RF Board Design for Next Generation Wireless Systems

Transcription

1 RF Board Design for Next Generation Wireless Systems Page 1

2 Introduction Purpose: Provide basic background on emerging WiMax standard Introduce a new tool for Genesys that will aide in the design and verification of RF and microwave designs Target Audience: Designers tasked with developing RF architectures for emerging communication markets Page 2

3 Agenda Emerging RF Communication Technologies Overview Emerging Technologies Design Challenges Improvements & Additions to the Agilent Genesys Design Platform Momentum GX Technology Overview Design & Verification of WiMax Circuit Components Design Methodology Review Q&A Page 3

4 Emerging RF Communication Technologies WiMAX- Worldwide Interoperability for Microwave Access: A wireless Metropolitan-Area Network technology (MAN) Provides interoperable broadband wireless connectivity to fixed, portable and nomadic users Provides 50 KM(30 miles) of service area without need of LOS and data rates as high as 75 Mbps Sufficient bandwidth to service hundreds of businesses and homes with a single base station Based upon IEEE support for licensed and unlicensed bands Page 4

5 WiMAX Technology Adopters Page 5

6 WiMAX Technology OFDM Modulation OFDM = orthogonal frequency division multiplexing Data is transmitted on multiple subcarriers for each symbol Subcarriers are spaced so that at each subcarrier peak, all other subcarriers have nulls. This creates orthogonality of the subcarriers. Transmitting on multiple carriers allows slower symbol rate for same data throughput (bits/sec/hz) Less susceptible to narrowband interference and multi-path Frequency Page 6

7 WiMAX Technology Adaptive Modulation and Coding Overcomes multi-path issues by slowing symbol rate Where S/N ratio is highest QAM modulation can be used Provides high speed access to a larger customer base QAM 64 QAM 16 QPSK Page 7

8 Design Challenges for Emerging Technologies Increased circuit complexity Designs operate as TDD or FDD or both Higher frequencies 2GHz 11GHz Increase parasitic effects Smaller circuits, coupling between networks degrades signal integrity Non ideal behavior of both lumped and distributed components Closed form solutions to circuit elements is not accurate enough Compact mobile systems (battery solutions) Radiation effects, wanted and not Cost restraint Manufacturability Page 8

9 Design Challenges for Emerging Technologies Common RF system components Each of these components offer unique challenges for RF engineers: Antenna design Oscillator design Mixer design IF filter design RF receiver / transmitter design MW filter design Page 9

10 Design Challenges for Emerging Technologies What tools are needed to address the technical challenges? A top level RF system tool to plan, optimize and specify component parameters such as Spectrasys A synthesis platform to help speed the development of the RF and MW components e.g. filters, mixers, oscillators etc. Both a linear and non-linear simulator for design and performance verification of noise, power, and spurious effects Yield analysis tools An accurate EM tool to design, optimize and verify the physical performance as a whole before going to manufacturing Agilent Genesys provides a full suite of tools necessary to ensure rapid design flow, verification and now adds Page 10

11 World Class 3D-Planar EM Simulation in Genesys Genesys now offers premier 3D-planar EM simulation technology: Momentum GX An industry proven* technology for simulating complex, multilayered 3D-planar networks from DC to light *Numerous external and internal benchmark tests over 15+ years market track record Page 11

12 Momentum GX Technology Overview What is Momentum GX? A 3D planar EM simulator (2D with Z directed currents) for multi-layer board analysis that enables RF and microwave engineers to expand the range of accuracy of their passive circuits and models Based upon the Method of Moments modeling technique Conformal geometry discretization insures optimal coverage of arbitrary shapes for resonators, matching elements and parasitic effects Momentum works seamlessly within the Agilent Genesys design environment to compute S,Y, and Z parameters Page 12

13 Momentum GX Technology Overview Momentum GX Features: Conformal meshing technology for optimal arbitrary geometry and spacing discretization Dual mode RF and MW simulation solvers (32 and 64 bit versions) Quasi static RF mode for much faster simulations of large/complex designs without significant 0 impact on simulation accuracy Full-wave Microwave mode accounts for all radiation and dispersion effects for full simulation accuracy of smaller component and sub-circuit designs 0 Automatic Genesys co-simulation with linear and non-linear networks AFS Adaptive Frequency Sweep function provides broadband analysis with fewer frequency points Thick metal modeling for accurate interconnect characterization Page 13

14 Momentum GX Technology Overview When to use Momentum GX? Passive matching networks design & verification Passive component modeling: New structures or improving limited closed formed models or where models do not exist Layout verification Include the effects of pads on filters Signal Integrity Antenna Design LTCC design and verification Page 14

