Review Article EMI Susceptibility Issue in Analog Front-End for...

Review ArticleEMI Susceptibility Issue in Analog Front-End forSensor Applications

Anna Richelli

Department of Information Engineering University of Brescia Via Branze 38 25123 Brescia Italy

Correspondence should be addressed to Anna Richelli annarichelliingunibsit

Received 22 July 2015 Revised 9 November 2015 Accepted 15 November 2015

Academic Editor Fernando Benito-Lopez

Copyright copy 2016 Anna RichelliThis is an open access article distributed under the Creative Commons Attribution License whichpermits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

The susceptibility to electromagnetic interferences of the analog circuits used in the sensor readout front-end is discussed Analogcircuits still play indeed a crucial role in sensor signal acquisition due to the analog nature of sensory signals The effect ofelectromagnetic interferences has been simulated and measured in many commercial and integrated analog circuits the maincause of the electromagnetic susceptibility is investigated and the guidelines to design high EMI immunity circuits are provided

1 Introduction

Current trends in consumer electronics highlight anincreased interest in ubiquitous electronic devices This isespecially true in the field of sensors which can enable avariety of applications including interactive environments formedicine [1ndash5] military target tracking automotive [6 7]and environmental monitoring networks [8 9] Analogcircuits still play a crucial role in sensor signal acquisitiondue to the analog nature of sensory signal they are indeedwidely used in the sensor readout front-end since it directlyinterfaces the sensor [10ndash12] Analog circuits are indeedemployed for signal conditioning and conversion generationof bias and reference voltages and currents and systemsinterfacing

In recent years integrated sensor systems have becomewidely commercially availableThese systems usually containmicrosensor array and sensor electronics [13ndash15] When thesensor integration is not feasible due to economical or techni-cal reasons off-chip sensors may also be used Neverthelessthe common feature is that the sensor electronics sensorsignal conditioning processing and conversion generationof necessary bias and reference voltages as well as currentscontrol clock signals and sensor system interface are locatedon a single chip or a chip set

In the literature much attention is paid to many aspectssuch as the resolution of a sensor system The final limit

of the resolution is represented by the sensor-input referrednoise This noise may contain contributions of the sensoritself and of sensor electronics and therefore a lot of attentionhas been paid in noise reduction techniques to improve thesensor resolution

Another important issue is that the noise can be generatedby neighboring circuits and enter the system due to crosstalkwhich can be either capacitive (due to stray capacitances) orconductive and inductive through the power supply rails

In the literature the effect of the noise and the crosstalkhave been widely investigated and many noise reductiontechniques and guidelines are depicted and provided [16]

However when several analog and digital subsystems arerequired to coexist on the same chip eventually sharing thesame power sources as in the sensor applications anotherissue is becomingmore andmore important the immunity toelectromagnetic interferences (EMIs) As an example of thisscenario in Figure 1 a schematic view of a pressure sensorwith highlighted analog and digital blocks is shown

In such a system EMI may arise from external circuitsand from subsystems integrated on the same die spreadingthrough the supply lines and the IO interconnections

In the sensor design the influence of EMI is generally nottreated explicitly or even neglected

This paper describes the effect of the electromagneticinterferences in analog circuits widely used in the sensorinterface general-purpose operational amplifiers and voltage

Hindawi Publishing CorporationJournal of SensorsVolume 2016 Article ID 1082454 9 pageshttpdxdoiorg10115520161082454

2 Journal of Sensors

Pressuresensor

Temp

Senseamp

ADCMUX

Clockoscillator

Trimlogic

Digital signalprocessing and

control

Reference +

AnalogDigitalMEMS die

regulator

Figure 1 Example of a sensor circuit with highlighted analog anddigital blocks eventually sharing the same chip and power supplies

references Measurement results of the EMI susceptibilityin commercial devices are provided and the state-of-the-art design of high EMI immunity amplifiers and voltagereferences is depicted In particular in Section 2 the problemof electromagnetic interferences will be briefly introducedand the results of measurements performed on severalcommercial amplifiers victims of EMI will be provided inSection 3 the design of high-immunity amplifiers will bedepicted and in Section 4 the guidelines to design high EMIimmunity voltage references will be provided and finallyconclusions will be drawn

2 The Problem of ElectromagneticInterferences in the Analog Circuits

Electromagnetic interference (EMI) effects may arise froma wide class of sources (cellular telephones CD playerslaptop computers etc) as an example aircraft may be sus-ceptible to electronic interferences because of their relianceon radio communication and navigation systems whoseelectromagnetic spectrum ranges from 10 kHz (navigationsystems) to above 9GHz (weather radar) Furthermore themassive introduction of electronics in automotive may causea number of problems cellular telephone transmitters forinstance can induce disturbances in braking systems (ABS)EMImay arise from inside the automobile aswell alternatorsignition systems switching solenoids and electric starters arepotential sources of such disturbances Furthermore due tothe high density of components packed on printed circuitboards as well as the increasing speed of mixed analogdigitalcircuits IC designers have to consider EMI during designphase Neglecting these aspects may lead to failures onintegrated circuits induced by spurious signals includingEMI at frequencies outside the working bandwidth of thecircuit Two different interferences should be considereddepending on the way they reach the circuits the distributedones and the conveyed ones However considering the chip

t+

minusVdc

Figure 2 Effect of EMI conveyed into the input pin of an operationalamplifier in voltage follower configuration

size and the frequencies themost important are the conveyedones

In recent years the effects of the conveyed EMI werecarefully investigated both theoretically and experimentallyin order to findpossible preventionmethodologies [17ndash25] inparticular in high-performance digitalanalog ICs that mayinclude several operational amplifiers The most sensitivecircuits to EMI are indeed the analog ones and among themthe OpAmps

