Download ESDEMC_TN003 ESD Simulator Calibration Method for IEC61000-4-2 & ISO10605 (PDF)

1. Calibration Objective

The objective of this report is to present calibration parameters required for ESD simulators, verify their performance, and compare the results to the requirements of the IEC 61000-4-2 or ISO10605 standard.

2. Requirements and Equipment

2.1 Tip voltage Verification

Both IEC61000-4-2:2008 and ISO10605:2008 specify that the tip voltage or the HV source of an ESD simulator must be verified with a high voltage meter or electrostatic voltmeter.

Table 1 Simulator tip/HV source voltage tolerance.
When using a contact high voltage meter (>100 G Ohm input impedance) for calibration, the HV source will need to continuously charge the tip to maintain the voltage level, otherwise the meter will discharge the tip and the voltage reading will decrease gradually. ES105-100 High-Impedance High-voltage Meter from ESDEMC satisfies the requirements for HV calibration (>100 G Ohm input impedance and measures up to 100 kV with less than 2% tolerance).

Because the ESD simulator tip is sharp and small, the capacitive coupling between the tip and a non-contact electrostatic meter is weak, and therefore <± 5% accuracy may not be achievable. Further, most precision non-contact electrometers do not measure to ±25 kV. This would require a coupling factor for calibration between the discharge tip and the sensor of the non-contact electrometer. ES102 Vibrating Capacitance Electrometer from ESDEMC satisfies the requirements for the HV calibration (non-contact measurement with self-calibration up to 1 kV). With the coupling factor integrated with the externally calibrated HV source a measurement range of 200 V to 200 kV with less than 2% tolerance is obtained.

2.2 Contact discharge mode current verification

Both IEC61000-4-2:2008 and ISO10605:2008 standards specify that the ESD contact mode discharge current waveform meet the requirements listed in Table 2.

Table 2 Contact mode discharge current waveform parameters.
ES613 ESD Simulator from ESDEMC satisfies the requirements for both IEC61000-4-2:2008 and ISO10605:2008 (ES613-20 up to ±20 or ES613-30 up ±30 kV).

A4001 ESD Current Target from ESDEMC satisfies the requirements for both IEC61000-4-2:2008 and ISO10605:2008 (up to ± 30 kV).

A4002 ESD Current Target Adapter Line from ESDEMC satisfies the requirements for both IEC61000-4-2:2008 and ISO10605:2008 to calibrate the frequency response of both ESD target and adapter line.

3. Test Setup:

The ESD current target should be mounted in the center of a 60” x 60” (1.2 m x 1.2 m) or larger vertical calibration plane. The plane can be one wall of a Faraday cage. The target is mounted to a 40 mm diameter hole centered in the plane and fastened by 8 screws and lock-washers. An oscilloscope, attenuators, and cabling are located inside the enclosure, or on the other side of the plane from the ESD simulator. Figure 1 illustrates a possible setup.

Connect the attenuator directly to the ESD target output. If it is expected that the output voltage will exceed the oscilloscope input voltage rating additional attenuation may be used. Please refer to the Attenuation Calculation section below for details on selecting proper attenuation. Connect the ESD ground return cable to the target plane according to the standard. A simplified block diagram is shown in Figure

Attenuation Calculation

In the diagram above, a 20 dB attenuator is used in the measurement of an ESD discharge event, and an oscilloscope is represented as a 50 Ohm load. Because of the 20 dB attenuator the voltage seen at the input of the oscilloscope is 1/10 of the voltage incident at the target, or
V2= V1/10.
Because the attenuator is terminated in 50 Ohm, the input impedance seen at port 1 is 2.08//50 Ohm = 2.00 Ohm, meaning
V1 = Iesd ×2.00 Ohm
Where, IESD is the current into port 1 during a discharge event. The 2.08 Ohm resistor is the specification for an ESDEMC factory calibrated A4001 Target. This may be different for other manufacture’s targets. The ratio between ESD current and voltage present at the oscilloscope is then
Iesd / V2 = 5:1
This ratio is useful for determining how much attenuation is required for oscilloscope safe measurements because the currents for different high voltage set points are known. For example, during an 8 kV ESD test a discharge current, IESD, is expected to have a 30 A peak, corresponding to a peak voltage at the oscilloscope of 6 V. Additional attenuation should be added at the beginning of any new measurement setup to ensure safety of equipment until confidence in the setup is established.
An ESD Source Voltage versus Recommended Target Attenuator Size table is calculated below for reference. It is based on a 50 Ohm 5 Vrms real time oscilloscope measurement (a measurement range of 8 V with 1 V/div). The green zone is a safe operating area, and the numbers therein are the peak voltages seen at the oscilloscope. The yellow zone is a boarder-line area and should probably be avoided because when considering the ±15% peak current tolerance margin from standard, it might not be enough. A GHz high speed Oscilloscope has max voltage reading of 8V or 10 V at maximum scale:

Table 3 ESD Source voltage and Recommended Target Attenuation Setups.
Expected Waveform (for IEC standard)

The expected 4kV IEC 61000-4-2 standard waveform is shown in Figure 4.

Measurement 8kV IEC Result

Table 4 IEC 61000-4-2 contact discharge current waveform parameters.

4. FAQ Section

4.1 How do oscilloscope bandwidth / sampling rate affect calibration?

Some ESD events have been measured with a rise time <100 ps and the actual ESD waveform may be even faster. The bandwidth needed to resolve such a fast rise time is approximately 0.35/rt, or 3.5 GHz for a 100 ps rise time. Without enough bandwidth or sampling rate, the rise time will be down sampled and not adequately captured. A simplified comparison of the same rise time with not enough and enough sampling rate, respectively, is shown below,

In addition, the oscilloscope bandwidth / sampling rate could affect the measured first peak value as the first peak contains high frequency components. Even a waveform measured with the same oscilloscope with different sampling rates will show different results. This could lead to an ESD simulator appearing to have passed the standard with a slower sampling rate, but actually failing with a higher sampling rate. An example of this is shown below,

4.2 When buying an ESD Target, can I buy only the ESD target and use the cable and attenuators already in house for the calibration?

The standards require the ESD Target-Attenuator-Cable Chain (up to the connection to the oscilloscope) and the oscilloscope to be calibrated before the ESD simulator calibration test. If the ESD target is calibrated without the attenuator and cable, the ESD Target will have to be recalibrated with the new cable and attenuator. Or one should characterize the effects of their own cables and attenuators to compensate for them mathematically.
For cable selection, the standard requires the test cable to be well shielded and low loss. A RG400 cable no more than 1 meter long is preferred by the standard. RG 214 is 1/2 the loss and is commonly available, but may not be available with SMA connectors. Most high speed oscilloscopes use SMA or improved BNC connectors.
For attenuator selection, the frequency response needs to be flat up to 4 GHz to make the overall transfer impedance of Target-Attenuator-Cable Chain flat according to test standard. Also the attenuator needs to be able to handle a relatively large peak power rating.

4.3 How do the other setup parameters affect the waveform?

Table 5 Parameters and their influence