Hello:
I have attached a schematic for a Common-emitter voltage amplifier. I have also
attached an ac analysis that I computed manually. My results and LTSpice are not identical. Does anyone know which results are correct and why the difference?
Assume hfe = 100, Rs = 50Ω
re’ = 25 mV / 1.01 mA = 24.75Ω
rc = RC║RL = 4KΩ║10KΩ = 2,857Ω
Av = rc / re’ = 2,857Ω / 24.75Ω = 115.43
Rin = R1║R2║hfe * re’ = 829.93Ω║24.75Ω = 621.52Ω
Av-Divider = Rin / Rs + Rin = 621.53Ω / 50Ω + 621.53Ω = 0.9255
If Vin = 1 mA
Vin’ = Vin * Av-Divider = 1 mV * 0.9255 = 925.54 uV = 0.92554 mV
Therefore Vout = Vin’ * Av = 0.92554 mV * 115.43 = 0.106840 mV
Ic = Vout / RL = 106.84 mV / 10KΩ = 10.68 uA
Ib = Ic / hfe = 10.68 uA / 100 = 106.00 nA
Ie = Ib + Ic = 106.00 nA + 10.68 uA = 10.79 uA
Ai = hfe = 100
Av = 115.43
Ap = Ai * Av = 100 * 115.43 = 11,543
In particular, I am looking at Vout of 100.642 mV in Spice versus my Vout of 106.840 mV.
Any help would be appreciated.
David
I have attached a schematic for a Common-emitter voltage amplifier. I have also
attached an ac analysis that I computed manually. My results and LTSpice are not identical. Does anyone know which results are correct and why the difference?
Assume hfe = 100, Rs = 50Ω
re’ = 25 mV / 1.01 mA = 24.75Ω
rc = RC║RL = 4KΩ║10KΩ = 2,857Ω
Av = rc / re’ = 2,857Ω / 24.75Ω = 115.43
Rin = R1║R2║hfe * re’ = 829.93Ω║24.75Ω = 621.52Ω
Av-Divider = Rin / Rs + Rin = 621.53Ω / 50Ω + 621.53Ω = 0.9255
If Vin = 1 mA
Vin’ = Vin * Av-Divider = 1 mV * 0.9255 = 925.54 uV = 0.92554 mV
Therefore Vout = Vin’ * Av = 0.92554 mV * 115.43 = 0.106840 mV
Ic = Vout / RL = 106.84 mV / 10KΩ = 10.68 uA
Ib = Ic / hfe = 10.68 uA / 100 = 106.00 nA
Ie = Ib + Ic = 106.00 nA + 10.68 uA = 10.79 uA
Ai = hfe = 100
Av = 115.43
Ap = Ai * Av = 100 * 115.43 = 11,543
In particular, I am looking at Vout of 100.642 mV in Spice versus my Vout of 106.840 mV.
Any help would be appreciated.
David
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