fast discrete PHEMT one-shot

With a low-resistance drain load like that, you don't care too much about the low drain impedance of the pHEMT. The old Avago ones were around 160 ohms iirc. The transconductance is high enough (400 mho or something ridiculous like that) that you get gobs of voltage gain even so.

Really really crappy for followers though!

Cheers

Phil Hobbs

Yay! Eccles-Jordan ride again.

millimho or

Rds-on is about 2 ohms with a half a volt or so on the gate.

Interestingly, they seem to keep turning on harder with insane gate voltages, like +1 or so. Ig is about 16 mA, way past abs max, at 1 volt, but I'll just pulse it so it will be fine. Right?

Tell me about that. My triggered 50 MHz colpitts oscillator squegged at around 4 GHz. Tons of jitter.

I designed a new osc using a BUF602 and it's great.

I think that was a bistable. I don't know when the monostable was invented.

People tend to roll eyes when I use one-shots in logic designs. I can't see why.

Probably because the classical TTL and CMOS multivibrator chips are so horrible.

The CMOS versions of the 555 are about the best, which is amusing since they’re the ones that get all the abuse.

My usual rule is that one-shots are fine if you can accommodate a factor of

Joerg used to wrap feedback loops around them.

Cheers

Phil Hobbs

Since the first multivibrator circuit, the astable multivibrator oscillator, was invented by Henri Abraham and Eugene Bloch during World War I, it probably isn't the right name.

You can't trigger a one-shot immediately after it has been triggered, and the pulse width you get can be reduced if you re-trigger it too soon after it has generated it's pulse, when it hasn't entirely recovered.

Using a properly terminated delay line to set the output pulse width could reduce this uncertainty, but I've never done it.

Ghiggino, K.P., Phillips, D., and Sloman, A.W. "Nanosecond pulse stretcher",Journal of Physics E: Scientific Instruments, 12, 686-687 (1979).

just used two 5GHz wide-band transistors (BFT95) and was perfectly horrible, but it did what Dave Phillips and Ken Ghiggino had wanted me to give them, and Ken Ghiggino wrote it up rather badly, but I was able to rework the short paper into a form that was publishable and looks nice on Ken's CV.

The fact the laser pulses it was designed to detect arrived at a steady

The SN74123 retriggerable one-shot, and a Fairchild equivalent, are over 50 years old.

And "it's" is not the possessive form. It's means "it is."

But it can also mean "it has" and who cares anyway. I often find, when typing fast, that I used the wrong form when I re read my sentence. I even typed dentence then and had to change the d.

One-shots were frequently used in logic designs when gates were four per package because designers still knew what they were doing with components such as resistors, capacitors, inductors etc. I'm sure some still do but not many.

You've got to admit that his pompous lecture, about all the inherent defects of one-shots, was amusing.

I tweaked my phemt one-shot a bit, just for fun. I might even have a use for it.

One cool old circuit that predated ICs was the uni-shot, a single transistor and three passives. It was used in model airplane r/c transmitters. One of the three passives was a joystick pot.

But you don't get a new pulse when you retrigger a retriggerable monostable - you just stretch the one you had already started.

I do know that but produce the mistake as a typo from time to time, as you are well aware.

And you've snipped the rest of my post, without marking the snip.

John Larkin objects to any post that doesn't flatter him. One that points out that he didn't do his home work is even more objectionable.

Eccles-Jordan (more correctly Abraham-Bloch) used valves - they predate transistors as well as integrated circuits.

Uni-shot is unfamiliar to me, I called them “half-shots”. Cascaded as required.

Or rather when I did do it

Sloman, A.W. and Swords, M.D. "A fast and economical gated discriminator", Journal of Physics E: Scientific Instruments, 11,

I didn't do it to get a more stable delay but rather because I needed narrower pulses than I could get out of any monostable I could buy at the time. As the paper notes, the MC10198 could have delivered, but it wasn't available when I was putting the circuit together.

One of the delay lines I used - 350 mm of 50R coaxial cable, or 1.6nsec

- would have been too short for even the MC10198 - but the rest (5nsec,

The 5GHz BFT95 was pretty new when I used it, and I got told about it by one of the microwave guys at EMI. The Sloman and Swords paper preceded the time I could get that kind of advice.

The 2n918 I did use in the 1978 paper was only good for 600MHz.