DC/DC Converter Controlled Power Amplifier module

DC/DC Converter Controlled
Power Amplifier module for
WCDMA Applications
Jongsoo Lee, Eddie Spears, Jeff Potts
Outline
• Motivation for DC/DC Converter PA
• DC/DC converter
• Power Detector
• Integrated Power Amplifier with DC/DC converter
• Results
• Conclusions
2
Improve efficiency of PA at back off
Urban Current*Probability
Vcc=3.2Volts, Frequency=1.88GHz, Switch Point=20 dBm
0.3
Adaptive bias control is a lab experiment and is manually adjusted to maintain -48dBc ACPR
Current(mA)*Probability
0.25
0.2
0.15
0.1
0.05
0
-50
-40
-30
-20
-10
0
10
20
Power Output (dBm)
Load Switch
RF6000-3
RF6100-3
RF6100-3 ABC
PAA
Load Switch ABC
PA Efficiency at Back Off - Parallel Amplifier
•
•
•
•
Two different sizes of PAs for high and low power
At back-off, only small size of PA works
Chain match at the output is important
Good performance / hard for multi-band
Ref : J. Kim et al, “An MMIC smart power amplifier of 21% PAE at 16dBm power level
for W-CDMA mobile terminals,” GaAs IC Symposium2002
PA Efficiency at Back Off - Doherty Amplifier
•
•
•
•
Main (smaller size) and Peaking amplifier
At low power, only main amp works
Load pulling effect to give lower load line at peak
output power
Good performance but bulky size for mobile
applications
PA Efficiency at back off - DC/DC Converter PA
RF Input
PA Efficiency at back off - DC/DC Converter PA
• Good things
• No need for dedicated matching at output
• typical output matching network is used
• good PAE at back off power
• suitable for multi-band applications
• better performance with buck-booster converter
over load mismatch (VSWR variation)
• and so on…
Efficiency of PA at back off - DC/DC Converter PA
• Bad things
• Need two different dies (Si & GaAs)
• Difficult to achieve module size smaller than
• 4x4 mm2
• Requires big inductor and capacitor (added cost)
• Noise from DC/DC converter
• and so on…
DC/DC converter & Power detector
DC/DC Converter
DCR < 0.1
RFMD DC/DC converter (0.5m CMOS)
DC/DC Converter – measured
RLOAD = 5
4
100
90
3.5
80
3
Vout (V)
2.5
60
2
50
Vout - 5 Ohms
1.5
40
30
Efficiency - 5 Ohms
1
20
0.5
10
0
0
Vset (V)
Efficiency (%)
70
Power Detector Design
VBIAS1
VBIAS2
R4
VBIAS4
R3
INPUT
(RF)
VOUT1
Q1
R1
R8
R7
C2
Q5
C1
Q4
Q3
ICS4
VBIAS3
VOUT2
Q2
R2
Attenuator
R5
ICS1
R6
C3
R9
ICS2
ICS3
Decision
Circuit
• Non-diode detector – high speed & wide band
• Temperature compensated current source
• Maintain minimum VSET to DC/DC
OUTPUT
(DC)
Power Detector Design
VBAT = 3.4V
Voltage drop due to DCR of inductor
3.5
Power Detector
3
DC/DC Output
Voltage (V)
2.5
VCC2MIN = 1.2V
for linearity requirement
2
1.5
1
0.5
0
0
5
10
15
20
Output Power (dBm)
25
30
Integrated PA Module with DC/DC Converter
WCDMA PA from RFMD
• RF5198 WCDMA PA (3x3mm2)
• 1920MHz ~ 1980MHz
• 3V WCDMA region 1
• 27.5dBm peak output power
• 43% PAE at Pout
• -40dBc ACPR @ 5MHz
• Integrated Power detector
(diode type)
Power Amplifier with DC/DC Converter
VCBIAS VREG
RFIN
RFOUT
VBAT
Cout
DC/DC Converter
(4.7 F)
Output
Lout
(1.5 H)
• Laminate size : 6x6 mm2
• 3D EM simulation
• Eval board : Rogers
• Include wire bonding effect
• Lout =1.5H (0.078 DCR)
• 4.7F 0603 cap
• used for co-simulation in ADS
Power Amplifier with DC/DC Converter
45
0
PAE
35
Room Temp
1950MHz
3GPP Signal
ACPR (5MHz offset)
-10
30
-20
25
-30
20
15
-40
10
-50
Pout = 16dBm
5
0
-60
0
5
10
15
Pout (dBm)
20
25
30
ACPR (dBc)
40
Gain (dB) / PAE (%)
Pout = 27.5dBm
Gain
Power Amplifier with DC/DC Converter
45
40
DC/DC Converter Control
35
Fixed 3.4V Supply
Voltage
PAE (%)
30
Room Temp
1950MHz
3GPP Signal
25
16.8% @ 16dBm
20
15
10
8.6% @ 16dBm
5
0
0
5
10
15
Pout (dBm)
20
25
30
Power Amplifier with DC/DC Converter
600
DC/DC Converter Control
Total Current (mA)
500
Fixed Supply Voltage
400
Room Temp
1950MHz
3GPP Signal
300
200
136.6mA @ 16dBm
100
70.7mA @ 16dBm
0
0
5
10
15
Pout (dBm)
20
19
25
30
Power Amplifier with DC/DC Converter
-120
-123dBm/Hz
322KHz
RxNP (dBm/Hz)
-125
2.5MHz
Room Temp
1950MHz
3GPP Signal
-130
-135dBm/Hz
-135
-140
-145
RBW = 30KHz
-150
0
5
10
15
20
Pout (dBm)
25
30
35
Conclusion
• Integrated PA module with DC/DC converter is demonstrated.
• Overall PA module size is 6x6mm2.
• Closed loop type of power detector is presented.
• DC/DC buck converter controls VCC2 of PA.
• PAE has been improved from 8.6% to 16.8% @ 16dBm.
• PAE at peak power is 40%.
• ACPR @ 27.5dBm is -39dBc at 5MHz offset.
• Receive band noise is reduced to -135dBm/Hz.