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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!!!
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