level shifter

he

es to negative logic voltages. =A0Gives reasonable speed with crap transist= ors. =A0Not too precise. =A0I don't know if it can be adapted to your use. = Proper output voltages require setting the resistors properly.

We were using BFT92s for that sort of work back in 1989. They worked then, so they should still work now. Don't forget the base stopping resistor. There are reputed to be better ways of stopping them oscillating, but a 27R SMD in series with the base (and close to it) is dead simple and very reliable.

-- Bill Sloman, Nijmegen

I was "trained" much earlier ;-) ...Jim Thompson

I've engaged in arguments with some CAD "librarian" over whether or not it'd be "acceptable" to have two symbols for op-amps, both with VCC and the top and VEE on the bottom, but one with + above - and the other with

- above + -- me arguing that sure, why not -- it's useful?, and him arguing that it was too much extra effort or some such nonsense.

(Another solution is to just make the symbol heterogeneous and have a little box with VCC and VEE on it and leave them off the op-amp symbol itself altogeter; this is especially attractive for dual- and quad-amps. He didn't like that either, of course.)

This same guy also took it upon himself to re-draw parts of engineers' schematics such that they were more to his liking (and, if he didn't make any mistakes in the process -- which was not always the case --, still electrically identical) and release those as the official copies. I was amazed that this was considered acceptable; I'd never worked anywhere else where it would have been tolerated. But it was part of a (IMO) broken engineering department where the engineering manager didn't have any engineering background (formal or as a hobby), had never used a CAD program, etc., so policies were (again IMO) often seemingly unfounded.

Moral of the story: Try not to work for companies where the managers don't have a technical background.

Well, at least not as a regular employee. Being a consultant for such places might be kinda interesting!

---Joel

;-) ...Jim Thompson

How about using the flop to drive a schottky diode switch that robs a PNP current source? (Resistor load on the p-hemt gate sets the swing.)

That's fast, stable, and accurate.

James

On Thu, 08 Mar 2012 12:50:13 -0800, John Larkin wrote:

This looks OK. The 5K resistors can be two quad packs, so the parts count isn't bad.

Version 4 SHEET 1 880 680 WIRE 160 -208 -128 -208 WIRE 448 -208 224 -208 WIRE 512 -208 448 -208 WIRE 528 -208 512 -208 WIRE 448 -160 448 -208 WIRE -224 -32 -320 -32 WIRE -64 -32 -224 -32 WIRE 0 -32 -64 -32 WIRE 112 -32 80 -32 WIRE 160 -32 112 -32 WIRE 272 -32 240 -32 WIRE 304 -32 272 -32 WIRE 448 -32 448 -80 WIRE 448 -32 384 -32 WIRE 112 -16 112 -32 WIRE -320 16 -320 -32 WIRE 368 32 336 32 WIRE 448 32 448 -32 WIRE 512 32 448 32 WIRE 528 32 512 32 WIRE 112 64 112 48 WIRE 336 64 336 32 WIRE 688 64 656 64 WIRE 704 64 688 64 WIRE 816 64 784 64 WIRE 832 64 816 64 WIRE 272 80 272 -32 WIRE 304 80 272 80 WIRE 448 96 448 32 WIRE 448 96 368 96 WIRE 656 96 656 64 WIRE 784 96 784 64 WIRE -128 112 -128 -208 WIRE -64 112 -128 112 WIRE 0 112 -64 112 WIRE 112 112 80 112 WIRE 160 112 112 112 WIRE 272 112 240 112 WIRE 304 112 272 112 WIRE -128 128 -128 112 WIRE 112 128 112 112 WIRE -224 144 -224 -32 WIRE -176 144 -224 144 WIRE 336 144 336 128 WIRE 368 144 336 144 WIRE -176 192 -224 192 WIRE 272 192 272 112 WIRE 384 192 272 192 WIRE 112 208 112 192 WIRE 272 224 272 192 WIRE 656 224 656 176 WIRE 784 224 784 176 WIRE -320 240 -320 96 WIRE -272 240 -320 240 WIRE -224 240 -224 192 WIRE -224 240 -272 240 WIRE -128 240 -128 208 WIRE -128 240 -224 240 WIRE 384 240 384 192 WIRE -320 256 -320 240 WIRE 272 352 272 304 WIRE 384 368 384 320 WIRE 416 368 384 368 WIRE 432 368 416 368 WIRE -320 384 -320 336 WIRE 272 480 272 432 FLAG 656 224 0 FLAG 784 224 0 FLAG 688 64 V+ FLAG 816 64 V- FLAG 368 32 V+ FLAG 368 144 V- FLAG 272 480 0 FLAG -320 384 0 FLAG 416 368 V- FLAG 512 -208 GATE FLAG 112 64 0 FLAG 112 208 0 FLAG -64 -32 Q FLAG -64 112 Qbar FLAG 512 32 BOOT FLAG -272 240 Vcm SYMBOL Opamps\\UniversalOpamp 336 96 R0 SYMATTR InstName U1 SYMATTR Value2 Avol=1Meg GBW=4Meg Slew=10Meg SYMBOL voltage 656 80 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 WINDOW 0 -85 38 Left 2 WINDOW 3 -75 85 Left 2 SYMATTR InstName V1 SYMATTR Value 5 SYMBOL voltage 784 80 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 WINDOW 0 56 36 Left 2 WINDOW 3 61 72 Left 2 SYMATTR InstName V2 SYMATTR Value -5 SYMBOL voltage -320 240 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 WINDOW 0 61 51 Left 2 WINDOW 3 53 92 Left 2 SYMATTR InstName V3 SYMATTR Value 1.955 SYMBOL voltage -320 0 R0 WINDOW 3 -253 -77 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR Value PULSE(-0.4 0.4 1u 250p 250p 50u) SYMATTR InstName V4 SYMBOL res 400 -48 R90 WINDOW 0 -53 58 VBottom 2 WINDOW 3 -46 59 VTop 2 SYMATTR InstName R1 SYMATTR Value 5K SYMBOL res 256 -48 R90 WINDOW 0 -56 53 VBottom 2 WINDOW 3 -44 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 5K SYMBOL res 96 -48 R90 WINDOW 0 -56 53 VBottom 2 WINDOW 3 -45 52 VTop 2 SYMATTR InstName R3 SYMATTR Value 5K SYMBOL res 96 96 R90 WINDOW 0 -39 54 VBottom 2 WINDOW 3 -37 55 VTop 2 SYMATTR InstName R4 SYMATTR Value 5K SYMBOL res 256 96 R90 WINDOW 0 -42 42 VBottom 2 WINDOW 3 -36 42 VTop 2 SYMATTR InstName R5 SYMATTR Value 5K SYMBOL res 288 320 R180 WINDOW 0 55 70 Left 2 WINDOW 3 56 35 Left 2 SYMATTR InstName R6 SYMATTR Value 5K SYMBOL res 400 336 R180 WINDOW 0 -57 76 Left 2 WINDOW 3 -64 40 Left 2 SYMATTR InstName R7 SYMATTR Value 85k SYMBOL e -128 112 R0 WINDOW 0 50 47 Left 2 WINDOW 3 52 82 Left 2 SYMATTR InstName E1 SYMATTR Value -1 SYMBOL cap 224 -224 R90 WINDOW 0 -20 78 VBottom 2 WINDOW 3 -48 7 VTop 2 SYMATTR InstName C1 SYMATTR Value 330n SYMBOL res 432 -176 R0 WINDOW 0 58 41 Left 2 WINDOW 3 59 76 Left 2 SYMATTR InstName R8 SYMATTR Value 5K SYMBOL cap 96 -16 R0 WINDOW 0 47 29 Left 2 WINDOW 3 49 57 Left 2 SYMATTR InstName C2 SYMATTR Value 2n SYMBOL cap 96 128 R0 WINDOW 0 57 32 Left 2 WINDOW 3 59 62 Left 2 SYMATTR InstName C3 SYMATTR Value 2n SYMBOL res 288 448 R180 WINDOW 0 55 70 Left 2 WINDOW 3 56 35 Left 2 SYMATTR InstName R9 SYMATTR Value 300 TEXT -448 -136 Left 2 !.tran 100u TEXT -584 128 Left 2 ;DIFFERENTIAL PECL TEXT -528 176 Left 2 ;MC10EP51