In order to investigate the EMI effects on a genericamplifier the interfering signals are often represented by asinusoidal waveform generated with zero DC mean valuesuperimposed on the pins connected to long wires (longwires indeed act as antennas for EMI) [18 20]The amplifieris in the voltage follower configuration as reported in theliterature [21ndash23] and shown in Figure 2 since it is the worstcase condition because the input differential pair experiencethe largest disturbance One of themost undesirable effects ofinterferences is the shift of the output DCmean value (offset)that may asymptotically force the amplifier to saturation [23ndash25] Furthermore among all the possible interfering signalsthe ones superimposed on the input pins of the operationalamplifier are the most difficult to prevent [24 25]This is dueto the fact that the adoption of external filters may modifythe original input signals which are often very weak As far asthe power pins are concerned easy filtering can prevent thedangerous DC offset from being formed

The maximum measured EMI induced voltage offset ofsome commonly used commercial amplifiers is listed inTable 1 all the amplifiers were connected in a voltage followerconfiguration and the interfering sinusoidal signal appliedto the noninverting input pin had an amplitude of 1 V ata frequency ranging from 100 kHz up to 1GHz The powersupply was set to 12V Several samples of the most widelyused technologies are listed bipolar jfet and CMOS Theamplifiers were measured on a simple PCB following theschematic illustrated in Figure 3 A 33120A Hewlett-PackardRF function generator has been used with 50Ω matchingload to generate the EMI the power supply and the biasingvoltages were supplied by E3630A Hewlett-Packard powersupply The board interconnections were designed as shortas possible along with straight paths and ground shields inorder to minimize all the undesired signals arising from themeasurement setup itself The resistor 119877

1in Figure 3 is used

for the matching load while 1198621and 119862

2are power supply

filters of respectively 100 nF and 10120583F furthermore theoutput pin is connected to an RC (119877

2= 1 kΩ 119862

3= 1 nF)

filter with cut-off frequency of 160 kHz in order to evaluate

Journal of Sensors 3

Table 1 Measured EMI induced offset in commercial amplifiers

Amplifier Technology Voltage offset Critical frequenciesUA741 BJT 650mV 01MHzndash3GHzAD705 BJT 350mV 03MHzndash1GHzNE5534 BJT 360mV 3MHzndash06GHzOPA177 BJT 360mV 06MHzndash01 GHzOP176 JFET InBJT Out 200mV 3MHzndash1GHzMC33181 JFET InBJT Out 210mV 6MHzndash06GHzCA3140 CMOS InBJT Out 350mV 01MHzndash1GHzICL7611 CMOS 380mV 03MHzndash03GHz

Vdd

R1

R2

R2

C1

C1

C2

C2 C3

C3

GndGnd

Gnd

Gnd

Gnd Gnd

Gnd

Gnd

Vss

VEMI Voutminus+

minus+

minus+

sim

Figure 3 Schematic of the PCB used to characterize the EMIsusceptibility of several commercial amplifiers

the mean voltage that easily and accurately quantifies the DCshift due to EMI effects Clearly the measured offset voltageis significant and can cause failures (due to debiasing) in thecircuits connected to the OpAmps Finally to have an easyview of the EMI effect in some commercial amplifiers theinduced offset in mV is plotted in Figure 4

3 The Design of High EMI Immunity OpAmps

As stated above among all the possible interfering signals theones superimposed on the input pins are the most difficult toprevent

When electromagnetic interference is injected in theinput pins of an operational amplifier the latter generatesan EMI induced offset voltage because of the nonlineardistortion taking place in the input differential pair [20]

This behavior is correlated to the slew rate asymmetry andto the unequal parasitic capacitances which play a significantrole respectively at low-medium frequencies and at highfrequencies outside the working bandwidth [20 24 25]

Recently some solutions have been proposed to intrinsi-cally improve the immunity of the amplifiers to EMI signalsarising from the input pins For example in [26] the design ofan input stage is reported based on a double cross-connecteddifferential pair along with a simple high-pass filter as shownin Figure 5 The cross-connected differential pair becomesactive only in the passband of the RC high-pass filter Morerecently in [27] a comparison between the architecture

0

200

400

600

800

1000

Frequency (MHz)

Offs

et v

olta

ge (m

V)

uA741CA3140

ICL7611

10minus1 100 101 102 103minus400

minus200

1Vp EMI (noninverting input)

Figure 4 Measured EMI induced offset in uA741 CA3140 andICL7611

M1 M2M4M3

Vin+Vin

minus

II

VBBVBB

Figure 5 The high EMI immunity cross-coupled differential pairwith high-pass filter proposed in [26]

proposed in [26] and a simple differential pair with an RClow-pass filter as the one in Figure 6 has been illustrated

However as stated above a filtermaymodify the responseof the amplifier and thus it can just operate at out-of-bandfrequencies while the EMI effects are relevant also at low-medium frequencies

Another solution has been proposed in [28] based ona double differential pair in this architecture the nominaldifferential pair is bootstrapped using bulk biasing the useof a bootstrapped differential pair results in an advantageouseffect of the parasitic capacitances presented at the commonsource of the differential pair In the design example shownin [28] the bootstrapped differential pair exhibits an EMIimmunity two orders of magnitude larger than the classicdifferential pair Nevertheless following this approach only


M2M1Vin

+Vin

minus

I

Figure 6 A simple RC filter on the input differential pair as the onediscussed in [27]

a P-type differential input stage can be fabricated in a stan-dard CMOS technology the N-type stage requires indeed atriple-well technology due to the bulk biasing

EMI resistant differential pairs are proposed in otherrecent works as well [29 30] among them a simple andinteresting approach to enhance the EMI immunity is basedon an RC filter connected to an auxiliary differential pair asproposed in [31ndash33]The RC filter on the auxiliary differentialpair introduces indeed a pole-zero doublet and allows for alarger GBW product and a better phase margin comparedto the RC filter connected to the main differential pair stillshowing an improved EMI immunity

Another successful approach to intrinsically reduce theEMI effects without adding any kind of filter is presentedin [34] and is based on the design of strongly symmetricaltopologies The symmetrical topology proposed in [34] isbased on two identical fully differential source cross-coupledamplifiers combined in cascade connection in order toachieve a large gainThe circuital scheme is shown in Figure 7This topology is very useful when the output slew rate ofthe OpAmp is an important task moreover such a schemeleads to a strong symmetry of the output voltage thanks to themirrored path of the signals Indeed as shown in Figure 7 theinput voltages are applied to the gates of both M2a and M2bin order to bias the NMOS differential pair and to the gatesof M1a and M1b to bias the PMOS differential pair

