Simple Frequency Reference

       I needed a quick 10MHz frequency reference for doing simple measurements. My Agilent 33120A uses a 40MHz 100PPM crystal oscillator so there were times where I needed something with a little better stability.

       A rubidium reference standard or GPS disciplined oscillator would be ideal but is bulky and probably overkill. But that will be a project for next time.

       This project uses a 10MHz crystal oscillator from Abracon which has about 0.5PPM frequency tolerance and about 1.5PPM drift on the entire operating temperature range. Better crystals are available but I just used what I had on hand. Added a buffer using a HEX schmitt inverter, onboard regulator and a BNC jack and it's all set.

       Input supply is 7-16V, Current consumption is about 20mA unloaded, 40mA into a 50 Ohm load, Output voltage is about 5Vp-p into Hi-Z, 2.5Vp-p into a 50 Ohm load.

Circuit schematic diagram.

Waveforms. Yellow: oscillator output, blue: 33120A output set to square wave.

Circuit is simple enough that I decided to just build it on perf board.

I didn't have a 50Ohm terminator so I had to improvise.

Bench setup. The internal clock of the 33120A is a little slow (but still within the 100PPM spec)
so I had to set it a little higher for it to sync with the oscillator waveform.

The reason I put the oscillator on a socket: So I could change it if I needed a different frequency.
I connected pin11 of the socket to VDD for the square oscillators to work plugging it on the lower half of the socket.

Page created and copyright R.Quan © 31 Jan 2014.