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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 )
.op
.end

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
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
walid

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• 2 months later...

(1) How far or close these results to the real life, can i depend on it initially?

Hi Walid,
Doesn't your sim program have built-in spec's for common transistors? A typo can mess it up.
The sim program works with "typical" spec's. The actual results with "real" transistors having a wide range of current gain and Vbe will be much different. Change the current gain in the program to see if the circuit still works.

(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.

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