Iec 61967 6 2008

The magnetic field Hx_dB is calculated from the measured value of the Vp as corrected by Cf calibration factor of magnetic probe, see annexes A and B with the following equation B.12 tak

Measurement philosophy

RF emissions from a PCB are primarily generated by the RF current from the onboard IC, which influences PCB traces, ground and supply planes, and connected cables, all of which can function as RF antennas The level of emissions is directly proportional to the driving RF current and is significantly impacted by PCB design, the radiation effectiveness of the pseudo-antennas, and the noise coupling path coefficients.

IC to the pseudo-antennas

For this emission mechanism, the driving force of the IC can be a significant parameter for both users and manufacturers to estimate and predict the electromagnetic characteristics of a

The emission driving force of a PCB, module, or system can be assessed by measuring the RF currents produced by the integrated circuit (IC) under test Consequently, the RF noise current measured serves as a key indicator of the unwanted electromagnetic emissions generated by the IC.

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Measurement principle

This test method utilizes a miniature triplate-structured magnetic probe to measure RF current on the power supply and I/O pins of an IC under test The probe accurately assesses the magnetic field at a specific height above the conductor on a standardized test board RF current is derived from the measured magnetic field using a specified formula, ensuring high repeatability through precise mechanical placement of the probe Additionally, the method's frequency range can be extended, allowing for higher frequencies without significantly affecting accuracy This approach offers a convenient and effective means of characterizing and comparing ICs.

General

General test conditions are described in IEC 61967-1.

Frequency range

The effective frequency range of this measurement method is 0,15 MHz to 1 000 MHz The maximum frequency can be extended, if desired, subject to the limitations of the test set-up

The upper frequency limit of a magnetic probe is influenced by its high-frequency characteristics and its proximity to the tested line, as detailed in annex B In the low-frequency range of 0.15 MHz to 10 MHz, utilizing a low-noise pre-amplifier is recommended to enhance the measurement's dynamic range.

General

For general information on test equipment see IEC 61967-1.

Magnetic probe

The magnetic probe shall be a triplate-structured strip line composed of a three-layer PCB

Recommended probe construction details are shown in figures 1, 2, 3 and 4

An SMA connector is positioned at the edge of the PCB, opposite the rectangular loop section of the probe The attachment pads for the SMA connector are located on layers 1 and 3, interconnected by four vias Additionally, the strip conductor pattern is situated on layer 2, linking to the center pin of the SMA connector.

Probe spacing fixture and placement

The output voltage of the probe is influenced by the distance between the probe tip and the strip conductor being measured, making it essential to maintain a precise spacing of 1 mm To achieve this, a probe spacing fixture should be utilized to ensure a consistent distance of 1.0 mm ± 0.1 mm between the probe's rectangular loop portion and the strip line on the IC test board Alternatively, the entire probe can be integrated into a fixing block designed to maintain the specified spacing accurately, as illustrated in figure 10.

The output voltage of the probe is influenced by the angle of placement (ϕ) relative to the microstrip line being measured Experimental measurements indicate that to maintain an amplitude error of less than –2 dB, the placement angle must be kept below 15° For further details, refer to Annex D.

Signal line pattern on layer 2

Pads for SMA connector on layer 1 and 3

Via for SMA connector through layers 1, 2, and 3

Rectangular loop portion for detection

Via for SMA connector through layers 1, 2, and 3

Ground plane patterns on layer 1 and layer 3

Figure 2 – Magnetic probe – First and third layers

Figure 3 – Magnetic probe – Second layer

Layer 1: 0,035 mm Layer 2: 0,035 mm Layer 3: 0,035 mm Insulator

Figure 4 – Magnetic probe – Layer construction

General

General test set-up requirements are described in IEC 61967-1

The measurement set-up and circuit schematic of the magnetic probe measurement method are shown in figures 10 and 11, respectively.

Probe calibration

The magnetic probe must be calibrated to ensure precise correlation between the measured magnetic field intensity and the estimated RF current, following the calibration method outlined in annex A, which details the microstrip line method.

Modifications to standardized IC test board

Layer arrangement

The IC test board shall have a minimum of four layers It is recommended to use a four-layer

The IC test board, illustrated in figures 5 and 6, may include extra layers between the top layer and the microstrip ground layer to facilitate additional signal and power routing The construction of the IC test board must adhere to the specified guidelines.