NMOS and PMOS differential pairs are connected withcross-coupled sources Hence the input voltages are symmet-rically applied to the gates of the 2nd differential pairsM3 andM4

Thus any voltage mismatch due to stray elements andnonidealities is removed by this cross-connectionThis leadsto a very symmetrical path for both signals across theamplifier and to an EMI immunity more than 2 orders ofmagnitude increased as clearly demonstrated by the plot inFigure 8 where the EMI induced offset is compared to that ofthe uA741

The architecture proposed in [34] is unfortunately notsuited for the ultralow voltage supply of current integratedcircuits This is mainly due to the complex cascode connec-tions

Therefore an alternative solution is proposed derivedfrom theMiller amplifier [35]The overall schematic is shownin Figure 9

Finally a circuit that enhances the EMI immunity ofamplifiers by deleting the common mode signals has beenrecently proposedThe EMI induced voltage generated at theoutput of the input stage 119881os is indeed due to the differentialand the common mode signals 119881dm and 119881cm as calculated inthe following mathematical expression

119881os

=

intinfin

minusinfin

1003816100381610038161003816119867cm (119895120596) sdot 119881cm (119895120596) sdot 119881dm (119895120596)1003816100381610038161003816 sdot cos120601 sdot 119889120596

119881GS12 minus 119881119905

(1)

In a differential amplifier the differential signals cannot ofcourse be removed but the common mode components canbe deleted The schematic of the common mode cancellationcircuit proposed in [36] is shown in Figure 10 If the circuitis properly sized (by choosing the right value of the resistors)the commonmode signals are cancelled while the differentialsignals are doubled

Consequently the resulting EMI susceptibility is reducedas plotted in Figure 11 where the offset is compared betweenthe original amplifier and the one modified by including thecommon mode cancellation stage

4 Design of High EMI ImmunityVoltage Reference

It is well established that analog CMOS circuit design relieson close geometry matching of components which yieldsprecise ratios of component values As this applies onlyto a lateral geometry defined within the same mask onlyrelated components (ie components of the same natureso to speak) can be well matched On the contrary thedefinition of absolute values and tolerances is rather pooras it depends on various material properties and technologyprocessing steps Nevertheless absolute reference values areoften needed The on-chip reference generation is usuallyconfined to voltage reference generation using the bandgapprinciple which utilizes parasitic pnp-bipolar transistors of aCMOS process for this purpose

It is worth adding that in the literature much attentionis paid to many quality aspects such as the mean relativetemperature dependency and the accuracy but the influenceof electromagnetic interferences is only recently treatedexplicitly

In order to reach a clear comprehension of the EMI ona bandgap reference circuit it should be pointed out that inmany applications analog and digital subsystems are requiredto coexist on the same chip sharing the same power sourcesIn such a system electromagnetic interferences may arisefrom external circuits and from subsystems integrated on thesame die spreading through the supply lines leading to largeunexpected fluctuations of the power supply as illustrated inFigure 12

In order to investigate the EMI effects on bandgap refer-ences the interferences are modelled by means of spurioussignals applied to the power pins As already stated EMIsare represented bymeans of undamped sinusoidal waveformsthat allow for an easy measurement in laboratory


M14a M14b

M16a

M11a

M9a

M11b

M9b

M8aM19a

M17a

M10a

M13a

M20a

M18a

M15a

M8b

M19b

M17b

M10b

M13b

M20b

M18b

M15b

M16b

M12a M12b

In A

Vout BVout A

Vdd

In B

Vp5

Vp6 Vp6

Vp5

Figure 7 Highly symmetrical fully differential source cross-coupled amplifier proposed in [34]

1000

800

600

400

200

0

minus200

Offs

et (m

V)

105 106 107 108 109 1010

Frequency (Hz)

uA741

OpAmp in [34]

Figure 8 Measured EMI induced offset a comparison between theuA741 and the amplifier proposed in [34] in the case of 1119881

119901EMI

signal

Among the various voltage reference architectures themost popular circuit is the bandgap reference based on pnjunctions OpAmp and ratioed resistors [37] On the otherhand in order to meet the important constraints of lowpower supply voltage and lowpower dissipation it is desirable

to use simple architectures avoiding operational amplifiersand additional circuits Therefore many different bandgaparchitectures were also designed [38]

The first considered reference is the ldquoBrokawrdquo circuitshown in Figure 13 [37] an improved version widely used inrecent ICs is often called ldquoKuijk bandgaprdquo [39] and it is basedon ratioed resistors and OpAmp along with the parasiticbipolar pnp transistors provided by the CMOS technology

For Brokaw and Kuijk bandgap circuits a few topologiescan be found in the literature [40ndash44] showing a low EMIsusceptibility Here the basic topology is often improved byenhancing the EMI immunity of the operational amplifierfollowing the approaches depicted in Section 3 by changingthe bandgap bias current and by introducing filter capacitorsLayout and technological techniques to reduce the couplingbetween the power supply net and the poly resistors arealso useful to increase the immunity to electromagneticinterferences [40]

In Figure 14 an example of a high EMI immunity bandgapvoltage reference is shown based on the solution proposed in[44]

As investigated in [44] the original CMOS voltagereference designed in AMS CXQ 08 120583m process was verysusceptible to the 1119881

119901interferences arising from the power

supply rails showing a large offset as plotted in Figure 15To reduce its susceptibility a fully differential folded cascodeamplifier with high EMI immunity has been used instead ofthe single ended Miller amplifier and two capacitors wereadded on the most critical nodes The simulated offset of themodified ldquoKuijkrdquo bandgap is shown in Figure 16 The CMOS


M7

M9

M3

M13

M11 M10

M12

M5

M2M1

M4 M6

M8

Vout+Vout

minus

Vin+Vin

minus

Vdd

Vb2

Vb1

Figure 9 Highly symmetrical fully differential amplifier for low voltage supply proposed in [35]

