C
Chris Carlen
- Jan 1, 1970
- 0
Hi:
I'm contemplating the design of an amplified photodiode instrument that
should be able to bias a photodiode for photoconductive operation, and
provide a positive voltage output of at least 0-10V into a high-Z load.
There would likely be three stages of active circuitry, a
transimpedance amp, an adjustable extra gain stage, and a
buffer/line-driver. Max bandwidth of about 10MHz. I won't be
optimizing the design for noise other than making sure power is clean,
the board layout is decent, mid-range parts with fairly low-noise as
well as low-power are chosen, and the circuitry is enclosed in a metal
can for shielding. This does not need to be a "shot-noise limited"
design, a task that is beyond my capabilities.
It would be preferable to power it with a single 9V battery. However,
to meet the specs, this would then require some DC/DC conversion to make
a split supply for ease of op-amp circuitry. Or perhaps I'd power
from 2x9V batts, and just use a switched-cap chip to generate -V for the
first transimpedance stage. That way the DC/DC could be less
complicated and not need to supply much power.
But can a DC/DC be incorporated in a way that will not substantially
increase the noise of the system? In other words, would you even
consider putting any form of DC/DC into a can with a photodiode amp, and
expect to avoid adding any noise to the system that would not have
originally been present?
If it hopeless to avoid adding noise by putting a DC/DC into the can
then I'll have to settle for a remote split DC supply fed by a cable.
Thanks for input.
--
Good day!
________________________________________
Christopher R. Carlen
Principal Laser&Electronics Technologist
Sandia National Laboratories CA USA
[email protected]
NOTE, delete texts: "RemoveThis" and
"BOGUS" from email address to reply.
I'm contemplating the design of an amplified photodiode instrument that
should be able to bias a photodiode for photoconductive operation, and
provide a positive voltage output of at least 0-10V into a high-Z load.
There would likely be three stages of active circuitry, a
transimpedance amp, an adjustable extra gain stage, and a
buffer/line-driver. Max bandwidth of about 10MHz. I won't be
optimizing the design for noise other than making sure power is clean,
the board layout is decent, mid-range parts with fairly low-noise as
well as low-power are chosen, and the circuitry is enclosed in a metal
can for shielding. This does not need to be a "shot-noise limited"
design, a task that is beyond my capabilities.
It would be preferable to power it with a single 9V battery. However,
to meet the specs, this would then require some DC/DC conversion to make
a split supply for ease of op-amp circuitry. Or perhaps I'd power
from 2x9V batts, and just use a switched-cap chip to generate -V for the
first transimpedance stage. That way the DC/DC could be less
complicated and not need to supply much power.
But can a DC/DC be incorporated in a way that will not substantially
increase the noise of the system? In other words, would you even
consider putting any form of DC/DC into a can with a photodiode amp, and
expect to avoid adding any noise to the system that would not have
originally been present?
If it hopeless to avoid adding noise by putting a DC/DC into the can
then I'll have to settle for a remote split DC supply fed by a cable.
Thanks for input.
--
Good day!
________________________________________
Christopher R. Carlen
Principal Laser&Electronics Technologist
Sandia National Laboratories CA USA
[email protected]
NOTE, delete texts: "RemoveThis" and
"BOGUS" from email address to reply.