power management design challenges and...
TRANSCRIPT
Power Management Design
Challenges and Techniques for
Power Amplifiers in 2G/3G/4G
Multimode Handsets
William O. Keese
National Semiconductor
© 2010 National Semiconductor Corporation. PWR SoC 2010.
National Semiconductor’s Innovation in
RF SMPS for Handsets
• Creator of first DCDC for RF PA in 2004
• Shipped in significant volumes since 2005
• Continuous innovator
– First GSM support
– First Boost support
– First
• Estimate: RF DCDC has saved 2 Mega Watts of Power over the last 5 years
• DCDC for RF PA will ship in all 3G and 4G handsets by 2012
2
Requires NDA
© 2010 National Semiconductor Corporation. PWR SoC 2010.
Multi-mode Multi-band RF Transmitter
with variable PA Vcc supply
3
RF Power
Vcc PA =0.5 to 3.4V
•Typical smartphone includes 2 to 5 3GPP bands plus
•Quad band GSM/EDGE
© 2010 National Semiconductor Corporation. PWR SoC 2010.
Technology & Market Trends
Highly Integrated
System Platforms
Transmitter PA
Efficiency
Improvements
Smartphone
Power Gap
Standards
Evolution
4
© 2010 National Semiconductor Corporation. PWR SoC 2010.
Buck DCDC + PA Reduces Worst Case
Thermal of Highly Integrated Phones
Transmitter PA
Efficiency
Improvements
Smartphone
Power Gap
Standards
Evolution
5
Reduced Thermal Emissions of PA by > 20%
57° C 44.7° C
PA ONLY
VBATT = 4.2V
VCC = 4.2V
RFOUT = 26dBm
Temp = 57 C
PA with DCDC
VBATT = 4.2V
VCC = 3.4V
RFOUT = 26dBm
Temp = 44.7 C
© 2010 National Semiconductor Corporation. PWR SoC 2010.
Smartphone Power Gap
Highly Integrated
System Platforms
Transmitter PA
Efficiency
Improvements
Standards
Evolution
6
Enabling longer charge cycle, smaller form factor
1000
1200
1400
1600
1800
2000
2200
FY09 FY10 FY11 FY12 FY13 FY14
mA
-h
Smartphone Power Gap
Battery Capacity
Smartphone (no RF power)
Smartphone (with RF power)
Source: IMS & internal NSC
© 2010 National Semiconductor Corporation. PWR SoC 2010.
Handset Transmit Power Profile
Normalized Cumulative Distributions
Highly Integrated
System Platforms
Transmitter PA
Efficiency
Improvements
Standards
Evolution
7
Constant growth in data consumption and use of
BW drives need to improve PA system eff
© 2010 National Semiconductor Corporation. PWR SoC 2010.
DCDC + PA Transmitter Efficiency
Improvements
Highly Integrated
System Platforms
Smartphone
Power Gap
Technology
Trends
8
DCDC dynamically adjusts PA supply voltage to
optimize efficiency during lower power RF Tx
Without DCDC
PA IDC
With DCDC
© 2010 National Semiconductor Corporation. PWR SoC 2010.
DCDC + PA Transmitter Efficiency
Improvements
Highly Integrated
System Platforms
Smartphone
Power Gap
Technology
Trends
9
© 2010 National Semiconductor Corporation. PWR SoC 2010.
0.0%
5.0%
10.0%
15.0%
20.0%
25.0%
-10.00 -5.00 0.00 5.00 10.00 15.00 20.00 25.00
Eff
icie
ncy
RF Power out (dBm)
3GPP Band 1
LTE 5MHz QPSK,
Freq = 1977.5MHz
Vbatt = 3.7V
Advantage
With DCDC
Highly Integrated
System Platforms
Transmitter PA
Efficiency
Improvements
Smartphone
Power Gap
10
From “NICE TO HAVE” in 2/2.5G
to “MUST HAVE” in 3G
Standards Evolution
© 2010 National Semiconductor Corporation. PWR SoC 2010.
