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Tri-state buffer high impedence

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iVenky

iVenky

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What will happen when tri-state buffer provides high impedence?

I knew that at high impedence the current flowing will be almost zero. From which direction would you see an high impedence (either when you look towards the input or when you look towards the output?).




Thanks in advance.:razz:
 

The tri-state is an output state, the buffer input will show high impedance unconditionally.
 

I need the circuit for buffer (i.e. how the transistors are connected inside the buffer).

Thanks in advance.
 

Hi,
Here is the CMOS level diagram for tristate inverter.
Similar approach has been taken for tristate buffer also.

Tristate inverter.gif

For additional information please look in to
CMOS VLSI Design by Neil Westy Chapter 1, page no 15
 

Hi is it possible to achive Hi-Z by using one FET?
for i.e. while 5V Dc comes to the drain & the gate is grounded does the source sees Hi-Z?
 

while 5V Dc comes to the drain & the gate is grounded does the source sees Hi-Z?
Click to expand...
No, 5V or '1'.

A tri-state buffer should be able to send '0', '1' and 'Z', so the output stage needs at least two transistors (N + P).
 
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thanks yet i'm intersted in only ('1' or Z outputs) without the '0'. so in such case can i use one FET as described above?
 

No i'm researching Hi -Z state by my self...
 

If you only want '1' or Z then one PMOS transistor will do that. One will pull high, off will be high impedance. I assume that something else would provide some sort of load otherwise it would be difficult to tell the 1 from the Z.

Keith.
 
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Thank you this is the answer i looked for, because many people talked about Tri-state yet i could find the configurations of its implementation.

Moreover i'm intersted of understanding if (in general) Mcu GPIO can be programed to such operation of being '1' or 'Z' mode by SW implementation. or it depends on its HW?
for insteance if the HW for output implemented by Pull up res. so probobly such I/O won't be able to be in Hi-Z but only '1' or '0'.
So what i ask is if there are MCus with HW that allows their output be programed to Hi-Z
 

The "Open Drain" outputs on microcontrollers (e.g. PICs) are similar to what you are wanting except they do '0' and 'Z' not '1' and 'Z'. They simply use the NMOS transistor to ground and don't turn on the PMOS. What you want is the opposite.

Microcontroller outputs are effectively high-Z if you change them to inputs - that is common if you are doing bi-directional communication.

Keith.
 
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