Microwave Power Amplifiers with DigitallyControlled Power Supply for High Efficiency and Linearity

1
Microwave Power Amplifiers with
Digitally-Controlled Power Supply for High
Efficiency and Linearity
Mahim Ranjan, G. Hanington, Peter Asbeck
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DSV Amplifier for Improved Efficiency

• Efficient amplifiers for increased wireless
  handset battery life Vary
  power supply voltage with the envelope of the
  input signal using a DC-DC Converter

Vrf
Vdd
Vmin
time
DSV Amplifier
DSV
Class B
Class A
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DSV Amplifier Implementation

• Envelope detector feeds the input of the DC-DC
  converter which varies the bias point, reducing
  DC power consumed and thus improving efficiency

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Boost DC-DC Converter

• Transform low battery voltage
• to voltage more favorable for high
  efficiency
• Vary voltage in accordance with signal level

3.3V 10V
High Frequency Operation
Faster response Smaller L and C
Signal Envelope Information
Need fast switching transistor Use same
technology as PA
5
Implementation Problems

• Variation in amplifier AM-AM and AM-PM
  characteristics with Vdd

• Effect of time delay in the DC-DC
  Converter

Amplifier gain at different supply voltages
Simulated amplifier response to predistorted
input with different time delays introduced in
the DC-DC converter
Frequency roll-off of DC/DC converter
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Microwave Power Amplifier with Digitally
Controlled Power Supply
Battery 3.3V
Vdd
Vcontrol
DSP
I,Q
RF in

• . Generates I and Q
• Computes Vcontrol for the given I and Q using
  the DC/DC converters transfer function
• Predistorts the input using the gain/phase
  characteristics of the amplifier at the computed
  Vdd
• Ip (I?cos ?dist Q?sin ?dist) /Gdist(A, Vdd)
• Qp(Q?cos ?dist - I?sin ?dist) /Gdist(A, Vdd)
• Adjusts for the delay in the DC/DC converter

RF Out
PA
HP ESGD 4000 Dual Arbitrary Waveform Generator
GaAs MESFET Power Amplifier
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Experimental Results
Pout
Power amplifier output with and without
pre-distortion. ACPR improvement of 8dB
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Flyback DC-DC Converter

• Use a flyback converter instead of a boost
  converter to achieve higher efficiency

Vout range 0.5V-8V
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Efficiency Improvement Ideal Dynamic Supply
Voltage Amplifier
Class B amplifier
VddRLIrfmax/2Vmin Pout1/8 RLIrf2 IdcIrf/p Po
ut/Pdc p/4RLImax/(RLImax2Vmin)Pout/Poutmax
0.5
Efficiency Computed for Vmin0.1Vmax
Dynamic Supply Voltage Amplifier
DSV
Class B
VddRLIrf/2Vmin Pout1/8 RLIrf2 IdcIrf/p Pout/
Pdc p/4hconvRLIrf/(RLIrf2Vmin)
Class A
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Flyback DC-DC Converter Status

• Need a low-loss transformer core which would
  - operate at 10MHz
  - be able
  to handle 1A of current - coupling
  of at least 0.93
  - have an inductance of about 200nH.
• Located a suitable core with help from Hitachi
  Metals (Japan). Currently awaiting the arrival of
  the core.
• Acquired the HBT to be used as a switch in the
  flyback converter from Conexant Systems Inc.

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Conclusion

• Demonstrated a Dynamic Supply Voltage amplifier
  under digital control with improved linearity and
  efficiency
• Currently working towards developing a flyback
  DC-DC converter which would result in higher
  efficiency