RF Power Management Evolution in
Mobile Devices
RF
Performance
Constraints
• Transmit Spectral Mask
• Voltage Switching Transients
• Low Supply Noise
Talk Time
Improvement
• PA + DCDC Architecture Improvement
• Light Load Efficiency Enhancement
• Low Voltage Battery support
Solution Size
Reduction
• Multi-mode PA support
• Smaller Switch Inductor
• Integrated Inductor
11
© 2010 National Semiconductor Corporation. PWR SoC 2010.
Increased RF Performance
• High current capability (up to 2.5A)
• High efficiency (up to 96%)
– At Heavy and Light Loads
• Performance requirements for the DCDC converter extend into the PA requirements.
– Detailed understanding of the RF performance is mandatory
– Rx Band Noise
– EVM, ACLR, PvT
12
RF Spectral
Constraints
© 2010 National Semiconductor Corporation. PWR SoC 2010.
13
Transmit Spectral Mask
Adjacent Channel Leakage Ratio
• Pout ACLR1 Linearity meets ACLR spec with 6 dB margin
• Higher data rate uplink possible (16QAM) at Vbatt = 3.4V
• Pout degraded and ACLR1
Linearity does not meet -40
dBc
• Lower data rate uplink
(QPSK) at Vbat = 3.2V
RF Spectral
Constraints
© 2010 National Semiconductor Corporation. PWR SoC 2010.
14
Transient Performance
• Wcdma Inner Loop Power Control
– During active transmission in wcdma or HSPA the UE will ratchet the Tx output power up or down
– Window < +/- 25 usec for transitioning between two successive power levels
• GSM Power Ramp
– Power vs. Time template requires tight output regulation
– For DCDC with fast transient response, it is beneficial to adjust the PA Vcc on a slot-by-slot basis
GSM Multi-Slot Timing
0 1 2 3 4 5 6 7
GSM burst
Vdcdc
Enable DC
Initialize PA Vcc
PA Vcc
change
(slot to slot)Disable
DCDC
4.615ms
PA Vcc
change
(slot to slot)
RF Spectral
Constraints
© 2010 National Semiconductor Corporation. PWR SoC 2010.
RF Noise
• Wideband noise
– Stringent noise requirements for 3GPP Rx frequency bands as well as GPS
– Switching frequency ripple must be extremely low at higher harmonic frequencies
• RFIC operating voltage is dropping from 2.5V to < 1.8V
– Critical components pulled from RFIC into RF PMU
• DCDC for PA
• LDO’s
• DCDC for RFIC
15
RF Spectral
Constraints
© 2010 National Semiconductor Corporation. PWR SoC 2010.
RF Power Management Evolution in
Mobile Devices
RF
Performance
Constraints
• Transmit Spectral Mask
• Voltage Switching Transients
• Low Supply Noise
Talk Time
Improvement
• PA + DCDC Architecture Improvement
• Light Load Efficiency Enhancement
• Low Voltage Battery support
Solution Size
Reduction
• Multi-mode PA support
• Smaller Switch Inductor
• Integrated Inductor
16
© 2010 National Semiconductor Corporation. PWR SoC 2010.
17
Transmitter Efficiency Improvements
• Transmitter Needs
• Power amplifier efficiency is optimized for max POUT
• Majority of time POUT is lower PA is at poor efficiency
• Variable Supply
• Optimize supply voltage based on POUT
• Improve PA efficiency at lower powers
No Savings
(Past)
More Power Savings?40% Savings
with DCDC
High SpeedTracking
Talk Time
Improvement
© 2010 National Semiconductor Corporation. PWR SoC 2010.
Envelope Tracking System Architecture
• Components: Chipset, ET Modulator and PA
– Significant enhancement of PA efficiency with high-PAR signals and medium to high TX power levels
– Supporting all modulation methods up to full LTE
• Open-loop vs. Closed loop solution
• Less modifications to firmware
• More cost effective, less processing
18
Talk Time
Improvement
© 2010 National Semiconductor Corporation. PWR SoC 2010.
