RFMD wideband line of GaN

Multi-Octave Practical Power Amplifier Realization using GaN on SiC

D. Runton, T. Driver, K. Krishnamurthy, M. LeFevre, K. Shallal

WMG: Broadband PAs for Wireless Communications

• Motivation

• RFMD GaN Technology

• PA Design Topology Overview

• PA Design Methodologies

• Design Examples

• Summary

Agenda

Motivation

JTRS Radio

PMR Portable Radio

Market Drivers

Why GaN?

• Higher efficiency

– Reduce heatsink requirements,

smaller size

– Increase battery life

• Wide bandwidth

– Replace 3 or more amplifiers with

1 amplifier

• Improved battery life / reliability

• Multi-standards for inter-operability

• Wide-band architecture

• Leverage COTS components

Milcom and Public Mobile Radio

Amplifiers

F

vE

Pmax 2

2

s

4

g

Property Si GaAs GaN

Eg (eV) 1.1 1.4 3.4

vs (10 7 cm/s) 0.7 0.8 2.5

Power Frequency Limit

Power Bandwidth Limit

• High power density (V, I) enables high impedance

• Low pF/W enables broadband

Wideband HPA’s covering multiple communication bands

)ln(

Lo

lowhigh

QF

FF

LD

MO

S

LD

MO

S

LD

MO

S

0

500

1000

1500

2000

2500

0 10 20 30 40 50 60

Vds (V)

Ids

(m

A)

Vgs: +1V to -4V

Transistor Parameters

Parameter Value Units

Id-max 1000 mA/mm

Peak gm 225 mS/mm

Vp -3.5 V

Vbr(GD) >450 V

ft 11 GHz

fmax 18 GHz

Power Density 7.5 W/mm

Peak Power 16.5 W

Peak Drain Eff 71 %

Optimum load 31.4+j46.1 W

[1] Class AB Bias: Vds=48V, Ids = 20 mA/mm

[2] frequency = 2.14 GHz

2.2 mm device

.1 1 10 100 -10

0

10

20

30

40

Gain

(d

B)

GMax (dB)

|H(2,1)| (dB)

Frequency (GHz)

ft fmax

Broadband Topologies

Topology Advantages Disadvantages

Resistive FB - lumped implementation - Output not designed for Zopt

- good S22 - Tuning Zload affects

gain flatness and S11

- Rf Pdiss / leakage issues

RLC Lossy Match - Simple/lumped design

- output optimized for Zopt

- Input optimized for gain - Lumped circuit, so flatness

- All-pass network at input thermal design is critical

implies excellent S11

Distributed Amp

- best bandwidth and gain - Zload optimization for each

- dissipation spread out cell is complicated

- poor efficiency

- implementation feasibility issues

Internal Design Match Topology and Design

• Input Match options as shown above

• Use standard DOE design principles

• Output – no matching

• Provides most flexibility

• Takes advantage of GaN high impedances

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.0 1.0

-30

-25

-20

-15

-10

-35

-5

freq, GHzdB

(SP

ara

m_P

assiv

eM

atc

h_P

E1D

2789..

S(1

,1))

dB

(SP

ara

m_P

assiv

eM

atc

h_P

E1D

278A

..S

(1,1

))dB

(SP

ara

m_P

assiv

eM

atc

h_P

E1D

278B

..S

(1,1

))dB

(SP

ara

m_P

assiv

eM

atc

h_P

E1D

278C

..S

(1,1

))

7 Passive Model, S11 (dB)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.0 1.0

13

14

15

16

17

12

18

freq, GHzSP

ara

m_P

assiv

eM

atc

h_S

E1D

2789..

