1. Dynamic power supply design for high-efficiency wireless transmitters using GaN FETs
D. Cucak
The topic of this project is application of GaN FETs and filter design methodology in a dynamic power supply for highly efficient wireless transmitters. The main objectives of the filter design are generation of the envelope reference with minimum possible distortion and high efficiency of the amplifier obtained by the optimum trade-off between conduction and switching losses. This optimum point was determined using power losses model for synchronous buck with sinusoidal output voltage. On the other hand, application of GaN FETs showed significant efficiency enhancement comparing to the prototypes with Si MOSFETs with good values for FOM.
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Motivation and Objective
Envelope Tracking and Envelope
Elimination and Restoration techniques
Synchronous Buck as Envelope Amplifier
GaN FETs
Wireless and broadband services – growing on a daily basis
Radio base stations – low efficiency!
The main reason – poor efficiency of linear amplifier
ET and EER – efficiency increasement techniques
Envelope Amplifier needs to have
Fast dynamic response (bandwidth and slew rate)
High efficiency
Proposed topology: Synchronous Buck with GaN FETs
GaN devices – significantly better FOM!
Device
Type
Vds_max [V]
Ron[mΩ]
QG[mΩ] (Vgs=5V)
FOM
EPC1015
GaN 40 4
11.6
46.4
EPC1014 16 3 48
BSC016N04LSG Si
2.3 60
138
Efficiency measurements
Static characteristics: Vin=24V, Rload=4Ω, variable duty cycle
Dynamic measurements: 64QAM and WCDMA, switching frequency: 5MHz
64QAM, BW=1MHz RLOAD = 4Ω
EPC1014
EPC1015
PD57070
BSC016N04LSG
Pout, avg[W]
41.1
43.3
42.8
42.7
Eff [%]
87.6
85.9 78
84.2
WCDMA, BW=500kHz RLOAD = 3Ω
EPC1014
EPC1015
PD57070
BSC016N04LSG
Pout, avg[W]
31.2
32.3
31.8
32.6
Eff [%]
87.2
79.8
79.3
82.6
Filter design methodology
Vout
𝑖 𝐿 𝑖 𝐿𝑜𝑎𝑑 (j2π 𝐹 𝑚𝑜𝑑 ) = A
Design parameter
The optimum trade-off between the conduction and switching losses.
How to minimize the losses by filter design?
Modeling of GaN devices
Developed high frequency black box model for commercially available EPC GaN FETs
Switch-based large signal model: losses & performance prediction of our topology
Modeling of GaN devices
Two main goals
A physical model that provides a dependence of the switching behaviour and power losses on the technological parameters of the transistor
CONCLUSIONS
The obtained efficiency measurements showed significant efficiency enhancement by application of GaN FETs
comparing to standard Si MOSFETs. For 64QAM and WCDMA signals, EPC1014 prototype showed around 5% higher efficiency comparing to fast switching Si BSC016N04LSG, at 5MHz of switching frequency. Filter design methodology
for optimum trade-off between the bandwidth and efficiency was proposed and experimentally verified for sinusoidal output voltage.