# 97 Mhz sine wave to square wave

#### lordofentropy

Joined Apr 10, 2010
58
I have a 97 Mhz sine wave (~5 Volts) that I want to make into a square wave and then send it into some D flip flops. However, it would appear this signals frequency is to much for a schmitt trigger, or even a comparator as far as I can tell. Any suggestions?
Thank you.

#### Georacer

Joined Nov 25, 2009
5,182
What Flip Flops do you want to use? They may be too slow for your clock too.

#### lordofentropy

Joined Apr 10, 2010
58
I already took care of that problem.

#### Georacer

Joined Nov 25, 2009
5,182
Would you like to explain why this isn't a problem to you? It might be interesting information.

#### lordofentropy

Joined Apr 10, 2010
58
By adding a delay line to the common D flip flop divide by two circuit, the internal frequency of the device can be lowered to an acceptable range. After one of the high frequency pulses triggers the flop-flop all following input pulses are ignored until the effect of the trigger propagates through the flip-flop and the delay line back to the D input. Hence, by adjusting the duty cycle slightly I am making the flip flop capable of dividing a high frequency.

This part of the circuit works fine, however going back to the problem I want to condition a high frequency sine wave into a square wave. I don't have any experience in conditioning higher frequency wave forms, just much lower ones.

#### Kermit2

Joined Feb 5, 2010
4,162
By amplifying the signal to the 20 or 30 volt range, you could then apply a clamp to limit the signal to 5 volt or 3.3 volt(whichever you're using) thereby creating a waveform that closely resembles a 'square' wave.

Clip it!

#### lordofentropy

Joined Apr 10, 2010
58
Kermit2,

Can you recommend me some op amps to use to amplify the signal and if possible point me in the direction for the amplifying circuit; I do not have any RF experience, and what I did know I forgot years ago...

#### SgtWookie

Joined Jul 17, 2007
22,230
I don't think Kermit realized how fast an amplifier would have to be in order to accomplish that feat.

You might take a look at ECL:
http://en.wikipedia.org/wiki/Emitter-coupled_logic
We were using ECL logic circuits at frequencies well over 100MHz back in the early 1980s. It's sort of an odd duck nowadays, as it uses 0v for Vcc, and -5.2v for Vee. I don't know why one couldn't operate it using +5.2v for Vcc and 0v/GND for Vee.

It's rather particular about signal levels, and using adequate bypassing is a must. However, if you could use a few ECL D-type FF's to scale the frequency down, you could then use a comparator with hysteresis as a Schmitt trigger to get back to TTL or other desired logic levels.

#### kubeek

Joined Sep 20, 2005
5,791
lordofentropy, if you have a D that´s capable of 97MHz, then why not send the sine straight to the D? The transisions could be fast enough.
Could you post the rest of the circuit?

#### zero_coke

Joined Apr 22, 2009
294
I suggest somehow clipping the sine wave using some special opamp that is fast enough to handle the speed of the signal.

#### Audioguru

Joined Dec 20, 2007
11,248
I suggest somehow clipping the sine wave using some special opamp that is fast enough to handle the speed of the signal.
The harmonics of a 97MHz square-wave reach to more than 970MHz which is much too high for an opamp.
An old LM324 quad or LM358 dual opamp has trouble above only 23kHz. A 43 years old 741 opamp has trouble above only 9kHz.

Most very high speed logic circuits switch fine when fed a sinewave.

#### Papabravo

Joined Feb 24, 2006
20,615
I don't think Kermit realized how fast an amplifier would have to be in order to accomplish that feat.

You might take a look at ECL:
http://en.wikipedia.org/wiki/Emitter-coupled_logic
We were using ECL logic circuits at frequencies well over 100MHz back in the early 1980s. It's sort of an odd duck nowadays, as it uses 0v for Vcc, and -5.2v for Vee. I don't know why one couldn't operate it using +5.2v for Vcc and 0v/GND for Vee.

It's rather particular about signal levels, and using adequate bypassing is a must. However, if you could use a few ECL D-type FF's to scale the frequency down, you could then use a comparator with hysteresis as a Schmitt trigger to get back to TTL or other desired logic levels.
We did this. It is called PECL for Positive ECL.

Joined Dec 26, 2010
2,148
Ultra-fast comparators capable of this sort of speed have been made - here is an example ( I do not know if this particular device would fit your needs, or even if it is still widely available.). http://www.analog.com/static/imported-files/data_sheets/AD8611_8612.pdf

What I can tell you for sure is that the physical layout required to get this sort of thing to work well is a bit of an art. One of my first tasks as an engineer was to use Plessey 968* ECL output comparators in an impulse noise detector, about 30 years back.
The layout learning curve was pretty steep, as during my training I had not handled anything much above 1MHz.

#### MrChips

Joined Oct 2, 2009
29,858
I would use a 74F161 for a fast counter, good to 120MHz. You should be able to feed the sine signal directly into the CLOCK.

You need to show your circuit diagram.

#### lordofentropy

Joined Apr 10, 2010
58
Thank you all for all the input, I will look further into the presented information and get back to you all once I get some things ordered. Also, off the topic some; what would be a good circuit simulator program that has a large library of parts and/or parts can relatively be easy to integrate into the library. The last time I used any circuit simulation it was Psplice 9.2....several years ago.

#### zero_coke

Joined Apr 22, 2009
294
Multisim is good but it's been giving me a lot of trouble lately even though it's using the same PSpice engine that came out years and years ago. You could look into it, it's very intuitive and a nice GUI along with. Maybe I was just using it wrong...

#### DickCappels

Joined Aug 21, 2008
10,104
If your sine wave has sufficient drive capability and it swings through the logic high and logic low levels for your D F/F, then you will probably be fine just applying the sine wave directly to the input. Just be sure you don't exceed the maximum risetime specified in the datasheet (if it is even specified for your device).