An old "500MC biquinary counter"

Here's a copy of the circuit as it appeared in Electronics magazine back in 1966. The diodes are 1N752A Zeners. It's redrawn here so it's easier to understand. Just a divide-by-5 ring counter. Looks like the Zeners are there to protect the B-E junctions of the right-hand transistor of each stage.

Cheers, Dave M

OK... I thought this NG could accept small attachments... Guess not. See the image at

Sorry for the confusion, Dave M

Thanks, they are indeed zeners and it is indeed a 500MHz circuit. I'd never thought that.

Sometimes it does but most news servers clip that away. Most also won't let people subscribe to binary groups so a.b.s.e. has outlived its usefulness.

Being a ring counter means it only has to toggle at 1/5 the input frequency?

Clifford Heath.

There's some details missing, though: the input, I guess, has to be pulses.

And, it has to change polarity every five inputs (so, a flip/flop following divides by two, its Q and /Q outputs can gate that behavior).

Or, am I missing something? It certainly doesn't have any provision for reset...

The 2K resistors never see a current change. ECL was neat.

piglet

Could it be a step recovery diode? I'm not sure how that would be of use in this circuit.

BTW, why do you say this is a bi-quinary counter? It looks to me like a ring counter, but without an inversion, so just a shift register. But then I can't figure out how the durn thing works, so I'm not sure what it is. Is this the quinary part of a bi-quinary counter?

No, that's just a Schmitt-trigger. Not the same.

Cheers, James Arthur

Hey! At >10GPa, CO2 is as good as SiO2 or GeO2, so there!

Tim

Just going off the title of the original post on that "SeekIC" schematic dumping-ground site.

I'm trying to pull up that post but unfortunately I'm not having any luck finding it again... :-(

What is biquinary anyway? The name suggests the operation of the 7490.

Could it have been discreet? I don't see how it could count anyway, unless those 'diodes' are very exotic things.

It's a non-standard standard decimal encoding scheme. Generally there is a two and a five portion (hence bi-quinary) of the digit. The two is just a ff and often the five portion is a ring counter for maximum speed. Sometimes not.

Another solution/coding is a five-bit Johnson counter.

I don't see a reset.

Semiconductors are not known for being talkative, whether or not they're discrete.

Joerg sure seems to have some that aren't very quiet.