modified 8 years ago

Tristate Buffer

01:40:48

This circuit is a simple tristate buffer. The top input is the control which blocks the signal when high but let’s it pass when low. The bottom input is the signal and gets inverted when passed and does nothing when blocked.

published 8 years ago

BillyT

8 years ago

Needs a bit more work ...

jason9

8 years ago

Why?

BillyT

8 years ago

When the top signal blocks the bottom signal, there is still an output of 2.5 V, high enough in some circuits to still be classified as an output signal.

hurz

8 years ago

BillyT, sure there is still some voltage. Maybe stored in some capacitance. Question how much energy does it need to bring it down to 0 volt. Or what is in tristate the output impedance?

BillyT

8 years ago

Hurz, a pull down resistors, about 50k would appear to do the trick. Does the circuit really require that many Fets.

hurz

8 years ago

But 50kOhm is not highZ its 50kOhm. Suppose you put 10 of them at the same bus you would get already 5kOhm! HighZ is used to be invisible as much as possible.

hurz

8 years ago

And the number of fets looks fine to me. The driver itself is an inverter, which is with two fets surrounded to power it or make it highZ. Because the NMos need a logic inverted signal he needs two more fets as inverter. Does not look to overcomplicated, just perfect.

add comment in editor

EveryCircuit is an easy to use, highly interactive circuit simulator and schematic capture tool. Real-time circuit simulation, interactivity, and dynamic visualization make it a must have application for professionals and academia. EveryCircuit user community has collaboratively created the largest searchable library of circuit designs. EveryCircuit app runs online in popular browsers and on mobile phones and tablets, enabling you to capture design ideas and learn electronics on the go.