HPM Effects on Electronic Components and the Importance of This Knowledge in Evaluation of System Susceptibility

Gunnar GSransson FOA Defence Research Establishment, P.O. Box 1165, S-581 11 Linkoping, Sweden. Email: gungor@lin.foa.se.

Abstract: Electronic components have been investigated con- sidering HPM effects. This includes the nature and types of effects and also how the parameters (power, frequency etc.) of the microwave radiation will influence the effects. We also looked at differences in susceptibility between different com- ponent types, technologies, manufacturers, different samples of the same type, technology and manufacturing etc. The results show that this knowledge is important for testing and assessing system susceptibility.

INTRODUCTION The HPM susceptibility level for a system is dependent on the combined effects from shielding [ 11, coupling to cables [2] and component susceptibility [3]-[5]. All three things are signifi- cant for microwave system susceptibility, estimating, testing and hardening.

HPM can interfere with a system even if the system is not intended to work at microwave frequencies. The basic mecha- nism of interference is rectification in the nonlinear pn- junctions. This effect will introduce frequency components, which are dependent on the modulation of the microwave. Thus, low frequency (low compared to microwaves) analog and digital circuits can be disturbed.

The main goal in our component susceptibility program To get knowledge of: l Type of effects that arise. l Understanding of the effects. l Effects versus the parameters of the microwave

(power, frequency etc.). l Susceptibility levels. l Differences between technologies, circuit types, manufac-

turers and samples. l How to use the results in system analysis. l What type of results that are necessary.

To develop: l Test methods. l Component measurement system

(including instrumentation, test setup and test fixtures).

The above-mentioned is very important in order to correctly perform and analyze tests of systems, to calculate/estimate system hardness and to harden systems.

In electronic systems the microwave power is often picked up by cables and wiring and conducted into the electronic circuits. When testing electronic components we also could have used irradiation, but our conception is that it is better to use direct injection. Thereby we can concentrate on the behavior of the DUT (Device Under Test) and remove the uncertainties asso- ciated with the field to wire coupling.

COMPONENT MEASUREMENT SYSTEM At FOA we have developed a measurement system including test fixtures. The system must be designed in such a way that we can inject, control and measure the microwave into a low frequency electronic component, which is not matched to or intended to handle microwave frequencies. At the same time the component also has to be supplied with its normal voltages and signals to a number of pins, signals which also have to be measured at the time of the microwave injection.

Test setup A simplified block diagram of a test setup is shown in figure 1. Many of the parts are left out, but the principal is shown. It can be divided into two parts. One part consists of a microwave source and equipment for controlling and measuring the pa- rameters of the microwave. The other part consists of a test fixture with the DUT and instrumentation for supplying, con- trolling and measuring voltages, currents and signals with which the DUT normally is working.

TEST SET

MICROWAVE GENERATOR

I

i P‘,WPP kK,$‘,“R POWER METER and/or

PULSE DETECTOR TECTOR

POWER METER ‘IETER LJ and/or /or 1 PULSE DETECTOR TECTOR

AMPLIFIERS 0.3 - 18 GHz

Figure 1. Simplified block diagram of a measurement system for investigating HPM effects in electronic components.

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At the output of the amplifiers diiectional couplers are con- nected (for simplicity, only one of the amplifiers and the di- rectional couplers is shown in figure 1) in order to measure both the incident and reflected power. By that we can calculate the absorbed power. In the described test setap we have a diplexer or a bias-T between the microwave source and the DUT. The reason for this is that, at the same pin where the microwave is injected, we also want to supply the DUT with low frequency (and/or DC) signals, and we also must be able to measure these different signals. The injected microwave can also propagate to other inputs/outputs at the DUT. Therefore it can be necessary to use diplexers or bias-T:s there too.

We want to know both the incident and reflected power at the DUT. But it is not possible to measure directly at the compo- nent pins. Therefore we need a test fixture. Also, in order to exchange components in an easy manner we need a socket between the leads and the component. The mismatch this in- troduces must be of such a magnitude that it can be tolerated.

Substrate (dumid)

a) Microstrip view @IL socket will be mounted on the q&site side)

b) Ground plane view @IL socket will be mounted on this side)

c) Side view (OIL socket mounted)

Figure 2. Example of micrastrip line board for a DIP KC-circuit

We have found that a test fixture built with a microstrip line board is a good choice. For the substrate we have used duroid. An example is shown in figure 2. One side, the ground plane, is coated with copper. On the other side, microstrips are proc- essed. We have found that the best way is to mount the socket on the ground plane side, both of mechanical and electric rea- sons. The socket shall have as low a profile as possible in

order to have the leads between the microships and the in- put%utputs of the DUT short. The end of the socket pins are cut as near as possible to the solder point to avoid antenna effects. The microstrip line board is placed on an aluminum frame with the gmund side faced to the frame and in galvanic connection (see photo in figure 3).

