Laboratory work №1.
Study of a power amplifier with feedback
Objective of the work
1. Study of power amplifier with feedback.
2. Study of the influence of feedback depth on amplifier performance.
Work execution sequence
The program is launched by double-clicking on the file“Issled_usil_OS.exe”.
The appearance of the amplifier under study is shown in Fig 1.
Fig. 1. The circuit diagram of the amplifier under study
The amplifier is covered by a common feedback loop, serial in voltage.
The executable module is divided into two parts (Fig. 2).
The first part shows the circuit diagram of the amplifier under study.
The second part of the module shows the values of the variable parameters:
- h21e - transistor parameter;
- Rl - load resistance, Ohm;
- RinCB - input resistance of a transistor in a common base circuit, Ohm;
- Se - slope of the pass-through characteristic, A/B;
- Uin - input voltage, V;
- R - feedback resistance, Ohm.
The values of the frequency limits of the study are entered in hertz.
Fig.2. View of the executable module
2. The values of the variable parameters are entered into the free
"windows" in their units of measurement. The values can be entered as integers,
fractional numbers and in exponential form. In the variable parameters, the integer
and fractional parts are separated from each other by a decimal point " , ". The period
" . " cannot be used as a separator.
The following examples of entered values are given correctly:
0,05; 5е3 (or 5∙103=5000); 5е-6 (or 5∙10-6=0,000005); 3,6е-12 (or 3,6∙1012
).
Parameters
of the
amplifier
circuit
h21Е
1
Task options
2
3
4
5
6
7
40
50
80
90
100
60
70
Rl , kOhm
5
6
7
8
9
10
11
RinFC , kOhm 10
20
30
40
50
10
20
SE, А/В
0,01 0,02 0,03 0,04 0,05 0,01 0,02
Uin, В
0,5 0,6 0,7 0,8 0,9
1
0,8
RFC, RFC 1 0,68 0,75 0,82 0,91 1
kOhm RFC 2 2,7 3,3 3,9
3
3,6
RFC 3 6,8 7,5 8,2 6,8 7,5
Parameters
Task options
of the amplifier 8
9
10
11
12
circuit
h21E
40
50
60
70
80
Rl , kOhm
12
7
8
9
10
RinFB , kOhm 30
40
50
30
40
SE, А/В
0,03 0,04 0,01 0,02 0,03
Uin, В
0,9 0,5 0,6 0,7 0,8
RFC, RFC 1 1,3 0,91 1
1,2 0,68
kOhm RFC 2 3,9
3
3,6 2,7 3,3
RFC 3 7,5 8,2 6,8 7,5 8,2
1,2
2,7
8,2
1,5
3,3
6,8
13
14
90 100
11
12
50
20
0,04 0,05
0,9
1
0,75 0,82
3,9
3
6,8 7,5
3. After entering the parameters to be changed, you must click the
"Calculation" button.
In this case, the following power amplifier parameters are calculated for the
entered parameters with and without feedback:
1) Output voltage Uout, V;
2) Gain K;
3) Feedback depth F;
5) Input resistance of the amplifier Rin, Ohm;
6) Output resistance of the amplifier Rout, Ohm.
4. To see the calculated values, press the "2-block" button at the top of the
software module (Fig. 3).
5. When you press the "3-block" (Fig. 4) and "4-block" (Fig. 5) buttons, the
amplifier's frequency response is calculated in the low and high frequency ranges,
respectively.
The program calculates (Amplitude-frequency characteristic) the amplifier's
frequency response in the low and high frequency ranges (frequency distortions in
the low frequency range) at ten points. The first column shows the frequency values
for which the calculations are made. The second column shows the amplifier's
frequency distortions in the absence of feedback. The third column shows the
frequency distortions in the presence of feedback. Frequency distortions are given in
relative units.
Fig.3. Calculation of power amplifier parameters
Fig.4. Calculation of the frequency response in the low frequency region
Fig. 5. Calculation of the frequency response in the high frequency region
Submission of the report
1. The report should include
- the purpose of the research;
- the circuit of the power amplifier with feedback under study;
- data for calculations, according to the option.
