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Technical Briefing
PRFI Ltd.The Plextek Building, London Road, Great
Chesterford,Saffron Walden, CB10 1NY, UK
T: +44 (0) 1799 796464 E: [email protected] W: www.prfi.com
Custom designed MMICs allowthe desired functionality
andperformance to be optimisedwhilst minimising size andpotentially
reducing productioncosts. Whilst the upsides areclearly attractive,
the con-sequences of a custom designedMMIC failing to meet
therequired performance criteria canbe costly. As well as the
expense ofthe re-design and a secondfabrication run, the
detrimentalimpact on project timescales canbe even more costly.
First timeright design success is thereforehighly sought after and
it is theability to consistently andaccurately predict
performanceprior to manufacture that allowsthis.
Introduction
This white paper reviews some recentMMIC designs carried out by
PRFIthat demonstrate how highly accurateMMIC performance
predictions can beachived. Close agreement betweenmeasured and
modelled performanceis exhibited across a wide range ofcircuit
functions, operational fre-quencies and process nodes and
alldesigns were first pass successes.Insight is also given into the
designmethodology associated with thedevelopment of these MMICs,
inparticular detailed EM simulation isessential to achieve such
closeagreement. All of the designs presentedwere developed using
ADS fromKeysight.
The following design examples arepresented:
● 3rd Order Elliptical High PassFilter for the 39GHz 5G Band
● 6 to 18GHz Single Stage FeedbackAmplifier
● Power Amplifier MMIC for the26GHz 5G Pioneer Band
● 6 to 23GHz Double Balanced Mixer
● 20 to 30GHz SPDT Switch MMICfor 24GHz, 26GHz and 28GHz
5Gbands
● SMT packaged mm-wave MMICs
Sheet Code 0618
PRFI Closes theGap betweenMeasured andModelled MMIC
Performance
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PRFI Ltd.The Plextek Building, London Road, Great
Chesterford,Saffron Walden, CB10 1NY, UK
T: +44 (0) 1799 796464 E: [email protected] W: www.prfi.com
6 to 18GHz Single Stage FeedbackAmplifier
The single stage feedback amplifiershown in Figure 3 is, like
the filter, asub-circuit from a larger multi-func-tion MMIC. This
is a wideband 6 to18GHz gain block designed on a WINSemiconductor
0.25µm GaAs PHEMTprocess. It uses shunt resistive feed-back to
cover the full 6 to 18GHz bandwith a flat gain versus
frequencyresponse and good input and outputreturn losses.
The measured versus modelled s-pa-rameters are plotted in Figure
4 below.Measured results were made RFOWand are shown in blue with
simulatedperformance in red. Agreementbetween measured and modelled
per-formance is again excellent.
effort being made to minimize layoutparasitics.
The next stage of the design process isthe most critical and
time consumingand must be completed with great carein order to
obtain good measured tomodelled performance. The layoutmust be EM
simulated, step by stepwith careful optimisation of the designand
layout at each step to maintainoptimum performance. Determinationof
the most appropriate mesh densityis a compromise between
simulationspeed and accuracy. In the case of
thisfilter, the input and output 50Ω routingtrack
were also included in this proc-ess. They link to adjacent blocks
in themulti-function MMIC and have a sig-nificant impact on the
performance ofthe filter.
Figure 2 compares the RFOW meas-ured performance of the filter
sub-circuit to the simulated. The solidtraces are the measured
response andthe dashed traces the simulated. Excel-lent agreement
between measured andmodelled is demonstrated to beyond40GHz.
3rd Order Elliptical High Pass Filterfor the 39GHz 5G Band
This filter was designed as part of amulti-function 5G MMIC
addressingthe 37GHz (37 – 38.6GHz) and 39GHz(38.6 – 40GHz) 5G
bands. Its purposewas to provide rejection below bandwith low
insertion loss across the fullRF operating band. It was
fabricatedon one of WIN Semiconductors’0.15µm InGaAs pHEMT
processes.The filter was realised as an independ-ently testable
sub-circuit, as shown inthe photograph of Figure 1.
The design process commences withthe realisation of a simple
elliptic filterusing ideal capacitors and inductors(Ls and Cs). The
capacitors are thenreplaced by Metal Insulator Metal(MIM)
capacitors from the foundryPDK (Process Design Kit) and thefilter
is re-optimised. This stage isnormally straightforward and
hasminimal impact on performance. Theinductors are then replaced
with highimpedance transmission lines, againusing the foundry PDK
models. Thefilter is again re-optimised. Layout ofthe filter is now
undertaken with every
Figure 1: Photograph of 3rd order elliptical highpass filter
test cell
Figure 2: Comparison of measured to simulated
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PRFI Ltd.The Plextek Building, London Road, Great
Chesterford,Saffron Walden, CB10 1NY, UK
T: +44 (0) 1799 796464 E: [email protected] W: www.prfi.com
Power Amplifier MMIC for the26GHz 5G Pioneer Band
The EU’s Radio Spectrum PolicyGroup (RSPG) recommended the26GHz
(24.25 to 27.5GHz) band as thePioneer Band for mm-wave 5G inEurope.