A PNP current-steering pair would work too. But it wouldn't be as fast as the capacitor, and fast bipolar transistors always seem to oscillate for me. If you put in enough base resistance to tame them, that slows things down.

This goes inside a little pulse generator that I'd like to run as fast as possible, 200 MHz maybe, and every ns in this path slows it down.

The PNP current source could be slow, but used only to DC-sustain a direct capacitive-coupled path. That has possibilities and hazards.

Why inductor ("FB")? And if "FB" means "feedback", where from? 'Splain, please.

Ferrite Bead

Clumsy, adds delay.

The PNP current source would be dead-slow, isolated by RL, that's the idea.

Getting rid of the fast switch(es) entirely and cap-coupling the swing is better still.

Your diff-amp thing is pretty good.

James

Sorry, FB means ferrite bead. They work great to isolate a fast node from the capacitance of something like the collector of a transistor or, like here, the drain of a fet. They are really just low-Q inductors.

Interesting idea. Maybe solve the issue that PSpice has power pins on all 4 sections of, for example, the LM324. Maybe use your "box" idea as an overlay... after all, schematics are for human viewing and comprehension, netlists for simulation and layout... I just have to solve the netlist issue :-(

You would not believe some of the stuff I have to endure. That gig last summer on Long Island, made me lots of $$, but I was otherwise treated as dirt. ...Jim Thompson

Cadsoft Eagle makes this very easy: You place an opamp and it has no supplies at first. Well, it does but they don't display. Then you can contort it to your hearts desire, upside down, flipped, rotated, whatever. Now you click an "invoke" function and up pop the supply pins. Scoot them over the opamp symbol, done.

My vote goes for plus above minus. I grew up with that.

I've never had that happen, ever. They always treated me like I was the guy that will fix all the ailments. The topper were Asians and this was quite embarrassing to me. I was brought into the engineering area by the boss and then introduced. Of course business cards were exchanged, very important there. It is customary to _never_ just slip it into your shirt pocket like we do here but hold it in both hands, study it intensely, then place it into your leather business card holder (must have) and bow. "Oh, massa of science, massa of science" and they all bowed several times. One of them had a Ph.D. ...

And how do you take care of all the Vbe drift? Pully a PHEMT into enhanced is not for the faint of heat ;-)

No, FB means fullback (football formation) :-)

Putting them wherever you want? That does sound handy.

"Invoke" is kinda an odd (generic) name for such a function...

Yabbut for something like an instrumentation amplifier the drawing ends up looking kinda silly (lots of additional crossing wires) unless you flip + and - on one of the amps. :-)

---Joel

Sorry, meant "pulling a PHEMT"" :-)

Yes, wherever you want. Some folks place them all into the corner of a schematic page. Personally I really do not like that. I even try not to do that with bypass caps because it makes it so hard for the guys (me ...) who has to do the noise fixing.

Eagle is weird in that respect. For example, "Cut" really means "Copy". In the beginning I always clicked that with white knuckles.

Doesn't look silly to me :-)

Ahh! Ideal resistor!