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High Efficiency Amplifiers for EDGE Applications Based on Enhancement-Mode Junction PHEMT. J.C. Clifton, L.Albasha Sony Semiconductor & Electronic Solutions M.Willer Sony CSBD 13 th September 2004. Id, Ig. Id. Vth. Ig. Vg. Schottky HEMT Vf = 0.7 (V). Technology: Sony J-PHEMT.
High Efficiency Amplifiers for EDGE Applications Based on Enhancement-Mode Junction PHEMT
J.C. Clifton, L.Albasha
Sony Semiconductor & Electronic Solutions
13th September 2004
Phase detectorTypes of EDGE (8PSK) Power Amplifier
Linear/Backed-Off PA Approach
Fixed Vdd=3.5V Operation
Backed off Input Power, Pin
Coupler for PACL
Increased Vgg for linear operation
Polar Loop Approach
Phase Modulator or VCO
Advantage: Drive Level and Power Control (eg drain regulation) similar to GMSK (constant Envelope)
Issue: Method of Envelope insertion and correction
Corrected Envelope inserted onto drain or gate supply
Corrected RF Output Signal
Corrected Drain Voltage (max=3.5V)
Associated Drain Current
DRAIN VOLTAGE/CURRENT CHARACTERISTICS
Loop Dynamics optimised to minimise Error Voltage whilst ensuring loop stability over range of control and supply voltages
RF Output Signal make to track EDGE Envelope by AM Correction Loop
PAE: 40-45% using fast DC-DC converter
Phase error significantly reduced. Resulting EVM of 3.2%. Further reduced with the addition of simple pre-distortion circuit. Simulated PAE of 44%.
PA operated in saturated mode. Gate tracking circuit designed to exhibit constant gain over input envelope. Simulated efficiency of 50%.
Resulting phase variation of <10° over envelope and EVM of 1%.
Phase error due to compression is partly offset by impact of phase variation caused by gate bias shifts required to keep gain constant
Gate AM correction circuit reduced EVM from 16% down to 3%.
-36.1dBc, 400KHz offset
-54.3dBc, 400KHz offset
Implementation Issues for PA in compression: AM Correction loop design –extreme sensitivity of gate voltage to EVM and ACPR.
Required improvements for product:
Objectives Met with Modified Linear PAModifications compared to conventional Linear PA to Improve Efficiency at back-off and simplify power control scheme
V2 for EDGE
GMSK O/P Matched
Input Step Attenuation: EDGE HI, GMSK LO
Vramp (GSM & EDGE)
Vd supply=VbatteryModified Linear PA: Measured Performance
(excluding VGA consumption required for conventional PA)
Measured Pout/Temperature Characteristics
Temperature stable, variable gain PA
Power Error Budget
Frequency Variation < +/-1.0dB
Temperature Variation < +/-1.0dB
WORST CASE < +/-2.0dB
RX Noise: -82.3dBm/100KHz @20Mhz offset from carrier
(-10dBm input power, 28.3dBm Output)