R
Roger Bourne
- Jan 1, 1970
- 0
Hello all,
I will have a n-well/p-substrate photodiode (PD) on a asic.
I am currently in the midst in attempting to quantify the impact of
the parasitic substrate bjt that will be formed with the nearby n-
wells. (E=cathode of PD, B=anode of PD, a.k.a grounded (0V) substrate,
C=nearby nwells @ +1.5V). In order to minimize the [collector-base
current contribution to the emitter] AND the [emitter-base current
contribution to the collector], I plan to have the photodiode
surrounded by a massive ring of substrate contacts. Thus the parasitic
bjt aplha parameter will be as near as zero as possible, tending to
mimic the bjt behavior to 2 diodes. However, I do not know how to
evaluate how destructive the bjt will be to the photodiode's
photocurrent resolution. In other words, how much of the collector
current from the reverse-biased CB junction actually makes to the
emitter.
The photodiode needs to be able to measure photocurrents in the range
of (less than 100fA), and as such needs no additional currents to be
injected from the collector (even though they are ~Is).
Does anyone have any data/info/advice concerning the parasitic
substrate bjts of nwell (photo)diodes and their anullment w.r.t to a
ring of substrate contacts?
Any help will be appreciated
-Roger
I will have a n-well/p-substrate photodiode (PD) on a asic.
I am currently in the midst in attempting to quantify the impact of
the parasitic substrate bjt that will be formed with the nearby n-
wells. (E=cathode of PD, B=anode of PD, a.k.a grounded (0V) substrate,
C=nearby nwells @ +1.5V). In order to minimize the [collector-base
current contribution to the emitter] AND the [emitter-base current
contribution to the collector], I plan to have the photodiode
surrounded by a massive ring of substrate contacts. Thus the parasitic
bjt aplha parameter will be as near as zero as possible, tending to
mimic the bjt behavior to 2 diodes. However, I do not know how to
evaluate how destructive the bjt will be to the photodiode's
photocurrent resolution. In other words, how much of the collector
current from the reverse-biased CB junction actually makes to the
emitter.
The photodiode needs to be able to measure photocurrents in the range
of (less than 100fA), and as such needs no additional currents to be
injected from the collector (even though they are ~Is).
Does anyone have any data/info/advice concerning the parasitic
substrate bjts of nwell (photo)diodes and their anullment w.r.t to a
ring of substrate contacts?
Any help will be appreciated
-Roger