M1 M2

R1R1

Vbias

Vinp

Vxp R2R2 VxmVinm

Figure 10The commonmode cancellation circuit proposed in [36]it is used as input stage to increase the EMI immunity in a Millerdifferential amplifier

0

50

100

150

200

Frequency (MHz)

Out

put o

ffset

vol

tage

(mV

)

Original amplifierAmplifier in [36]

101 102 103 104

Figure 11 Simulated EMI induced offset comparison between theoriginalMiller differential amplifier and the onemodified by addingthe common mode cancellation stage depicted in [36]

Bandgap Other circuitry

Vdd

Vref

Vss

Figure 12 Scenario of EMI pollution in electronic circuits

Vout

minus

+

A1

nAA

Figure 13 The ldquoBrokawrdquo voltage reference circuit

voltage reference has been fabricated in theAMSCXQ08120583mprocess and the test chip was measured exhibiting a highlevel of EMI immunity as demonstrated by the measurementresults plotted in Figure 17 the offset is indeed several ordersof magnitude reduced


Fully differential

Folded cascode

Q nQ

IN+

INminus

Vdd

Vref

Vout

C1

C2

R2

R A1

R B1

minus

+

Figure 14 Schematic of the EMI-improved ldquoKuijkrdquo bandgap pro-posed in [44]

0

minus200

minus400

minus600

minus800

minus1000

minus1200

minus1400

Offs

et (m

V)

EMI on the Vdd pinEMI on the Gnd pin

100 101 102 103 104

Frequency (MHz)

Figure 15 Offset of the bandgap voltage references caused by 1119881119901

EMI signal superimposed to the power supply rails

The second considered bandgap topology uses ratioedtransistors biased in strong inversion along with the inverse-function technique to produce temperature-insensitive volt-age references [45] With regard to this bandgap topologyanalysis and simulations emphasized that the differential

Frequency (MHz)

minus100

0

100

200

300

Offs

et (m

V)

Bandgap with F-diff OpAmp

100 101 102 103 104

Bandgap with F-diff OpAmp C1 and C2

Bandgap with F-diff OpAmp and C1

Figure 16 Offset of the bandgap circuit modified by using a fullydifferential amplifier and two capacitors as shown in the schematicof Figure 14

minus20

minus15

minus10

minus5

0

5

10

15

20

Offs

et (m

V)

100 101 102 103 104

Frequency (MHz)

Figure 17 Measured EMI induced offset of the high-immunitybandgap proposed in [44]

pairs (M1-M2 and M3-M4) play a significant role in EMIsusceptibility Hence in order to improve the immunity tointerferences M1-M2 and M3-M4 are created in insulatedwells and a small capacitor (1 pF) is connected between 119881

119904

and ground In Figure 18 the schematic of the bandgap circuitmodified following this approach is shown The simulationsdemonstrated the validity of this approach considering 1119881

119901

EMI signal superimposed to the supply rails the maximuminduced offset of the original circuit was more than 300mVwhile the offset of the modified bandgap is less than 20mV inthe whole frequency range


M4M3M2M1

M6M5

M10M9M8M7M13M11

M12 M14

Gnd

C

Insulated wellInsulated well

Vdd

Vref

Va Vs

Q1 Q2

Vbe2Vbe1

Figure 18 OpAmp-less and resistorless bandgap circuit with enhanced EMI immunity presented in [45]

5 Conclusions

In the frame of a higher attention towards the problem ofelectromagnetic susceptibility the design of analog circuitswidely used in the sensor systems is discussed In particularthe effect of the electromagnetic interferences is briefly intro-duced in the most common analog amplifiers and voltagereferences Several and recent solutions to increase the EMIimmunity are presented the resulting amplifiers and voltagereferences exhibit an EMI susceptibility reduced by 2 orders(or even more) of magnitude compared to the classical ones

Conflict of Interests

The author declares that there is no conflict of interestsregarding the publication of this paper

References

[1] A Bababjanyan H Melikyan S Kim J Kim K Lee andB Friedman ldquoReal-time noninvasive measurement of glucoseconcentration using a microwave biosensorrdquo Journal of Sensorsvol 2010 Article ID 452163 7 pages 2010

[2] C Hu and S Hu ldquoCarbon nanotube-based electrochemicalsensors principles and applications in biomedical systemsrdquoJournal of Sensors vol 2009 Article ID 187615 40 pages 2009

[3] O Atalay W R Kennon and E Demirok ldquoWeft-knittedstrain sensor for monitoring respiratory rate and its electro-mechanical modelingrdquo IEEE Sensors Journal vol 15 no 1 pp110ndash122 2015

[4] S Salman L Z Lee and J L Volakis ldquoA wearable wrap-aroundsensor for monitoring deep tissue electric propertiesrdquo IEEESensors Journal vol 14 no 8 pp 2447ndash2451 2014

[5] L Fanucci S Saponara T Bacchillone et al ldquoSensing devicesand sensor signal processing for remote monitoring of vitalsigns in CHF patientsrdquo IEEE Transactions on Instrumentationand Measurement vol 62 no 3 pp 553ndash569 2013

[6] M Sakairi ldquoWater-cluster-detecting breath sensor and appli-cations in cars for detecting drunk or drowsy drivingrdquo IEEESensors Journal vol 12 no 5 pp 1078ndash1083 2012

[7] A M Cailean B Cagneau L Chassagne M Dimian and VPopa ldquoNovel receiver sensor for visible light communicationsin automotive applicationsrdquo IEEE Sensors Journal vol 15 no 8pp 4632ndash4639 2015

[8] E Kampianakis J Kimionis K Tountas C KonstantopoulosE Koutroulis and A Bletsas ldquoWireless environmental sensornetworking with analog scatter radio and timer principlesrdquoIEEE Sensors Journal vol 14 no 10 pp 3365ndash3376 2014

[9] J Segura-Garcia S Felici-Castell J J Perez-Solano M Cobosand J M Navarro ldquoLow-cost alternatives for urban noisenuisance monitoring using wireless sensor networksrdquo IEEESensors Journal vol 15 no 2 pp 836ndash844 2015

