voltage threshold for interrupts

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Hi,

I am designing a module where low voltage threshold for interrupts
are desirable. A high of 0.5V and low of 0.2V are ideal but I am not sure
if current interrupt hardware can distinguish this kind of subtle
difference.I would appreciate it if anybody could tell me whether this is
possible, or how difficult it may be, or some reference systems which
has implemented such low voltage-threshold interrupts.

Thanks in advance,

lin




Re: voltage threshold for interrupts

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The exact levels at which interrupt inputs trigger depends on the
technology of the parts used.  If, as you describe, you have specific
needs that differ from your part's characteristic, you could provide
additional circuitry, perhaps using op-amps, to process the input.

The major problem with your specification is that there is little
"dead band" between the high and low states, and your system will
suffer due to insufficient noise immunity.

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Re: voltage threshold for interrupts

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I cannot use amplifiers. The circuit I am developing should use a low
power as possible and amplifiers or other preprocessing units usually
consume power.

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I certainly agree. With help from google, I find some low-voltage
microcontrollers
have a "dead band" of about 0.9V but it is still to large for my device. Are
there
any microprocessors or interrupt handler circuit that can accept a high/low
of 0.5V/0.1V?

Thanks!

lin



Re: voltage threshold for interrupts
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I don't know of *any* logic that works with IO voltages below 1 volt.
You can get micropower analog components.  What you are trying to do is
not a normal digital function and should not be considered as such.
Find a comparator with a low enough power consumption and work with
that.  Some even have a reference built in.

Re: voltage threshold for interrupts

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This depends on what you consider low power. For example, the TLV370x family
of comparators consumes around 600 nA/channel. Is this acceptable?
(Note that the speed is rather moderate, around 40 us.) There are some
comparators with even lower quiescent current, but they tend to have an
open-drain output which then consumes some power.

Another possibility would be to use the internal comparator of a
microcontroller. It consumes probably a lot more, but you can
switch it on only once in a while to check if something has
happened in the inputs, in case your speed requirements allow this.

Of course, your total power consumption will depend on how you make
the reference voltage for the comparator. You'll need to use megaohm
resistances in any case.

You could use an amplifier to amplify your input signals to acceptable
levels. However, linear amplifiers provide a worse power-to-speed
ratio than comparators.

- Ville

--
Ville Voipio, Dr.Tech., M.Sc. (EE)

Re: voltage threshold for interrupts
<snip>
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  There are uC available that include very low power
Comparitors, that can drive the INTERRUPT logic.
  These allow you to define your own voltage threshold levels.
  Look at the www.Cygnal.com families, and also
the Philips P89LPC9xx families.
  IIRC, the Cygnal ones can run < 1uA of comparitor Icc adder.

-jg


Re: voltage threshold for interrupts
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Interrupts have nothing to do with it.  You are interested in
logic levels.  Receivers for such low level swings will normally
be based on long-tailed pairs, op-amps, etc.  Your best bet for
cheap available ICs for the range might be RS485 receivers, which
will convert to the usual logic levels.

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Re: voltage threshold for interrupts
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Maybe what he's looking for is a comparator between the
interrupt pin and his source.  I can imagine some sort
of opto or inductive sensor that he wants to derive an
interrupt from.


Re: voltage threshold for interrupts
On Sun, 11 Jan 2004 19:34:51 -0500, "Lin Gu" <l g u @ i n a m e . c o
m> wrote:

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If you want precise voltage thresholds like that, I think you'll need
to use an analog comparator to measure the voltage, with the
comparator's output generating a logic level signal to be used for the
processor's interrupt input.

Digital inputs to microcontrollers (or digital ICs) are not intended
for precision voltage measurements.



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