USING ADS TO SIMULATE ACTIVELY TUNED

ANTENNAS WITH HIGH PERFORMANCE RF

MEMS

Keysight RF Design Seminar

Eindhoven (NL), April 29th 2015

Roberto Gaddi

rgaddi@cavkin.com

1

OUTLINE

Cavendish Kinetics and SmarTune™ introduction

Tuning the antenna aperture: why and how?

How ADS can help the early design phase

Linear and non-linear parameters of interest

Conclusions

2

CAVENDISH KINETICS: AT-A-GLANCE

www.cavendish-kinetics.com

Cavendish Kinetics LTD

BusinessTunable RF Solutions focused initially on cellular/ mobile handsets.Locations: (HQ)San Jose ,CA; (DC) Hertogenbosch, Netherlands + Dallas, TX

Target Market Size $ 800M: RF Tunable Capacitors, > $2.5B in Tunable RF & Programmable Filters

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

Technology: SmarTune™ :Proprietary (.18µm) CMOS Foundry compatible embedded MEMS solution

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

Status In Production with several Chinese Mobile OEM’s (Nubia, …)

Patents & IP 40 Key Core Patents, +100 Patent Applications

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

FAB & Supply Chn Tower Jazz, STATS ChipPAC, JSI

Venture Backing Tallwood Venture Capital, Wellington Partners, Celtic House Ventures, Qualcomm Ventures

Key LeadershipCEO: Paul Dal Santo (Silicon Image, AMD, Motorola), CTO/VP Eng: Richard Knipe (TI), EVP Ops: AtulShingal (NSC, SiRF, Inphi), VP Mkt: Larry Morrell (Impinj, Cypress), VP WW Sales: Dan Smith (R2 Semi, TI),VP Products: Paul Tornatta (CTO; SkyCross), Lars Johansson, VP Product Marketing (BroadCom, Beceem)

CK APPLICATIONS ROADMAP

Consumer & Market Requirements will demand tuning throughout the RF chain

LNA

PAPA

Simplified FEM

…

…

LNA

PAPA

LNA

PAPA

TUNABLE IMPEDANCE MATCHING

ENABLES:Increased TRP, TIS

Higher Efficiency

Reduced Power

Lower System Loss

Matching Network

PA

PA LOADING

TUNABLE FILTERS & DUPLEXERS TUNABLE ANTENNAS

ENABLES:Increased Bandwidth

Higher Efficiency

Smaller Form Factor

Reduced # of Antennas

ENABLES:Improved Efficiency

Increased BW

Reduced Power

@Multiple Freq. & Power Levels

ENABLES:Improved Efficiency

Reduced Size

Lower Cost

RF SWITCHES

Multi-Band

Multi-Mode

MIMO / Diversity Antennas

Display size increasing, bezel decreasing

Metal frames and covers

Thin form factors

LTE CHALLENGE FOR RF FRONT END

Industry has adopted tunability and reconfigurability as a “must have”

Global band allocations / requirements, device usage models, and platform industrial design trends are putting pressure on mobile device RF performance.

SPECTRUM

COVERAGE FOR

LTE

■ Typically a high end smartphone will have to cover multiple bands in all spectrum region, but not at the same time band select tuning is possible

■ CA (carrier aggregation) will also require 2 or 3 bands to be active at the same time!

http://niviuk.free.fr/lte_band.php

ANTENNA IS THE WEAKEST LINK

Biggest Loser has the Best Opportunity for Improvement antenna aperture tuning

Losses in the radio portion of mobile device

Amplifiers Filters Switches Matching Antenna

Loss (dB) 0-0.20 1.0 -2.0 0.5 – 1.0 .25 - .50 3-8

Loss (%) 5 20 - 37 10 - 20 6-10 50% - 85%

LNA

PAPA

Fixed Match

Antenna Efficiency runs between 15% up to 60% efficient Depends on Industrial Design, Frequency, and Bandwidth

APERTURE TUNING COMPARED TO IMPEDANCE

MATCHING

AIT AFT

RF Front End

Antenna Feed Point

AIT makes the RF Front End Happy

Some Improvement

AFT makes the Entire System Happy

BIGImprovement

TYPICAL MOBILE ANTENNA TUNING METHODS (PIFA)

Other used antenna types such ILA (monopole) and loop can also be tuned in a similar fashion…

DVC – connected to low band resonant element

DVC – parasitic connection to high band resonant element

• Biggest potential gain thanks to limited losses in (fixed) capacitors technology

Changing the ground leg electrical length

• Sub-optimal due to relatively large losses in (fixed) inductors

• Need very accurate inductors for high band tuning…

9

COMPONENT REQUIREMENTS FOR ANTENNA TUNING

10

Antenna Performance

Impact Requirements for Aperture Tuning

Antenna Efficiency

TRP, TIS Low CminLow ESRHigh Q

Cmin 0.4 pFESR < 0.5 OhmQ> 150 @ 2GHZQ> 225 @ 750 MHz

Tuning Range Band Coverage

C-range >3:1Voltage handling

3:1, 4:1, 5:1SRF>8GHz

Low Noise TISCA

High IIP3Low harmonicsLow parasitics

IIP3 > 70 dBmTx spurious< -85dBmRx spurious< -120dBm

Small Size Cost, Performance

Board spaceLow cost

2 mm2

Most important features for aperture tuning: Voltage handling, Q factor, Ratio, Cmin

