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PA Workshop. High Efficiency SiGe BiCMOS WCDMA Power Amplifiers With Dynamic Biasing Techniques by Junxiong Deng 1 , Prasad Gudem 2 , Larry Larson 1 , Peter Asbeck 1 1 University of California at San Diego 2 Qualcomm, San Diego, CA. Presentation Outline. Research Goals

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pa workshop
PA Workshop

High Efficiency SiGe BiCMOS WCDMA

Power Amplifiers

With Dynamic Biasing Techniques

by

Junxiong Deng1, Prasad Gudem2, Larry Larson1, Peter Asbeck1

1University of California at San Diego

2Qualcomm, San Diego, CA

presentation outline
Presentation Outline
  • Research Goals
  • Proposals and Implementation
    • Standard Bias Techniques
    • Dynamic Current Biasing
    • Dynamic Voltage Biasing
  • Status and Future Work
  • Conclusion
research goals
Research Goals
  • SiGe BiCMOS Power Amplifiers for WCDMA applications with far higher efficiency than existing approaches
  • Good Average Efficiency
    • Although peak efficiency is more than 50%

for class AB, but average efficiency is only 2%

  • High Output Power (+27dBm)
  • High Power Gain ( > 21dB)
  • Low Noise Figure (10dB)
  • Small Error Vector Magnitude (EVM<10%)
  • Adjacent Channel Leakage Ratio (ACLR>33dB for 5MHz)
standard biasing techniques
Standard Biasing Techniques

Constant current biasing

A

  • The DC current does NOT change as RF power increases
standard biasing of pa constant current biasing

120

mA

120

mA

Standard Biasing of PA – Constant Current Biasing

Constant current biasing: Poor Linearity!

  • The key here is to realize that the average collector currents needs to remain constant. Therefore the quiescent base-emitter voltage falls as shown in the figure on the left. Note that the drop in quiescent base-emitter voltage results in a degradation of the linearity of the amplifier because the current would clip at lower input power.
standard biasing of pa constant voltage biasing

120

mA

450

mA

120

mA

Standard Biasing of PA – Constant Voltage Biasing
  • Constant Voltage Biasing
    • The advantage is that the DC current increases as the RF power increases. Due to this increase in DC current the linearity of the RF amplifier improves. At the same time, compared to a power amplifier always burning large bias current, constant voltage bias scheme also saves much power.
  • Good enough? No!
dynamic current and voltage biasing principle
Dynamic Current and Voltage Biasing Principle
  • Dynamic Biasing Strategies: DCB, DVB, and DCB+DVB

(DCB means Dynamic Current Biasing; DVB means Dynamic voltage biasing.)

Previous Researches:

  • DCB: Conexant, RFMD
  • DVB: UCSD (Prof. P. Asbeck)

Motorola (J. Staudinger)

Challenges:

  • DCB: gain change
  • DVB: gain change, cost, chip size (dc-dc converter)
dynamic current biasing gain and phase issue
Dynamic Current Biasing – Gain and Phase Issue
  • How does gain and phase change?

Idc

PA

QPSK

(a)

(b)

dynamic current biasing gain and phase issue1
Dynamic Current Biasing – Gain and Phase Issue
  • How do the gain and phase change?

Gain change:

    • Constant # of devices: gain change > 8 dB;
    • Dynamically switching devices: gain change < 1 dB

Phase change:

    • Due to Cjc, Cpi and gm with bias current

Simplified BJT model

dynamic current biasing implementation
Dynamic Current Biasing - Implementation
  • Dynamically switch number of transistors’ fingers and change the bias current

 This keeps the gain more constant @ low bias current

Circuit Schematic of Dynamic Current Biasing

dynamic current biasing simulation results
Dynamic Current Biasing – Simulation Results

DC Current and Gain under different bias conditions

  • constant bias’s average efficiency: 2.4%
  • dynamic bias’s average efficiency: 5.8% (improved by 140% !!!)
  • gain almost constant !!!
dynamic voltage biasing general principle
Dynamic Voltage Biasing - General Principle

High-power

low-power

Schematic of Series Connected Voltage Reduction Topology

dynamic voltage biasing implementation
Dynamic Voltage Biasing - Implementation

- Schematic of Output Stage with

hi-power and low-power groups

dynamic voltage biasing simulation results
Dynamic Voltage Biasing – Simulation Results

(Courtesy P. Asbeck)

Pe

ClassAB

1stepDCB

1stepDVB

Ideal DCB

dynamic voltage biasing simulation results1
Dynamic Voltage Biasing – Simulation Results
  • Average Efficiency Comparison

 This shows dramatic improvements compared to class AB

status and future work
Status and Future Work
  • Dynamic current biasing chips (IBM 6HP) are being tested.
  • Send full dynamic voltage biasing chips to foundry by October.
conclusions
Conclusions
  • In summary, research has been carried out to improve average power efficiency of WCDMA PA, by doing dynamic current and voltage biasing.
  • The key point of our research is to keep power gain to be constant while improving average power efficiency. Simulation results have indicated the validity and effectiveness of the proposed method. Measurement results will come out soon.
  • With our dynamic biasing techniques, average power efficiency can be improved by more than 200%!!!