10-GHz Divide-By-100 Prescaler Connects to 100-MHz Counter


Ryder, W. (2008). 10-GHz Divide-By-100 Prescaler Connects To 100-MHz Counter. Electronic Design, 56(23), 58.


The prescaler described here connects to the front end of a 100-MHz frequency counter to extend its coverage range to 10 GHz. The circuit is a far less expensive way to measure frequencies above 100 MHz than buying a 1- or 10-GHz frequency counter. The divider was built inexpensively. Creating this low-cost prescaler required some tradeoffs, and some rules were not followed (discussed later in the article).

When you use this or any similar prescaler, the two least significant digits will be lost. If the frequency being measured is 9,123,456,789 Hz, the frequency will be displayed as 9,123,456,7XX Hz. Having the last two digits not shown shouldn’t be a problem, considering the frequencies being measured.

A second source of error is the frequency counter itself. The counter should be tested for accuracy. You can do this by connecting the output of a 100-MHz signal generator to the counter and counting for one or 10 seconds. Also, the counter time-base oscillator should be calibrated using WWV or a similar source.

Read more from SRI