Figure 5 shows a photographof a Power Amplifier (PA) MMICdesigned
by PRFI for 5G applicationsin this band. It was fabricated on oneof
WIN Semiconductors’ 0.15µmInGaAs pHEMT processes and wasoptimised
for best efficiency whenoperating backed-off from compres-
sion to maintain modulation fidelity.The die size is 3.5mm x
1.2mm withscope for reduction to 3.0mm x 1.2mmusing a production
mask set.
Figure 6 shows measured to simulateds-parameters, the quiescent
bias pointis 210mA from 6V. Measured perform-ance is in blue and
simulated in redshowing the measured gain response(S21) virtually
overlaying the simu-lated. The S11 is below -18dB acrossthe full
26GHz 5G band. The outputwas matched for best efficiency
whenoperating backed-off from compres-
sion but the S22 is still a very respect-able -12dB worst case
across the fullPioneer Band.
Figure 7 shows the RFOW measuredand simulated output power and
poweradded efficiency (PAE) against back-off from P-1dB at 26GHz.
The simu-lated traces use dashed lines and themeasured use solid
lines. The outputpower at P-1dB is 26dBm with a PAEof 30%. The
measured to simulatedPAE is in very good agreement acrossa wide
range of back-off.
Figure 3: Die photograph of the 6 to 18GHzsingle stage amplifier
test cell
Figure 4: Comparison of measured to simulateds-parameters for
the 6 to 18GHz gain block
Figure 5: Die photograph of a 26GHz 5G PA MMIC
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PRFI Ltd.The Plextek Building, London Road, Great
Chesterford,Saffron Walden, CB10 1NY, UK
T: +44 (0) 1799 796464 E: [email protected] W: www.prfi.com
6 to 23GHz Double Balanced Mixer
Other areas in which PRFI has signifi-cant design expertise
include MMICmixers. One such design is the 6 to23GHz double
balanced mixer shownbelow in Figure 8. This was designedon Qorvo’s
0.13µm PHEMT process,TQP13. It has an RF and LO frequencyrange of 6
– 23GHz and can operatewith IF frequencies in the range of DC-
4GHz. Typical conversion loss isaround 7dB with an IIP3 of
22dBm.The LO to RF rejection is excellent ataround 45dB.
Figure 9, shows conversion gain whenthe mixer is configured as a
downconverter with high side RF, and an LOinput power of +15dBm.
The measuredconversion gain across the RF inputrange of 6 to 23GHz
is within 1dB ofsimulated with an average value of-7dB. The input
referred third orderintercept point (IIP3) for the mixer inthis
configuration is shown in Figure10; the LO input power was
again+15dBm and the tone spacing 10MHz.The average IIP3 across the
band isaround 22dBm for both measured andmodelled and for a given
RF frequencythe measured IIP3 is typically within2dB of the
modelled.
Figure 6: 26GHz 5G PA RFOW measured andsimulated small signal
response
Figure 7: 26GHz 5G PA RFOW measured andsimulated power and PAE
at 26GHz
Figure 8: Die photograph of 6 to23GHz double balanced mixer
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PRFI Ltd.The Plextek Building, London Road, Great
Chesterford,Saffron Walden, CB10 1NY, UK
T: +44 (0) 1799 796464 E: [email protected] W: www.prfi.com
20 to 30GHz SPDT Switch MMICfor 5G
The next MMIC to be reviewed is asingle pole double throw
(SPDT)switch that operates with low insertionloss and high
isolation across the 5Gbands at 24GHz, 26GHz and 28GHz.It was
designed on WIN Semiconduc-tors’ 3µm PIN diode process. The
diemeasures 3mm x 1mm and a photo-graph is shown below in Figure
11. TheDC control pads are on the top-side,the common RF port is on
the bottomside and the switched RF ports are onthe left and right
hand sides.
The switch was measured RFOW withthe left hand side RF path
enabled andthe right hand side path disabled.Applying a negative
voltage to a path’scontrol pin enables that path (turningthe diodes
“off” and setting it into itslow loss state); applying +3V
disablesthe switch path (turning the diodes“on” and putting that
path into its highloss, isolating, state). The on-stateswitch draws
a total of 20mA from the+3V supply. The negative bias on
theoff-state arm determines the powerhandling of the switch. A
negative biasof -15V allows operation to power
levels of +33dBm without significantcompression.
