What's an impedance for TTL and CMOS logics
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What's an impedance for TTL and CMOS logics

[From: ] [author: ] [Date: 11-06-15] [Hit: ]
7400, 74L00,74S00,74LS00,74ALS00,74AS00.......
I cant find an answer for this question and I am not sure if impedance is the same as resistance.

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It's not something you ever need, or is specified by the manufacturer.

Take TTL, which comes on about 6 or more different grades, all with different parameters. 7400, 74L00, 74S00, 74LS00, 74ALS00, 74AS00.

Picking one of these, ALS00, there are 4 different measurement points.
Input low. VIL, 0.5 volts and 100µA, which translates to 5kΩ
input high, VIH, 2.7v and 20µA, which is 135kΩ
output low, VOL, 0.5v and 8 ma which is 62Ω
output high, VOH 3v and 0.4 ma, which is 7.5kΩ

But the resistances are irrelevant. What matters is the current and the fan out ratios.
Note that the other families, and some other parts in the same family, will have different numbers.

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