6 ms·
Transistors in TTL logic use mA of input current because they're bipolar, not FET transistors.
by averagewall 9y ago
Transistors in TTL logic use mA of input current because they're bipolar, not FET transistors.
- lisper 9y agoThat's true, but we're talking about computers here. Computer chips don't use TTL, they're all CMOS, which uses FETs (MOSFETs to be precise).
- kevin_thibedeau 9y agoCMOS didn't exist when the first transistorized computers were made.
- lisper 9y agoAh, right. I thought the OP was referring to modern CPUs.
- blattimwind 9y agoIn classic TTL the input currents are also very asymmetric, e.g. for a high level you mustn't draw more than a few dozen µA out of an input, for a low level you have to draw something like 1.5 mA or so. This is different from current-steering based logic (all kinds of ECL, including CML/SCL) were the current in the circuit stays the same, but only takes a different path depending on state. Supply current is largely independent of circuit state with these.