Figure 3. Photo of a test fixture.

Before a test fixture will be used it must be characterized, i.e. the S-parameters are measured. This is done with the socket mounted, but without a DUT. The results show that if the test fixtures are made in the way described they will be very good for frequencies up to about 15 GHz.

EXPERIMENTS Both digital and analog circuits have been investigated. The experiments have been performed by direct injection of mi- crowave power into the components, and the effects versus power and frequency have been investigated. For the power we can get the dependence of the incident power, but to get the susceptibility dependence of the injected power is not enough, because the results are depending on the characteristic imped- ance of the cable and/or wire through which the microwave is injected into the DUT. The results of the investigations shall be such that they only are related to the component and thus can be used in different systems. Hence we have in most cases chosen to relate the results to the absorbed power instead of the incident power. Therefore we have to measure both the incident and reflected power to be able to calculate the ab- sorbed power.

Digital circuits Circuits of different technologies, e.g. TIZ and CMOS, have been investigated. Below are some experimental results of logic digital circuits and results of quartz crystal controlled clock oscillators. Typical results are pointed out.

Experimental results on HCMOS. A number of High Speed CMOS (HCMOS) logic digital circuits have been studied in respect to HPM. The circuits were chosen so that each circuit

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type is from different manufacturers and at least three samples of every type from one and the same manufacturer are in- cluded. The investigations have been performed by injecting the microwave both into the inputs and outputs (with inputs are meant all kinds of inputs as e.g. enable inputs). The tests have also been made for numerous combinations of ones and keros at the different inputs.

Below are shown some examples of the experimental investi- gations of the more simple circuits (these results are also rele- vant for more complex circuits investigated, because these are made up of simple building blocks).

There is a strong dependence on frequency. The effects de- crease rapidly with frequency. We also have found differences between circuits (circuits of equal types) from different manu- facturers, but small differences between different samples (of the same type) from the same manufacturer.

Experiments on TTL. Some experimental investigations have also been made on TTL logic devices. The effects are about the same as for CMOS, but TTL devices are more sensitive. Among the different TTL technologies (Standard, FAST, Low Power Schottky etc.) Low Power Schottky seems to be the most sensitive.

A: PincS B: Pinc=l b0 mW ‘c pin(LL200 mW”“- D: Pinc=4bO mW E: Pinc=8bO mW _

f=O.8 GH;

Input voltage [v]

a) Microwave power fed to the input.

e I

OO A :

1 I&t voltage3D/]

4 5

b) Microwave power fed to the output

Figure 4. Example of microwave effects on an HCMOS NAND Gate (coupled as an inverter). Pm&incident microwave power and f = microwave frequency.

An example of microwave effects on logic digital devices is that the transfer characteristic changes when the microwave power is injected at the input. This means that the input threshold voltage shifts and the output voltage changes (see figure 4a). When the microwave power is injected into the output the voltage there will shift (see figure 4b). There will also be some, but less, influence on the input voltage in this case. For three-state devices, when the output is in the high impedance state, the output transistor can begin to conduct more or less, i.e. the output isolation will decrease. If we have a gate with a Schmitt-trigger function this function will dete- riorate or disappear. Other effects may be that both the input and supply current increases.

Exueriments on Clock oscillators. Experimental investigations of microwave effects on quarts crystal controlled clock oscil- lators have been performed. Both TTL and CMOS-oscillators have been included.

The selection of the samples was made to give a basis for dif- ferences in susceptibility between: l Technologies (TIL and CMOS). l Different manufacturers. l Samples of the same type and manufacturer.

Measurements: l Changes in the clock pulses. l Increase in supply current. Susceptibility levels have been determined.

The investigations have been performed for: l Microwave power levels: 2 mW - 1W. l Microwave frequencies: 300 MHz -14 GHz.

Figure 5 shows one of test setups. There are no inputs (besides that for the power supply) to the oscillators. Thus the micro- wave was fed to the output. To be able to inject the microwave and also to be able to measure both the microwave and the clock pulses we use a bias-T or a diplexer at the output of the oscillator. Measurements of the clock pulses were done using an oscilloscope from which they were plotted. Figure 6 shows susceptibility versus microwave frequency for one of the TTL oscillators.

I LOAD

Figure 5. Test setup for the TTL oscillators (the picture shows only the DUT part of the measurement setup)

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Results: The effects decrease rapidly with microwave frequency. CMOS-oscillators have a much higher hardness to HPM than those in TTL technology. A power factor of 20-40, depending on the frequency. The susceptibility level for TTL-oscillators can be as low as about 10 mW at 300 MHz. The differences between various samples of equal type and manufacturer can be as high as +35%. Differences between samples of equal type but from differ- ent manufacturers can be a factor of up to 40.

