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prepared by Prof. George Slack (EE)prepared by Prof. George Slack (EE)

Copyright © 2006 Rochester Institute of TechnologyAll rights reserved.

Noise ImmunityNoise ImmunityTransients and ESD Transients and ESD

Practical Design ConsiderationsPractical Design Considerations

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noise immunity

• Circuit noise immunity is the ability of a device or component to operate in the presence of noise disturbance .

• Electro Static Discharge is the sudden discharge (i.e. transients, surge). To the circuit, this is a rapid high voltage, low current situation.

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When is Noise Immunity design needed?

• Senior Design I– Paper Design wks 1-8

• Senior Design II– Prototype device testing wks 1- 3.– Pre-integration testing with lab equipment

DUT (device under test). Wks 3- 6

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Where does noise get into Where does noise get into electronics?electronics?

• 6.4.1 Sources *6.4.1 Sources *

• through ground connections and loopsthrough ground connections and loops• through power supply connectionsthrough power supply connections• through signal inputsthrough signal inputs• through inadvertent ESD through inadvertent ESD

– (human touch, lightning)(human touch, lightning)

• through Inductive devices (motors)through Inductive devices (motors)

• Electronic Instrumentation Design, Kim R. FowlerElectronic Instrumentation Design, Kim R. Fowler

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How does noise get into How does noise get into electronics? electronics?

Energy CouplingEnergy Coupling

(Conductive, Inductive, Capacitive)(Conductive, Inductive, Capacitive)• EMI - Current surgesEMI - Current surges

((EElectrolectroMMagnetic agnetic IInterference) An electrical disturbance in a nterference) An electrical disturbance in a system due to natural phenomena, low-frequency waves system due to natural phenomena, low-frequency waves from electromechanical devices or high-frequency waves from electromechanical devices or high-frequency waves (RFI) from chips and other electronic devices. Allowable limits (RFI) from chips and other electronic devices. Allowable limits are governed by the FCC.are governed by the FCC.

RFI – high impedance devices requiring very RFI – high impedance devices requiring very limited current.limited current.

((RRadio adio FFrequency requency IInterference) High-frequency electromagnetic waves nterference) High-frequency electromagnetic waves that emanate from electronic devices such as chips. that emanate from electronic devices such as chips.

If the source is sufficiently strong this can enter your circuit.If the source is sufficiently strong this can enter your circuit.

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ESD and unwanted signalsESD and unwanted signals

• Fatal to Electronics:Fatal to Electronics:• Inadvertent user misuse.Inadvertent user misuse.• Extreme cases of user abuse and Extreme cases of user abuse and

solutions:solutions:– Bridge to block reverse polarity,Bridge to block reverse polarity,– Schottky diode: very fast switching times and Schottky diode: very fast switching times and

low forward voltage drop. As low as 0.15 volts low forward voltage drop. As low as 0.15 volts for low ma applications. for low ma applications.

– Zener diode across the input. Zener diode across the input. – Circuit breaker – GFICircuit breaker – GFI

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Bare exposure to a CMOS gateBare exposure to a CMOS gateReduce TransientsReduce Transients

Protect from?Protect from?• Misuse during debug and testing.Misuse during debug and testing.• ESD and reverse polarityESD and reverse polarity

– Solution: Diode circuits to protect Solution: Diode circuits to protect against against

• reduce transientsreduce transients– Component Specification SheetsComponent Specification Sheets– Solution: Low pass filterSolution: Low pass filter

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Polarity Protection

+ Input Port–

(+)

(–)

+

Input Port

–

1N5822 or 1N5817

1N4001

Schottky diode

see 7.4.1 page 238, MOSFET solution

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Over-voltage Protection

Fuse

1N5339 (5.6V for a 5.0V input)

+ input port–

(+)

(–)Zener diode

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Over-voltage Protection for Digital Inputs

Vdd

Acrobat Document

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Minimize BandwithMinimize BandwithOne solution: Lowpass FilterOne solution: Lowpass Filter

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1. If considering various output devices, review various manufactures specification sheets .

2. Current (i.e. CMOS versus TTL ).3. Control Voltage (Vdd vary from 1.5 VDC to 12

VDC typically) 4. Needed minimum Signal Transient Response. 5. RLC loads (dangerous current and voltage spikes) 6. Apply to Thevenin Equivalent Circuits

– Source electronics– Device being driven

Knowing Your Design Specification

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Harness -Twisted PairHarness -Twisted Pair

When purchasing harness cable:When purchasing harness cable:• Unshielded Twisted Pair (UTP)Unshielded Twisted Pair (UTP)• Shielded Twisted Pair (STP) Shielded Twisted Pair (STP)

Study the manufacturer’s Specification to Study the manufacturer’s Specification to match to your needs.match to your needs.

