Hi In the modern version of the 5680 the VCXO is at exactly 60 MHz. The PLD has a fixed divide by 6 to generate the 10 MHz output. There's no dithering or DDS stuff between the VCXO and the output. All of the DDS stuff is in the loop that drives the gas cell. The DDS is an Analog Devices part.
Hope that helps. Bob -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Chris Albertson Sent: Wednesday, November 16, 2011 1:26 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] FE 5680A "new version" - Filtering the 10 MHz On Tue, Nov 15, 2011 at 10:22 PM, Sylvain Munaut <[email protected]> wrote: > But a DDS would require a DAC somewhere. Here, I see can see the trace > from the PLD pin, to the LC filter to the RF connector ... and I > probed the PLD output, it's a square wave. I don't know how this device works, an someone posted that how it works dedends on which version of the device you have. But many times they will use pulse width modulation rather then a DAC. Basically you output a square wave but you vary the duty cycle and then after filtering you have analog. call it a combination of a one bit DAC and dithering if you like. This is also how "class D" audio amps work. They use a one bit DAC and a filter. Sounds crude but it can work well and sound good. Again I don't know how this device works, but do want to point out that a "square" wave can in fact be the analog output (after filtering) Chris Albertson Redondo Beach, California _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
