Difference between latch and buffer

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.

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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

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Bob Eldred

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

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Rich Grise

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.

    I can think of 2 cases here.
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