MaxG

ain

1S

Para

m_P

assiv

eM

atc

h_S

E1D

278A

..M

axG

ain

1S

Para

m_P

assiv

eM

atc

h_S

E1D

278B

..M

axG

ain

1S

Para

m_P

assiv

eM

atc

h_S

E1D

278C

..M

axG

ain

1

Max Gain (dB) Input Return Loss, S11 Max Gain (dB)

Internal Design Simulation Methodology

• Design Methodology

• Design/Simulate Input circuitry

• Assume Ideal Match (choose load impedance)

Practical Output Matching

Balun

Lumped Element

Transformer

Design Example 45W, 20-1000MHz

Performance

• Vdq = 50V, Idq = 130mA

• Bandwidth: 20 – 1000 MHz

• Gain: 17.5±1 dB

• Input return loss: < 11 dB

• Output power: 50.3 W at 512 MHz

• PAE: 70% at 512 MHz

0.5 1.0 1.50.0 2.0

5

10

15

20

0

25

-15

-10

-5

0

-20

5

freq, GHz

dB

(S(1

,1))

dB

(S(2

,2))d

B(S

(2,1

))

17 20 23 26 2914 32

29

32

35

38

41

44

47

26

50

10

20

30

40

50

60

70

0

80

Pin (dBm)

Outp

ut P

ow

er

(dB

m) G

ain

(dB

), PA

E (%

)

• Uses 6.6mm device periphery

• Designed for 25Ω source and load impedance

• frequency target is 20-1000MHz

• Multi-chip module approach with GaAs passive

die and GaN HEMT active die.

• Minimizes SiC die area as the matching circuits

are large at low GHz frequencies and below.

Balun Matching

• Two 25W matched unit amplifiers are combined together.

• Broadband 45W amplifiers are first designed for operating in a 25W system.

• Two such PAs are combined using a broadband 1:1 Balun at input and output to convert the differential 25W impedance to a 50W system.

• Gate bias feeds isolated through a resistor, and connected together.

• The high-Q bias feed inductors at drain of each device are connected together.

• 300W ferrite (at 100 MHz) at the drain bias feed to extend low frequency performance.

Balun Design

• For high frequency isolation the coax

length is quarter wave long at the upper

cut-off frequency.

• This results in a 4 turn coil for the chosen

ferrite diameter.

• Broadband coiled balun is formed by winding

a rigid coax around a ferrite rod

• Coiling increases self-inductances and the

ferrite improves low frequency cut-off

• Advances in low-loss ferrites make them

suitable for GHz range

• A 43 material ferrite rod from Fair-Rite Corp

with 5mm diameter is used - provides high

permeability at low frequency and low loss at

high frequency

• 50Ω coax with 0.22dB/ft loss, that can handle

124W at 500MHz is used

• The center and outer conductor are

connected to unbalanced signal and ground

at one end and to the differential balanced

signal at the other.

• The ferrite forces equal and opposing current

at the inner and outer conductor and isolates

the 180º signal from the input ground at low

frequency

Balun Performance

Measured performance

• Insertion loss (back-back) : 0.34 dB

• Insertion loss per balun : 0.17 dB

• Return loss: better than 20 dB

90W PA Module CW Performance

• Frequency: 100 – 1000 MHz

• Gain over band: 15.1 – 16.3 dB

• Output power: 82 – 107.5 W

• Efficiency: 51.9 – 73.8 %

Vdq = 50V, Idq = 265mA

Design Example 80W Module, 100-800MHz

0.3 0.5 0.7 0.90.1 1.0

12

13

14

15

16

17

11

18

-30

-25

-20

-15

-10

-5

-35

0

freq, GHz

dB

(S(2

,1))

dB

(S(1

,1))

dB

(S(2

,2))

Small Signal Sweep

1.0

E8

2.0

E8

3.0

E8

4.0

E8

5.0

E8

6.0

E8

7.0

E8

8.0

E8

9.0

E8

1.0

E9

1.1

E9

0.0

1.2

E9

46

47

48

49

50

51

52

53

54

45

55

RFfreq

Po

ut (d

Bm

)

Output Power

Simulated Performance

• Vdq = 48V, Idq = 300mA


• Gain: 11±1 dB

• Input return loss: < 11 dB

• Output power: 80W across the band

• PAE: >50% across the band

• Uses 15.5mm device periphery

• designed for 50W source, 12.5W load impedance

• frequency target is 100-800MHz

• Multi-chip module approach with GaAs passive

die and GaN HEMT active die.