I

log Microwave frequency [Hz]

Figure 6. Susceptibility level versus microwave frequency for one of the TTL oscillators. Susceptibility level is here defined as the maximum allowed absorbed microwave power to secure that half of the manufacturers guarantied voltage noise margins will be left for other disturbance sources than HPM.

Some remarks from the investigations of digital circuits. The results show how important it is to have knowledge about the behavior of the components if a test of a system shall be fully relevant and also for calculating/estimating the suscepti- bility level of a system. Thus a conclusion is that an exchange of components shall not be done without knowledge of the component susceptibilities, even if they are compatible and have the same specified electrical behavior. If this is not taken into consideration the hardness of the system against HPM may be changed. We also found unacceptable microwave effects, which will not be detected at standard system tests (e.g. Schmitt-trigger functions). Both the input and supply current will increase which can cause system problems.

Amzlog circuits Here are, as examples of analog components, shown some results from experimental investigations on OP-Amps (Operational Amplifiers) and ADC:s (Analog-to-Digital Con- verters).

Exuerimental results on OP-Amps. The investigated OP-Amps were of different technologies (bipolar and FET transistors). Each type had samples from different manufacturers and at

least three samples of each type and manufacturer were in- cluded. Below are shown some examples from the investigations of how the OP-Amps will be influenced when microwave power is fed to the inputs. Microwave coupled to the inputs was con- sidered to be the most sensitive for the OP-Amps. If we in this investigation measure the output voltage we will find that this voltage will change with microwave power, but the values will only be valid for the special circuit coupling we use. The out- put voltage changes can be different for various circuit cou- plings even if we have the same voltage gain in all of them. We have to find those effects of the microwave which are independent of the application.

The microwave effects are changes in offset voltage and bias currents. These changes are independent of the application. It is of technical and practical reasons not possible to measure these parameters directly. But if we use three (the unknown parameters are three) different circuit coupling configurations, where used voltage gain and values of used resistors has to be known, we can by the output voltage values calculate the pa- rameters. Thus, the microwave has, for every distinct fre- quency and power, to be fed into all the three couplings. The parameters can be calculated by using all three output voltage values. It is not possible to calculate the changes in a parame- ter by using only one coupling configuration, because changes in the other parameters also influence the output voltage.

For routine or industrial testing it is important to get the re- quired information using as few measurements as possible. Therefore it is of great benefit if we also can find formulas for the effects versus power and, if possible, also versus fre- quency.

The change in offset voltage and bias current show a linear relationship (at a constant frequency) versus absorbed power, and both offset voltage and bias current are inversely propor- tional to the microwave frequency raised to a constant. Thus:

I I V k, OS TXP

I I 4

Mb ==FXP Where V,, = change in offset voltage [V]

AIb =change in bias current [A] P = absorbed power [W] f = microwave frequency [GHz]

k, , k, , k, and k, = constants Typical results have been: k, = 1.4x102, k, = 1.8~10~ for

bipolar circuits and k, =0.82, k, = 1.8~10-~ for FET. The constants k, = k, = 1.8 for both bipolar and FET. The dia- gram in figure 7 shows an example of change in offset voltage for a bipolar OP-Amp when microwave power is injected.

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Thus, from these measurements we have got measures of the microwave effects, which are independent of the application. From these we can calculate the susceptibility for different applications and need not to repeat the investigations for every application. This is important for routine or industrial meas- urements.

The experiments were performed for a limited power- and frequency domain. Whether the formulas are valid outside these domains has not been shown. But the studied domain is that of most interest for HPM effects.

10' “““‘I “““I “““b “““1 “‘.‘.‘I ...- LMIOI Raytheon 0.3 GHz

lo-6 lo-5 IO4 IO4 lo-” 10-l loo Absorbed microwave power [WI

Figure 7. Effects on an OP-Amp when microwave power is fed to the input.

The results show that the investigated OP-Amps are very sen- sitive to HPM (generally more sensitive than digital cir- cuits).The results show that those with bipolar transistors are 100-200 more sensitive than those with FET transistors. The differences between different samples of the same type and manufacturer are relatively small. There can be some differ- ences between different manufacturers but not so large (up to about a factor two).

For the bipolar OP-Amps in the frequency range 0.3 -5.0 GHz it may be enough with microwave power between some tenth of mW to some mW to cause upset (see figure 7). The suscep- tibility is, as has been seen, dependent on the microwave fre- quency, but also on the application of the OP-Amp. Therefore it is not possible to generally point out any unique susceptibil- ity level. Also important is that those with FET transistors are less sensitive than those with bipolar transistors. Thus, if we want to have low susceptibility for HPM, we shall not choose bipolar.

Exueriments on ADC:s. Experimental investigations were carried out for microwave power fed to the analog inputs of the circuit.

