Frequently Asked Questions
General Questions
Q. For an upcoming manufacturing test application, I will need to verify the width of an 11 nanosecond pulse in one of the tests and measure a 50 dB difference in between two signals at 44 MHz and 34 MHz.
Since I will need a 1 ns time resolution on the pulse, I need a 1 GS/s acquisition card. Do I need a separate card for the dynamic range measurement?
A. You are correct in assuming that you will need a 1 GS/s acquisition card for the pulse measurement. You should buy the CompuScope 82G.
Since your acquisition memory requirement seems to be pretty low, you should buy the version with the lowest on-board memory (2M) and save some money.
For the dynamic range measurement, you have two choices:
First, you can use a 14 bit, 100 MS/s acquisition card, such as a CompuScope 14100. Its 63 dB SNR and 65 dB SFDR will ensure good measurement at 34 and 44 MHz.
Second, you can use the same CompuScope 82G and over-sample the signal. Over-sampling is a technique employed by many oscilloscopes to give you more "resolution".
For example, you could still sample the signal at 1 GS/s, but average 8 adjacent points to yield one "high resolution" point. This resulting record will have an effective sampling rate of (1 GS/s div 8) = 128 MS/s and a theoretical resolution of 11 bits, resulting in a theoretical dynamic range of 66 dB.
In reality, the dynamic range will be closer to 58 dB, still good enough for your application.
In fact, what this technique does is to average a specific number of adjacent points in the record, thereby canceling any high frequency random noise. Hence the increase in Signal to Noise Ratio (SNR) and Spurious Free Dynamic Range (SFDR).
It must be noted that any non-random noise will not be canceled using this approach.
The main advantage of this approach is that you do not have to buy an extra CompuScope card, shaving a few thousand dollars off your capital cost.
The main disadvantage of this approach is that you need CPU processing time to calculate the "high resolution" data.
Another disadvantage is that there is an upper limit to the dynamic range that the 8 bit digitizer chipset can provide without introducing data anomalies. For CompuScope 82G, this limit is approximately 60 dB.
back
print this
email this
