Calling the logic chip gurus

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Hi there - I'm hoping to find a buffer with complementary outputs. Or in other words - a buffer and an inverter on one chip. Does such a beast exist? My hope is to find a way to get matched propagation delay between the inverted and non-inverted signal.

Thanks!

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Which logic family?
Whatare the rise and fall times requirements?

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Have you considered an opamp with differential outputs, set at unity gain? Specifically those designed to drive differential pairs. Those are designed to have matched propagation delays and characteristics. I think AD has some.

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The logic family is not terribly important. I'd prefer a device with Schmitt trigger inputs. It will be run with a 5V supply. I don't have specific rise and fall time requirements - mostly I just want them matched. Within a ns would be nice. Honestly - if I can't find something better - most inverters are fast enough that I'm thinking I'll just count on the inverter being so fast that the propagation delay isn't a factor.

A differential op-amp would be fine, but overkill for my application I think. I've also seem some things like RS-422 drivers - but I was hoping for something cheap.

Thanks!

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A RS422/485 driver maybe? I looked at 74xxx logic, but the few ICs with complementary outputs like the '265 seem to be long gone.

Why is the matched delay important? If this is a synchronous system you could follow the signals with a D flipflop. Or use the flipflop as the source of the matched delays.

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There are a few logic devices with complementary outputs. Flipflop is one crude example that comes to mind. I don't think you are going to find anything with zero skew (that is what it is called - the difference in delay in two parallel channels).

An RS422 driver has complementary outputs. It is sort of 5V CMOS output. Relatively low skew.

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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OK - I'll take a look at all of these. I'm sure I can find something that'll work. I had hoped that there was a family that just included the complementary output - guess no luck there!

As long as I've got your all's attention... Are there any buffers or inverters with a really closely defined Vin voltages? I'd prefer Schmitt trigger, but that's not a requirement. I want to be able to use the part essentially as an inaccurate comparator. But most parts have huge Vin threshold ranges. Like multiple volt ranges. If I could find a part that gave a 200mV range that'd be good enough. Even better if that range is 3.3V compatible...

Maybe that's asking too much?

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RS485 receiver usually have around 200mV difference threshold between their inputs.

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You can use a 74HC14 schmitt and run the output of the first gate into a second gate and then use the first gate and second gate outputs for the inverted and non inverted levels. I would imagine you can find a 3.3v one on the TI web site.

http://www.nxp.com/documents/data_sheet/74HC_HCT14.pdf

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You can use two dual input XOR gates and feed your signal into one pin on each gate.
The other two pins get tied low and high respectively and that will give you inverted and non inverted signals with same ( or as close as practicable ) delay times through the gate(s).
Cheap nasty and on the one piece of silicone.

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XORs have a bit more delay than a normal gate. Check the variation in the delay between the inverted and noninverted mode; it MIGHT not be the same. Otherwise, a great idea.

There is also a complex gate structure called "AND-OR-INVERT" that might be useful.

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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ignoramus wrote:
You can use two dual input XOR gates and feed your signal into one pin on each gate.
The other two pins get tied low and high respectively and that will give you inverted and non inverted signals with same ( or as close as practicable ) delay times through the gate(s).
Cheap nasty and on the one piece of silicone.

And if you have any gates left over, make some breast implants.

Four legs good, two legs bad, three legs stable.

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Use a small CPLD and create your own function that does exactly what you want.

Leon Heller G1HSM

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Mr Brown..

Yes. But You will have to put up with a half A cup.