www.cavendish-kinetics.com

DESIGN CONSIDERATIONS FOR DEVELOPING ACTIVE ANTENNA SOLUTIONS Paul Tornatta VP, Product and Customer Engineering

131212-1

1

OUTLINE

CK Introduction

Aperture Tuning vs. Impedance Matching

Requirements for Aperture Tuning Components

Detailed Analysis of Critical Performance Parameters

• ESR (Q)

• Cmin

• Tuning Range

Implementation Examples

• Prototype Board

• Mobile Broad Band Device

• Smart Phone

Summary

2

CAVENDISH KINETICS: AT-A-GLANCE

Cavendish Kinetics LTD

Business Tunable RF Solutions focused initially on cellular/ mobile handsets. Locations: (HQ)San Jose ,CA; Dallas, TX, (DC) Hertogenbosch, Netherlands Sales/Support Locations: US, China, Korea,Taiwan

Value Proposition High Performance Tunable RF Components to enable increased data rates, lower power operation, longer battery life, & reduced BOM costs

Technology: NanoMech™ :Proprietary CMOS –based embedded MEMS solution

Differentiation Ultra Small Form Factor , High Quality Factor, High Tuning Ratio, Low Power

Status Ramping Volume Production

Patents & IP 44 Key Patents granted, >100 Patents in process

Solution Vectors Antenna (band select) Tuning, Impedance Matching, PA Tuning (loading), Filters

FAB & Supply Chn Tower Jazz, STATS ChipPAC, JSI

3

APERTURE TUNING VS. IMPEDANCE MATCHING

PIFA Antenna

Radiating Element

Feed Point

Shorting Pin

Ground Plane

An antenna is a transition device, or transducer, between a guided wave and a free-space wave, and vice-versa.

Free Space Wave

Guided Wave

UP

Aperture Tuning – Optimizes radiation efficiency from the antenna terminals into free space

Impedance Matching - Optimizes power transfer from the transmission line (guided wave) into the antenna terminals

Matching

Network

DVC

4

EXAMPLE: IM AND ANTENNA TUNING AT DELIVERS IMPROVED PERFORMANCE

7X improvement

at 750 MHz vs

doing nothing

Reference: Icilli, D, Antennova, Antenna Systems

Conference, 2011

IM Resulting Efficiency

AT Efficiency E

ffic

iency

[%]

Effic

iency

[%]

No Actions

AT only

IM only

Envelop with IM Tuning

Envelop with AT Tuning

Efficiency with AT @ 750 Mhz

Efficiency with IM @ 750 Mhz

Envelope with IM tuning

Original Antenna Efficiency

Efficiency matched @ 750 Mhz

14X improvement

at 750 MHz vs.

doing nothing Implementation Cost Less than IM

2x Better results than Impedance Matching

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KEY NEEDS FOR APERTURE TUNING Antenna

Performance Impact Metric Requirements

Antenna Efficiency

TRP, TIS Low Cmin

Low ESR High Q

Cmin 0.8pF, 0.6pF Q> 150 @ 2GHZ Q> 225 @ 750 MHz

Tuning Range Band Coverage

C-range >3:1 Low ESL High SRF

4:1, 5:1 SRF>8GHz

Low Noise TIS High IIP3 Low harmonics Low parasitics

IIP3 > 65dBm Tx spurious< -85dBm Rx spurious< -120dBm

Small Size Cost, Performance

Low parasitics Low cost

~2 mm2

Most important features for aperture tuning: Q, C-Range, Size, and Cmin

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TARGET SPECIFICATIONS 32CK301: ANTENNA “BAND SELECT” TUNER: ENABLES “SMART” ANTENNAS

APPLICATION Band Select (main antenna)

USAGE Single antenna to cover 8+ bands

KEY CARE-ABOUTS Cmin, Cratio (tuning ratio), Q, IP3

PARAMETER TARGET SPECIFICATION UNITS

Resolution 5 bits bits

Step Size <25 fF

Supply Voltage 1.62V - 1.98V V

Vrf RMS (MAX) 50 V

Max RF Power +36 dBm

Third order distortion (IIP3) > +65 dBm

Min Capacitance 0.4 pF

Max Capacitance 1.0 pF

Cmax/Cmin ratio* 2.5:1 Cmax/Cmin

Quality Factor (C Max) > 100 @ 2GHz

Operating Temp -40 to +85 °C

Storage Temp -65 to +175 °C

Switch life 1.00E+09 Cycles

RF self actuate 50 Vrms

Switching time 50 us

Chip size ~ 2 mm2

Product Family: 32CKxxxS/R, C range 0.4pF – 5pF Control Interface: SPI, RFFE

Note: All specs assume the user-side of bump

Control block

CLK

CS

SDA

VDD

GND2*RFGND

RFSPI Interface

ESD Prot.