• Minimizes SiC die area as the matching circuits

are large at low GHz frequencies and below.

Transformer Matching

• Single 50W matched amplifier

• Broadband 80W amplifier is designed for operating with a 50W input impedance.

• Amplifier is designed based on ideal 12.5W output impedance.

• The challenge is to create this impedance

• The PA drives a broadband 4:1 transformer to convert the 12.5W impedance to a 50W system.

Transformer Match

XMB0220B5050 Features: • 30-1000 MHz

• 4:1 Transformer (50Ω to 12.5 Ω)

• Broadband

• Defense Applications

• High Power > 100W

• Very Low Loss < 0.5dB


Vdq = 48V, Idq = 300mA (class-AB)

Performance


• Gain: >10dB

• Input return loss: <-12 dB

• Output power: 80W

• Efficiency: 52.5 – 57.7%

Design Example Unmatched FETs

Lumped Element Match

• Single 50W matched amplifier

• Broadband design “generally” hitting target impedances.

• The challenge is to create this impedance

• Determine Target Impedances • Actual impedance from loadpull

• Non-linear model simulation results

Z0= 10Ω

56

56

56

56

60 60

60

60

64

64

46

48

48

48

50 50

50

52

52

52

54

54

Z0(g

am

ma_ld

1_im

ag)

Z0(gamma_ld1_real)

Efficiency 2.0GHz Pin = 35dBm

4 5 6 7 8 9 10 11

-1

0

1

2

3

4

Eff Meas Eff Sim Data Point

Wirebond model

Package Model

Unit Cells with manifold model

strip

strip strip

Q=1.

0

VSWR=1.

7

uStrip+C Match

L+C Match

Lumped Element Topology

30W PA Module 700-2400MHz Simulations

Output

Impedance

S11 Match to

50Ω



• Gain: >10dB



• Efficiency: >25%

2.7pF

0.4pF

1.0pF

2.0pF


Performance


• Gain: >10dB




Combination Matching

• Two 25W matched unit amplifiers are combined together.

• Broadband 100W peak power amplifiers are first designed for operating in a 6.25W system.

• Two such PAs are combined using a broadband 4:1 Transformer followed by a balun to convert the differential 25W impedance to a 50W system.

• Gate bias feeds isolated through a resistor, and connected together.

• The high-Q bias feed inductors at drain of each device are connected together.


Freq

(MHz)

Pin

(W)

Zload Zs PAE

(%)

Pdel (W)

30 31 7 + j 0 13 + j 4.7 41 52

65 31 8 + j 0 9 + j 9 43.6 51.7

100 31 7 + j 0 9 + j 7.4 44 52

225 31 8.4 +j 0 7 + j 6 50 52

380 31 7 + j 1 2 + j 4.1 52 52.5

512 31 7 + j 3 2.6 +j 2.7 55 52

Design Target


• Gain: >16dB


• Output power: 100W PEP


• Determine Target Impedances • Actual impedance from loadpull

• Non-linear model simulation result

• Notice Zload is almost purely real at 7-8Ω • This drives 4:1 topology at 6.25Ω per side




• Gain: >16dB




100W PA Module 2-tone Performance

Performance


• Gain: >16dB




Summary

• Emerging SDR architectures require wideband, high power

amplifiers with high efficiency, compact size and low cost

• GaN-on-SiC technology adoption continues for high power

commercial and military applications

• Demonstrations include:

• 90W (dual device module), 100–1000 MHz, >51% drain efficiency

• 80W (single device), 100-800MHz, >51% drain efficiency

• 30W (single device), 700-2400MHz, >28% drain efficiency

• 100W peak power (dual device), 30-700MHz, >18% drain efficiency

Documents

RFMD wideband line of GaN