[10] B J Hosticka ldquoAnalog circuits for sensorsrdquo in Proceedings of the33rd European Solid-State Circuits Conference (ESSCIRC rsquo07)pp 97ndash102 IEEE Munich Germany September 2007

[11] A Marzuki Z A Abdul Aziz and A A Manaf ldquoA reviewof CMOS analog circuits for image sensing applicationrdquo inProceedings of the IEEE International Conference on ImagingSystems and Techniques (IST rsquo11) pp 180ndash184 PenangMalaysiaMay 2011

[12] Y Hong T Liang T Zheng et al ldquoA distance compensatedapproach used in wireless passive pressure sensor readoutsystem for high temperature applicationrdquo Journal of Sensors Inpress

[13] O S Jahromi and P Aarabi ldquoTheory and design of multiratesensor arraysrdquo IEEE Transactions on Signal Processing vol 53no 5 pp 1739ndash1753 2005

[14] W S Singh B P C Rao S Thirunavukkarasu and T Jayaku-mar ldquoFlexible GMR sensor array for magnetic flux leakagetesting of steel track ropesrdquo Journal of Sensors vol 2012 ArticleID 129074 6 pages 2012

[15] R Daly S Kumar G Lukacs et al ldquoCell proliferation trackingusing graphene sensor arraysrdquo Journal of Sensors vol 2012Article ID 219485 7 pages 2012


[16] J Long A He A Liu and X Chen ldquoAdaptive Sensing withreliable guarantee under white Gaussian noise channels ofsensor networksrdquo Journal of Sensors vol 2015 Article ID532045 21 pages 2015

[17] M Ramdani E Sicard A Boyer et al ldquoThe electromagneticcompatibility of integrated circuitsmdashpast present and futurerdquoIEEE Transactions on Electromagnetic Compatibility vol 51 no1 pp 78ndash100 2009

[18] I Chahine M Kadi E Gaboriaud A Louis and B MazarildquoCharacterization and modeling of the susceptibility of inte-grated circuits to conducted electromagnetic disturbances upto 1 GHzrdquo IEEE Transactions on Electromagnetic Compatibilityvol 50 no 2 pp 285ndash293 2008

[19] V Ceperic and A Baric ldquoModelling of electromagnetic immu-nity of integrated circuits by artificial neural networksrdquo in Pro-ceedings of the 20th International Zurich Symposium on Electro-magnetic Compatibility pp 373ndash376 IEEE Zurich SwitzerlandJanuary 2009

[20] I Gil and R Fernandez-Garcia ldquoCharacterization and mod-elling of EMI susceptibility in integrated circuits at highfrequencyrdquo in Proceedings of the IEEE International Symposiumon Electromagnetic Compatibility (EMC EUROPE rsquo12) pp 1ndash6IEEE Rome Italy September 2012

[21] J-M Redoute and M Steyaert EMC of Analog IntegratedCircuits Springer Dordrecht The Netherlands 2010

[22] C R Paul Introduction to Electromagnetic Compatibility JohnWiley amp Sons 1992

[23] A S Poulton ldquoEffect of conducted EMI on theDCperformanceof operational amplifiersrdquo Electronics Letters vol 30 no 4 pp282ndash284 1994

[24] G Masetti S Graffi D Golzio and Z M Kovacs-V ldquoFailuresinduced on analog integrated circuits by conveyed electromag-netic interferences a reviewrdquo Microelectronics Reliability vol36 no 7-8 pp 955ndash972 1996

[25] G Setti and N Speciale ldquoDesign of a low EMI susceptibilityCMOS transimpedance operational amplifierrdquoMicroelectronicsReliability vol 38 no 6ndash8 pp 1143ndash1148 1998

[26] F Fiori ldquoOperational amplifier input stage robust to EMIrdquoElectronics Letters vol 37 no 15 pp 930ndash931 2001

[27] C Walravens S Van Winckel J M Redoute and M SteyaertldquoEfficient reduction of electromagnetic interference effects inoperational amplifiersrdquo Electronics Letters vol 43 no 2 pp 84ndash85 2007

[28] J-M Redoute and M Steyaert ldquoEMI resisting CMOS differen-tial pair structurerdquo Electronics Letters vol 42 no 21 pp 1217ndash1218 2006

[29] J-M Redoute and M S Steyaert ldquoEMI-resistant CMOS differ-ential input stagesrdquo IEEE Transactions on Circuits and SystemsI Regular Papers vol 57 no 2 pp 323ndash331 2010

[30] F Fiori andP S Crovetti ldquoComplementary differential pair withhigh immunity to RFIrdquo Electronics Letters vol 38 no 25 pp1663ndash1664 2002

[31] A Richelli ldquoCMOS OpAmp resisting to large electromagneticinterferencesrdquo IEEE Transactions on Electromagnetic Compati-bility vol 52 no 4 pp 1062ndash1065 2010

[32] B Subrahmanyam D Das M Shojaei-Baghini and J-M Red-oute ldquoA balanced CMOS OpAmp with high EMI immunityrdquo inProceedings of the International Symposium on ElectromagneticCompatibility (EMC Europe rsquo14) pp 703ndash708 GothenburgSweden September 2014

[33] A Richelli G Matig-a and J-M Redoute ldquoDesign of a foldedcascode opamp with increased immunity to conducted elec-tromagnetic interference in 018120583m CMOSrdquo MicroelectronicsReliability vol 55 no 3-4 pp 654ndash661 2015

[34] A Richelli L Colalongo and Z M Kovacs-Vajna ldquoIncreas-ing the immunity to electromagnetic interferences of CMOSOpAmpsrdquo IEEE Transactions on Reliability vol 52 no 3 pp349ndash353 2003


[36] A Richelli and J-M Redoute ldquoIncreasing the EMI immunity ofCMOS operational amplifiers using an on-chip common-modecancellation circuitrdquo in Proceedings of the IEEE EMC EuropeConference pp 698ndash702 IEEE Gotheborg Sweden September2014

