probe characterization amber precision instruments, inc. (api) jul. 23, 2014
TRANSCRIPT
Probe Characterization
Amber Precision Instruments, Inc. (API)
Jul. 23, 2014
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Our EMI Probes
EMI Probes:- Up to 6 GHz- Up to 20 GHz- Up to 40 GHz
Optional EMI Probes;Choose:- Size- Frequency range- Field Component
* EMI Hx 2 mm
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Characterization Structureup to 15 GHz
50 Ohms Microstrip Line (MSL)
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Characterization Structureup to 40 GHz
50 Ohms Air-Dielectric* Coplanar Waveguide (CPW)
* To avoid the effect of non-TEM waves on probe characterization at higher freqs (>15 GHz).
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Probe Characterization Setup
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Typical EMI Probe S21
1 2 3 4 5 6 7 8 9 10
x 109
-65
-60
-55
-50
-45
-40
-35
-30
Frequency [Hz]
|S21
| [dB
]
* EMI Hx 2 mm: up to 10 GHz
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What Are the Specs?
108
109
1010
-65
-60
-55
-50
-45
-40
-35
-30
Frequency [Hz]
|S21
| [dB
]
108
109
1010
-65
-60
-55
-50
-45
-40
-35
-30
Frequency [Hz]
|S21
| [dB
]
20 dB/dec Line
Log freq: Low freq with 20 dB/dec slope
* EMI Hx 2 mm
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What Are the Specs?
High freq: How high the probe measures?
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
x 1010
-65
-60
-55
-50
-45
-40
-35
-30
Frequency [Hz]
|S21
| [dB
]
* EMI Hx 2 mm
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What Are the Specs?
108
109
1010
-100
-90
-80
-70
-60
-50
-40
-30
Frequency [Hz]
|S21
| [dB
]
Hx Field, = 0
Unwanted Field, = 90
Unwanted field: Decoupling of unwanted components
* EMI Hx 2 mm
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What Are the Specs?
108
109
1010
-65
-60
-55
-50
-45
-40
-35
-30
Frequency [Hz]
|S21
| [dB
]
107
108
109
1010-90
-80
-70
-60
-50
-40
-30
Frequency [Hz]
|S21
| [dB
]
Low freq: How low the probe measures in a “practical” setup?
20 dB/dec slope
60 dB dynamic range
4 MHz
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High Freq Probe
109
1010
-90
-80
-70
-60
-50
-40
-30
Frequency [Hz]
|S21
| [dB
]
Hx Field, = 0
Unwanted Field, = 90
* EMI Hx 1 mm L: up to 20 GHz
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Probe Factor
* EMI Hx 2 mm
108
109
1010
20
30
40
50
Frequency [Hz]
|PF
| [dB
(A/m
)/V
]
Measured Probe FactorTheoretical Open-Circuit Probe Factor
Probe factor: Provide probe factor SmartScan imports probe factor SmartScan measures and calculates system factor
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Other Methods ofData Presentation
• How other people characterize their probes?
• How the characterization data is presented?
• Is their data presentation fair?
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Example* of 10 kHz (?) to 6 GHz Probe Data Presentation
Let’s analyze the data!Extract
* Aprel: http://media.wix.com/ugd/36d46a_46d2902bfdd24c25b401582e6a488370.pdf
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Is Freq Scale OK?
Why the freq axis of extracted data don’t
match?!
Let’s see!
Let’s analyze the data!
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Is Freq Scale OK?
0.99999 GHz 1.3 GHz 1.3 GHz 1.3 GHz 1.1 GHz
Why all ticks are equal?!
Well, not a big deal. Maybe just a typo!
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Lower Frequencies
Why all ticks are equal?!
Well, not a big deal. Maybe just a typo!
What happened to lower freqs?!
Is it extrapolated or really measured?
What is the measurementinstrument setup (IF BW,
span, no. of points, etc.) to measure down to 10 kHz?
Is it a “practical” setup?
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Plot It Differently
104
105
106
107
108
109
-120
-100
-80
-60
-40
Frequency [Hz]
|S21
| [dB
]
What if we plot it in a different way
(log freq)?
104
105
106
107
108
109
-120
-100
-80
-60
-40
Frequency [Hz]
|S21
| [dB
] 20 dB/dec Line
The probe is NOT purely inductiveat lower freqs(as claimed).
Is it probe issue?Or, measurement
issue?Or, simply not
extrapolated the right way?
Note: Simple extrapolation (even if it is done the right
way) does NOT mean probe can measure down to that
freq!
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How about 10 kHz to20 GHz (?) Probe?
Extract
Let’s analyze the data!
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Flat Response (?)
Let’s analyze the data!
The data is from -30 dB to -60 dB. Why the scale
is from 0 to -180 dB?!
Well, it looks better* this way! :-)
*“flat response acrossthe frequency range”
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Plot It Differently
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
x 1010
-50
-45
-40
-35
-30
Frequency [Hz]
|S21
| [dB
]
What if we plot it in a different way
(tight scale)?
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Plot It Differently
What if we plot it in a different way
(log freq)?
108
109
1010
-50
-45
-40
-35
-30
Frequency [Hz]
|S21
| [dB
]
108
109
1010
-50
-45
-40
-35
-30
Frequency [Hz]
|S21
| [dB
]
20 dB/dec Line
The lower freqs seemsto be fine for this prob.The deviation might be
just data extractionerror.
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108
109
1010
-50
-45
-40
-35
-30
Frequency [Hz]
|S21
| [dB
]
20 dB/dec Line
Higher Frequencies
How about the higher freqs?
There is about 20 dB notch @
13 GHz!
A deep notch is usuallya BIG red flag for
“unwanted field” coupling!
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Higher Frequencies
The question is:How to make sure this probemeasures the “desired field” up to 20 GHz (as claimed)?
The “unwanted field” decouplingdata of probe need to be provided.
This probe is suspected to work <10 GHz,
unless the rejection info is available!
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10 kHz to 40 GHz Probe
Let’s analyze the data!
Extract
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Flat Response (?)
Let’s analyze the data!
Same question:The data is from -35 dB to -55 dB. Why the scale
is from 0 to -120 dB?!
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Plot It DifferentlySingle Probe Solution (?)
What if we plot it in a different way(tight scale and
log freq)?
1010.2
1010.3
1010.4
1010.5
1010.6
-50
-45
-40
-35
Frequency [Hz]
|S21
| [dB
]
This info is NOT sufficient to evaluate the probe up
to 40 GHz!
The “unwanted field” decouplingdata of probe need to be provided.
What does happen to lower freqs?Does this probe have sufficient
sensitivity to measure down to 10 kHz?!
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Another Example* of Data Presentation
* Detectus AB: http://www.detectus.se/products_nearfieldprobes.html
Again, the data is from -30 dB to -60 dB. Why the scale is
from 0 to -60 dB?!
Without unwanted field data, there is no sufficient info to
evaluate the probe.
Log freq scale is required forlow freq evaluation.
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What to Look for inProbe Characterization Data?
• Unwanted field rejection data need to be provided to determine higher usable freq.
• Is lower usable freq achievable in a “practical” setup?
• Is the probe purely inductive/capacitive at lower freqs?
• Is the characterization structure (MSL, CPW, etc.) suitable for freq of interest?
• What is the measurement setup/condition?
• Is the scale proportional to data range?