Envelope Tracking Modulator
• High performance analog circuitry
– Wide bandwidth requirements
– Fast transitions between peaks and valleys
19
0 0.5 1 1.5 2 2.5 30
1
2
3
4
5
Voltage [
V]
0 0.5 1 1.5 2 2.5 30
0.2
0.4
0.6
0.8
1
Time [usec]
Curr
ent
[A]
Ideal Vcc
Measured Vcc
Simulated IccLTE PA Icc vs. Time
Talk Time
Improvement
© 2010 National Semiconductor Corporation. PWR SoC 2010.
Light Load Performance Enhancement
50%
60%
70%
80%
90%
100%
-4 -2 0 2 4 6 8 10 12 14 16 18 20 22 24
Pout (dBm)
Eff
ien
cy %
Talk Time
Improvement
Handset spends a lot of time at lower power levels
– Low Voltage, Low Current
– Traditional DCDC performance drops off at light loads
Without light load
enhancement
With light load
enhancement
© 2010 National Semiconductor Corporation. PWR SoC 2010.
Wider Battery Operating Range
• Buck-Boost
– Increases usable region of battery
– No MPR Backoff required
– Larger coverage area
– Higher Data Rates
21
Extended RF spec compliant
region of operation with
Boost-Buck DCDC
Talk Time
Improvement
© 2010 National Semiconductor Corporation. PWR SoC 2010.
RF Power Management Evolution in
Mobile Devices
RF
Performance
Constraints
• Transmit Spectral Mask
• Voltage Switching Transients
• Low Supply Noise
Talk Time
Improvement
• PA + DCDC Architecture Improvement
• Light Load Efficiency Enhancement
• Low Voltage Battery support
Solution Size
Reduction
• Multi-mode PA support
• Smaller Switch Inductor
• Integrated Inductor
22
© 2010 National Semiconductor Corporation. PWR SoC 2010.
23
Filters
Tx/Rx
Duplexers
SAWs
LPFs
N:1
TRX Path
Control
Antenna
Tuning
Element
Power Amp Modules
Output
Matching
Networks
ANT
PA Bias
Controller
PA Driver
Bias
RFIC/
LNA
Supply
PA Output
Bias
Adaptive
Bias
Controller
PA Ramp/
Envelope
Biasing Blocks
DCDC SUPABoost
Power
Detect
VSWR
Det
Temp
Sensor
Alarm
Sensors
LNAs
RF Front End Integration
Solution Size
Reduction
© 2010 National Semiconductor Corporation. PWR SoC 2010.
24
ConvergedFront-End
RF Power
RF Power
Tuning Elements
0.5 to 4.5 V
TraditionalFront-End
0.5 to 3.4V
Multi-mode PA Support
Solution Size
Reduction
© 2010 National Semiconductor Corporation. PWR SoC 2010.
25
Controlling SMPS for PA Module
• Multiple options to consider
– Interface type (Analog or Digital).
– Controller type (RFIC or BBIC).
– Single-chain or multi-chain PA Modules.
– Multi-slot power ramping for GSM/EDGE.
SMPS
RFIC
BBIC
Solution Size
Reduction
© 2010 National Semiconductor Corporation. PWR SoC 2010.
Reducing Switch Inductor Size
– Smaller inductor value reduces filtering of switching noise
– Higher switching frequency trades off efficiency due to AC switching losses
• DCDC on Ferrite
– Parasitic inductance on all pins
– Especially critical on power and grounds
– Max height constrained to ≤ 1.0 mm
– DC resistance increases
26
Solution Size
Reduction
DCDC
DCDC
DCDC
© 2010 National Semiconductor Corporation. PWR SoC 2010.
Conclusions/Challenges
• New Multi-mode Multi-band handsets are demanding higher and higher levels of performance
• Variable RF PA supply is required for next generation of slim trim and high data rate smartphones
• Maintaining RF noise performance with DCDC for PA is not trivial
27
© 2010 National Semiconductor Corporation. PWR SoC 2010.
28
National’s RF Front End Benefits
Increased
Usage
Time
Decreased
Thermal
Emissions
Small
Solution
Size
Reduced
BOM Cost
Increased
Coverage
Area
>25% >20% <10mm2 >5% >10%
Measurable
Benefits
© 2010 National Semiconductor Corporation. PWR SoC 2010.