Oscilloscope measurement methods above 6GHz

An oscilloscope should be measured every year or every 2,000 hours of use to ensure that the oscilloscope's indicators meet the specifications and that the oscilloscope can be used as a standard to measure and inspect the electronic equipment under test. The

most commonly used tool for measuring oscilloscopes is the 9500B oscilloscope meter, but because the highest frequency of the 9500B is only 6.4 GHz, it can only measure oscilloscopes of 6 GHz and below. However, the bandwidth of oscilloscopes has now exceeded 30 GHz, and the latest 90000-Q series oscilloscopes have a bandwidth of 63 GHz. Oscilloscopes with 13 GHz and 20 GHz bandwidths are already widely used. We need new measuring instruments and methods to measure oscilloscopes with bandwidths above 6 GHz.

Oscilloscopes with bandwidths above 6 GHz mainly measure the following indicators:

• Analog Bandwidth (Maximum Frequency)
• Rise Time Measurement
• Offset Accuracy
• DC Gain Accuracy
• Time Scale Accuracy

1. Measurement of analog bandwidth
 The instruments and accessories for measuring the analog bandwidth of an oscilloscope are listed below:

• Microwave signal source: E8257D
• Power meter and power sensor: N1913A+E4413B
• Power divider: 11667B or 11667C
• Coaxial cable: 8120-4948 (SMA-SMA) or N5180-60204 (2.4mm-2.4mm) + 11901A/11901C (2.4mm-3.5mm)

  The metering connection diagram is shown below:
The function of the power meter is to measure the true power (as a standard value) and compare it with the power measured by the oscilloscope itself to determine whether the nominal bandwidth of the oscilloscope meets the -3dB bandwidth requirement.
During the test, different vertical sensitivities need to be tested separately, from 5mv/div to 1v/div. Each channel must also be tested single-ended. The power reading of the oscilloscope uses Vrms for automatic parameter measurement. During the test, it is necessary to first test a reference gain (tested with a 50MHz sine wave), and then test a gain at the bandwidth frequency. Each gain is judged using -3dB. The test results are recorded in the table below.
Vin is the result of the test using the power meter. The power test value of the power meter must be converted into a Vrms value. The conversion formula is:
Vout is the result of the automatic measurement test using the oscilloscope Vrms. 2. Rise time measurement The instruments and accessories for measuring the rise time of the oscilloscope are listed below:

• 7ps fast edge generator: N2806A
• Attenuator: 8493C/8490D

When measuring, directly connect the N2806A measuring pulse generator to the oscilloscope, and use the oscilloscope to measure the rise time to determine whether it meets the specification requirements. For different vertical sensitivities, you can use an attenuator to attenuate before measuring. 3. Measuring the offset accuracy The instruments and accessories for measuring the offset accuracy of the oscilloscope are listed below:

• Digital multimeter: 3458A or 34410A
• BNC coaxial cable: 8120-1840 (2 pieces)
• Adapter: 1250-0781 (BNC Tee (m) (f) (f)), 1251-2277 (BNC (f) to dual banana)

The metering connection diagram is shown below:
In the figure, the AUX OUT output of the oscilloscope is connected to the BNC tee, one end of the tee is connected to the oscilloscope channel 1, and the other end of the tee is connected to the digital multimeter. [page]
In the oscilloscope, set the AUX OUT output DC voltage, use the oscilloscope and multimeter to measure respectively, and then calculate the offset accuracy.
When testing with the oscilloscope, average 256 times, and then use Vavg to test the average voltage.
Before testing, also test the 0 voltage level error separately.
When testing, first set AUX OUT to +400mv, -400mv, 0mv respectively, and use the oscilloscope and multimeter to test the results respectively. Use the following formula to calculate the result, and take the larger of the two formula calculation results as the test result.
Then set it to other values ​​and perform measurements respectively. The measurement results are recorded and calculated as shown in the following table.


4. Measurement of DC gain accuracy
The instruments and accessories for measuring the DC gain accuracy of an oscilloscope are listed below:

• Digital multimeter: 3458A or 34410A
• BNC coaxial cable: 8120-1840 (2 pieces)
• Adapter: 1250-0781 (BNC Tee (m) (f) (f)), 1251-2277 (BNC (f) to dual banana)

The metering connection diagram is consistent with the connection diagram for paranoid accuracy.
The oscilloscope test parameters and AUX OUT settings during the test are also similar and are not listed here.
The calculation formula is listed below.
The measurement results are recorded and calculated as follows:

5. Measurement of time scale/time base accuracy
The instruments and accessories for measuring the time scale/time base accuracy of oscilloscopes are listed below:
The metering connection diagram is shown below:
Configure the microwave generator to output an OdBm sine wave, frequency: 10.00002000MHz.
Set the oscilloscope: 100mV/div sensitivity, 100KSa/s sampling rate, 20ms/div time base, 0V measurement threshold, 20mv hysteresis.
Perform: Frequency measurement on channel 1 of the oscilloscope.
Accumulate 10 captures.
Convert the average frequency value to the time base error: subtract 20Hz, divide by 10Hz/ppm.
Calculate the test limits: Test Limits=+-(0.100+0.100xYears Since Calibration) (for 90000-X oscilloscopes)
The measurement results are recorded and calculated as follows: