A high efficiency Class-E amplifier utilizing GaN HEMT technology - presentation

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```					             High Efficiency Class-E
Amplifier Utilizing GaN HEMT
Technology

William L. Pribble, Jim M Milligan, and
Raymond S. Pengelly

Cree Inc
4600 Silicon Drive,
Durham, NC 27703

Creating Technologies That Create Solutions™
Does Efficiency Matter?
1.6
Dissipated Power/Output Power

Class A
1.4

1.2
Class B
1
Switchmode
0.8
Class D,E
0.6                                                 Class C,F?
0.4

0.2

0
0.4   0.5   0.6      0.7      0.8   0.9   1

Effciency

Increasing efficiency from 50% to 80% reduces dissipated power by
80% for a fixed output power
Switchmode amplifier configurations can operate above 80% efficiency

Problem: Extend switchmode operating frequency beyond VHF

Creating Technologies That Create Solutions™                                                         2
Why Switch Mode Amplifiers?
With a suitable high frequency transistor
technology they offer very high efficiencies
compared with Class A/B amplifiers
GaN HEMT technology is ideal
–   High fT
–   Low input capacitance
–   Manageable output capacitance
–   Low RDSON
GaN HEMT is the first technology to offer the
ability of realizing switch mode amplifiers to
well over 3.5 GHz!
Creating Technologies That Create Solutions™           3
Class E Amplifier Basics

FET used as switch is                                          DCVS

assumed to have high off-
ID=V1
V=1 V

resistance
Switch on-resistance                                           IND
ID=L2             IND        CAP

assumed to be constant
L=L1 nH           ID=L1      ID=C1
L=L2 nH    C=C2 pF

and must be minimized to
2
D
1        T

achieve high PAE
G
RES
S                 ID=R1
3                     R=RL Ohm
ACVS

Output capacitance
ID=V2
Mag=1 V
Ang=0 Deg

assumed to be
independent of switch
voltage                                                  κo         j⋅ θ         Optimum Class-E fundamental
Q factor of output circuit                         ω⋅ C1                         1995

assumed large enough to
suppress harmonics –
“flywheel” effect insures
sinusoidal output
Creating Technologies That Create Solutions™                                                                                4
Class E Power Calculations
Relates peak output power for ideal class-
pout ⋅ rl
vcc :=                    E wavefroms to supply voltage – This
0.577         value is ~78% of peak Class-B output
power

To achieve peak Class-E output power as shown,
peak voltage is calculated to be 3.56Vcc, peak drain
current 2.86Idc (Solid State Radio Engineering – Krauss, Bostian, Raab)
Typical class-B voltage waveforms peak at ~2X the
supply voltage
Ideal class-E operation produces lower power for
higher peak voltage – but with 100% efficiency

The optimum class-E device must exhibit both low Ron
and high breakdown voltage to function as a switch
Creating Technologies That Create Solutions™                                      5
Basic Class E Equations/Limitations

Imax                          Fundamental frequency limit for ideal class-e
fmax :=                                                      operation related to output capacitance
− 12
56.5⋅ 10          ⋅ cs ⋅ vcc
cs=C1

2                                                                           GaAs PHEMT
Class-E Peak Current (A/mm)

1.8
1.6
1.4                                                           0.05
1.2                                                                           High-Voltage GaAs
0.1
1
0.15
0.8
0.6                                                           0.2
Cree GaN – qualified
0.4                                                                           process available 1st
0.2                                                                           quarter 2006
0
0    10          20        30           40       50                     Cree GaN Process Goal
Operating Drain Voltage (V)

Plot shows required peak current vs supply
voltage for operation at 4GHz for given output
capacitance
Creating Technologies That Create Solutions™                                                                                          6
Summary of Class-E Device Requirements

High switching speed (related to input capacitance)
required for switchmode operation – Ft as much as
10X operating frequency to minimize transition-time
loss
Low on-resistance/high peak current to approximate
ideal switch and increase peak operating frequency
High breakdown voltage to accommodate class-E
peak voltage for > 50 watt output power

Gallium Nitride HEMT is the only presently available
technology which provides these attributes

