Highly Efficient and Linear Power Amplifiers for Wireless Communications

1
Highly Efficient and Linear Power Amplifiers for
Wireless Communications

• Professors P.M. Asbeck, L. Larson
• J. Hinrichs, J. Keyser, M. Iwamoto

2
Motivation

• Most wireless handset PAs are of the Class AB
  variety
• Class AB has good linearity, reasonable
  efficiency
• Could use switching mode Class D or E for better
  efficiency, but very non-linear
• Solution Class S PA driven by bandpass ??
  modulated source

3
Theory

• BP?? modulator shapes quantization noise out of
  band
• Single tone at 10 MHz encoded into two-level
  binary signal (fs40 MHz)
• Must filter out harmonics at output of PA due to
  pulse shape

4
Implementation

• Scaled down version implemented with 40 MHz clock
  frequency
• 8192 bit sequence generated with Matlab and
  loaded into HP pattern generator
• Limitation is maximum clock frequency of pattern
  generator -- clock frequency must be 4x that of
  RF output
• Push-pull topology chosen
• 2 n-channel MESFETs used as switching elements
• Transformer-style baluns provide the differential
  input signal and perform power combining at the
  output

5
Experimental Results

• Scaled down version with 40 MHz clock and 10 MHz
  signal
• Pout 20 dBm
• Vdd 2.5 V
• Idc 79.7 mA
• Important results
• drain efficiency ?51.2
• IM3 -39.9 dBc

6
3.2 Gbps Serializer
Power Amplifier Signal Source
7
Serializer Details

• Conexant Has Supplied CX60061 OC-192 Serializer
  Eval Board
• Data rates up to 10 Gbps possible in future
• 200 MHz pattern generator clock, 3.2 GHz
  serializer clock must be in sync
• Two signal sources, common 10 MHz reference
• or Divide-by-16 circuit on 3.2 GHz clock
• Possible preamp - Conexant Laser Driver IC

Input all 1s
8
Bandpass ?? DSP Transmitter

• Advances in CMOS will allow baseband signal to be
  upconverted and modulated digitally.
• I and Q data at lower sampling frequency are
  multiplied by series of /- ones at much higher
  frequency to achieve upconversion
• Digital BP?? modulator generates bit stream for
  Class S PA

digital upconverter
Analog
Digital
Bandpass ?? modulator
9
Bandpass ?? DSP Transmitter

• Advantages
• Can be integrated with DSP hardware already
  present in handset
• More flexible with software programmability
• Decreased sensitivity to component variations
• Implementation complexity must be avoided
• Need multiplier free structure
• System can be designed using only adders, sign
  flips, and delay elements.

10
Bandpass ?? DSP Transmitter
11
Summary

• Current Status
• Bandpass ?? Class S PA demonstrated at 10 MHz
• 50 drain efficiency and -40 dBc linearity
• Current Research
• 161 serializer being built to generate 3.2
  gigabit data stream for 800 MHz PA
• All digital upconverting and modulating
  architecture being investigated for possible IC
  fabrication