Inverter not inverting properly...

[brad]

Hi all, just thought i'd post here to see if anyone can shed some light on an annoying problem.

I have a clock pulse of around 4Mhz going into an inverter (which SHOULD be able to handle upto 32Mhz) but it doesn't seem to be doing a good job of inverting. Look at how far off the mark it is. By the way I have used various inverters and it's all the same (7404's that is)

Anyone know why I am having issues with something that should be so basic?

The original pulse train is the top and the inverted is on the bottom:

screen-capture-20.png (114.87 KiB) Viewed 10398 times

[bitfogav]

I can't say that ive had much to do with inverters, but they should be pretty basic to work with or so to think?.

Some suggestions which im sure you've already tried Brad?

1. Some 0.1uf caps on the power lines to reduce noise?.

2. Ive also read that the unused inverter Input lines need to be tied to VCC or GND.

All unused inputs of the device must be held at VCC or GND to ensure proper device operation.

3. What happens if you use a lower Frequency Input? I know you said it should work at 32mhz, but im wondering if they cant really handle a constant pulse?.

[Garth]

Are you measuring right at the inverter IC, or somplace farther away on the board? (I'm wondering if you're seeing the effects of board problems, not inverter problems.)

[brad]

Thanks for the input there guys.

1 did have a 0.1uF cap in the circuit and I was measuring directly at the inverter output. However once I shorted all unused inputs to ground, it did make a big improvement. I always thought that you only needed to do that with CMOS logic chips...

I'll be doing a write up of my findings (when I get some spare time that is...)