IEC 61967-1, except as noted below in the case of n layers in general

1) Top layer (layer 1): The IC under test shall be put on layer 1 See IEC 61967-1

2) Layer next to the bottom layer (layer n−1): A ground plane area shall be formed on layer n−1 to provide a reference for the microstrip structures on the bottom layer The ground plane can cover the entire layer or can be limited to the area under the microstrip structures as shown in the dotted line area of figures 7 and 8 This ground plane area shall have a minimum width of 11 mm and a minimum length of 14 mm

3) Bottom layer (layer n): The microstrip conductor lines for measurement and peripheral ground planes shall be on layer n The microstrip conductor lines shall be in accordance with figures 7 and 8 for power lines and I/O lines, respectively The width of the strip conductor line shall be 1,0 mm at maximum to achieve a high spatial resolution See annex C for details The length of the microstrip conductor lines should be between 14 mm and 25 mm in length to avoid standing waves.

Layer thickness

It is strongly recommended to use a PCB insulator thickness of 0.6 mm between layer n−1 and layer n Additionally, the coplanar gap between the measurement line and the coplanar ground planes should be a minimum of 2.0 mm, which must be at least three times the thickness of the insulator.

Decoupling capacitors

Decoupling capacitors (C1, C2) are essential components that should be positioned between the power supply lines and ground planes on the test board, as illustrated in figure 11 To ensure low RF impedance, capacitor C2 must be located as close as possible to the measurement area of the power supply line, with a maximum distance of 25 mm from the via to the V DD land, as depicted in figure 7 Additionally, capacitor C1 should be installed between the IC V DD land and the IC ground, as shown in figure 9.

I/O pin loading

The RF current of a single I/O pin can be measured individually, following the layout specifications outlined in figures 8 and 9 Each pin must be connected to an impedance matching network with a resistance of 150 Ω, as depicted in figure 11 Additionally, the impedance matching network should be loaded with either a 50 Ω resistor (R3) or the 50 Ω input impedance of standard measurement equipment.

V DD and ground and signal

Insulator (Layer 1 to Layer 2) : 0,40 mm (Recommended)

Insulator (Layer 2 to Layer 3) : 0,40 mm (Recommended)

Insulator (Layer 3 to Layer 4) : 0,60mm (Strongly recommended)

Layer 2 -Power/signal Layer 3 -Power/ground/signal

Figure 5 – Standardized IC test board – Sectional view 1

Layer 3 -Power/ground/signal Layer 4

Figure 6 – Standardized IC test board – Sectional view 2 – Measurement line

Via to V DD land:0,8 mm diameter

Overlapped plane width between layer 3 and layer 4 ground planes: 3,0 mm min.

Via: 0,8 mm diameter Layer 3 (microstrip ground plane pattern)

Figure 7 – Power line pattern on the standardized IC test board – Bottom layer

I/O signal strip width: 0,3 mm Coplanar gap: 2,0 mm min.

Overlapped plane width between layer 3 and layer 4 ground planes:

Layer 3 (microstrip ground plane pattern)

Figure 8 – I/O signal line pattern on the standardized IC test board – Bottom layer

Power supply line pattern to V DD 1 (see figure 7)

Example of I/O signal line pattern

* The RF current probe defined in IEC 61967-4 may be used for measurement of ground current, or this pattern shall be short-circuited if not used.

Power supply line pattern to V DD 2 (see figure 7)

Figure 9 – Multi-power lines on the standardized IC test board – Bottom layer

Ground layer for microstrip (layer n–1)

Molded fixing block of magnetic probe

Space between the microstrip line and magnetic probe tip:

General

The general requirements for the test procedure are described in IEC 61967-1.

Test technique

The magnetic probe must be positioned at a specified height above the test line on the test board, as outlined in section 6.3 The output voltage (\$V_p\$) from the magnetic probe is recorded using a spectrum analyzer or measuring receiver, in accordance with IEC 61967-1 The magnetic field (\$H_{x\_dB}\$) is then calculated from the measured \$V_p\$ value, adjusted by the calibration factor (\$C_f\$) of the magnetic probe, following the equation provided in annex B (B.12).

RF current (I_dB) is then obtained using the following equation (B.13) with a transfer constant

(C h ) for a typical example of the test board as described in annex B:

I_dB = V p _dB + C f _dB – C h _dB (dB A) (B.13) where

V p _dB = V p value in dB (dB V);

C f _dB = C f value in dB (dB S/m);

C h _ dB = C h value in dB (dB 1/m)

The C h _dB value is influenced by the insulator thickness of the microstrip board, as illustrated in Figure 12 The optimal insulator thickness between layers n – 1 and n should range from 0.1 mm to 1.6 mm For a recommended thickness of h = 0.6 mm, the C h _dB value is 30 (dB 1/m) When using different insulator thicknesses, the RF current can be calculated using equation (B.13) with the corresponding C h _dB value, as depicted in Figure 12.

General

The test report shall be as described in IEC 61967-1

The test report shall contain all specific requirements.

