cheap analog square function?

I've made a dual slope pulse width magnifier with them, 20-30ns to

One of the precious moments when you note that you were REALLY lucky! (repeatable 5 ps performance over temp)

Gerhard

Clean livin', that's what it is. ;)

Cheers

Phil Hobbs

But Renesas still makes the HFA3096, which is faster, even if the base series resistance is a bit high, as you pointed out when I last drew their parts to your attention.

There is a way of compensating for that - EMI Central Research had a hyperbolic function generator which relied on a transistor to feed an exponentially decreasing current into a capacitor, and it used a bit of positive feedback to take out the base resistance.

My name is on the relevant patent U.K. patent 2028503 "Improvements in or relating to ultrasonic apparatus"; assigned to EMI Ltd in 1978. I didn't invent it - my name got on the patent (somewhat to my surprise) for the digital scheme for generating hyperbolically increasing digital numbers.

You've got to increase the voltage applied to the base terminal of the transistor to compensate for voltage drop across the base resistance.

That's actually very easy to do if you can put a current mirror between the collector of the transistor and the rail. The current going into the mirror collector current is proportional to the base current, so you can use it to develop and extra voltage drop of the right size between the base of the hyperbolic transistor and the negative rail. There's got to be a pot in there somewhere to be twiddled reflect the actual base resistance and current gain of the transistor making the hyperbola.

I don't think that is the way we did it - it got bundled into the system for starting the hyperbolic voltage at right point - but whatever we did was pretty simple.