G
Guy Macon
- Jan 1, 1970
- 0
I am working on a circuit to detect a very faint spot of IR
light on an X-Y PSD photodiode. I can make the spot as
bright as I want, but brighter equals more IR LEDs and a higher
cost. Response time is not an major issue; I would like to
modulate my source in the 1khz to 10khz range, but will go
much lower if needed.
I made two test PWBs with short leads, ground plane,
and guard rings, using two opamp stages as follows:
My first stage is an opamp in transimpedence (current to
voltage) mode. "+" is gnd, and "-" has a photodiode to ground
and a large feedback R and small feedback C from the opamp output.
(I have no bias on the photodiode now, but will be experimenting
with using a small (0-50mV) bias later).
My second stage is a standard inverting opamp voltage gain stage.
One of my PWBs uses single opamps (+2, -3, out6, +vcc7, -vcc4)
and the other uses a quad (+1/7/8/14, -2/6/9/14, out1/7/8/14,
+vcc4, -vcc7).
I am running tests with the best opamps I know of and with the
cheapest opamp I know of. I am looking for the best tradeoff
between receiver cost and transmitter cost.
For the singles, I am using a Linear LT1792 for the first
stage and a LT1793 for the second. I chose them because
the LT1792 has (0.8fA/sqrtHz) of current noise and the LT1793
has (4.2nV/sqrtHz) of voltage noise. For the quad I am using
an LM324 because I can get them for six cents each.
That pretty much covers the high-performance end and the
cheap end. Now I need to try a few opamps that are between
the two extremes. Can anyone recommend a few parts that
have a good tradeoff between low current noise, reasonable
voltage noise, low cost, and which match one of the two
pinouts I am using?
light on an X-Y PSD photodiode. I can make the spot as
bright as I want, but brighter equals more IR LEDs and a higher
cost. Response time is not an major issue; I would like to
modulate my source in the 1khz to 10khz range, but will go
much lower if needed.
I made two test PWBs with short leads, ground plane,
and guard rings, using two opamp stages as follows:
My first stage is an opamp in transimpedence (current to
voltage) mode. "+" is gnd, and "-" has a photodiode to ground
and a large feedback R and small feedback C from the opamp output.
(I have no bias on the photodiode now, but will be experimenting
with using a small (0-50mV) bias later).
My second stage is a standard inverting opamp voltage gain stage.
One of my PWBs uses single opamps (+2, -3, out6, +vcc7, -vcc4)
and the other uses a quad (+1/7/8/14, -2/6/9/14, out1/7/8/14,
+vcc4, -vcc7).
I am running tests with the best opamps I know of and with the
cheapest opamp I know of. I am looking for the best tradeoff
between receiver cost and transmitter cost.
For the singles, I am using a Linear LT1792 for the first
stage and a LT1793 for the second. I chose them because
the LT1792 has (0.8fA/sqrtHz) of current noise and the LT1793
has (4.2nV/sqrtHz) of voltage noise. For the quad I am using
an LM324 because I can get them for six cents each.
That pretty much covers the high-performance end and the
cheap end. Now I need to try a few opamps that are between
the two extremes. Can anyone recommend a few parts that
have a good tradeoff between low current noise, reasonable
voltage noise, low cost, and which match one of the two
pinouts I am using?