Difference between latch and buffer

[aman]

Can any of you guys please comment on the following definitions which I
think are right.

Latch is something once enabled holds the value for infinite time as
long has it has Vcc and ground connections.

Buffer is something which holds the value for finite time during which
you need to read it. It can essentially be a part of sample and hold
circuit.

Please correct me if I am wrong.

 

[Bob Eldred]

"aman" <aman.bindra@gmail.com> wrote in message
news:1111435186.067005.248690@o13g2000cwo.googlegroups.com...

Can any of you guys please comment on the following definitions which I
think are right.

Latch is something once enabled holds the value for infinite time as
long has it has Vcc and ground connections.

Buffer is something which holds the value for finite time during which
you need to read it. It can essentially be a part of sample and hold
circuit.

Please correct me if I am wrong.

Your right about a latch, it is a digital circuit that hold a state as long
as power is applied. They are usually made from "D" flops and must be
clocked. This type changes state with the clock edge depending on the input.
They do not change state with the input state only. In other words, if the
output is high and the input goes low, the output will only change to low
when the next clock edge comes. Some latches use "R-S" flip-flops that chang
state with a set or reset signal and do not require a clock.

A buffer may or may not have a latch in it. It's purpose is to drive a line
or to drive a number of other circuits, to apply more current to a digital
signal. In addition many buffers can operate tri-state where they have a
high impedance mode that doesn't load other connected driving circuits. Many
times they are bi-directional and can transmit or receive. When there is no
internal latch, the output follows the input without a clock, some invert
the signal.

Analog buffers are high input impedance amplifiers and are used for sample
and hold as well as to drive lines or other circuits. The usually have unity
gain. Their purpose is to reduce loading and provide isolation in analog
devices.
Bob

 

[Jamie]

aman wrote:

Can any of you guys please comment on the following definitions which I
think are right.

Latch is something once enabled holds the value for infinite time as
long has it has Vcc and ground connections.

Buffer is something which holds the value for finite time during which
you need to read it. It can essentially be a part of sample and hold
circuit.

Please correct me if I am wrong.

i'll give it a shot.

Latch
something that holds data that was latched in
at some time interval from a source that may or has
already changed its value of the source since the
latch state took place.
in other words, once a value is latched from a
source, it does not care what the value of the source
changes to, the latched value will be what you see until
you relatch again.

---
Buffer.
I can think of 2 cases here.
one, a unity gain amplifier to represent a source value
with out effecting the characteristics of the source.
what this means is like Load impedance or capacitance effects
that could change the behavior of the source.
--
now in the digital sense.
A buffer is like a cache, info is backed up in memory/registers to be
read later. this way, you don't lose any data while what ever is used to
read it at the most convenient time is performed.
normally in these types of buffers, when data is read out of them
they usually do so in either FIFO(First in First out) or LIFO (Last in
First out);
normally the FIFO is use in most apps., but you do have the LIFO in
cases of Stack related type functions.

in this type of system, a Latch is not needed because the buffer is
capturing all data for you to read when able.
of course, there are limits to buffers! a good design should not
allow this to exceed the limit.
Latches can hold data when the latch state is done but, data will be
ignored until you relatch again.

hope that helped.

 

[Rich Grise]

On Mon, 21 Mar 2005 11:59:46 -0800, aman wrote:

Can any of you guys please comment on the following definitions which I
think are right.

Latch is something once enabled holds the value for infinite time as
long has it has Vcc and ground connections.

Buffer is something which holds the value for finite time during which
you need to read it. It can essentially be a part of sample and hold
circuit.

Please correct me if I am wrong.

Yes, you are wrong. A latch does hold the value indefinitely - they
come in 'transparent' and 'D-type' or 'edge-triggered'. The transparent
kind transfers its input to the output all of the time that the clock
is active, and holds when the clock goes inactive; the d-type or edge-
triggered holds what's there at the active clock edge.

A buffer is just a straight-through inverting or noninverting amplifier,
that has greater drive capability than the circuit it's buffering.

HTH!
Rich