Creating Technologies That Create Solutions™                7
Class-E Switch Mode Amplifier Simulation using
Class-E
Cree GaN HEMT Large-Signal Model
Large-Signal
Current (I)         Voltage (across Q1)

80                                                                                                    2.0

60                                                                                                    1.5

Current (A)
Voltage (V)
C1 absorbed       RL
(I)                                         40                                                                                                    1.0
in device

20                                                                                                    0.5

0                                                                                               0.0
0.0                0.2              0.4             0.6         0.8         1.0
Freq = 2.0 GHz
time, nsec
Q1 = Cree 15 watt GaN HEMT                                                   50                                                                          100

RON = 1.7Ω
Output Power (dBm)
40                                                                          80

VD=V=35V                                                                     30                                                                          60

PAE (%)
RL=26 , C1=0.64pF, L1 = 50uH                                                 20                                                                          40

L2=13nH,C2=0.612pF                                                           10                                                                          20
POUT=10 Watts, =82%
0                                                                          0
10   12         14    16         18   20         22   24     26   28
Input Power (dBm) @ 2GHz

Creating Technologies That Create Solutions™                                                                                                                                           8
World Record 2.0 GHz
High Efficiency GaN Amplifier
Measured Performance @ 30 V
43                                                   90
42                                                   80
41                                                   70
Output Power (dBm )

40                                                   60
39                                                   50   power
38                                                   40   pae

37                                                   30
36                                                   20
35                                                   10
34                                                   0
1.7   1.8     1.9      2      2.1   2.2   2.3
Frequency (GHz)
Fabricated High Efficiency GaN Hybrid

Class E Hybrid amplifier
Vd = 30 volts
50 input/output
10 W POUT, 88% Drain Efficiency!
– 1.9 – 2.1 GHz!

Creating Technologies That Create Solutions™                                                  9
Approach Validated at Higher
Frequencies and Moderate Bandwidths
Measured Data                                                                           Measured Data
50                                                         90                                50                                              80
48                                                         80                                48                                              78
46                                                         70                                46                                              76

Output Power (dBm)
Output Power (dBm)

44                                                                                           44                                              74
60
42                                                                                           42                                              72
50   power                                                                              power
40                                                                                           40                                              70
40   pae                                                                                pae
38                                                                                           38                                              68
30
36                                                                                           36                                              66
34                                                         20                                34                                              64
32                                                         10                                32                                              62
30                                                         0                                 30                                               60
2.5   2.6     2.7         2.8         2.9   3   3.1                                       3.25   3.3   3.35     3.4     3.45   3.5   3.55
Frequency (GHz)                                                                       Frequency (GHz)

~10 Watts RF Out                                                                           ~10 Watts RF Out
12 dB Power Gain                                                                           11 dB Power Gain
76-82% PAE                                                                                 72-78% PAE
2.7 – 2.9 GHz                                                                              3.3 – 3.5 GHz

Cree’s GaN Technology Enables High-Power
High Frequency Class-E Operation
Creating Technologies That Create Solutions™                                                                                                                               10
Approach Validated at Higher Power Levels
amp 1
Output Power, dBm
50
49.5

output power (dBm )
49
48.5
48                                               amp 1
47.5
47
46.5
46
1.85    1.9      1.95        2    2.05   2.1
frequency (ghz)

amp 1
80
75
70

pae
65                                                 amp 1
63 Watts Peak RF Output Power                                  60

18 dB Power Gain                                               55
50
75% PAE                                                          1.85     1.9      1.95        2     2.05   2.1
frequency (ghz)
2 GHz Operation

Creating Technologies That Create Solutions™                                                                                    11
Summary
GaN HEMT-Class E amplifier / ET
demonstrated linear PAE of 54%
–   Much Superior to GaAs MESFET and LDMOSFET
–   Demonstrates “leapfrog” in efficiency when compared
to conventional Class A/B biased amplifiers deployed
today
–   High Power GaN HEMT-Class E modules built &
measured
–   Overall efficiency in ET system at 56% with 20 Watts
average power under CDMA 2000
–   Approach suitable for telecom. bands including 3.5GHz
WiMax

Creating Technologies That Create Solutions™                       12

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