[time-nuts] minimalist sine to square

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sat Jan 20 21:43:34 EST 2018


An npn emitter follower with collector connected to the 10V supply will produce a 4.2V swing in a 50 ohm load.

However it only works well if reflections from the load are small.

Otherwise, assuming that you want a 0-5V signal at the 50 ohm load  its possible to build a back matched driver using 3 BJTs that will switch 200mA into a 25 ohm load with transition times around 5ns or so. Faster transition times require using transistors  with ft's somewhat greater than 300MHz.

However the 10V rail current increases to 200mA when the output is 5V at the 50 ohm load.

Bruce


> 
>     On 21 January 2018 at 08:43 Jerry Hancock <jerry at hanler.com> wrote:
> 
>     Tom might have started this as I was playing around with PICDIV and had asked him the best conditioning circuit. Turned out I had all the parts to copy the TADD-2 including the mini circuits transformer so that’s what I did. It works well, pretty sensitive, etc. I’ve also used the bias trick with a TTL or CMOS buffer when I needed to convert SPIDF signals to baseband for driving an optical connection.
> 
>     Now that I had the input conditioned, I need to drive a 50ohm load with the signal coming from the PICDIV. Can someone point me at a circuit using transistors and 10V if possible?
> 
>     I am trying to duplicate one channel of the TADD2 so I can bring 10Mhz down to 10Khz.
> 
>     Thanks
> 
>     Jerry
> 
>         > > 
> >         On Jan 20, 2018, at 11:21 AM, Poul-Henning Kamp <phk at phk.freebsd.dk> wrote:
> > 
> >         --------
> >         In message <eb956eca-4534-0463-031b-232f8bdbd62f at earthlink.net>, jimlux writes:
> > 
> >             > > > 
> > >                 > > > > 
> > > >                 I played with that, I used a small transformer to balance the signal
> > > >                 and then into LVDS receiver through a voltage divider. Worked well,
> > > >                 but I didn't measure the jitter, it was just for a micro-controller.
> > > > 
> > > >             > > > 
> > >             You can also do it with capacitive dc block to one side, and some
> > >             resistors - the ap notes describe it. The receivers are a fairly high Z
> > >             input, so you pick the voltage divider resistors to make the termination
> > >             resistance right for the incoming signal.
> > > 
> > >         > > 
> >         Yes, but that doesn't give you galvanic isolation, which I think is almost
> >         mandatory unless it is a metrology situation.
> > 
> >         --
> >         Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
> >         phk at FreeBSD.ORG | TCP/IP since RFC 956
> >         FreeBSD committer | BSD since 4.3-tahoe
> >         Never attribute to malice what can adequately be explained by incompetence.
> > 
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> >     > 
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