit equal to $$R_E = R1||R2||R4$$ So, in conclusion, your reasoning is correct Well, the equation for the Zin and voltage gain looks for the emitter follower with the bootstrap (positive feedback) at the input simulate this circuit – Schematic created using CircuitLab looks like this: $$Z_{IN} = \frac{(r_eR_E + R_3(r_e + R_E))\cdot (1 + \beta)}{R_3 + (\beta+1)r_e }\approx \frac{R_3}{1 - A_V}||(r_e+R_E)(\beta+1)$$ $$A_V = \frac{(R_3+r_e) R_E}{r_e R_E + R_3r_e + R_3R_E} = \frac{R_E}{R_3||r_e + R_E} \approx \frac{R_E}{r_e+R_E}$$ Of course $$\R_E\$$ is for your circuit equal to $$R_E = R1||R2||R4$$ So, in conclusion, your reasoning is correct 1 answered Dec 27 '17 at 19:55 G36 5,76111 gold badge55 silver badges1111 bronze badges Well, the equation for the Zin and voltage gain looks for the emitter follower with the bootstrap (positive feedback) at the input simulate this circuit – Schematic created using CircuitLab looks like this: $$Z_{IN} = \frac{(r_eR_E + R_3(r_e + R_E))\cdot (1 + \beta)}{R_3 + (\beta+1)r_e }\approx \frac{R_3}{1 - A_V}||(r_e+R_E)(\beta+1)$$ $$A_V = \frac{(R_3+r_e) R_E}{r_e R_E + R_3r_e + R_3R_E} \approx \frac{R_E}{r_e+R_E}$$ Of course $$\R_E\$$ is for your circuit equal to $$R_E = R1||R2||R4$$ So, in conclusion, your reasoning is correct