[time-nuts] FE-5680A internal signal waveforms (60, 30, 10 MHz)

beale beale at bealecorner.com
Mon Dec 12 13:29:24 EST 2011

I have two of the FE-5680A (FEI P/N 217400-30352-1) Rb references, and I'm looking at the signals on digital side of the PCB inside, in particular the Xilinx CPLD, that is the XC9572XL in a 64-pin package.  Here is a photo with the signals marked:

pin 64 has a nice looking 60.00 MHz sine wave, I gather this is the input signal to the CPLD.
pin 22 has a 30 MHz square wave, although it has some ripples (see scope trace in same Picasa album)
pin 49 has a 10 MHz "square" wave but with a very odd shape. 

Pin 49 is the signal which is LC filtered (?) to become the 10 MHz sine wave out on the internal J8 mini-connector, and the external DB9.  The signal is about 3.3 Vpp, but becomes an 11 Vpp sine wave at the far side of a blue part (inductor?) marked 2R2J.

The 10 MHz sine out on my unit has some noticeable amplitude noise, at least a few %. Since I'm only using the signal as a digital clock, I prefer a square wave, assuming the fast edge will give me lower jitter. A 200 MHz Rigol scope reads a risetime of 2 ns on CPLD pin 49, but the waveform looks so noisy and odd (see below), maybe I would be better off just squaring up the output sine.  ...maybe if pin 49 was disconnected from the sine output filter, it would be more square (?)


-John Beale

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