What is the difference between the nand gate ic's 74ls00 and 74ls132?
The 74LS00 is a logic NAND gate with normal logic level inputs.
This means that the inputs has a low range below 0.8V, unrecognised
range and a high range above 2V. At any time a input signal crosses
those levels, a change in state can be expected. Applicable to the
LS family, they have a floating input that means it is uncertain
the state of logic level if no input is connected. Therefore never
assume that since the input is not connected that the circuit will
assume a zero, it can be either zero or one.
The 74LS132 is also a NAND gate logic function. But different to
the Logic level input it uses what we call a Schmitt trigger input
to improve noise immunity in a circuit. In simple terms; it's
really nothing more than a comparator input. But the Schmitt
trigger also have a hysteresis, which help to eliminate the affect
what noise have on the circuit.
On a more technical note
Each circuit contains a 2-input Schmitt trigger followed by a
Darlington level
shifter and a phase splitter driving a TTL totem pole output.
The totem pole is basically a push-pull output stage constructed
with two p-n-p transistors and a diode on the output.
The comparator function would mean that there is a particular
threshold level on the input and if the input voltage pass the
particular level, the output or intermediate state of the function
will change state. In the case of multiple logic inputs the change
of input state does not necessarily mean a change in output state
and therefore I will refer to an intermediate area inside the
function related to the input state.
The hysteresis create a high and low trigger points. This cause
the input to at least pass the high trigger point of about 1.6V
before the intermediate state will change or drop below the 0.9V
before the intermediate state change back again. Therefore the
practical unit will not have one particular level to change state
but these two fixed trigger points must be used.
It sounds like it complicates matters but it really helps to
handle input noise signals which makes the Schmitt trigger a handy
device. Making it a good device for signal conditioning of logic
signals in some applications.
Also take note that the high and low hysteresis trigger points
may vary with supply voltage. In fact I do not recommend it as
standard practice to use a Schmitt trigger to evaluate analogue
levels, some engineers may differ but I would rather refer to a
real comparator circuit design where you have more control over
precision, trigger points and reference levels. But may be
considered for logic inputs from sensors or conditioning of logic
signals
Some circuits may also employ Schmitt trigger devices for
oscillators and contact debouncing