[time-nuts] FE-5680A internal signal waveforms (60, 30, 10 MHz)
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: https://picasaweb.google.com/109928236040342205185/FE5680A#5685304134718133138 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 (?) https://picasaweb.google.com/109928236040342205185/FE5680A#5685304143859526258 -John Beale ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] FE-5680A internal signal waveforms (60, 30, 10 MHz)
Was the probe grounded using a spring clip off the probe tip, hitting the nearest ground that is tied directly to the 9572? If not, the waveform captured is not the waveform present during operation. Also, using a 10pF probe on a 2ns risetime signal is quite a heavy load / impedance mismatch. I've used 100:1 low capacitance probes (Zin = 5000 Ohms, Cin = 2pF or less) to mitigate that problem at less cost than a good FET probe. I also suspect the filter impedance is not constant versus frequency, leading to additional distortion of the square wave. Bob LaJeunesse From: beale be...@bealecorner.com To: time-nuts@febo.com Sent: Mon, December 12, 2011 1:29:24 PM Subject: [time-nuts] FE-5680A internal signal waveforms (60, 30, 10 MHz) ... 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 (?) https://picasaweb.google.com/109928236040342205185/FE5680A#5685304143859526258 -John Beale ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] FE-5680A internal signal waveforms (60, 30, 10 MHz)
Hi If you are getting 11 V p-p, I'd bet you don't have the 10 MHz output terminated in 50 ohms. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of beale Sent: Monday, December 12, 2011 1:29 PM To: time-nuts@febo.com Subject: [time-nuts] FE-5680A internal signal waveforms (60, 30, 10 MHz) 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: https://picasaweb.google.com/109928236040342205185/FE5680A#56853041347181331 38 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 (?) https://picasaweb.google.com/109928236040342205185/FE5680A#56853041438595262 58 -John Beale ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
