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Most instrument show stationary RMS, maximum, minimum, average, or other value of the measured quantity that is observed over a certain time. Development and verification process requires observation of signal waveforms, i.e., the information how the signal changes over time. In that case oscilloscopes are usually used. The oscilloscopes were mostly analogue devices in the past but nowadays most of them are digital since the digital electronic became very inexpensive and digital oscilloscopes can provide many additional and useful features like automatic measuring of different parameters, signal analysis, data storing, comparing of signals, etc.

Main parameter that divides oscilloscopes is bandwidth; oscilloscopes with higher bandwidth allows observation of signals having faster rise/fall times. Nowadays the bandwidth of the oscilloscopes could range from below 1 MHz and could significantly exceed 10 GHz. Similarly, as voltmeters, oscilloscopes have high input impedance, typically 1 MΩ. On the other hand, high input impedance is not appropriate for oscilloscopes having very high bandwidth therefore 50 Ω impedance is used for measurements beyond 100 MHz. In some cases, also other input impedances like 75 Ω became available on modern oscilloscopes.

Other equipment related to oscilloscope measurements:

  • Oscilloscopes are usually calibrated with a special oscilloscope calibrator that can produce special and accurate signals in terms of voltage and time.
  • Sometimes users want to measure different signals that could not be observed solely with the oscilloscope, e., voltages exceed maximal input voltage of the oscilloscope, signal must be observed in differential mode without using the ground, current instead of voltage is parameter of interest. In these cases, general probes, high-voltage probes, differential probes, and current probes could be used.
  • The signal of interest is sometimes digital instead of analogue. In this case the users want simultaneous observation of several different signals (8, 16, 32, 64 and more) at very high clock frequencies. On the other hand, accurate information about the voltage is not needed but just the information if the signal detects logical 0 or 1. Those instruments are called logical analyzers.
  • Sometimes users need to analyze the signal thoroughly using a PC and in this case the digitizers (i.e., analogue-to-digital converters, ADC) are used to sample waveforms and store the data to computer. Digitizers could be roughly divided according to sampling frequency (bandwidth) and number of bits (accuracy).

At SIQ we can perform accredited calibration of all instruments described above. Typical parameters that are calibrated are gathered below.

Calibration of test equipment at SIQ


For low-frequency oscilloscopes (bandwidth less than 500 MHz) we typically calibrate:

  • vertical gain accuracy at 50 Ω and 1 MΩ
  • time-base accuracy
  • rise time
  • frequency response

For oscilloscopes with higher bandwidth, we additionally calibrate:

  • DC input resistance
  • null offset
  • offset setting
  • RMS noise level
  • input reflection coefficient (VSWR)


We can calibrate different types of probes (general probes, differential probes, high voltage probes and current probes). Calibrated parameters for each probe are given in brackets:

  • general probes (DC gain accuracy, frequency response, rise time)
  • differential probes (DC gain accuracy, frequency response, rise time)
  • current probes (AC and DC current accuracy, transfer impedance )
  • high-voltage probes (AC and DC voltage accuracy, input resistance, frequency response, rise time)

The bandwidth and rise time of a probe are measured with oscilloscope. We recommend using customer’s oscilloscope since the probes are typically used in that way. However, the bandwidth of the oscilloscope should exceed the bandwidth of the probe otherwise the performance of oscilloscope limits the performance of the probe.

Logical analyzers

Calibration of logical analyzers are usually performed according to manufacturer’s performance tests. Generally, the accuracy of the logic levels threshold and timing is calibrated.


Digitizers are calibrated according to manufacturer’s performance test, customers’ requirements or using different guides. Generally, voltage accuracy and timing are calibrated.

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  • SIQ Ljubljana