L`amplificateur audio.

L’amplificateur audio.
PROJET
D’ELECTRONIQUE
ANALOGIQUE
2008
-
2009
PEPITONE Kévin
RAGOT Lise
Electronique
Première année
Groupe G1

1
S
S
S
O
O
OM
M
MM
M
MA
A
AI
I
IR
R
RE
E
E
Index des Figures -------- p2
Première partie :
1. Project overview and specifications. -------- p3
a. Specifications
b. Presentation
2. Operational amplifier structure. -------- p4
3. Push-pull power stage using MOS transistors. Amplifier
classes. Why Class B is more effective. -------- p4
a. Choice of the class
b. The Push-pull
4. Layout using an ideal current generator to eliminate
crossover distortion. -------- p6
a. Crossover distortion
b. Solution in order to eliminate crossover distortion
Deuxième partie :
5. Amplificateur de tension. -------- p11
6. L’étage d’entrée de type amplificateur différentiel. --- p12
7. La contre réaction globale. -------- p14
8. Le filtre d’entrée. -------- p15
9. Complément : la régulation de la température. -------- p16
Conclusion -------- p17
ANNEXE 1 : Dossier de fabrication. -------- p19
ANNEXE 2 : TP1 – Amplificateur de puissance classe B. --- p28
ANNEXE 3 : TP2 – Amplificateur différentiel. -------- p35

2
I
I
I
N
N
ND
D
DE
E
EX
X
X D
D
DE
E
ES
S
S F
F
FI
I
IG
G
GU
U
UR
R
RE
E
ES
S
S
Première partie :
Figure 1 : Amplifier schematic.
Figure 2 : Amplifier control and band-width filter schematic.
Figure 3 : Common collector assembly with both MOS transistors.
Figure 4 : Push-pull crossover distortion graph.
Figure 5 : NMOS transistor schematic.
Figure 6 : NMOS transistor charactéristic.
Figure 7 : Push-pull schematic without distortion.
Figure 8 : Push-pull and current generator schematic with various value.
Figure 9 : Parametric study graph.
Figure 10 : Push-pull and current generator schematic with r=4200Ω.
Figure 11 : Graph without distortion.
Figure 12 : Push-pull schematic with current mirror.
Deuxième partie :
Figure 13 : Amplificateur de tension.
Figure 14 : Amplificateur de tension et condensateur.
Figure 15 : Schéma de l’amplificateur différentiel.
Figure 16 : Amplificateur différentiel en petits signaux.
Figure 17 : Schéma du montage avec l’amplificateur différentiel.
Figure 18 : Rétroaction de l’amplificateur.
Figure 19 : Montage de la rétroaction
Figure 20 : Schéma du filtre.
Figure 21 : Fonctionnement du filtre.
Figure 22 : Etage de régulation de la température.
Annexe 1 :
Figure 23 : Schéma global de l’amplificateur audio.
Figure 24 : Etage de routage de la carte sur le logiciel Orcad Layout .
Figure 25 : Schéma représentant l’emplacement des composants sur la carte.
Figure 26 : Aperçu du typon de notre carte électronique.
Figure 27 : Typon de notre carte électronique sur sa face inférieure.
Figure 28 : Typon de notre carte électronique sur sa face supérieure.
Figure 29 : Amplificateur audio.
Figure 30 : Oscillogramme qui nous a permis de trouver une amplification de 13,6.
Figure 31 : Oscillogramme pour un signal d’entrée à 20Hz.
Figure 32 : Oscillogramme pour un signal d’entrée à 20kHz.
Figure 33 : Oscillogramme pour un signal d’entrée carré à 1kHz.
Figure 34 : FFT du signal d’entrée (sinus à 1kHz).
Figure 35 : FFT de notre signal de sortie.

3
P
P
P
R
R
RE
E
EM
M
MI
I
IÈ
È
ÈR
R
RE
E
E P
P
PA
A
AR
R
RT
T
TI
I
IE
E
E
1. Project overview and specifications.
a. Specifications
This project aimed to design and make an audio amplifier which delivers a power higher or equal to
10W.
However, this amplifier must be a HIFI amplifier. So it is necessary to respect the specifications :
- Load impedance : 8Ω
- Input impedance : higher than 1kΩ
- Output maximum power : 10W for a level of input tension equal to 1V
- Rate of distortion lower or equal to 0,1%
- Band-width included between 20Hz and 20kHz (equivalent to the audible band frequency)
b. Presentation
An amplifier is a device that enables an input signal to monitor an output signal. The output signal
had some of the characteristics of the input signal but it was generally larger in terms of voltage,
current, or power. In order to listen to the output signal, the amplifier was linked to a speaker.
The amplifier can be represented with this schematic :
The first step was to choose the amplifier so that the specifications are respected. This amplifier must
contain a current and a voltage amplifier at the same time.
Figure 1 : Amplifier
schematic
.

4
2. Operational amplifier structure.
The amplifier was composed of two parts :
- The first one was the amplifier which is used to perform the signal;
- The second one was the filter which selects the band-width [20Hz;20kHz].
The filter was placed before the amplifier. However, when the filter is before the amplifier, the
amplifier does not amplify noise. So, two resistors R1 and R2, permitting amplifier stability, was used
to control the amplifier.
The amplifier structure could be resumed thanks to this schematic :
3. Amplifier classes. Why Class B is more effective. Push-
Pull power stage using MOS transistors.
a. Choice of the class
The end stage of the device requires the signal current to be amplified. Several solutions can be used
in order to amplify this current : A or B power amplification class. A and B classes are the most
common amplifier used.
The A class was eliminated for this project because it uses 100% of the input signal. There is neither
saturation nor blockage. Therefore the biasing conditions imposed
0 0
0 0
S S
I V
≠⇒≠
.
Consequently the power efficiency was reduced.
So, the schematic was designed with a B class amplifier. Indeed, it presented fewer advantages in this
project : crossover distortion was lower and power was more important.
Where
1
1 2
R
R R
α =+
.
Figure 2 : Amplifier control and band-width filter schematic.