Compact 74AC14 pulse generator PCB

[rfmerrill]

Look up "absolute maximum ratings" in the datasheet
There is also "recommended operating conditions"; I think I actually designed to stay within the recommended limits under normal operation and below absolute maximum under output short circuit to ground.

When you said you "used the minimum", the minimum of what?
Are you saying there's an absmax rating that is exceeded if you have too many gates? Not enough gates?

My guess is that what you meant was: using only a single gate can exceed the absmax output current

[rfmerrill]

By the way, I think you should add vias near GND pins of the driver chips (assuming the bottom is ground). Otherwise the return current has to take a round trip around the whole bunch.

the top is ground, the bottom is VCC, and I have a void in the middle on both sides where the high speed traces run, someone suggested it.

I made this to learn anyhow, so if it has problems that's not a failure

I'm relying on the small size (the drivers are SC70) to keep the return paths relatively short, plus I kept extra margin on the sides of the board so the plane has more surface area.

[rfmerrill]

Parts finally came and it works pretty well! No more ringing. Time to borrow a better scope to see how good it really is

I used 10uF 0805s for all of the bypass caps, plus added a 100uF electrolytic at the input. The output voltage is lower since the AUC chips run at 2.7V, but voltage wasn't really what I was looking for

At 2.7V with a 50 ohm load, each of the 220 ohm 0201 resistors dissipate at the very most ((2.7V/50 ohm)/5)^2 * 220 ohm = 25mW, which is well below their 50 mW rating

[rfmerrill]

Measured on a Keysight 6 (8?) GHz scope (but bandlimited to 500 MHz according to the UI anyway--I guess it doesn't support higher bandwidth with just a 50 ohm input?)


410 ps rise time!



Only three cycles of ringing and no lower-frequency ringing


Falling edge has no ringing, but fall time appears somewhat longer?