15 Momentum GX Technology Overview New topologies Non standard coupler and filter design Signal Integrity Adjacent conductors as well as between layers Manufacturability Monte Carlo Analysis on Er, dimensions etc. Reducing component count Replacing lumped inductors and capacitors with trace elements Improved models for standard structures Steps, tees, open grounds etc. Page 15

16 EM Solvers & Meshing Techniques Typical Grid-based EM solvers Uses grid dimensions not those of component values Suffer from big/small problem Large distances and small dimensions Grid for smallest = large memory Grid for largest = inaccuracy Page 16

17 EM Solvers & Meshing Techniques Momentum s superior conformal meshing technique: Accurate simulations of all geometries Far less memory required Faster solutions (much faster in RF mode) Page 17

18 Design & Verification Of Circuit Components Specific WiMAX design tasks for Momentum GX: Planar antenna design and verification WiMAX system supports phased array antennas WiMAX fixed installations will require an inexpensive highly direction antenna RF/MW Filter verification and co-simulation with active components Include the effects of walls and cover height as well as the complex interaction with active components for linear and non-linear simulation IF/Baseband Filter structures co-simulation and pad mitigation Include the effects of pad parasitics on lumped filter response Page 18

19 Design & Verification of Circuit Components Planar patch antenna design and verification Single patch to multi-element phased arrays Page 19

20 Design & Verification of Circuit Components 3 GHz Patch Antenna Design Example Start with simple circuit model Dimensions taken from literature Tune return by adjusting tap position and size of radiating element Adjust dimensions based on frequency displacement Page 20

21 Design & Verification of Circuit Components Results for optimized patch dimensions: Width and height expanded by 10% Tuned feed point placement for 3 GHz Page 21

22 Design & Verification of Circuit Components Statistical analysis: Use of Monte Carlo and swept parameter analysis to determine manufacturability Set limits on substrate variability Er swept from 3.9 to 4.9 Know your substrate! Page 22

23 Design & Verification of Circuit Components Radiation pattern for single patch antenna verified with EMDS Gain 3.6 db Efficiency 81% Page 23

24 EMDS Solves Complex 3D Structures 3-D Sample Structures Page 24

25 EMDS Far Field Plots & Antenna Parameters Far Field Plots Antenna Parameters Page 25

26 Lessons Learned An accurate EM simulation tool is indispensable in designing and verifying planar antenna performance Determining operating frequency Return loss Radiation pattern Statistical and swept analysis is required to ensure manufacturability Momentum GX is an indispensable tool necessary to ensure first pass success EMDS complements the design flow offering true 3D problem solving Page 26

27 Design & Verification of Circuit Components Microwave Filter Design Example Frequency range 3.4 GHz to 3.6 GHz WiMAX band 3 pole Butterworth, maximum flatness across band Microstrip construction Start with Genesys M/Filter (microwave filter synthesis tool) Page 27

28 Design & Verification of Circuit Components Microwave filter design example: Choose filter type Band pass, Low pass etc. Shape Chebyshev, Bessel etc. Select filter subtype a. Stepped b. Hairpin c. Edge coupled d. Interdigital etc. Page 28

29 Design & Verification of Circuit Components Microwave filter design example: Selection of subtype depends on several factors Size Ease of manufacture Cost Recurring response frequencies Comb subtypes are one of the most compact and have a selectable RPB (recurring passband) but are the more costly Page 29

30 Design & Verification of Circuit Components Microwave filter design example: Select: 1. Reference Z 2. band edges 3. Order 4. Upper and lower frequencies 5. Resonator Zo 6. Tapped input? 7. Length of input line Page 30

31 Design & Verification of Circuit Components Microwave filter design example: Select to create a layout Select manufacturing process Page 31

32 Design & Verification of Circuit Components Microwave filter design example: Select manufacturing process Page 32

33 Design & Verification of Circuit Components Microwave filter design example: Note shift between synthesized filter in Momentum response Both center frequency and bandwidth differ Correction is made to filter dimensions to compensate for offsets Non-adjacent Page 33

34 Design & Verification of Circuit Components Microwave filter design example: Final version of filter dimensions center filter and establish the stated bandwidth Note that the original filter has shifted to a lower center frequency and wider bandwidth Making these corrections prior to manufacturing release is essential The ability to correct for modeling errors non-adjacent resonator coupling etc. is possible through the use of Momentum GX Page 34