[37] J Hu Y Yin and H Deng ldquoDesign of a high-performanceBrokaw band-gap referencerdquo in Proceedings of the InternationalConference on Anti-Counterfeiting Security and Identification inCommunication (ASID rsquo10) pp 126ndash129 IEEE Chengdu ChinaJuly 2010

[38] A E Buck C LMcDonald S H Lewis and T R ViswanathanldquoA CMOS bandgap reference without resistorsrdquo IEEE Journal ofSolid-State Circuits vol 37 no 1 pp 81ndash83 2002

[39] K E Kuijk ldquoA precision reference voltage sourcerdquo IEEE Journalof Solid-State Circuits vol 8 no 3 pp 222ndash226 1973

[40] NMontemezzo E Orietti S Buso GMeneghesso A Nevianiand G Spiazzi ldquoA discussion of the susceptibility of a Brokawbandgap to EMIrdquo in Proceedings of the IEEE InternationalSymposium on Electromagnetic Compatibility (EMC rsquo06) pp796ndash801 August 2006

[41] E Orietti NMontemezzo S Buso GMeneghesso A Nevianiand G Spiazzi ldquoReducing the EMI susceptibility of a kuijkbandgaprdquo IEEE Transactions on Electromagnetic Compatibilityvol 50 no 4 pp 876ndash886 2008

[42] J-M Redoute and M Steyaert ldquoKuijk bandgap voltage refer-encewith high immunity to EMIrdquo IEEETransactions onCircuitsand Systems II Express Briefs vol 57 no 2 pp 75ndash79 2010

[43] S Yang P-I Mak and R P Martins ldquoA 104120583W EMI-resistingbandgap voltage reference achievingmdash20dB PSRR and 5 DCshift undera 4dBm EMI levelrdquo in Proceedings of the IEEE AsiaPacificConference onCircuits and Systems (APCCAS rsquo14) pp 57ndash60 IEEE Ishigaki Japan November 2014

[44] A Pretelli A Richelli L Colalongo and Z M Kovacs-VajnaldquoReduction of EMI susceptibility in CMOS bandgap referencecircuitsrdquo IEEE Transactions on Electromagnetic Compatibilityvol 48 no 4 pp 760ndash765 2006

[45] A Pretelli A Richelli L Colalongo and Z Kovacs-VajnaldquoRobust design of bandgap voltage references with low EMIsusceptibilityrdquo in Proceedings of the IEEE Symposium on Elec-tromagnetic Compatibility pp 298ndash302 Arlington Va USAAugust 2003

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014


Active and Passive Electronic Components

Control Scienceand Engineering

Journal of



RotatingMachinery


Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design



Shock and Vibration


Civil EngineeringAdvances in

Acoustics and VibrationAdvances in



Electrical and Computer Engineering

Journal of

Advances inOptoElectronics


Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of


Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014


Chemical EngineeringInternational Journal of Antennas and

Propagation




Navigation and Observation



DistributedSensor Networks



Pressuresensor

Temp

Senseamp

ADCMUX

Clockoscillator

Trimlogic

Digital signalprocessing and

control

Reference +

AnalogDigitalMEMS die

regulator

Figure 1 Example of a sensor circuit with highlighted analog anddigital blocks eventually sharing the same chip and power supplies

references Measurement results of the EMI susceptibilityin commercial devices are provided and the state-of-the-art design of high EMI immunity amplifiers and voltagereferences is depicted In particular in Section 2 the problemof electromagnetic interferences will be briefly introducedand the results of measurements performed on severalcommercial amplifiers victims of EMI will be provided inSection 3 the design of high-immunity amplifiers will bedepicted and in Section 4 the guidelines to design high EMIimmunity voltage references will be provided and finallyconclusions will be drawn

2 The Problem of ElectromagneticInterferences in the Analog Circuits

Electromagnetic interference (EMI) effects may arise froma wide class of sources (cellular telephones CD playerslaptop computers etc) as an example aircraft may be sus-ceptible to electronic interferences because of their relianceon radio communication and navigation systems whoseelectromagnetic spectrum ranges from 10 kHz (navigationsystems) to above 9GHz (weather radar) Furthermore themassive introduction of electronics in automotive may causea number of problems cellular telephone transmitters forinstance can induce disturbances in braking systems (ABS)EMImay arise from inside the automobile aswell alternatorsignition systems switching solenoids and electric starters arepotential sources of such disturbances Furthermore due tothe high density of components packed on printed circuitboards as well as the increasing speed of mixed analogdigitalcircuits IC designers have to consider EMI during designphase Neglecting these aspects may lead to failures onintegrated circuits induced by spurious signals includingEMI at frequencies outside the working bandwidth of thecircuit Two different interferences should be considereddepending on the way they reach the circuits the distributedones and the conveyed ones However considering the chip

t+

minusVdc

Figure 2 Effect of EMI conveyed into the input pin of an operationalamplifier in voltage follower configuration

size and the frequencies themost important are the conveyedones

In recent years the effects of the conveyed EMI werecarefully investigated both theoretically and experimentallyin order to findpossible preventionmethodologies [17ndash25] inparticular in high-performance digitalanalog ICs that mayinclude several operational amplifiers The most sensitivecircuits to EMI are indeed the analog ones and among themthe OpAmps

In order to investigate the EMI effects on a genericamplifier the interfering signals are often represented by asinusoidal waveform generated with zero DC mean valuesuperimposed on the pins connected to long wires (longwires indeed act as antennas for EMI) [18 20]The amplifieris in the voltage follower configuration as reported in theliterature [21ndash23] and shown in Figure 2 since it is the worstcase condition because the input differential pair experiencethe largest disturbance One of themost undesirable effects ofinterferences is the shift of the output DCmean value (offset)that may asymptotically force the amplifier to saturation [23ndash25] Furthermore among all the possible interfering signalsthe ones superimposed on the input pins of the operationalamplifier are the most difficult to prevent [24 25]This is dueto the fact that the adoption of external filters may modifythe original input signals which are often very weak As far asthe power pins are concerned easy filtering can prevent thedangerous DC offset from being formed

