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C-E Amp circuit sim using spice


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I write the following prog to simulate the circuit shown in Fig.C-E below:
common E Amp freq response
VCC 7 0 DC 12
VS 1 0 AC 1
Q1 4 3 5 Q_2N2222A_N
RS 1 2 1K
C1 2 3 2uF
R1 3 0 10K
R2 7 3 30K
RC 7 4 4.3K
RE 5 0 1.3K
C3 5 0 10uF
C2 4 6 0.1uF
R3 6 0 100K
.MODEL Q_2N2222A_N NPN( IS=11.9F NF=1 NR=1 RE=649M RC=1
+      RB=10 VAF=83.5 VAR=41.7 ISE=350F ISC=350F
+      NE=1.58 NC=1.58 BF=204 BR=5 IKF=149M
+      IKR=149M CJC=13.1P CJE=30P VJC=2.87 VJE=678M
+      MJC=330M MJE=330M TF=531P TR=69N EG=1.11
+      KF=0 AF=1 )

The .op command results are:

NAME        Q1                   
MODEL        Q_2N2222A_N         
IB          1.25E-05           
IC          1.71E-03           
VBE          6.66E-01           
VBC        -1.74E+00           
VCE          2.40E+00           
BETADC      1.37E+02           
GM          6.53E-02           
RPI          2.35E+03           
RX          1.00E+01           
RO          4.90E+04           
CBE          8.44E-11           
CBC          1.12E-11           
CJS          0.00E+00           
BETAAC      1.54E+02           
CBX          0.00E+00           
FT          1.09E+08           

And I need to discuss some of these results with you:
(1) How far or close these results to the real life, can i depend on it initially?
(2) RPI is the i/p impedance looking into the base of Q1, so, the total i/p impedance is: R1//R2//RPI = 1.8K ohm. so we can look at the i/p portion of the circuit as: Vs connected in series with Rs then to C1 then connected inseries to that 1.8k.
    if we look at Vs as a MIC and Rs as the impedance of the MIC and C1&Rtot as a high pass filter, is the value of C1 suitable and why?
(3) What exactly these parameters mean: GM, RX, RO, CJS, CBX.
(4) FT is (as I remember) is the freq at which the gain =1, that is at this freq there is no amplification, Is this OK?
(5) In the MODEL Q_2N2222A_N, BF = 204 is this the upper value that this Q can reach?
(6) In the MODEL Q_2N2222A_N, what these mean: NF=1 NR=1 NE=1.58 NC=1.58 IKF=149M IKR=149M VJC=2.87 VJE=678M MJC=330M MJE=330M TF=531P TR=69N EG=1.11 KF=0 AF=1
thats all
thank you in advance


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  • 4 weeks later...

Hi Guys,
I've been playing with a Spice simulator program.

I took an ordinary single transistor amplifier stage then fed it a signal level that is lower than would cause the transistor to saturate or be cutoff.
With the emitter resistor bypassed, it had high gain but also had 40% distortion. The top part of the wave was severely compressed and you can't even read its gain.
Without the emitter bypass capacitor its gain was reduced but the negative feedback also reduced its distortion to 3%.


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