Arthur Pini

's profile
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Consultant

I am a technical support specialist and electrical engineer with over 50 years experience in the electronics test and measurement industry. I have supported oscilloscopes, real-time spectrum analyzers, frequency synthesizers, digitizers and arbitrary waveform generators for leading manufacturers.


Arthur Pini

's contributions
  • 12.10.2015
  • Measure frequency response on an oscilloscope
  • Hi Jim, I used to work for Nicolet Scientific back in the 70's and early 80's. They designed and manufactured real time spectrum analyzers, the precursors to the SR780. Stanford Research does a good job getting the cost out of instruments. After that I went on the scopes, arbitrary waveform generators and digitizers. Art
  • 12.10.2015
  • Measure frequency response on an oscilloscope
  • Hi Jim, Welcome to the world of digital signal processing! The FFT is constrained to have a maximum span of one half the sample (Nyquist limit) and a resolution bandwidth of the reciprocal of the signal duration. Since most scope's have fixed duration time base steps you do have less flexibility in setting the maximum span. Some of the more current scope offer a Spectrum Analyzer mode which allows you to set center frequency and span and they set the sample rate and signal duration to come as close as possible to the desired values. Of course, some digital scopes actually have a built in spectrum analyzer. If you want to measure frequency response with a scope set the sampling rate to a higher value so that the Nyquist span is above the bandwidth of the device being measured. You can still measure the frequency response even if there is some extra spectrum being displayed. You have some nice toys in your garage labs! Have a happy Holiday Art
  • 05.31.2015
  • Correlation: An overlooked oscilloscope measurement
  • Hello Rick, ACSN stands for autocorrelation signal to noise, it is a magnetic storage related measurement but can be used elsewhere. As the name implies it measures signal to noise ratio. If you look at the correlation function in the first paragraph you can see it involves the product of a function with itself (auto-correlation) or another waveform (cross-correlation). The resultant quantities, after the indicated average, are mean squared values so the units are those of power. Hence, the logarithmic ratio is one of power and the multiplicative factor should be 10 and not 20 as we are comparing power ratios. Art
  • 05.05.2015
  • Signal processing boosts digitizer performance
  • Hello Sean, Thanks for your comment. As you point out there are many possible algorithms for computing a moving average. Each has its own advantage. The user has the option of using whichever suits his needs but they may need to write the code to implement it themselves. The point of the article is that this processing function is available to improve the measurement result..
  • 05.05.2015
  • Signal processing boosts digitizer performance
  • Hi Martin, Moving averages can be done in both ways. When used in financial analysis the second method you suggested (x-4, x-3, x-2, x-1, x.) is used. This produces a relative shift between the input and output signals. In scientific and engineering analysis the former, symmetrical form, ( x-2,x-1, x, x+1, x-2) is used. The symmetry keeps the input and average values 'in phase'. Spectrum's SBench 6 software, used in this example specifically defines the algorithm as being symmetrical: " Moving Average The moving average (smooth) function takes a an average around the current sample of the sample itself and a defined number of neighbor samples. As a result random noise is reduced: The „Window Width“ parameter define how many samples around the current sample are used for averaging. A value of 5 for example will result in the following average function: new_sample[x] = (sample[x-2] + samples[x-1] + sample[x] + samples[x+1] + sample[x+2]) / 5"
  • 04.09.2015
  • Limit the range of a waveform measurement
  • Hello Hithesh, Read operations, like those that appear in the left most burst in figure 2, are either 0 or 180 degrees relative to the strobe signal. So a read operation is occurring at the beginning (left side) of the trace. Write operations occur with a fixed delay between data an strobe. In figure 2 that delay is about 770 ps. The right side of the z2/z3 traces show a write operation. Art
  • 02.12.2015
  • Annotate oscilloscope displays for better documentation
  • Hi Steve, There is a trade off between font size and waveform visibility. On the oscilloscope the screen is 10 to 15 inches diagonally bur when you paste it into a word document in portrait mode it is only about five inches so you do lose resolution. Martin's suggestion helps but it does take up a lot of space having images in landscape mode. When writing, I generally transfer the important information from the image into the text. Art