2. The calculated data should be summarized in tables 1, 2, 3.
Table 1
Calculation of amplifier parameters
Indicator
No feedback With feedback (С обратной связью)
(Без обратной
RFC1
RFC2
RFC3
Связи)
(RОС1)
RОС2
RОС3
0.1975330864 0.19654088 0,192817546 0.18621973
197531
0503145
396722
929
2365
Output
voltage Uout, V,
(Выходное
напряжение Uвых, В)
Gain factor K
0.2469135802 0.24567610 0,241021932 0,23277467
(Коэффициент
46914
0628931
99 5903
411
5456
усиления K)
Feedback depth F 1.00503703 1,024444444 1,06074074
(Глубина обратной
703704
44 444
074 074
связи F)
Input resistance of
3240000
3256320
3319200
3436800
the amplifier Rin,
Ohm
(Входное
сопротивление
усилителя Rвх, Ом)
Output resistance of the 10000
9949.88207 9761,388286 9427,37430
amplifier Rout, Ohm
54717
33 406
167 598
(Выходное
сопротивление
усилителя Rвых, Ом)
Table 2
Calculation of the frequency response in the low frequency region
Ylf
Frequency, Hz
300
600
900
1200
1500
1800
2100
2400
2700
3000
No feedback
0.9876068145
0.9968580107
0.9985998971
0.9992117181
0.9994952848
0.9996494222
0.9997423967
0.9998027546
0.9998441421
0.9998737495
Ylf
Frequency, Hz
300
600
900
1200
1500
1800
2100
2400
2700
3000
No feedback
0.9876068145
0.9968580107
0.9985998971
0.9992117181
0.9994952848
0.9996494222
0.9997423967
0.9998027546
0.9998441421
0.9998737495
With feedback
0.9881642653
0,9970012361
0.9986638795
0.9992477729
0.9995183790
0.9996654671
0.9997541880
0.9998117839
0.9998512772
0.9998795295
Ylf
Frequency, Hz
300
600
900
1200
1500
1800
2100
With feedback
0.9877248398
0.9968883499
0.9986134517
0.9992193565
0.9995001775
0.9996528215
0.9997448948
0.9998046676
0.9998456538
0.9998749740
No feedback
0.9876068145
0.9968580107
0.9985998971
0.9992117181
0.9994952848
0.9996494222
0.9997423967
With feedback
0.9889254571
0.9971965170
0.9987510918
0.9992969130
0.9995498535
0.9996873337
0.9997702574
2400
2700
3000
0.9998027546
0.9998441421
0.9998737495
0.9998240891
0.9998610010
0.9998874063
Table 3
Calculation of frequency response in the high frequency region
Yhf
Frequency, Hz
8000
9000
10000
11000
12000
13000
14000
15000
16000
17000
No feedback
0.0397774110
0.0353635708
0.0318309957
0.0289398134
0.0265299368
0.0244904474
0.0227420692
0.0212266388
0,0199005168
0,0187303216
Yhf
Frequency, Hz
8000
9000
10000
11000
12000
13000
14000
15000
16000
17000
With feedback
0.0399774519
0.0355414740
0.0319911659
0.0290854613
0.0266634743
0.0246137321
0.0228565622
0.0213335096
0.0200007164
0.0188246336
No feedback
0.0397774110
0.0353635708
0,0318309957
0.0289398134
0.0265299368
0.0244904474
0.0227420692
0.0212266388
0.0199005168
0.0187303216
With feedback
0,0407481525
0,0362268927
0,0326082692
0,0296466167
0.0271779730
0.0250887304
0.0232976883
0.0217452698
0.0203867741
0,0191880074
Yhf
Frequency, Hz
8000
9000
10000
11000
12000
13000
14000
15000
16000
17000
No feedback
0.0397774110
0.0353635708
0.0318309957
0.0289398134
0.0265299368
0.0244904474
0.0227420692
0.0212266388
0.0199005168
0.0187303216
With feedback
0.0399774519
0.0355414740
0.0319911659
0.0290854613
0.0266634743
0.0246137321
0.0228565622
0.0213335096
0.0200007164
0.0188246336
3. Plot graphs of the dependencies Uout(Rос), K(Rос), F(Rос), Rin(Rос), Rout(Rос).
4. Plot graphs of the frequency response in the low-frequency region in the
absence and presence of feedback, and draw the appropriate conclusions.
5. Plot graphs of the frequency response in the high-frequency region in the
absence and presence of feedback, and draw the appropriate conclusions.
6. The report on the work is prepared by each student separately.