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Classification of Power Amplifiers
Series-fed Class A Power Amplifiers
Transformer Coupled Class A Amplifiers
1
EE2603-01 Electronic Circuit Analysis
EE2603-08 Electronic Circuit Analysis
Classification of Power Amplifiers
2
VCC
RCR2
R1RE
B
C
E
vo
IB
IC
vin
Q
IC
IBQ
ICQ
VCC
VCE
VCEQ
Class A operationClass A operation
In Class A operation, IIn Class A operation, ICC should be flowing the whole cycle (should be flowing the whole cycle (22pp)) Q point is at the center of the operating range. IQ point is at the center of the operating range. IBQBQ>>00
Here RHere R1 1 and Rand R22 provide required Iprovide required IBQBQ for class A operation. Q point is for class A operation. Q point is at the center of the operating range. Iat the center of the operating range. IBQBQ>>00
EE2603-01 Electronic Circuit Analysis
EE2603-08 Electronic Circuit Analysis 3
VCC
RLR2
R1RE
B
C
E
vo
IB
IC
vin
VCC
RL
R2
R1RE
B
C
E
vo
IB
vin
n:1
SeriesSeries--fed Class A fed Class A Power AmplifierPower Amplifier
Transformer Coupled Transformer Coupled Class A Power AmplifierClass A Power Amplifier
Class A Power AmplifiersClass A Power Amplifiers
Here dc power from VHere dc power from VCCCC is converted into ac output power in Ris converted into ac output power in RLL
EE2603-01 Electronic Circuit Analysis
EE2603-08 Electronic Circuit Analysis 4
VCC
RC
R1RE
B
C
E
vo
IB
IC
vinQ
IC
IBQ=0
ICQ
VCC
VCE
VCEQ
Class B operationClass B operation
In Class B operation, IIn Class B operation, ICC should be flowing half cycle (should be flowing half cycle (pp)) Q point is at cutoff (IQ point is at cutoff (ICC==00) of the operating range. I) of the operating range. IBQBQ==00
Here RHere R1 1 provides required Iprovides required IBQBQ ==0 0 for class B operation. Q point is at for class B operation. Q point is at the cutoff of the operating range. Ithe cutoff of the operating range. IBQBQ==00
EE2603-01 Electronic Circuit Analysis
EE2603-08 Electronic Circuit Analysis 5
RL
R2
VCC
R2
OTL Class B Power OTL Class B Power AmplifierAmplifier
Output TransformerOutput Transformer--LessLess
RL
R2
VCC
R2
-VCC
OCL Class B Power OCL Class B Power AmplifierAmplifier
Output CapacitorOutput Capacitor--LessLess
Transformer Transformer Coupled Class B Coupled Class B Power AmplifierPower Amplifier
Vin
RL
Q1
Q2
VCC
Class B Power AmplifiersClass B Power Amplifiers
Here dc power from VHere dc power from VCCCC is converted into ac output power in Ris converted into ac output power in RLL
EE2603-01 Electronic Circuit Analysis
EE2603-08 Electronic Circuit Analysis 6
VCC
RCR2
RE
B
C
E
vo
IBQ
ICQ
vin
D
Q
IC
IBQ
VCC
VCE
ICQ
180
>180
Class AB operationClass AB operation
In Class AB operation, IIn Class AB operation, ICC should be flowing more than half cycle (>should be flowing more than half cycle (>pp)) Q point is at small amount above cutoff (IQ point is at small amount above cutoff (ICC>>00) of the operating range. I) of the operating range. IBQBQ>>00
Here RHere R2 2 and diode Dand diode D provides required small Iprovides required small IBQBQ for class AB for class AB operation. Q point is above the cutoff of the operating range. Ioperation. Q point is above the cutoff of the operating range. IBQBQ>>00
EE2603-01 Electronic Circuit Analysis
EE2603-08 Electronic Circuit Analysis 7
RL
R2
VCC
R2
D
D
OTL Class AB Power OTL Class AB Power AmplifierAmplifier
Output TransformerOutput Transformer--LessLess
RL
R2
VCC
R2
-VCC
D
D
OCL Class AB Power OCL Class AB Power AmplifierAmplifier
Output CapacitorOutput Capacitor--LessLess
Transformer Transformer Coupled Class AB Coupled Class AB Power AmplifierPower Amplifier
Vin
RL
Q1
Q2
VCC
R2D
Class AB Power AmplifiersClass AB Power Amplifiers
Here dc power from VHere dc power from VCCCC is converted into ac output power in Ris converted into ac output power in RLL
EE2603-01 Electronic Circuit Analysis
EE2603-08 Electronic Circuit Analysis 8
VCC
RC
R2
RE
B
C
E
voIBQ< 0
ICQ=0
vin
-VBB
Q
IC
IBQ< 0
VCE
ICQ
= 0
VCC
Class C operationClass C operation
In Class C operation, IIn Class C operation, ICC should be flowing less than half cycle (< should be flowing less than half cycle (< pp)) Q point is at below cutoff (IQ point is at below cutoff (ICC< < 00) of the operating range. I) of the operating range. IBQBQ< < 00
Here RHere RB B and and ––VVBBBB provides required below cutoff Iprovides required below cutoff IBQBQ for class C for class C operation. Q point is below the cutoff of the operating range. Ioperation. Q point is below the cutoff of the operating range. IBQBQ<<00
EE2603-01 Electronic Circuit Analysis
EE2603-08 Electronic Circuit Analysis 9
VCCRA
RE
E
vo
IBQ=0
ICQ=0
vin
RB IC
Tuned Class C RF Tuned Class C RF Power AmplifierPower Amplifier
Radio Frequency AmplifierRadio Frequency Amplifier
Class C Power AmplifiersClass C Power Amplifiers
Here dc power from VHere dc power from VCCCC is converted into ac output power in Ris converted into ac output power in RLL
EE2603-01 Electronic Circuit Analysis
EE2603-08 Electronic Circuit Analysis 10
t0
AmplifierLow-pass
Filter
Feedback
t0
t0
Sawtooth
generator
Input signal
wave
Output signal
wave
IC conducting only when digital version of the input wave is high ---- CLASS-D operation.
