Frequently Asked Questions
Questions Related to Specific Gage Products
Q.
I have an imaging application in which I would like to use my own clock signal to digitize the analog signal from the camera using CompuScope 1602 in order to obtain 16 bit resolution.
I have read in the hardware manual that this digitizer card uses "on-chip decimation". How does this affect me?
A. CompuScope 1602 uses an on-chip decimation filter to provide true 16 bit resolution .
Unlike some products on the market that claim "variable resolution" by playing mathematical games after the acquisition has already been done, CompuScope 1602 generates 16 bit digital codes straight from the ADC chip.
The decimation filter operates over multiple clock cycles to generate a single digitized sample code. The number of clock cycles it takes to generate one sample point is also called the Decimation Factor.
When you are supplying an external clock, you must take these decimation factors into account and provide a clock signal that is faster than the desired sampling clock frequency by this factor.
For example, if the desired clock frequency is 1 MS/s, you must supply an 8 MHz clock signal (decimation factor of 8).
On the other hand, if the desired clock frequency is 9 MS/s, you must supply an 18 MHz external clock (decimation factor of 2).
The following table shows the effect decimation factors have one the required external clock frequency:
Desired Decimation Required
Sample Rate Factor Ext. Clock
5+ MS/s to 10 MS/s 2 2*Sample Rate
2.5+ MS/s to 5 MS/s 4 4*Sample Rate
Lower than or equal to
2.5 MS/s 8 8*Sample Rate
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