I am designing a two stage amplifier, the first stage is a opamp adder and the second stage is a common emitter (see figure).
I have designed the two separately, for the opamp the specifications are Rin=50 Ohm, two source, A=1.
For the common emitter the specifications are Rout=50 Ohm, A=20, Fl=200 kHz, Fh=1 MHz (at least).
Some parameters:
Vcc=+6 V, Vee=-6 V, Beta=170, Gm=0.4 S, Ic=10.04 mA, rbe=420 Ohm, ro (common emitter) = 7968 Ohm.
I have simulate the two separately, Vs1=0.5 V(AC), Vs2=0.5 V(AC), Vs3=1 V(AC) and the results are (figure):
1) opamp
Fh = 1.52 MHz
2) common emitter
Fl = 150 kHz
Fh = 573 MHz
A = 14
Then I have simply connected the two (figure) and I have measured the overall results:
Fl = 127 kHz
Fh = 1.79 MHZ
those result are in contrast with the theoretical expectation, I expect that connecting two stage the bandwidth decrease but this does not happen on the simulation. The overall Fl is lower than the maximum of the two separately and the Fh is higher than the minimum of the two.
So where is the error? Does PSpice have some particular attribute to beware?
I have designed the two separately, for the opamp the specifications are Rin=50 Ohm, two source, A=1.
For the common emitter the specifications are Rout=50 Ohm, A=20, Fl=200 kHz, Fh=1 MHz (at least).
Some parameters:
Vcc=+6 V, Vee=-6 V, Beta=170, Gm=0.4 S, Ic=10.04 mA, rbe=420 Ohm, ro (common emitter) = 7968 Ohm.
I have simulate the two separately, Vs1=0.5 V(AC), Vs2=0.5 V(AC), Vs3=1 V(AC) and the results are (figure):
1) opamp
Fh = 1.52 MHz
2) common emitter
Fl = 150 kHz
Fh = 573 MHz
A = 14
Then I have simply connected the two (figure) and I have measured the overall results:
Fl = 127 kHz
Fh = 1.79 MHZ
those result are in contrast with the theoretical expectation, I expect that connecting two stage the bandwidth decrease but this does not happen on the simulation. The overall Fl is lower than the maximum of the two separately and the Fh is higher than the minimum of the two.
So where is the error? Does PSpice have some particular attribute to beware?
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