high
low
Efficiency is very high = over 90%
digital switching of the input wave
Class D Power AmplifiersClass D Power Amplifiers
EE2603-01 Electronic Circuit Analysis
EE2603-08 Electronic Circuit Analysis 11
VCC
RLR2
R1RE
B
C
E
vo
IB
IC
vin
Q
IC
IBQ
ICQ
VCC
VCE
VCEQ
RL
VCC/RL
Vo(PP) Maximum level
Any level
dc
ac
CQCCdc
L
2o
L
2o
ac
o
P
P
IVP
R8
)pp(V
R
22)pp(V
P
level)pp(VanyAt
%2525.0V
R2
R8
V
P
P(max)
R2
V
R2
V
VIV(max)P
R8
V
R
22)pp(V
(max)P
V)pp(Vlevel)pp(VimummaxAt
2CC
L
L
2CC
dc
ac
L
2CC
L
CC
CCCQCCdc
L
2CC
L
2o
ac
CCoo
SeriesSeries--fed Class A Power Amplifiersfed Class A Power Amplifiers
EE2603-01 Electronic Circuit Analysis
EE2603-08 Electronic Circuit Analysis
Transformer Coupled Class A Power Amplifiers
12
VCC
RL
R2
R1RE
B
C
E
vo
IB
vin
n:1
Q
IC
IBQ
ICQ
2VCC
VCE
VCEQ=VCC
n2RL
2VCC/n2RL
Vo(PP)
RE
dc
ac
CQCCdc
L2
2o
L2
2o
ac
o
P
P
IVP
Rn8
)pp(V
Rn
22)pp(V
P
level)pp(VanyAt
%505.0V
R
Rn8
V4
P
P(max)
R
V
R
VVIV(max)P
Rn8
V2
R
22)pp(V
(max)P
V2)pp(Vlevel)pp(VimummaxAt
2CC
L
L2
2CC
dc
ac
L
2CC
L
CCCCCQCCdc
L2
2CC
L
2o
ac
CCoo
EE2603-01 Electronic Circuit Analysis
EE2603-08 Electronic Circuit Analysis 13
IC(pp)
VO(pp)
10V
R2
R1
B
C
EIB
vin
3:1
vo(PP)
RL=8
%6.41416.015.1
4784.0
P
P)e(
W15.1mA2
2525510IVP)d(
W4784.0838
7.13.18
Rn
22)pp(V
P)c(
V33.53
V6.16)pp(V
3
1
)pp(V
)pp(V)b(
V6.167.13.18)pp(V)a(level)pp(VanyAt
dc
ac
CQCCdc
2
2
L2
2o
ac
Lo
L
oo
ExampleExample: Transformer Coupled class A is operating with V: Transformer Coupled class A is operating with VCCCC==1010V, RV, RLL==88, and , and transformer turn ratio n=transformer turn ratio n=33. Measurements at V. Measurements at VCECE gives Vgives VCECEmin=min=11..77V and V and VVCECEmax=max=1818..33V,and measurements at IV,and measurements at ICC gives Igives ICCmin=min=2525mA and ImA and ICCmax=max=255255mA. Find (a) mA. Find (a) VVoo(pp) ,(b) V(pp) ,(b) VLL(pp) (c) P(pp) (c) Pacac (d) P(d) Pdcdc (e) efficiency (e) efficiency at that moment.at that moment.