The maximum measured EMI induced voltage offset ofsome commonly used commercial amplifiers is listed inTable 1 all the amplifiers were connected in a voltage followerconfiguration and the interfering sinusoidal signal appliedto the noninverting input pin had an amplitude of 1 V ata frequency ranging from 100 kHz up to 1GHz The powersupply was set to 12V Several samples of the most widelyused technologies are listed bipolar jfet and CMOS Theamplifiers were measured on a simple PCB following theschematic illustrated in Figure 3 A 33120A Hewlett-PackardRF function generator has been used with 50Ω matchingload to generate the EMI the power supply and the biasingvoltages were supplied by E3630A Hewlett-Packard powersupply The board interconnections were designed as shortas possible along with straight paths and ground shields inorder to minimize all the undesired signals arising from themeasurement setup itself The resistor 119877

1in Figure 3 is used

for the matching load while 1198621and 119862

2are power supply

filters of respectively 100 nF and 10120583F furthermore theoutput pin is connected to an RC (119877

2= 1 kΩ 119862

3= 1 nF)

filter with cut-off frequency of 160 kHz in order to evaluate




Vdd

R1

R2

R2

C1

C1

C2

C2 C3

C3

GndGnd

Gnd

Gnd

Gnd Gnd

Gnd

Gnd

Vss

VEMI Voutminus+

minus+

minus+

sim








0

200

400

600

800

1000

Frequency (MHz)

Offs

et v

olta

ge (m

V)

uA741CA3140

ICL7611

10minus1 100 101 102 103minus400

minus200



M1 M2M4M3

Vin+Vin

minus

II

VBBVBB






M2M1Vin

+Vin

minus

I










119881os

=

intinfin

minusinfin


119881GS12 minus 119881119905

(1)









M14a M14b

M16a

M11a

M9a

M11b

M9b

M8aM19a

M17a

M10a

M13a

M20a

M18a

M15a

M8b

M19b

M17b

M10b

M13b

M20b

M18b

M15b

M16b

M12a M12b

In A

Vout BVout A

Vdd

In B

Vp5

Vp6 Vp6

Vp5


1000

800

600

400

200

0

minus200

Offs

et (m

V)

105 106 107 108 109 1010

Frequency (Hz)

uA741

OpAmp in [34]


119901EMI

signal










M7

M9

M3

M13

M11 M10

M12

M5

M2M1

M4 M6

M8

Vout+Vout

minus

Vin+Vin

minus

Vdd

Vb2

Vb1


M1 M2

R1R1

Vbias

Vinp

Vxp R2R2 VxmVinm


0

50

100

150

200

Frequency (MHz)

Out

put o

ffset

vol

tage

(mV

)


101 102 103 104



Vdd

Vref

Vss


Vout

minus

+

A1

nAA




Fully differential

Folded cascode

Q nQ

IN+

INminus

Vdd

Vref

Vout

C1

C2

R2

R A1

R B1

minus

+


0

minus200

minus400

minus600

minus800

minus1000

minus1200

minus1400

Offs

et (m

V)


100 101 102 103 104

Frequency (MHz)




Frequency (MHz)

minus100

0

100

200

300

Offs

et (m

V)


100 101 102 103 104




minus20

minus15

minus10

minus5

0

5

10

15

20

Offs

et (m

V)

100 101 102 103 104

Frequency (MHz)



119904


119901



M4M3M2M1

M6M5

M10M9M8M7M13M11

M12 M14

Gnd

C


Vdd

Vref

Va Vs

Q1 Q2

Vbe2Vbe1


5 Conclusions




References

















































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation












Vdd

R1

R2

R2

C1

C1

C2

C2 C3

C3

GndGnd

Gnd

Gnd

Gnd Gnd

Gnd

Gnd

Vss

VEMI Voutminus+

minus+

minus+

sim








0

200

400

600

800

1000

Frequency (MHz)

Offs

et v

olta

ge (m

V)

uA741CA3140

ICL7611

10minus1 100 101 102 103minus400

minus200



M1 M2M4M3

Vin+Vin

minus

II

VBBVBB






M2M1Vin

+Vin

minus

I










119881os

=

intinfin

minusinfin


119881GS12 minus 119881119905

(1)









M14a M14b

M16a

M11a

M9a

M11b

M9b

M8aM19a

M17a

M10a

M13a

M20a

M18a

M15a

M8b

M19b

M17b

M10b

M13b

M20b

M18b

M15b

M16b

M12a M12b

In A

Vout BVout A

Vdd

In B

Vp5

Vp6 Vp6

Vp5


1000

800

600

400

200

0

minus200

Offs

et (m

V)

105 106 107 108 109 1010

Frequency (Hz)

uA741

OpAmp in [34]


119901EMI

signal










M7

M9

M3

M13

M11 M10

M12

M5

M2M1

M4 M6

M8

Vout+Vout

minus

Vin+Vin

minus

Vdd

Vb2

Vb1


M1 M2

R1R1

Vbias

Vinp

Vxp R2R2 VxmVinm


0

50

100

150

200

Frequency (MHz)

Out

put o

ffset

vol

tage

(mV

)


101 102 103 104



Vdd

Vref

Vss


Vout

minus

+

A1

nAA




Fully differential

Folded cascode

Q nQ

IN+

INminus

Vdd

Vref

Vout

C1

C2

R2

R A1

R B1

minus

+


0

minus200

minus400

minus600

minus800

minus1000

minus1200

minus1400

Offs

et (m

V)


100 101 102 103 104

Frequency (MHz)




Frequency (MHz)

minus100

0

100

200

300

Offs

et (m

V)


100 101 102 103 104




minus20

minus15

minus10

minus5

0

5

10

15

20

Offs

et (m

V)

100 101 102 103 104

Frequency (MHz)



119904


119901



M4M3M2M1

M6M5

M10M9M8M7M13M11

M12 M14

Gnd

C


Vdd

Vref

Va Vs

Q1 Q2

Vbe2Vbe1


5 Conclusions




References

















































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










M2M1Vin

+Vin

minus

I










119881os

=

intinfin

minusinfin


119881GS12 minus 119881119905

(1)









