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Accurately measure True RMS of signals up to 300KHz, even with JTAG tools!

Even in an ever increasing digital world, functional testers will always be required to measure analogue voltages and currents. Often these measurements are simply DC, and easily measured, but AC signals also need measurement in many applications, especially when audio is involved (e.g. set-top box, voice systems, etc).
​The industry standard way to measure these signals is with a True RMS type measurement, but why?

Well the answer is quite simple. It is because RMS is the only AC voltage reading that does not depend on the shape of the signal being measured. For example, some test engineers will simply average a waveform, to ground, and then measure the result with a DC measurement system… yes, easy… but consider:
  • A 2Vpp symmetrical signal going from -1V to +1V will average to zero… not very good for testing if a circuit is working
  • A 2Vpp sine* wave going from 0V to +2V will average to 1V, but so will a square* wave and so will a triangular* wave.

*50% Symmetrical

These are extremely simple examples, but you can read more about why RMS measurement is really the only true way to measure AC signals by searching the web.

With the J-Testr, measuring True RMS AC signals is easily achieved using the compact, 4cmx3.5cm, four channel “AC Measurement Module” which has 4 multiplexed AC inputs, two channel selection lines, a DC analogue output and a digital frequency output. The selection lines and output signals simply connect back to the standard high accuracy ADC/DAC peripheral card such as to enable RMS and frequency measurements for 4 signals. 


The module is supplied with everything needed to easily and quickly mount onto the customer’s interposer card. Please see the module instructions for more information by clicking here.

The really unique feature of the module is that, as all J-Testr peripherals can be accessed via JTAG*, accurate AC measurements can be made directly from JTAG tools when/if required. This further helps manufactures to leverage more value from their ‘high value’ JTAG tools, and helps extend test coverage without moving away from their preferred JTAG tools.

For more information about J-Testr, please contact us.