CONDUCTED RF EQUIPMENT POWER AMPLIFIERS. Practical RF Immunity System Design Considerations

Transcription

1 CONDUCTED RF EQUIPMENT POWER AMPLIFIERS Practical RF Immunity System Design Considerations 1

2 Designing a System Key considerations are the amplifier and antenna combination Determining what Power Amplifier to select depends on The test level required by the standard The type of modulation required The antenna efficiency (Gain) The test environment Cable and other component losses 2

3 Usable Amplifier Power Saturated Power (Psat) Vs Linear Power (P1dB) Definitions Psat Highest power that the amplifier can generate P1dB Highest power where Pin Vs Pout curve is considered to be straight 3

4 CONDUCTED RF EQUIPMENT POWER AMPLIFIERS Modulation 4

5 80% AM CW AM (80%) 80% higher peak 1 khz

6 Effect of Saturation on Modulation O/P Modulation does not Match the Input O/P Modulation Matches the Input Modulation Modulation CW Input Level required for 10V/m CW Input Level required for 10V/m

7 Requirement of IEC >3.1dB Reduction 5.1dB Reduction CW Input Level required for 18V/m

8 Requirement of IEC to 7.1dB Increase 5.1dB Increase CW Input Level required for 10Vemf

9 Potential Change to IEC to 7.1dB Increase >3.1dB Reduction 5.1dB Reduction 5.1dB Increase CW Input Level required for 18V/m CW Input Level required for 10Vemf

10 Pulse Modulation CW (unmodulated signal) Pulse Modulation Period Pulse Duration

11 Effect of Saturation on Modulation Pulse O/P Modulation Matches the Input Modulation CW Input Level required for 200V/m

12 Harmonics Unwanted signals produced at multiples of the required fundamental frequency Broadband, power and field measuring devices cannot distinguish between the fundamental and harmonics Under testing possible False failures can be caused It may appear that an DUT has a problem at a frequency but it could be that the problem is at the harmonic frequency User may waste time and money on an incorrect fix Most antenna have better gain at higher frequencies This can magnify the level of the harmonic compared to the fundamental

13 What Happens to the Harmonics at and above P1dB

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17 Relative Level Harmonics of a Square Wave Harmonic Number

18 Harmonic Distortion Antenna Gain f1 3 x f1 Frequency IEC requires that the level of the harmonics measured at the uniform plane is at least 6dB less than the fundamental signal

19 CONDUCTED RF EQUIPMENT POWER AMPLIFIERS Conducted RF Immunity 19

20 Coupling devices CDN M CDN A CDN S CDN T Current injection probe EM clamp Attenuation clamp (decoupling only) Calibration adapters 20

21 Coupling Devices CDN Good Decoupling performance Majority of the injected signal goes towards the DUT Very little signal goes back to the mains or AE Most efficient Device Least power required from the amplifier Needs to be inserted in the cable May not always be convenient Can affect normal operation of the DUT

22 Testing with Coupling Devices other than a CDN EM Clamp Like a CDN have good Decoupling performance Majority of the injected signal goes towards the DUT Very little signal goes back to the mains or AE Not as efficient as a CDN Requires more power from the amplifier Physically larger than a CDN May not always be convenient Clamp on device Does not require cable under test to be broken 22

23 Testing with Coupling Devices other than a CDN BCI Clamp No Decoupling performance Injected signal goes in both directions Same signal goes to the mains or AE Not as efficient as a CDN or EM Clamp Requires more power from the amplifier Clamp on device Does not require cable under test to be broken 23

24 Example 24

25 Example 25

26 Bulk Current Injection (BCI) Power required depends on the test level and the selected BCI Probe Power = I 2 * 50 plus the Insertion loss of the probe

27 Testing with Coupling Devices other than a CDN Both devices have a low source impedance Not 150 Ω Although the calibration procedure is the same Attempt to achieve target level at output of the calibration jig When connected to a DUT with low common mode impedance much higher currents can be induced compared to a CDN User is required to monitor the RF current on the cable under test and limit it to the maximum level possible from a CDN I max = U 0 / Ω I = V emf /150 V emf 27

28 CONDUCTED RF EQUIPMENT POWER AMPLIFIERS Radiated RF Immunity 28

29 Radiated Immunity Power required depends on the test level and the selected antenna Trade of between efficiency and size Larger antenna are more efficient, if they will fit in the chamber

30 Basic Radiated Field/Power Calculation Power required to generate a field of E V/m at a distance d metres from the antenna Power (watts) = (E 2 * d 2 ) /( 30 * g) g = 10 (G/10) {g = ratio gain, G = gain (dbi) }

31 Additional Factors to be included Chamber variation No chamber is perfectly uniform The so called uniform area can have variation up to 6dB Potentially you could require 6dB more power = 4 times more

32 Test Field V/m Additional Factors to be included Modulation 80% Sinusoidal Amplitude Modulation (AM) Requires (= 3.24) times the power or +5.1dB Pulse Modulation (Pulse) and Frequency Modulation (FM) Requires no additional power Frequency MHz

33 Test Field V/m Radiated System (80MHz to 6GHz) PowerMeter1 (none) - PM Amp1 (none) - 80RF or Coupler Frequency MHz PowerMeter2 (none) - PM6006 SigGen1 (none) - ITS C 3 4 Switch1 - ITS6006 Amp2 (none) - AS or -500 Coupler2 PowerMeter3 (none) - PM C 2 Switch2 - ITS6006 or External Switch Antenna1 STLP 9128E Antenna2 STLP 9149 Chamber1 StressSensor1 Amp3 (none) - AS Coupler3

34 Radiated System (80MHz to 6GHz) PowerMeter1 (none) - PM6006 Amp1 (none) - 80RF or Coupler1 PowerMeter2 (none) - PM6006 SigGen1 (none) - ITS C 3 4 Switch1 - ITS6006 Amp2 (none) - AS or -500 Coupler2 PowerMeter3 (none) - PM C C 2 2 Switch2 3 Switch3 - ITS6006 or External Switch Chamber1 Antenna Antenna1 STLP 9128E StressSensor1 Antenna Antenna Amp3 (none) - AS Coupler3

35 Radiated System (80MHz to 6GHz)

36 Loss in Cables and components Typical example Test Rack to Antenna 1.5m rack to penetration (Loss GHz) 5m penetration to floor panel (underfloor cable) (Loss 0.8 1GHz) 3m floor panel to antenna (Loss 0.5 1GHz) Internal to rack 0.4m RF switch output rack bulkhead (Loss 0.1 1GHz) 0.4m Directional Coupler output RF switch input (Loss 0.1 1GHz) Werlatone C5982 Directional Coupler (Loss 0.1 RF Switch 2 Way N type (Loss GHz) TOTAL LOSS GHz Would be lower at 80MHz but much higher at 3GHz

37 5dB 6dB 7dB Frequency Loss Chamber AM Power MHz db db Watts Frequency Loss Chamber AM Power MHz db db Watts Frequency Loss Chamber AM Power MHz db db Watts

38 Summary In order to accurately design a system the following information is required: Required Frequency range and Field level Modulation type Chamber dimensions Chamber performance Cable routing, lengths 38

39 CONDUCTED RF EQUIPMENT POWER AMPLIFIERS Thank You for your Attention 39