M14a M14b

M16a

M11a

M9a

M11b

M9b

M8aM19a

M17a

M10a

M13a

M20a

M18a

M15a

M8b

M19b

M17b

M10b

M13b

M20b

M18b

M15b

M16b

M12a M12b

In A

Vout BVout A

Vdd

In B

Vp5

Vp6 Vp6

Vp5


1000

800

600

400

200

0

minus200

Offs

et (m

V)

105 106 107 108 109 1010

Frequency (Hz)

uA741

OpAmp in [34]


119901EMI

signal










M7

M9

M3

M13

M11 M10

M12

M5

M2M1

M4 M6

M8

Vout+Vout

minus

Vin+Vin

minus

Vdd

Vb2

Vb1


M1 M2

R1R1

Vbias

Vinp

Vxp R2R2 VxmVinm


0

50

100

150

200

Frequency (MHz)

Out

put o

ffset

vol

tage

(mV

)


101 102 103 104



Vdd

Vref

Vss


Vout

minus

+

A1

nAA




Fully differential

Folded cascode

Q nQ

IN+

INminus

Vdd

Vref

Vout

C1

C2

R2

R A1

R B1

minus

+


0

minus200

minus400

minus600

minus800

minus1000

minus1200

minus1400

Offs

et (m

V)


100 101 102 103 104

Frequency (MHz)




Frequency (MHz)

minus100

0

100

200

300

Offs

et (m

V)


100 101 102 103 104




minus20

minus15

minus10

minus5

0

5

10

15

20

Offs

et (m

V)

100 101 102 103 104

Frequency (MHz)



119904


119901



M4M3M2M1

M6M5

M10M9M8M7M13M11

M12 M14

Gnd

C


Vdd

Vref

Va Vs

Q1 Q2

Vbe2Vbe1


5 Conclusions




References

















































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










M14a M14b

M16a

M11a

M9a

M11b

M9b

M8aM19a

M17a

M10a

M13a

M20a

M18a

M15a

M8b

M19b

M17b

M10b

M13b

M20b

M18b

M15b

M16b

M12a M12b

In A

Vout BVout A

Vdd

In B

Vp5

Vp6 Vp6

Vp5


1000

800

600

400

200

0

minus200

Offs

et (m

V)

105 106 107 108 109 1010

Frequency (Hz)

uA741

OpAmp in [34]


119901EMI

signal










M7

M9

M3

M13

M11 M10

M12

M5

M2M1

M4 M6

M8

Vout+Vout

minus

Vin+Vin

minus

Vdd

Vb2

Vb1


M1 M2

R1R1

Vbias

Vinp

Vxp R2R2 VxmVinm


0

50

100

150

200

Frequency (MHz)

Out

put o

ffset

vol

tage

(mV

)


101 102 103 104



Vdd

Vref

Vss


Vout

minus

+

A1

nAA




Fully differential

Folded cascode

Q nQ

IN+

INminus

Vdd

Vref

Vout

C1

C2

R2

R A1

R B1

minus

+


0

minus200

minus400

minus600

minus800

minus1000

minus1200

minus1400

Offs

et (m

V)


100 101 102 103 104

Frequency (MHz)




Frequency (MHz)

minus100

0

100

200

300

Offs

et (m

V)


100 101 102 103 104




minus20

minus15

minus10

minus5

0

5

10

15

20

Offs

et (m

V)

100 101 102 103 104

Frequency (MHz)



119904


119901



M4M3M2M1

M6M5

M10M9M8M7M13M11

M12 M14

Gnd

C


Vdd

Vref

Va Vs

Q1 Q2

Vbe2Vbe1


5 Conclusions




References

















































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










M7

M9

M3

M13

M11 M10

M12

M5

M2M1

M4 M6

M8

Vout+Vout

minus

Vin+Vin

minus

Vdd

Vb2

Vb1


M1 M2

R1R1

Vbias

Vinp

Vxp R2R2 VxmVinm


0

50

100

150

200

Frequency (MHz)

Out

put o

ffset

vol

tage

(mV

)


101 102 103 104



Vdd

Vref

Vss


Vout

minus

+

A1

nAA




Fully differential

Folded cascode

Q nQ

IN+

INminus

Vdd

Vref

Vout

C1

C2

R2

R A1

R B1

minus

+


0

minus200

minus400

minus600

minus800

minus1000

minus1200

minus1400

Offs

et (m

V)


100 101 102 103 104

Frequency (MHz)




Frequency (MHz)

minus100

0

100

200

300

Offs

et (m

V)


100 101 102 103 104




minus20

minus15

minus10

minus5

0

5

10

15

20

Offs

et (m

V)

100 101 102 103 104

Frequency (MHz)



119904


119901



M4M3M2M1

M6M5

M10M9M8M7M13M11

M12 M14

Gnd

C


Vdd

Vref

Va Vs

Q1 Q2

Vbe2Vbe1


5 Conclusions




References

















































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










Fully differential

Folded cascode

Q nQ

IN+

INminus

Vdd

Vref

Vout

C1

C2

R2

R A1

R B1

minus

+


0

minus200

minus400

minus600

minus800

minus1000

minus1200

minus1400

Offs

et (m

V)


100 101 102 103 104

Frequency (MHz)




Frequency (MHz)

minus100

0

100

200

300

Offs

et (m

V)


100 101 102 103 104




minus20

minus15

minus10

minus5

0

5

10

15

20

Offs

et (m

V)

100 101 102 103 104

Frequency (MHz)



119904


119901



M4M3M2M1

M6M5

M10M9M8M7M13M11

M12 M14

Gnd

C


Vdd

Vref

Va Vs

Q1 Q2

Vbe2Vbe1


5 Conclusions




References

















































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










M4M3M2M1

M6M5

M10M9M8M7M13M11

M12 M14

Gnd

C


Vdd

Vref

Va Vs

Q1 Q2

Vbe2Vbe1


5 Conclusions




References

















































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation









Review Article EMI Susceptibility Issue in Analog Front-End for...

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