[time-nuts] IFCS 2020 tutorial - low noise electronics for time/frequency metrology

[Bruce Griffiths]

Attila

Another example somewhat similar to the DMTD is the Receiver in a laser DMI (Distance Measuring Interferometer). A photomixer the typical implementation consists of a photomixer (eg photodiode connected between gate and drain of NJFET source follower with boostrapped drain) + linear preamp + manually adjustable gain differential amplifier (eg MC1590) + differential line receiver.
The performance of this signal chain could likely be improved somewhat.
The distance moved is equal to the integral of the change in beat frequency between a pair of orthogonally polarised laser modes. A reference channel with stationary parts provides the frequency difference signal between the 2 modes as produced by the laser. The beat frequency is typically a few MHz (eg ~ 2MHz). Input signal levels at the photomixer are typically a few tens of microwatts (eg 50 uW) or so.

The small signal gain of the BJT differential pair you show is actually 2R/[2*(kT/(e*(I/2)))]  =IR/(2kT/e).

Bruce
> On 08 July 2020 at 14:25 Attila Kinali <attila at kinali.ch> wrote:
> 
> 
> Moin,
> 
> As some of you know, I have been allowed to give a tutorial on low noise electronics
> for this year's IFCS. As the whole conference has been turned into a virtual one,
> we were asked to record our tutorials and upload them. Additonally to the conference
> I decided to put my tutorial online for everyone to watch. You can find it at
> http://time.kinali.ch/ifcs_2020_tutorial/
> Though, I have to honestly admit, I am not proud of it. There is too much that
> I couldn't fit what should be in there, in in the 75' we were given. And there is
> quite a few things that I think I made too confusing. Nevertheless I hope it can
> be of use for some. Please let me know what you think, especially if you have ideas
> how I could improve the tutorial for the next time I'm giving it.
> 
> 
> 				Attila Kinali
> 
> PS: As this years IFCS is fully virtual, the registration is still open and the
> rates are IMHO quite reasonable: https://ifcs-isaf2020.org/registration
> If it's still too much, you can pretend you are a student. Nobody is checking
> this anyways.
> 
> -- 
> Science is made up of so many things that appear obvious 
> after they are explained. -- Pardot Kynes
> 
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