Documentation

The measurement data and parameters shall be documented in the test report, which shall include the following information:

– test board material and its specification,

– thickness of insulator between layer n – 1 and layer n,

– microstrip line conductor width, coplanar gap, and characteristic impedance,

– decoupling capacitors (capacitance values, physical dimensions, number of pieces used, and locations placed)

The test report must include a detailed description of the IC test board, which should encompass the schematic, parts list, and a visual representation such as a picture or artwork copy Additionally, it is essential to incorporate the measured data of RF currents.

Data shall be presented as a matrix of the frequency and the corresponding measured amplitude data at each measurement point and/or as a plot of this matrix

A description of any data processing used shall be a part of the test report

Figure 12 – Transfer constant for current calculation as a function of insulator thickness of microstrip board

Probe calibration procedure – Microstrip line method

The calibration of the magnetic probe for measurement is essential and should follow the outlined procedure Utilizing the microstrip line method allows for calibration under normal operating conditions, enhancing accuracy As illustrated in figure A.2, the probe calibration occurs on a reference microstrip line on a PCB, using the same setup as standard IC emission measurements on a test board Precise placement of the probe is crucial to minimize measurement errors and ensure consistent emission results.

NOTE The microstrip line method is further described in [5] 4

Use a pre-amplifier as specified in IEC 61967-1, if necessary

For optimal performance, follow the manufacturer's guidelines for calibrating the spectrum analyzer Ensure the attenuation is set to a suitable level and adjust the video bandwidth to at least three times the resolution bandwidth to avoid signal video averaging.

Use a microstrip line structure shown in figure A.1 The insulator thickness (h) of the microstrip board used shall be 0,6 mm, and the characteristic impedance shall be 50 Ω ± 5 Ω

For a dielectric constant of ε r = 4.7, the strip conductor width (W) is set at 1.0 mm, while the ground plane width (W g) of the microstrip line must be a minimum of 50 mm Additionally, the microstrip line should be at least 101.6 mm long to ensure adequate high-frequency performance.

In order to check the characteristic impedance, RF measurement equipment such as a network analyzer or a TDR oscilloscope should be used

NOTE Power required to obtain a sufficient signal to noise (S/N) ratio may be determined in advance over frequency range of interest

Figure A.1 – Cross-sectional view of a microstrip line for calibration

4 Numbers in square brackets refer to the bibliography

To calibrate the test setup, first measure the gain or loss, ensuring to include the pre-amplifier if utilized Next, position the probe over the microstrip line with the loop plane perpendicular to the ground plane and aligned parallel to the microstrip's longitudinal axis The probe's center should be within ±0.4 mm of the microstrip line's center.

The probe's face angle must remain within a 5° deviation from the microstrip line axis, and the distance from the microstrip line surface to the probe tip should be kept within 1.0 mm ± 0.1 mm Adhering to these placement restrictions is crucial for achieving accurate calibration factors, with the maximum error estimated to be less than ±1.6 dB.

The sensitivity deviations of the probes specified in this document are considered to be within ±1.0 dB Additional details regarding the influence of placement factors can be found in annexes B, C, and D To conduct the calibration, connect a signal generator to one end of the microstrip line and a 50 Ω terminal to the other end, while linking the magnetic probe connector to a spectrum analyzer as illustrated in figure A.2 Next, establish a field excitation around the reference microstrip line using the signal generator at a specific frequency within the desired frequency band, and record the RF signal level induced in the probe with the spectrum analyzer This procedure should be repeated at various frequencies across the frequency range to gather data for plotting a calibration curve for the probe under test The calibration factor can be determined using equation (A.1).

C f_dB is the calibration factor for the magnetic field (dB S/m),

Y is the distance (m) between the strip conductor and the centre of the loop of the magnetic probe, h is the insulator thickness (m) of the microstrip board used for calibration,

V p_dB is the output voltage of the magnetic probe (dB V),

V s_dB is the output voltage of the signal generator (dB V)

Molded fixing block of magnetic probe

NOTE A transmission loss of the microstrip line should be half the overall loss when the magnetic probe is placed in the centre of the microstrip line

Figure A.2 – Measurement set-up for probe calibration

Measurement principle and calibration factor

It is well known that magnetic flux density (B) around current (I) which flows in an infinitely long straight conductor is given by the following equation (B.1): r

B is the magnetic flux density (T); μ0 is the permeability of vacuum;

I is the current (A); π is the circular constant (ratio of a circle's circumference to its diameter); r is the shortest distance between line current and observing point

The relationship between B and the magnetic field (H) can be defined by the following equation (B.2) Equation (B.2) holds when t

Tiêu đề	Measurement of electromagnetic emissions, 150 kHz to 1 GHz – Part 6: Measurement of conducted emissions – Magnetic probe method
Chuyên ngành	Electrical and Electronic Technologies
Thể loại	Standard
Năm xuất bản	2008
Thành phố	Geneva

Định dạng
Số trang	90
Dung lượng	1,59 MB