[time-nuts] Minicircuits SYPD-1

[Gerhard Hoffmann]

Hi,

matching in the sense of selecting 4 equal ones won't help much with BJTs.

Take them from the same tape, that's enough. Also, the transformer ratio

does not matter much. Once VBE = 0.7V, the transistors switch on. The 
authors

write that thy use the BE junction as diodes, but that is not true. The 
transistors

are operated as switches. That's probably the reason why they are so good.

A different transformer ratio only shifts the level where the 0.7V Vbe 
is reached;

a dB more or less, not a big thing.


The power required for optimum return loss seems to be quite precise.

If you do not have enough for Vbe=0.7V, the switches will sit there 
idle, giving

bad return loss; having too much pumps a lot of current through the ring and

the mismatch will be to the short circuit side.

You could also drive them somewhat into saturation which would make

them slow. That's why I used a fast-ish transistor from the start.


In my case, 8 or 10 dBm made quite a difference from the 9dBm for 
optimum BW.

I have some MCL T1-6 and could check them over the weekend.


If you have more signal power, it's probably wise to split it to more PDs

and add the IF outputs.  This here seems to be an interesting Wilkinson:

<   https://www.digikey.de/products/de?keywords=1465-1815-1-nd    >

So it all boils down to el cheapo coils and Schnaps or beta-blockers for 
soldering.


In the case of JFETs as switches, your curve tracer could probably help 
a lot.

JFETs are all individuals, see Ic over Vgs for IF3601 / IF3602

< 
https://www.flickr.com/photos/137684711@N07/37321004540/in/album-72157662535945536/ 
    >


The IF3601 is a large geometry JFET with huge gm, that can deliver 0.3 
nV/rtHz voltage noise.

Four of them in parallel yield 160 pV/rt Hz; I could verify that but 
they were not

completely stable for inductive signal source impedance. If you want to 
simply parallel them,

one of them might happily sink 1A while the other is still completely 
cut-off.

They also seem to need more drain current than promised and the IF3602 duals

are not pairs in the closer sense. But no opposite outliers, OK.   
(avail. @ Mouser)


My newest creation uses a bootstrapped cascode to effectively remove the 
LARGE

input capacitance; that also seems to make it unconditionally stable, at 
least in simulation.

The new boards are spending this week in the Leipzig, DE customs office 
since someone

does not believe that PCBWAY in China can deliver 10 proto boards for 
$5.  :-[


Having such an amplifier after a ring mixer is probably overkill; a RF 
Schottky diode

may have easily a ohmic 50 Ohms component in series and two of them 
active in a ring

mixer guarantee 1.3 nV/rtHz thermal noise alone. (and that is NOT the 
half-thermal slope

resistance of the diode effect itself)


High power type3 ring mixers have additional resistors in series to the 
diodes to create

some back-bias. Those also create noise and so it should not come as a 
surprise that

high power mixers may be kings of IP3 but lose big time at the noise end 
of the scale.

< 
http://home.deib.polimi.it/svelto/didattica/materiale_didattico/materiale%20didattico_MRF/appnote/wj_Mixers_part_2.pdf 
    >


regards, Gerhard


Am 20.12.18 um 03:16 schrieb Jerry Hancock:
> Gerhard, would there be any advantage to matching the transistors?  I have a pretty accurate curve tracer.
>
> thanks,
>
> Jerry
>
>