[time-nuts] 50 ohm driver

Charles Steinmetz csteinmetz at yandex.com
Fri Mar 6 04:27:47 EST 2015


>I got excited when I found the SN74AS1004AD which has the exact same 
>function and pin out but delivers 48 mA per channel.  While one 
>output did give me 0-3.0 V into 50 ohm, combining them, as we do for 
>the 74AC, actually produced worse results.

Can you post a link to the datasheet for your product, so we have 
some idea of what you're attempting?

The AS devices are bipolar logic (fancy modern schottky TTL) -- they 
don't even pretend to pull closer than 1.5v to VCC (so, 3.5v with Vcc 
= 5v), and the spec is only >2v.  The datasheet clearly indicates 
this (if one didn't already know that they were bipolar parts from 
the AS series designation).

When you are depending on the analog performance of logic gates, it 
is up to you to pay attention to everything on the datasheet, not 
just one spec.

Any ringing on the line (from mistermination) will very likely 
destroy the AC14s if you run them with no series resistors.  At least 
build a discrete CMOS inverter stage with medium power, low-threshold MOSFETS.

Best regards,

Charles





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