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Amplify clock signal?

I bought some ECS -100 i MHz clock oscillators to use as an external clock to set a cutoff frequency in a Maxim lowpass filter (MAX281).

If I am reading the Maxim specs right, the oscillator's output voltage is too low. The notes say that when using an external oscillator, "the input on the COSC pin must swing close to the power rails (V+, V-)." I will probably power it with +1 5 V.

The notes go on to say: "Although standard 74HC00 series CMOS gates do not guarantee CMOS levels with the source and sink currents of the COSC pin, they will in reality drive the COSC pin. CMOS gates conforming to standard B series output drive have the appropriate voltage levels and current to simultaneously drive several chips."

I looked up the 74HC00 series CMOS gates and found that they are NAND gates. Will they really operate to amplify my clock signal? What am I missing, here? I also read some previous threads in the newsgroup that mention using a comparator for such, which I understand a little better.

If anyone would like to try to explain this to idiot child here, thanks in advance.

Amanda

Reply to
Amanda Robin
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It boils down to this: Your oscillators don't have enough "oomph" to directly drive the pin on the 281. So you need to feed the oscillator output into a NAND - your oscillator into input A, input B grounded (Or whatever other combination works - a pair of NOTs in line with each other would do just as well) to give you the signal at the "Y" pin at a level that *DOES* have enough "oomph" to drive the 281's pin.

In a way, the gate is acting like an amp, but that's just a side-effect of it doing its primary function - the logic operation - It sees your weak-but-present 1 from the osc on A, and the grounded (0) B input, says "1 NAND 0 equals 1", and outputs a "full strength" 1 signal, since for gates like the 7400, a weak "on" is no different than a super-strong "on".

And to clarify something before you confuse yourself: The "7400 series" isn't just one chip - The 7400 is indeed a NAND gate. But there's the 7401, and the 74243, and the 7411, and... (A whole bunch of them with numbers that start out "74", some with letters, like

74LS127 or 74HCT04) each one doing its own thing. Don't confuse one chip of the series with the whole series! By referring you to "the 7400 series", they're telling you that chips in that series are probably going to do the job of boosting your clock so that your signal can be used by the 281, even though the 281 docs may not think so. 
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Reply to
Don Bruder

(a really nice explanation as to why a NAND gate in the 7400 series would effectively "amplify" a clock signal)

Thanks very much. Off to find one that will work for me.

amanda

Reply to
Amanda Robin

You want 74Cxx or 40xx at 15V

Reply to
GPG

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