Practical Design Considerations Practical Design Considerations http://www.cirris.com/testing/twisted_pair/twist.html

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Harness Signal ResponseHarness Signal Response

Design Considerations: Design Considerations: data rate, distance, data rate, distance, noise, parasitic capacitance, reflections.noise, parasitic capacitance, reflections.

1.1. Frequency Response/ Rise Time needs Frequency Response/ Rise Time needs – DC to 100 khz Open Wire DC to 100 khz Open Wire – DC to 40 MB/s Ribbon Cable (less than 3’)DC to 40 MB/s Ribbon Cable (less than 3’)

• SCSI, SPI-3 applicationsSCSI, SPI-3 applications• http://www.csee.umbc.edu/~plusquel/650/slides/ribbon_cables.pdf

– DC to 300 mhz Twisted Pair - unshielded, DC to 300 mhz Twisted Pair - unshielded, ribbonribbon

– DC to 100/1000 MB/s 10/ 100/ 1000 BaseT DC to 100/1000 MB/s 10/ 100/ 1000 BaseT ethernet Cat 5 minimum spec. RJ45 connector.ethernet Cat 5 minimum spec. RJ45 connector.

– Coax, VHF 3000 megahz (scope probe, cable Coax, VHF 3000 megahz (scope probe, cable TV) attenuation, reflectance, Cable TV, RfTV) attenuation, reflectance, Cable TV, Rf• http://www.netspec.com/helpdesk/wiredoc.htmlhttp://www.netspec.com/helpdesk/wiredoc.html

– DC to 4 gigahz Fiber OpticsDC to 4 gigahz Fiber Optics

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Harness -Twisted PairHarness -Twisted Pair

What is does: Cancels out crosstalk from neighboring wires What is does: Cancels out crosstalk from neighboring wires and electromagnetic interference from external sourcesand electromagnetic interference from external sources

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CMOS characteristics Print out the CMOS characteristics Print out the specification sheets.specification sheets.

• 1 uA input? Not sure? Get the spec sheet!...1 uA input? Not sure? Get the spec sheet!...• Draw the equivalent circuit for each internal Draw the equivalent circuit for each internal

pin. That is, CMOS versus TTL input pin. That is, CMOS versus TTL input impedance, output is pull-up or pull-down impedance, output is pull-up or pull-down circuit, current limiting resistor value.circuit, current limiting resistor value.

• CMOS inputs have very high input CMOS inputs have very high input impedance which is good for low power impedance which is good for low power consumption for well protected electronics consumption for well protected electronics but susceptible to misuse when connecting but susceptible to misuse when connecting to the outside world. to the outside world.

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Isolating NoiseIsolating Noise

• Analog and Digital Optocoupler /Optoisolators Somewhat Analog and Digital Optocoupler /Optoisolators Somewhat expensive ($1/ channel) but good isolation.expensive ($1/ channel) but good isolation.– an electronic device that uses optics to transfer a signal while an electronic device that uses optics to transfer a signal while

keeping the receiving and transmitting circuits electrically keeping the receiving and transmitting circuits electrically isolated isolated

• http://www.analog.com (Analog Devices) (Analog Devices)• http://www.optoinc.com/• http://www.optoinc.com/optocouplers1.html

• Power connection.Power connection.• What does not work?What does not work?

– Fuses tipically are ineffective since a fuse is too slow to stop Fuses tipically are ineffective since a fuse is too slow to stop ESD current but good for harness shortcircuit.ESD current but good for harness shortcircuit.

• ShieldingShielding• Fiber OpticsFiber Optics

– When higher speed data is needed.When higher speed data is needed.

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IsolatorsIsolators

• Analog Devices, Isolators Analog Devices, Isolators http://www.analog.com/en/subCat/0,2879,767%255F827%255F0%255F%255F0%255F,00.html

• Isolators: Isolators: http://www.analog.com/en/prod/0,2877,ADuM2401,00.html

Acrobat Document

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components and spec sheets

http://www.electronicstalk.com/guides/short-circuit-protection.html

http://www.maxim-ic.com/appnotes.cfm/appnote_number/38

http://www.onsemi.com/PowerSolutions/taxonomy.do?id=298 EMI RFI

http://www.edn.com/article/CA326921.htmlhttp://www.bussmann.com/library/techspec/

TechSpec19_sup.pdf#search=%22short%20circuit%20protection%22

http://www.elecdesign.com/Articles/Index.cfm?AD=1&ArticleID=5195 UL 489 and UL1077 standards