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LVPECL and floating inputs

Software guy here working on a simple project thats becoming complicated

Please imagine the following scenario: device with lvpecl inputs. Possibility that the inputs may float (left unconnected). I reckon I should force the inputs to a default level,

If this were a TTL device, I would tie the input to vcc via a pullup or pull down. But its a differential - so I guess I need a voltage divider to balance the two inputs such that theres a difference of say

100mv between the two

How will this affect things when an input IS connected?

I know what you are thinking - is this dude dense or what? I am going to go down to the basement and fish out my ac/dc analysis book and read up on thevenin,superposition,mesh networks and various ways of analyzing circuits.

Its been awhile

Any pointers would help

Reply to
samiam
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Differential? Read the data sheet. Probably tie one input high to keep the current mirrors under it happy, the other input low. But it'll depend on the exact circuit.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
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Reply to
Jim Thompson

You could thevenin terminate them to slightly different voltages, offset in your preferred direction, both near the low end of the common-mode range. That should work OK.

What's the receiver device?

John

Reply to
John Larkin

SY100EP15V Mux

Reply to
samiam

That part has weak pullup/pulldowns so that it goes to a known state, equivalent to input low, if the inputs are truly open. But if you add your own terminations they will overpower those pulls, so you should make sure they add a small offset if you want the input to be in a known state when the signal source is gone.

John

Reply to
John Larkin

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