# AND gate output

Discussion in 'Electronic Basics' started by novice, Jul 6, 2006.

1. ### noviceGuest

If suppose the inputs of amplitude X and 2X are applied to the
2-input AND gate then what would be the amplitude of output ?

2. ### SimocGuest

And-gates are digital gates, so you can't input analog signal to them.
In digital system, there are just a low-level, which is usually 0V, and
a high-level, which is some voltage depending on the system. So you
must know what is the high level voltage in your and-gate. If it's a
basic TTL-chip, it's 5V. So you can't input any other amplitudes than
0V or 5V.

If both of its inputs are low (=have 0V on them), the output will be
low (0V)

If one of its inputs is low (0V) and the other is high (5V), the output
will be low (0V)

If both of its inputs are high (5V) then the output will be high (5V).

That's why is it AND-gate, as the input 1 AND input 2 must both be high
to get the output going high.

3. ### noviceGuest

Thanks a lot simoc for your valuable response.But if 4.8V and 5V are
given as inputs then what would be the output? 4.8V is also considered
as High.Right?

4. ### Ralph MoweryGuest

While the voltage may vary by a few tenths of a volt or so, digital logic
only has two states (well if you concider an undefined state 3 ) high and
low. Anything from about 0 to .8 is a low and from 2 to 5 is a high. The
area between about .8 and 2 is undefined and should not be in a digital
circuit . All the above should be for a 5 volt TTL circuit. Other voltages
and types of ICs will be similar in the way they work.

After all that, if you have an input gate with many inputs and they are all
high or low, the output will still be almost the same voltage, either the
normal high or low.

5. ### BobGuest

You need to look at the specs for a particular logic standard. Are you

TTL
LVTTL
4000 family CMOS
LVCMOS 3.3V
LVCMOS 2.5V
SSTL 2.5V
SSTL 1.8V
HSTL 1.8V
HSTL 1.5V
LVDS
BLVDS
LDT
LVPECL
PECL
ECL
GTL
....
which one???

Each standard will state, for inputs and outputs (a separate set of values
for each) --
max voltage for a '0'
min voltage for a '1'
along with many other characteristics.

Since you mentioned 4.8V and 5V, I'm assuming you're talking about TTL. For
TTL (commercial grade), an input sees a '0' if the voltage is less than
0.8V, and sees a '1' if the voltage is higher than 2.0V. Outputs (for a
given max load) will put out max of 0.4V for a '0', and minimum of 2.4V for
a '1'.

Don't be afraid to open some datasheets. There is really no other way to
learn the specifics

Bob

6. ### noviceGuest

If suppose I take TTL AND gate.Then both 4.8V and 5V are considered as
high.Obviously the AND output would be High.Now please tell me whether
the output will be 4.8V or 5V.

7. ### John FieldsGuest

---

Bob already gave you the answer, (shown below) and it's that the
output voltage for a TTL "high" can be anywhere between 2.4V and 5V
for a supply voltage of 5V.

8. ### SimocGuest

the quote, NOT ABOVE.

But then the answer It's usually nearly the operating voltage which
you input to the Vcc-pin of the chip. And it should be something about
5V, within the limits of its tolerance (I don't remember, see the
datasheet, although the 4.8V will be within the tolerance).

But actually it doesn't probably matter anyhow, as probably nothing
that will be fed by its output will "care" about such low (0.2V)
diference.

9. ### Alan BGuest

You are trying to drink whiskey from a bottle of wine. Analog circuits
deal with magnitudes, digital circuits deal with states. The magnitude of
the output of an analog circuit is dependent upon the magnitudes of the
inputs. The state of the output of a digital circuit is dependent upon the
states of the inputs. There is no direct relationship between the
magnitudes of the inputs of a digital circuit and the magnitude of its
output.

10. ### Guest

i am a novice in this area.just reply me if i am wrong
in digital ics the output voltage if in corresponding to the
vcc.
even if dont give any inputs the output will be high unless u dont
ground any of the pins in the case of AND gate. as ralph replied the
voltages 2v to 5v will be considered high,
then output will not be corresponding to the inputs but with the vcc
which may be +5v.
reply me if i am wrong

12. ### nitinGuest

------

thanks , i was wrong . i checked it out.
If suppose I take TTL AND gate.Then both 4.8V and 5V are
considered as
high.Obviously the AND output would be High.Now please tell me whether
the output will be 4.8V or 5V.
that novice asked. pls tell me abt
that.thans a lot

13. ### BobGuest

If you cannot read and understand the previous posts then the answer is that
you need to select a different career path. You will not be successful in
electronics. I promise you that this is true.

Bob

14. ### nitinGuest

-------

hey hey hey
i am sorry abt my mistake . u cant advice like that .
ive introduced myself as beginner. and if the questions or answers are
wrong, just justify urself.we are here to discuss and if u think u are
a an expert in electronics prove urself rather than talk more.
reply me . no thanks for ur assumption of my career in electronics.

16. ### jasenGuest

They already said the output will be somewhere between 2.4 an 5V.
This is assuming it's a TTL chip, and it's being used correctly.

Bye.
Jasen

17. ### Peter BennettGuest

Please try to use something resembling normal English - do not use "u"
when you mean "you". As a native English speaker, I find that very
distracting - I can't imagine the trouble "u" and "urself" will cause
those for whom English is a second language.

For bipolar TTL logic circuits, anything above 2.4 volts will be
considered a high. I think most parts will produce 3 - 3.5 volts for
a high, and around 0.4 volts as a low. (I've been working with this
stuff for so long that just looking at signal levels or waveforms, I
"know" what is "high" without having to really measure the voltage.)

CMOS logic will produce something over 4.5 volts for a high (assuming
5 volts power supply, and depending on the load the output is driving)

--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter

18. ### Alan BGuest

Hello. There is no answer to this question:

"Now please tell me whether the output will be 4.8V or 5V."

You must ask a different question.

19. ### nitinGuest

hello to everybody
I am sorry for those who got hurt there.
Now I am known to quite number of members.