35 Design & Verification of Circuit Components Microwave filter design example: Additional coupling options improve manufacturability Tapped input models are limited Momentum aides the development of models and corrections Page 35

36 Design & Verification of Circuit Components Microwave filter design example: Ensuring manufacturability Momentum Sweep of Er Linear Monte Carlo 5% Std Dev Spacing dimensions Er sweep Fo Page 36

37 Lessons Learned Closed-form distributed models are limited Radiation effects and loss modeling is limited Adjacent conductor coupling model does not include thick metal Via models limited to lumped equivalents Non-adjacent conductor coupling does not exist This is very important to coupled structures with several resonating elements Statistical and swept analysis is required to ensure manufacturability Momentum GX is an indispensable tool necessary to ensure first pass success Page 37

38 IF FILTER DESIGN 500 MHz IF (475 MHz to 525 MHz lumped Butterworth band pass filter) Evaluate the effect of using standard component values closest to synthesized values Substitute and evaluate the effect of using standard component measured S-data values instead of ideal components Compensate for shifts due to pad parasitics using Momentum Evaluate the effect of substrate ε r on filter performance Perform a Monte Carlo simulation on component values Start with Genesys Passive Filter synthesis tool Page 38

39 Design & Verification of Circuit Components IF filter design example: Passive Filter dialog Select the type Band pass, low pass etc. Select shape Butterworth etc. Select subtype Filter implementation Page 39

40 Design & Verification of Circuit Components IF filter design example: Differential filters available with a button press Page 40

41 Design & Verification of Circuit Components IF filter design example: Settings tab Set input/output impedances Set corner frequencies Number of sections or order Attenuation at cutoff Common filter inductor/capacitor* Defaults tab Finite Q elements specified *Common inductors or capacitors for specific filter types Page 41

42 Design & Verification of Circuit Components IF filter design example: Substitute standard values for continuous ones Synthesized values Standard 5% values Page 42

43 Design & Verification of Circuit Components IF filter design example: Substituting measured s-data components into the filter Effective inductance and capacitance values are shifted X L -X C SRF affects response Parasitic resistance affects insertion loss WHY THIS SHIFT? Page 43

44 Design & Verification of Circuit Components IF filter design example: Re-tuning with standard value measured components Evaluate s-data for effective capacitance or inductance If bandwidth or center frequency cannot be established filter redesign may be necessary We still need to evaluate the effect of our layout on the filter s performance Page 44

45 Design & Verification of Circuit Components IF filter design example: The effect of the layout pads on our filter s response Pads add capacitance at each node Coupling between pads This subtlety is lost without the aide of Momentum GX and co-simulation 80 MHz SHIFT, REDUCED BANDWIDTH Page 45

46 Design & Verification of Circuit Components IF filter design example: Effect of component parasitics and layout pads shifted the capacitance. 4.7pf->3.3pf 3.9pf->2.7pf 4.7pf->3.3pf 13pf->7pf 47pf->18pf 47pf->18pf 13pf->7pf Knowledge of these effects is not available without Momentum GX NOTE CHANGE IN LINEAR SIMULATION PLOT Co-simulation aides choosing the optimum values Page 46

47 Design & Verification of Circuit Components What else is needed to ensure manufacturability? Accounting for device and board variations Monte Carlo analysis of component tolerances Sweeping the expected r variation for our substrate Specify the require tolerances for substrate material and component tolerances Er swept 4.1 to 4.9 Page 47

48 Momentum Benchmarks Proven Performance vs. Measured Data Blue : Measured Red : Momentum Simulation Summary Frequencies: 54 User time :10m 51s Simulation Summary Frequencies: 6 User time : 1m 14s PC-XP Pentium M 1.6GHz, ADS 2005A Page 48

49 Lessons Learned Using standard value ideal parts is not practical Limited component Q s introduce losses in the passband Reactive parasitics with the components change their effective value Resonant frequencies due to parasitics limit the useful range of many lumped elements Layout pad size and placement dramatically alter the response of our filters Statistical and swept analysis is required to ensure manufacturability Momentum GX is an indispensable tool necessary to ensure first pass success Page 49

50 Wrap Up What did we discuss today? We reviewed the emerging WiMAX telecom market Discussed the design challenges for RF engineers meeting the demands of emerging technologies Introduced and discussed the addition of Momentum GX to the Genesys set of design tools including an overview of Momentum s unique technology We stepped through three design tasks related to WiMAX component development to illustrate the flow and verification process to ensure a successful product Page 50

51 Thank You! Q & A Page 51