DESIGN OF ELECTRONICS SYSTEM

SPECTRAL ANALYSIS FOR ELECTROMAGNETIC CONDUCTION (EMC)

AYANSOLA JOEL OLUGBOLAHAN

(00530441)

MSc ELECTRONICS AND COMMUNICATION ENGINEERING

LECTURER IN CHARGE

Dr PETER CALLAGHAN

DECEMBER 16th, 2010

SPECTRAL ANALYSIS FOR ELECTROMAGNETIC CONDUCTION (EMC)

Electromagnetic interference is produced by electrical circuit due to electromagnetic induction or radiation emitted from the Circuit device; it interrupts the performance of other circuits. The source of EMI could be switching signals, spurious/noise or RF signals. Increase in switching circuits gives rise to a wide spectrum of EMI as well as logic driven at high speed also results in higher EMI.

The harmonics of different wavelength were measured by difference in frequency and amplitude of different signal fed into the DSO, harmonics of data, clock and sync were taking differently and difference in wave signals were observed . Change in signal spectrum was as a result in the speed and frequency of operation of the circuit, there was significant fall in amplitude as harmonic frequency increased. Increase in device speed resulted in high frequency generating high noise level on the DSO. The bandwidth of the amplitude became narrower as speed and frequency increased, this shows that device clocked at high frequencies, might cause interference to other devices around them, with effects in operational degradation/distortion of the device in question and possibly miss-operation of other equipment, thus, the higher the amplitude the greater the interference that might be encountered.

Fourier analysis of the spectrum gave much insight into problems that could be associated with EMI in PCB. It was observed that good PCB and circuit design could help reduce or eliminate the EMI as well as using single ground point in low-frequency applications, single grounding is more complex in radio frequencies though as it requires a lot of circuitry consideration.

The spectrum analyzer sought and measured low-level signal while testing the black box in the Anechoic Chamber. The input noise level is a function of the input signal. The noise floor was the combination of losses by input attenuator, mixer conversion and so on combined with generated thermal agitation of various circuit elements both within the black box as well as Dburst device. Interferences from other devices was minimized in the Anechoic Chamber, by performing the experiment in a controlled room, relatively this shows how the systems behaves in the real world without interference from other devices. The device is expected to perform a bit below what was seen due to susceptible noises and interference it will picked up when exposed to other devices around. In the PCB experiment, the thermal agitation of the mounted components coupled with the clock frequency to give real time information about the circuit operation on the DSO, more so different load situation was observed on the PCB test using external load captured in appendix . The result obtained from ISIS Fourier analysis gave fine and stable distortion spectrum.

Noise distortion was high in the data PCB lab result, there were spikes and different peaks were noticed, but in ISIS, the lower peak stays the same without going down that much. ISIS can not been seen as a reliable instrument because it is a controlled environment that is not affected by disturbances by environmental impact.

Appendix A

Figure A1: ISIS Circuit Schematics of Closed DBURST PCB.

Figure A2: ISIS Circuit Schematics of Opened DBURST PCB.

Figure A3: Spectrum for Time Wave of Fig. A1.

Figure A4: Spectrum for Time Wave of Fig. A1.

Figure A5: Spectrum for Time Wave of Fig. A1.

Figure A6: Time Signal using transient analysis of circuit in Fig. A1 with circuit closed.

Appendix B

Figure B1: DBURST PCB.

Figure B2:Time Wave Capture of ‘clock’ DBURST Fig. A7.

Figure B3: Time Wave Capture of ‘sync’ DBURST Fig A7.

Figure B4: Time wave capture of External Source at ‘1 Kohms’ of DBURST Fig. A7.

Figure B5: Time Wave Capture of External Source ‘data’ DBURST Fig A7.

Appendix C

Position At frequency of 433MHz At frequency of 867MHz

Power (dbm) Power (dbm)1 -46.63 --61.482 -41.56 -61.083 -46.63 -63.014 -43.36 -58.885 48.44 62.66 -54.5 -65.8

Table1.0 Measurement result of EMI radiation electrical black box

Position At frequency of 433MHz At frequency of 867MHz

Power (dbm) Power (dbm)

1 -44.63 -59.48

2 -43.56 -64.1

3 -44.63 -61.01

4 -41.36 -56.88

5 -50.44 -64.6

6 -52.5 -63.8

Table 1.1 Showing addition of 2dbm due to cable loss

Position At frequency of 433MHzAt frequency of 867MHz

Power (W) Power (W) 1 1.0232E-08 3.6307E-11 2 7.4131E-09 2.4547E-10 3 6.1659E-09 5.1286E-10 4 9.1201E-08 1.5848E-10 5 1.8620E-08 3.0199E-10 6 5.6234E-09 4.1686E-10

Table 1.2 Showing the result of Power calculated in watts

Calculating the radiated EMI in field strength at 10m from the electrical black box using

antenna gain of 6 and 8 at a frequency of 433MHz and 867MHz respectively

= 4.87 X

= 3.54 X

= 2.94 X

= 4.35 X

= 8.88 X

= 2.68 X

Using antenna gain of 8 at frequency of 867MHz

= 2.31 X

= 1.56 X

= 3.26 X

= 1.00 X

= 1.92 X

= 2.65 X

At frequency of 433MHz At frequency of 867MHz

Position

Field strength Field strength

1 4.87E-11 2.31E-132 3.54E-11 1.56E-123 2.94E-11 3.26E-124 4.35E-10 1.00E-125 8.88E-11 1.92E-126 2.68E-11 2.65E-12

Table 1.3 Showing the result of calculated field strength