"Tim Wescott" wrote in message
...
johna@m wrote:
Should not we expect that the current, even at very small level, to be
half rectified by a diode, since the reverse resistance of the diode is
supposed te be far greater than the forward resistance?

Why can't we found this result in smulation. Is it a flaw in the
simulator (Simplorer) or is the theoric behavior of a diode that
changes in case of very small input ?

Regards,

John.

The diode behavior is a continuous curve, so for a small AC voltage you
won't see much change in the diode's resistance even at zero bias.
Unless you're modeling a really leaky diode, however, you are probably
seeing a situation where the diode's resistance is effectively shunted
by it's capacitance and you are seeing capacitive coupling rather than
conduction.

The point about continuous curve is well made.

The diode doesn't have to hard rectify. As long as it has a non-linear V-I
graph it will produce some audio. The more sharply curved the
characteristic, the more audio is produced.

In the valve days, the anode bend detector worked that way, using a valve
biased to operate on the curved part of the characteristic.

Roger

Roger Lascelles wrote:

"Tim Wescott" wrote in message
...
johna@m wrote:
Should not we expect that the current, even at very small level, to be
half rectified by a diode, since the reverse resistance of the diode is
supposed te be far greater than the forward resistance?

Why can't we found this result in smulation. Is it a flaw in the
simulator (Simplorer) or is the theoric behavior of a diode that
changes in case of very small input ?

Regards,

John.

The diode behavior is a continuous curve, so for a small AC voltage you
won't see much change in the diode's resistance even at zero bias.
Unless you're modeling a really leaky diode, however, you are probably
seeing a situation where the diode's resistance is effectively shunted
by it's capacitance and you are seeing capacitive coupling rather than
conduction.

The point about continuous curve is well made.

The diode doesn't have to hard rectify. As long as it has a non-linear V-I
graph it will produce some audio. The more sharply curved the
characteristic, the more audio is produced.

In the valve days, the anode bend detector worked that way, using a valve
biased to operate on the curved part of the characteristic.

Roger

Right. Take a look at a diode curve across a 100 uV region. Most diodes
will look pretty flat, even without considering the effects of
capacitance and other parasitics.

--
Paul Hovnanian
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My inner child can beat up your inner child.
-- Alex Greenbank