Applications for Schottky and PIN diodes

Hi,

I've been learning the fundamental and applications of Schottky didoes PIN didoes. I know that Schottky didoes are good for mixers and PIN didoes are good for switch design.

The only big different between Schottky and PIN diode is the reverse recovery time. PIN didoes take time to switch ON-OFF, but it could be in nanoseconds, which is pretty fast, depending on process technology. Other parameters should be similar such as Rs, Ct...

So my question is that why don't designers use Schottky diodes for switch design and PIN didoes for mixer design? In a mixer design, we want fastest switching time as possible to eliminate the IMD during transient time, but isn't nanosec pretty fast? The switching time of Schottky diodes are in fsec, but still not a good choice for switch design?
Is there a specific switching time required for mixer operations? I am really confused..

Please help. Thanks.

Your Schottky is not good for "switches" because its
depletion capacitance does not swing far enough in
either direction. The PIN "I" region gives the distance
you need for low C in reverse bias, the PN gives you a
huge stored charge that equates to a high forward
biased capacitance.

Schottkies also tend to leak worse.

A PIN diode storing charge will make mixer operation
"lumpy" (distortion / spurii) as the diode swings from
forward to reverse bias and the stored charge slug
comes out, then quits. Depending on the storage
time in relation to period this could look like a "glitch"
(broadband energy) or just a really messed up
waveform (when storage time is less than quarter-
period, but nontrivial) or a mixer that just doesn't
work right because the diode never turns entirely
"off" (storage time > half period).

dick_freebird said:

Your Schottky is not good for "switches" because its
depletion capacitance does not swing far enough in
either direction. The PIN "I" region gives the distance
you need for low C in reverse bias, the PN gives you a
huge stored charge that equates to a high forward
biased capacitance.

Schottkies also tend to leak worse.

A PIN diode storing charge will make mixer operation
"lumpy" (distortion / spurii) as the diode swings from
forward to reverse bias and the stored charge slug
comes out, then quits. Depending on the storage
time in relation to period this could look like a "glitch"
(broadband energy) or just a really messed up
waveform (when storage time is less than quarter-
period, but nontrivial) or a mixer that just doesn't
work right because the diode never turns entirely
"off" (storage time > half period).

Click to expand...

Thank you! It is absolutely making sense. Especially, "a mixer that just doesn't work right because the diode never turns entirely "off" (storage time > half period)".

Another thing that make Schottky and PIN diodes to be different is their ON resistance.
Schottky diodes ON resistance could be in the range of tens of ohms, when most of the PIN diodes have less than 1 ohm.
In a mixer high ON resistance could be somehow compensated, but in a power switch for example is impossible to be compensated, and the circuit lose power there.