[time-nuts] Surface Mount OCXO Questions

[Robert LaJeunesse]

A couple tricks I've learned along the way: 1) If using a switching supply is required to get a higher voltage, follow it with a good LDO to reduce the noise level. I've done this successfully for powering handheld radio microphones with built-in amplification, video amplifiers, and for operating a GPS receiver and antenna. 2) If there is a possible ground current path problem, break the ground path by using a unity gain "difference" amplifier like the AD8276, or a difference amplifier with gain like the INA145. The input is differential to the source signal, and the output has a moderately high impedance reference terminal that can be tied directly to the load device ground pin. I use this technique all the time to keep down the noise when driving remote analog loads that have large ground currents themselves. (Picture a 110W 40MHz transmitter running off 12V, at the bottom of a stack of other transceivers in the trunk of a police car - with 40A of
 lights flashing, etc.) 

Bob LaJeunesse


>________________________________
> From: "John C. Westmoreland, P.E." <john at westmorelandengineering.com>
>To: Discussion of precise time and frequency measurement <time-nuts at febo.com> 
>Sent: Wednesday, October 30, 2013 10:54 PM
>Subject: Re: [time-nuts] Surface Mount OCXO Questions
> 
>
>Graham,
>
>Good points - yes, I have this part currently in the design: TPS75833KTTT
>(LDO from TI) - putting another one down
>(just) for the OCXO isn't a problem.
>
>And a nice 12V rail isn't a problem either since this is for a radio with a
>nice 12V source.  Could I boost the 3.3V rail to
>12V or maybe 5V to 12V - sure - but your point about the switcher is well
>taken and I agree.  Having a nice, fat, analog
>ground plane isn't a problem either.
>
>And, this is just a 'dev' board so we can do what we need to make the OCXO
>work as good as possible.
>
>From their spec sheet:  '... the supply voltage sensitivity and load
>sensitivity is 5E-11 for a 5 % change in voltage or
>load impedance.'
>
>Thanks,
>John
>
>
>
>