7

0

1

2

3

4

5

6

0 5 10 15 20 25 30

Cap

acit

ance

(p

F)

Bit State

CAPACITANCE RANGE AND RESOLUTION OF DIFFERENT PRODUCTS

8

130 fF +/- 1.1%

80 fF +/- 1.9%

45 fF +/- 2.8%

29 fF +/- 4.1%

505S

503S

402S

301S

Step Size, % Sigma

APERTURE TUNING PIFA DESIGN FLOW

9

GUIDELINES FOR PICKING DVC LOCATION

Location effects frequency tuning range – more capacitance range is required at position 1

Select cap position so low band tuning does not effect the high band (close to a current zero

for the high band)

Select a location to use the minimum value of Cmax possible (toward position 2) – drives

higher low band efficiency

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DVC Placement Region

High Band Current Distribution

Low Band Current Distribution

2 1 Simplified Dual Band PIFA

DVC

POSITION OF DVC VS TUNING RANGE

DVC Position on the antenna effects tuning range

In the design flow steps 1-4, DVC position is important to get the full frequency tuning range using the smallest possible capacitance range

0.675

0.7

0.725

0.75

0.775

0.8

0.825

0.85

0.875

0.9

0.925

1 1.5 2 2.5 3 3.5

An

ten

na

Re

son

an

ce F

req

ue

ncy

[G

Hz]

Capacitance [pF]

1.5pF range design fRES

2.3pF range design fRES

Tuning Slope 90MHz/pF

Tuning Slope 136MHz/pF

DVC Placement Region

2 1

DVC

1

2

Placing the DVC farther “out” on the antenna increases the frequency change with capacitance Simplified Dual Band PIFA model

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-4.0

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1

IMPORTANCE OF HIGH Q LOW EQUIVALENT SERIES RESISTANCE (ESR)

Lower ESR = Higher Q

Q

1

ESR too high for net gain

Net Gain 2-3 dB

Net Gain 1-2 dB

Net Gain <1 dB

Antenna Performance (dB)

Baseline

Loss

Gain

ESR (Ω)

2-3 dB Improvement

Target

MEMS High Q SMT (no switch)

SOI/SOS switches ~0.6 -1.0 1W GaAs switches >1W

ESR

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USABLE Q CONSIDERING FREQUENCY AND CAPACITOR STATE

Q never drops below 225 for a practical antenna implementation

0

0.5

1

1.5

2

2.5

3

3.5

4

0

125

250

375

500

700 720 740 760 780 800 820 840 860 880 900

DV

C C

apac

itan

ce [

pF]

DV

C Q

Fac

tor

at T

arge

t Fr

eq

ue

ncy

Target Frequency [MHz]

Q at target frequency

C [pF]

Measured data

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IMPORTANCE OF C MIN – IMPACT OF C RANGE

Cmin

1.0 pF

0.6 pF

0.5 pF

0.33 pF

Cmin

1.0 pF

0.6 pF

0.5 pF

0.33 pF

Same Frequency Tuning Range with different C values

Significant improvement at the low end of the band (2-3 dB) is possible with lower Cmin

Not much change high end of the band

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DESIGN FLOW – TUNABLE ANTENNA FLOW MAPS INTO TRADITIONAL ANTENNA DESIGN PROCESS

1. Initial antenna design

Set Cmin

Toggle back and forth Cmin-Cmax

2. Check Bandwidth

3. Check High Frequency

4. Check High Band

Yes

No

Yes

No

Yes

No

5. Iterate Steps 1-4

6. Design Fixed Feed Match

7. Verify the matching network

8. Optimize Match

Yes

No

Yes

No

Proceed to active testing

Established Design Flow – Proven Multiple Times 15

EXAMPLE 1 – TE CONNECTIVITY METASPAN ANTENNA

Fixed Capacitor Tunable CK

Antenna Applications Board

Fixed Ceramic Capacitor

Performance comparison of fix value ceramic capacitors (without switch losses) to the DVC

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RETURN LOSS

dB

17

MEASURED EFFICIENCY

-5

-4

-3

-2

-1

0

700 750 800 850 900 950

MHz

Max

Mid high

Mid low

Min

5pF

4pF

2.7pF

-5

-4

-3

-2

-1

0

1700 1800 1900 2000 2100 2200

MHz

Max

Mid high

Mid low

Min

5pF

4pF

2.7pF

dB

dB

18

-5

-4

-3

-2

-1

0

700 750 800 850 900 950

Efficiency(dB)

Frequency (MHz)

Difference

Passive

DVC

LOW BAND COMPARISON BETWEEN DVC AND DISCRETE CAPACITORS

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Low band “penalty” for tunability: ~0.2dB average over fixed passive

EXAMPLE 2 – COMMERCIAL MOBILE BROAD BAND DEVICE, LOW BAND TUNING

(A)

(B) RF GG

(C)RF GG

A) Ground Shield B) Discrete Capacitor for Comparison C) DVC Mounted on Antenna Application Board

Ground plane 52 x 65 mm

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MEASURED EFFICIENCY – DVC COMPARISON TO FIXED CERAMIC CAPACITOR

Tota

l Eff

icie

ncy

%

21

Comparison of DVC to Fixed Cap

EXAMPLE 3 – 4G LTE SMART PHONE, HIGH BAND TUNING

RF ckt

1.2pF

Fixed Matching Network

B4 TX B4 RX B2 B12

Tunable High Band Fixed Low Band 699 746

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MEASURED EFFICIENCY COMPARED TO BROAD BAND PIFA

0%

10%

20%

30%

40%

50%

60%

70%

70

0

71

0

72

0

73

0

74

0

75

0

17

10

17

30

17

50

18

50

18

70

18

90

19

10

19

30

19

50

19

70

19

90

21

10

21

30

21

50

PIFA

AFT Cclip 0.5pF ANT#24

AFT Cclip 1.0pF ANT#24

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% E

ffic

ien

cy

SUMMARY

Aperture tuning preferred method – best performance

over frequency

Tuning element must meet key critical performance

parameters, like low ESR and low Cmin to be viable for

aperture tuning

CK MEMS meets key critical performance parameters

Easy to design with, design method verified in practice

several times

Examples show DVC works just like a discrete ceramic

capacitor with adjustable value

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