# High-precision timer (1 Viewer)

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#### Scott Nelson

Hi,

I am designing a board-level circuit to measure pulse width, in which I need a high-precision timer. I want to use a high-speed counter to implement the timer. Since the timer requires an accuracy of 500ps, this implies that the clock to the counter has to run at a frequency of 2GHz. Since I am not designing chip-level circuit, I would like to purchase such an external timer/counter which achieves such precision. Does Anyone have an idea what to buy? If such high precision timer is not easily available in the market, is there anyway I can solve the problem through other means?

Thanks!

#### Bob S

What is the range of pulse widths you need to measure, and do you require 500 ps resolution, or 500 ps accuracy? I have used simple transistor circuits to convert a pulse width to an analog voltage on a capacitor, which can be digitized by an ADC. The analog output voltage signal can be calibrated using pulse width standards.

Bob S

#### Scott Nelson

Thanks for the input! But What I need to measure is the width of arbitrary signal. Moreover, I also need to measure the signal transition time. How can a frequecy divider be useful in this scenario?

You can use a frequency divider (prescaler) to knock down the frequency of your signal to more manageable levels.

Here is simple divide by 128 or 256 chip:

http://cgi.ebay.com/MB506-FUJITSU-8-Pin-DIP-MB-506-FREQUENCY-PRESCALER-/370284928318?pt=LH_DefaultDomain_0&hash=item5636b39d3e

#### Scott Nelson

Thanks! the spec requires that the resolution to be 500ps, but does not specify the range of pulse widths. Moreover, I also need to measure the transition time of a digital signal (not pulse). I plan to input the signal to two comparators with pre-set start and stop thresholds to trigger and stop the counter. BTW, for the case of pulse, the shape is arbitary, which might mean converting pulse width to volatge not working.

What is the range of pulse widths you need to measure, and do you require 500 ps resolution, or 500 ps accuracy? I have used simple transistor circuits to convert a pulse width to an analog voltage on a capacitor, which can be digitized by an ADC. The analog output voltage signal can be calibrated using pulse width standards.

Bob S

#### Bob S

I still don't fully understand your application; e.g., resolution vs. accuracy requirement, etc.

This TAC (Time-to-Amplitude Converter, see Fig. 1) provides the general concept of storing pulse width information as a charge on a capacitor (C101, 330 pF). This circuit can provide resolution much better than 500 ps. Even though I have specific reservations about the design, the concept is correct.

http://www.ko4bb.com/~bruce/TAC.html

Bob S

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