The output digital word were measured in different applica- tions during microwave injection and the measurements were performed for l Microwave power level: 10 mW - 1 W. l Microwave frequencies: 300 MHz -8.0 GHz.

Figure 8 shows a simplified scheme of the test setup

Test object: A/D Converter ADC in CMOS flash conversion technique

hN

Pulse I I generator - -Lr

To oscillo scopes

(m chan- IIdS)

Figure 8. Simplified scheme of the setup for investigating HPM effects on an AD-converter.

The investigations showed, as expected, that the effects on the output data were dependent on the application. Thus we have to find a measure, if possible, which is independent of the application.

We found that if the measure of the microwave effect is ex- pressed as an equivalent error voltage at the analog input, this measure of the microwave effect seems to be independent of the application.

For microwave power up to about 0.8 W the error voltage tends to be approximately: l proportional to microwave power (se figure 9). l inversely proportional to frequency raised to a constant (se

figure 10).

10-l Microwave power [WI

Figure 9. Error voltage at the analog input on an ADC versus absorbed microwave power at 1 GHz

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,,.,.,........: I . . . . . . . . . . ..-. f ,... ;.; . . . . . . . . . . . . . . . .._... i &..i.

j :.,,...: ,... i.:. . . . f” j

: : :’

.f:..j.

IO8 9

Microwave ktuency [Hz] ‘;o’o

Figure 10. Error voltage at the analog input on an ADC versus microwave frequency at a constant absorbed power.

RESULTS FROM COMPONENT STUDIES SIGNIFICANT FOR SYSTEM TESTS.

System tests are only some special cases of all possible test conditions. Knowledge about components gives the possibility to l Choose the most relevant system tests. . Reduce the number of system tests. l Draw correct conclusions from system tests l Calculate susceptibility for other test conditions (other

frequencies etc.) than those performed.

The hardness of an equipment can be increased by ex- chauging certain sensitive components. l A complicated and costly increase of the shielding can be

avoided by changing these components to harder.

T%e results of a system test are strictIy valid only for the specific item tested. l Components in the various items can have equal nominal

electrical behavior, but different susceptibility.

It is very important that components are not being ex- changed without control. l Exchange of components can considerably change the

susceptibility of the equipment.

Durirtg components studies we have found unacceptable microwave effects, which will not be detected at standard system tests. l An example is digital circuits with Schmitt-trigger func-

tions. These circuits are often used to enhance the noise immunity of the equipment. This function may decrease or disappear during microwave irradiation.

When injecting microwave power into components an in- crease of the supply current may occur. The function of the component may not be affected but effects in the system will arise:

l The increase of the current causes voltage pulses (noise pulses) in the lines.

l The current increase can cause unacceptable increase of the temperature.

l The power supplies can perhaps not deliver the current.

CONCLUSION HPM susceptibility:

Large differences in susceptibility between technologies. Small differences between different samples (of the same type) from the same manufacturer. Very strong frequency dependence. Susceptibility de- creases rapidly with increasing frequency. Differences in susceptibility level between different manu- facturers. Differences of up to 16 dB were found.

HPMsusceptibilig level for analog devices: l Often dependent of the application. l Possible to get an application independent measure of the

microwave effect. The susceptibility level for different applications then can be calculated.

Knowledge of the behavior of components versus microwave parameters is important in order to: l Calculate/estimate system susceptibility levels. l Correctly perform and analyze system tests. l Harden a system.

ACKNOWLEDGEMENTS This work was financially supported by the Swedish Armed Forces, the Swedish Defence Material Administration and Ericsson Saab Avionics, Sweden.

REFERENCES [l] BBckstrijm M. and Lund&n O., Transmission Cross Section of Apertures Measured by Use of Nested Mode-Stirred Cham- bers, FOA Report FOA-R-96-00359-3.2-SE, FOA Defence Research Est., S-581 11 Linkcping, Sweden, Dec. 1996. [2] Silfverski6ld S., BBckstriSm M and Lor& J., Microwave Field-to Wire Coupling Measurements, Proc. of EMC’98 ROMA, Int. Symp. on Electromagnetic Compatibility, Sept. 14-18, 1998, Rome, Italy, pp. 452-457. [3] Richardson, R.E. Jr., Quiesent Operating Point Shift in Bipolar Transistors with AC Excitation, IEEE J. of Solid-State Circuits, Vol. SC-14, No.6, Dec. 1979, pp. 1087-1093. [4] Demoulin, B., Degauque P. and Scuka V., Effects ofElec- tromagnetic Interferences and Transient Disturbances on Electronic Devices and Equipment, Proc. 11’ Int. Symp. on EMC, Zurich, 1995, pp. 113-l 18. [5] Lubineau M. et al., On the Measurement of EMC in Inte- grated Circuits, Proc. 13’Int. Symp. on EMC, Zurich, 1999, pp. 649-652.

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