A plot showing the measured andmodelled S-parameters for the
enabledpath is given below in Figure 12showing very low insertion
loss (~0.66dB) and excellent agreementbetween measured and
modelled. Acomparison of the measured and mod-elled disabled path
isolation is givenin Figure 13 demonstrating a very highisolation
of over 45dB across the 20 to30GHz operating band.
Figure 9: Comparison of measured to simulatedconversion gain of
6 to 23GHz double balanced
mixer.
Figure 10: Comparison of measured tosimulated IIP3 of 6 to 23GHz
double balanced
mixer.
Figure 11: Die photograph of20 to 30GHz 5G PIN diode switch
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PRFI Ltd.The Plextek Building, London Road, Great
Chesterford,Saffron Walden, CB10 1NY, UK
T: +44 (0) 1799 796464 E: [email protected] W: www.prfi.com
Figure 12: 28GHz 5G PIN switch measured andsimulated, enabled
path s-parameters
Figure 13: 28GHz 5G PIN switch measured andsimulated, disabled
path isolation
SMT packaged mm-wave MMICs
The packaging of MMICs into lowcost SMT packages eases handling
andassembly and is therefore the preferredformat for most volume
applications.At mm-wave frequencies it is essentialthat co-design
and simulation of thepackage and MMIC is undertaken asan integral
part of the MMIC develop-ment process if optimum performanceis to
be obtained.
PRFI has experience of developingmm-wave MMICs using a range
ofSMT packaging approaches includingover-moulded plastic,
air-cavityplastic and custom laminate. Withplastic packaging a
custom leadframedesign is normally used to obtain bestRF
performance. The laminateapproach is inherently a customdesign. The
transition between theMMIC bond pad and the PCB onwhich the
packaged part is mountedmust be modelled and optimisedduring the
design process. The effectsof the bondpads, bondwires, PCB and
package leadframe must all beaccounted for and in the case of
over-moulded plastic the moulding com-pound itself must be
incorporated intothe EM simulation of the MMIC.
Figure 14 is a photograph of a plasticpackaged PA MMIC for the
28GHz 5Gband (27.5 – 28.35GHz) mounted onan evaluation PCB. It was
designed ona 0.15µm E-mode pHEMT processfrom WIN Semiconductors and
ishoused in a 4mm x 4mm over-moulded20 pin QFN package. A custom
lead-frame was designed as part of thedevelopment process to
optimise theRF performance of the packaged part.The PA includes an
on-chip tempera-ture compensated power detector andoffers a gain of
20dB with a P-1dB of26dBm and a PAE of 30%. The designwas optimised
for best PAE whenoperating with IMD3 products at-35dBc (which was
around 7dB back-off). At this operating point a PAE ofaround 7 to
9% was demonstrated.
The measured to modelled perform-ance of a packaged PA on the
evalua-tion PCB is plotted in Figure 15. ATRL calibration tile was
used to refer-ence the measured performance to theports of the
package on the PCB.
A custom laminate package was devel-oped for the 26GHz 5G PA
MMICfeatured earlier in this paper. Thepackage was a QFN format and
housedtwo MMICs to provide a dual channelcomponent as depicted in
the photo-graph of the evaluation PCB shown inFigure 16.
A comparison of the RFOW measuredperformance of the PA die to
the meas-ured performance of the dual channelpackaged component on
an evaluationPCB is shown in Figure 17. Bothchannels of the
packaged part areplotted as the solid traces; the dashedtraces are
the RFOW measured per-formance. The difference between theRFOW and
packaged part perform-ance is modest demonstrating thequality of
the RF package design.
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PRFI Ltd.The Plextek Building, London Road, Great
Chesterford,Saffron Walden, CB10 1NY, UK
T: +44 (0) 1799 796464 E: [email protected] W: www.prfi.com
Conclusion
This white paper has given an over-view of a proven approach to
accu-rately simulating custom MMICs. Across-section of recent
design workcarried out by Plextek RFI has beenpresented, which
demonstrates con-sistent first pass success through closemeasured
and modelled agreement.Such agreement was presented for a
Figure 14: 28GHz 5G PA in 4mm x 4mm overmoulded plastic QFN
Figure 15: Plastic packaged 28GHz PA for 5G,measured to
simulated performance
Figure 16: Dual channel 26GHz 5G PA in customlaminate
package
Figure 17: Measured s-parameters of two chan-nels of a packaged
PA compared to RFOW
range of circuit functions, operationalfrequencies and process
nodes.
By cultivating a company culture ofright first time design
success, PlextekRFI has enabled its clients to reducetheir product
development timescales,cost and risk.