Sometimes Hi-Z, but other times it may have to drive a clock receiver that is actually expects a current drive. Overdriving it with a little higher voltage is fine for the case where a current is expected... but with a current drive receiver, the passive solution won't work.
I'm still trying to debate whether a fast slew-rate VGA or one of those buffers is the way to go.
Some of the VGAs have slew rates of 13V/ns, which I think would be fast enough for my application. The advantage is that they can also produce a differential signal which is key. What worries me is I do'nt know what the clock will look like since I have never put a square wave through an opamp before :S
The digital logic solutions would reproduce the clock quite nicely at the levels I want, but I'm afraid that there would be mismatch if I use 2 to buffer a diff. signal. Is this a valid concern?
It pretty much comes out at the slew rate.
Using an extra inverter in one line causes a propagation delay for that line and not the other but with modern logic such as AUC or AUP that won't be much, a few nsec maybe. Also, if that's a concern you can LC-delay the other.
The most the impedance will be is around 50 ohms, with the pot at mid-scale, so this will drive nearly any logic family.
John
The AUP can take 3.6V inputs at any Vdd...that is in the AUP family summary.
You're keeping us guessing here, there are any number of possible solutions, but we'll never know what is reasonable from your limited description. The simplest logic gate solution would be as shown below, try to avoid anything that mentions Schmitt trigger inputs, these spell disaster for low jitter, they're real bad actually... View in a fixed-width font such as Courier.
. . . . . Vdd_Var>----+------. . | | . | | . | -------- . | | | . | | __ | . '--|-\\\\ \\ | _______ . | || >-|-----> CLK_VAR . .-------|-//__/ | . | | . | | | . | | | . CLK_3.3V>--+ | | . | | | . | | | . | | __ | . '-------|-\\\\ \\ | . | || >-|-----> CLK_VAR . .--|-//__/ | . | | | . | | | . | -------- overvoltage tolerant . | | . '------- dual/quad EXOR/NOR . | . --- whatever.... . /// . . .
Yup.
This is starting to sound like a need for pin driver electronics from high speed digital testers from the late 70's through late 80's.
Or possibly, specialized variable level high speed digital line drivers.
Joseph
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