need help designing a square wave generator....

[ketanrd01]

Hi everyone!!!,

I had designed a square wave generator ckt for upto 300 Khz using 7414.
Now i want to design one for a much higher frequency, like a hundred Mhz. Can someone please send me a circuit diag or link for the same since i couldn't find one.

Thanks in advance....

 

[Daniel Robertson]

Hi.

The 7414 will certainly not run at anywhere near 100 Mhz, and the 74LS series will only be good for up to around 32 to 35 Mhz.To get anywhere like 100 Mhz you would have to use ECL devices (emitter coupled logic) or discrete devices.

Daniel.

 

[(*steve*)]

He could use G series TTL.

 

[Harald Kapp]

Wow, I never heard of these before.

Anyway, at 100MHz you should be aware that your "square wave" will not look so square anymore. It will have rounded corners due to ever present damping of the higher harmonics.

 

[ketanrd01]

Thanks everyone!!!.....

 

[Daniel Robertson]

74G series may be an answer, but as said, you will find it hard to get very square wave. Then again, if you are using the standard R and C circuit around a single gate, you may have other problems.

Take a look here: http://www.potatosemi.com

Daniel.

 

[(*steve*)]

The question arises as to whether ketanrd01 requires a square wave or a TTL compatible signal.

The G series TTL (linked to both by myself and Daniel) would clearly produce a relatively fast rising and falling edge but it is interesting that the PO74G14 can do 1.125GHz into a 2pF load, but that the input capacitance of the gate itself is 4pF!

Of course it can do up to 100MHz into 50pF, so you're unlikely to hit that limit, but I wonder how often you'd see these running at the headline 1.125GHz?

On the very first point I raised, I have a 10MHz rubidium frequency standard with a TTL compatible output, and even that looks a lot more like a sine wave than a square wave.

 

[ketanrd01]

Thanks Daniel n steve...hope i can make one n post soon...

 

[Daniel Robertson]

Have you seen this? I fount it on the web.

Daniel.

 

[(*steve*)]

Have you seen this?

Yeah, those are certainly an excellent option if you want a fixed (and indeed very stable) frequency.

 

[ketanrd01]

Thanks again for your help Daniel sir...