REAL PHONE MODEL: CAN MODEL THIS? Common practice in the

industry is to perform the detailed antenna design at the very last step, where all other details of the industrial design are frozen

This give little room for real 3D EM optimization due to excessive level of details

Antenna fine tuning is done with copper sticky tape and surgery knife…

11

THE “MOCKUP” PHONE: TUNABLE ANTENNA EXAMPLE

A mockup phone is typically used for proof of concept before the industrial design starts

It is also simple enough to be modeled without too many 3D features

12

ANTENNA MODEL IN MOMENTUM

RF: feed point for TX and RX

DVC: digital variable capacitor connection port

13

RFDVC

A TUNABLE ANTENNA IMPLEMENTED IN ADS

14

~ 2mm2

CK SmarTuneDigital Variable Capacitor

RFGND GND

Digital Interface

1.8V Vdd, Ground

RF & Ground

TUNING RANGE VS. ANTENNA PARAMETERS

■ 2 key physical dimensions parameters for adjusting the tuned frequencies:

• Distance of DVC from feed

• Length of the PIFA

■ A given required frequency range can be achieved with many combinations of capacitance range, distance and length

Multi-dimensional problem with many degrees of freedom to optimize

15

Examples:0.5-1.65pF Cap range

Distance 20mm; trimming length from 45 to 60mm

Length 60mm; changing distance from 5 to 20mm

20

mm

15

mm 10

mm

5m

m

55

mm

50

mm

45

mm

60

mm

C=0.5-1.65pF

C=0.5-1.65pF

EFFICIENCY VS. CAPACITANCE LOADING

■ Even assuming ideal (lossless) capacitors the efficiency depends on amount of C loading

Efficiency maximization leads to use minimum amount of capacitance loading

16

EFFICIENCY VS. CAPACITANCE Q FACTOR

■ For a given capacitance loading and location, the impact of Q factor (ESR) on efficiency can be very large

Efficiency maximization is the driver for very low loss tuning technology

17

RMS VOLTAGE REQUIREMENTS

■ For a given PIFA length, moving the tunable capacitor away from the feed achieves tuning with a smaller capacitor, which is good for efficiency

■ But this leads to large RF voltage levels across the device, which becomes therefore a key spec for tuning technologies

RF voltage handling limits the permitted location for tunable capacitor

18

20

mm

15

mm

10

mm

5m

m

MEMS

SOI

GOALS DESCRIPTION

B8 and B12 taken as target tuning range: opposite ends of the low band spectrum

Return loss should be better than 6dB and RF voltage stay below 70V peak (50Vrms) in both bands

Each band can adopt a different value of tunable capacitance, within the range of the tunable capacitor

The location of the capacitor “Dist” is also an optimization parameter for the antenna

B8

B1219

OPTIMIZATION RESULTS

Tuning range is achieved but difficult to have a good return loss at both target bands

Voltage limit is maintained as a hard requirement due to reliability

20

OK

No

t O

K

OPTIMIZATION RESULTS WITH MATCHING NETWORK

A single fixed series capacitor improves the match for B12

Voltage limit is maintained as a hard requirement due to reliability

21

OK≈OK

To antenna feed

FURTHER DESIGN PARAMETERS The most important parameters related to the phone performance are:

• Antenna (total) efficiency: what % of the available power from the PA is radiated (passive test, phone RFFE is “off”)

• TRP (Total Radiated Power): how good can the antenna radiate the power delivered by the PA

• TIS (Total Isotropic Sensitivity): what is the smallest received power level that can be still decoded above a given BER level The level of intermodulation and harmonic distortion can greatly impact this parameter

• Spurious transmitted power: level of radiated spurious power outside the wanted TX band

Efficiency and TRP can be obtained as post-processing in the far field calculations from Momentum…

TIS does depend not only on efficiency but full response of the phone (EM noise) and base-band receiver: “impossible” to model so it is typically measured

Knowledge of the amount of transmitted and reflected harmonics is very useful in order to optimize TIS…

22

GENERATED HARMONICS: THE CARRIER

AGGREGATION “HORROR” SCENARIO

CA (carrier aggregation): multiple TX and RX channels are used at the same time in order to increase uplink and downlink speed

First implementations have 1TX and 2RX channels (improve download speed): same antenna shared for both bands

Some combinations of bands create potential intermodulation and / or harmonics design culprits

23

http://niviuk.free.fr/lte_ca_band.php

B1

2 T

X

B1

2 R

X

699-716MHz

729-746MHz

B4

RX

2110-2155MHz

2097-2148 MHz3rd harmonic

This problem is still open and unsolved for many elements in the radio chain…

REFLECTED HARMONICS SIMULATION BENCH

Reflected power is sensed by ideal directional coupler

24

Antenna EM model

DVC model with harmonics

CONCLUSIONS

■ Aperture tuned antennas are becoming a “must have” in high-end mobile devices due to band proliferation

■ State of the art tunable technology such as RF-MEMS can achieve the performance levels required

■ The design effort can become significant, especially for “traditional” antenna designers: a paradigm shift is required, circuit simulators must help

■ A combined circuit + EM simulation environment such as ADS offers all the tools to understand the design parameters and reach to an optimum solution

■ Unfortunately, most of the antenna design work is still done on hardware on a test bench (copper cutting and soldering)

■ Simplifying the learning curve for tunable antenna application (for example by generating a design guide) could help improving the quality of antennas in future devices

Thanks!!!