Re: I/p stage and o/p stage of analog i/o card,100khz,10v p-p
- I have a few questions about your design that may help us answer your
o Have you already designed the A/D and D/A portion of the circuit?
o You mentioned a programmable analog array. Which one are you using
and how is it used?
o Are you only asking about ESD protection and output short circuit
o How much ouput power are you generating?
There are at least two models used for ESD. One is the human body
model and the other is a machine model. They differ by the amount of
energy in the pulse and the rise times fall times etc.
o Which ESD model are you using?
There are many ways to protect the inputs of a device from ESD. Some
popular methods are:
o Series resistance with a capacitor to ground produces a low pass
filter. This is the cheapest and often an effective method of
protection. Some care must be given to the placement and selection of
the parts so that when a fast rise time pulse is applied, the
capacitor does not look inductive and the resistors look capacitive.
o Series resistance with a zener diode as a clamp. This is a very
effective method and it is fast. Zeners are better at voltages above
6V. At voltages below 6V they are more difficult to use because of
the soft "knee" voltage of zeners 5V and below. You have 10V inputs
so 12V zeners should work well for you. Often times a zener is used
in conjunction with a series capacitor and resistor.
o Fast signal diodes from the signal line to the power supply rails
are used if the impulses are of low magnitude and the supply rails
can absorb the energy. This is a common method of protecting signal
inputs because it produces a very well behaved clamp at the 0.7V
above and below the power supply voltages. It is also cheap, causes
no low pass filtering and it is very fast. Caution must be observed
if there is a possibility of a short from the signal input to a high
DC voltage that may increase the circuit supply rails.
o MOVs are often used for power line protection but are sometimes
used for signal line protection. They are good for high power
impulses but they have some other problems with aging and soft turn
o Gas discharge tubes are also used more for power line protection.
o Transorbs again are used for power line protection more than for
signal line protection.
o Tiny spark gaps in the PCB traces are used in some circuits. I
have seen them in phones and some instrumentation.
Careful layout must be observed in any method of ESD protection. If
the energy can go around your protection circuit then you have wasted
your efforts. There are several good books on the subject and I think
there is some information on the web.
Output short circuit protection can be achieved by selecting an
appropriate op amp for the output stage. The datasheets will say that
the output of a device is fully protected against short circuits to
ground or to the power supply rails.
--- In Electronics_101@y..., james rayudu <james_analog@y...> wrote:
> hello all,
> I am designing an analog i/p and analog o/p board.Can anybody tell
me what should be the
> 1) i/p stage of analog(10V p-p,100khz),i.e. what components come
into picture for esd protection,highvoltages, high i/p
impedance....will it be sufficient if i feed analog i/p of 100khz to
PGA(programmble gain amplfier/instrumentation amplifier).Please tell
me how do i give protection from esd,highvoltages..
> 2) what should be the o/p stage, for analog signal output of 10vp-
p,100khz,and + -10ma(0-20ma) current driving.and for any shortcircuit
> Any suggestions are welcome.
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