Convert Logic to Vdd and Vss

[GeneralZod]

I have a small dilemma where I wish to convert a logic signal in a circuit to swing from +5V to -5V.

The logic signal is a square wave going from 0V to 5V.

The logic signal should swing from +5V to -5V

I already have a split rail supply that works well, so supply is no problem.

I have implemented the LM311 quite nicely, it takes the logic signal and the open collector output is connected to +5V and -5V, but the problem is that the Lm311 is quite slow for the speed of the logic signals. Rise and fall is around 100nS, ideally it should be around 10nS or so...

Any ideas would be really appreciated.

Many thanks

Zac

 

[ccurtis]

Edit: I thought there were faster comparators that could do it in 10 nS or less, but I haven't found any that give a negative output.

 

[MikeMl]

Perhaps another approach. You effectively need an amplifier with a gain of -2 with a offset. A high-speed opamp should do it...

Found an LT6411

 

[ccurtis]

Nice.

 

[GeneralZod]

Very nice

Hi Mike,

Much appreciated nice and simple. I have looked through many data sheets, but the same as Curtis, most of the ultra fast comparators only switch from 0V to 5V on the output.

My head is a little hazy after looking at the entire circuit for awhile. It is always good to see someone else's suggestions when things get hazy...

I will order the LT opamp today and try it on a test board.

Btw, what simulation software are you using?

Cheers

 

[GeneralZod]

Not available

Mmmm..... Just checked on Element 14 for Australia, no evaluation board and no longer stocked.
I will have a look through my pieces here, I may have some high-speed op-amps. I'll post the numbers and results as soon as I find some.

 

[ccurtis]

Look for an op amp with a slew-rate of at least 1500V/us. Here's another option:

 

[MikeMl]

...

Btw, what simulation software are you using?

Cheers

LTSpice Best free software I have ever found...

LT6411 is available from Digikey