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PIN diode circutis no good at low frequencies? - RF Cafe Forums
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morangie18
Post subject: PIN diode circutis no good at low frequencies?
Posted: Thu Oct 12, 2006 9:04 pm
Lieutenant
Joined: Thu
Oct 12, 2006 8:56 pm
Posts: 2
Can someone please help a novice
understand why are PIN diode limiters, switches, attenuators etc...
never characterized or available for low frequency applications (e.g.
HF). What happens to make them no good down in that frequency range?
Top
IR
Post subject: Posted: Mon Oct 16, 2006 3:04
am
Site Admin
Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
Hello,
PIN Diodes are characterized
only for RF/Microwave frequencies because their resistance (In forward
bias) is not constant at low frequencies. Usually this resistance increases
at low frequencies (Below 10MHz) and is not stable with changing the
forward current.
Hope this helps.
_________________
Best regards,
- IR
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fred47
Post subject:
PIN DiodesPosted: Thu Oct 19, 2006 3:54 pm
General
Joined: Wed Feb 22, 2006 3:51 pm
Posts: 104
Hi!
A bit
more explanation for "low frequency" use of PIN diodes:
PIN diode
operation depends on the carrier (hole or electron) lifetime in the
intrinsic region. The longer the lifetime, the lower the frequency you
can use the PIN diode at.
I've seen successful use of PIN diodes
(with the appropriately long carrier lifetime) in an attenuator operating
at 455 kHz. The designer had to search fairly hard for an adequate diode,
though.
The carrier lifetime depends on the purity and defect
density of the intrinsic region, so it's only somewhat under manufacturer
control. I haven't seen many PIN diode data sheets that omit the lifetime
as a spec - but if you're implementing a circuit on an IC, the foundry
may not know what a PIN diode will do in their process, unless they've
gone out of their way to characterize it.
When the signal cycle
time T = 1/f is near the carrier lifetime, the PIN diode starts acting
like a regular diode.
Good Luck!
Fred
Posted 11/12/2012
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