Looking for very low threshold voltage NMOS and its PMOS counterpart...

[amal banerjee]

On Friday, September 22, 2023 at 1:43:45 PM UTC+5:30, Jan Panteltje wrote:

On a sunny day (Thu, 21 Sep 2023 23:20:09 -0700 (PDT)) it happened amal
banerjee <daku...@gmail.com> wrote in
e1f8fc46-a40d-4fb8...@googlegroups.com>:

On Thursday, September 21, 2023 at 10:54:43 AM UTC+5:30, Jan Pantel=
tje wrote:
On a sunny day (Wed, 20 Sep 2023 21:28:49 -0700 (PDT)) it happened amal
banerjee <daku...@gmail.com> wrote in
21592d6c-93a9-4852...@googlegroups.com>:

On Wednesday, September 20, 2023 at 8:51:50 PM UTC+5:30, John La> >rki=
n wrote:
On Wed, 20 Sep 2023 08:08:08 -0700 (PDT), amal banerjee
daku...@gmail.com> wrote:

Could some electronics guru please help ? I am looking for a very low=
(fe=
w milliVolts) VTO commercially available NMOS, and its corresponding PMO=
S.=

I am trying to use a reverse biased photodiode(very low output curren=
t) =
to
trigger a PMOS. The output voltage could then be used to trigger idea=
lly=
a
BJT. Any hints, suggestiosn would be greatly appreciated. Thanks in a> >dva=
nce.
What is VTO?

I don\'t think such a part exists. A photodiode might just barely turn
on a high-beta bipolar transisor.

What\'s the open-circuit voltage of the photodiode? What\'s the current?
Is a power supply available? If the pd is back-biased by a supply,
you\'d have lots of voltage available to turn on a mosfet.

A lithium battery might power a micropower comparator for decades.

Sorry for the confusion. \'VTO\' means threshold voltage for the mosfet..
The candidate photodiode is BPW31|34. The datasheet contains the followi> >ng=

data:
Open circuit voltage : 440 mV
In reverse bias, the diode is open circuit, so current should flow. The > >da=
rk current
is 12 pA.

Think \'current\'
the reverse photo-diode could drive the base of for exampe a NPN directly
photo diode current amplified by beta * R1 is output.
Note leakage etc..

------------------------ +
| |
--- R1 a few k
/ \\ |
--- |------------ out, negative going on light input
| c
---- b NPN beta 200
e
|
----------------- GND
I have tested your suggestion with SPICE simulations using an ordinary BJT(> >BC547) and two RF BJTs
(BFR92A, BFQ790) each biased(as per Vce, Ic values listed in their respecti=
ve datasheets) for beta
values(150-200). I am using a GaAs photodiode SPICE model, which uses a thi> >rd input node for an
input voltage for the incident light. The light is pulsed, @ 1.5 MHz, 15..0 > >MHz and 150.0 MHz with pulse
amplitudes in the low milliVolt(1-2) range. Of the three transistors BFQ790> > performs best, but like each
of the other two, the output voltage at the output 50.0 Ohm resistor is in > >the tenths of milliVolt range.
R1 is supposed to be several k, 100 k would be a good start
Add an emitter follower if you want to drive 50 Ohms
You could also use a darlington configuration in place of the first tranistor to mutiply beta / current gain to say 200 x 200

So the \'heavy\' version:

------------------------------------- +
| | | |
--- | R1 100 k |
/ \\ | | c
--- | |--zener---b NPN TR3
| c TR1 | | e
-- b NPN c | |-----> out, negative going on light input
e -------- b NPN | |
darlington e TR2 R3 R2 50 Ohm
| | |
----------------- GND
You could add a few volt zener in the base of TR3 to lower DC level output for no signal.
So for say 12 V supply drop the base of TR3 for no signal to about 1V.
The possibilities are endless.

Darlington for TR3 will let you output even more
Yes, your 150 MHz... is bit high for those transistors.. won\'t work.

Maybe a BFY90 in darlington mode with R1 220 Ohm will? Not tested.
Or triple darlington....
What is the photo diode reverse current with light on say a 12V supply?

The \'heavy\' version that you have is somewhat congested. If you are saying TR3(the transistor whose base
is connected to the photodiode anode) be a Darlington pair, I have tried that already in the SPICE simulation,
although without the 100k (R1). The simulation results were not good - both the output current through and
voltage across the 50 Ohm load were worse compared to the single transistor case. I will definitely try
out it out again with the 100k(R1). I did think about the emitter follower at the TR3 output, but after
I examined the single TR3 output(across the 50 Ohm) I did not pursue it. The last question
about the reverse bias current for photodiode I am not sure, because so far these are all based on
SPICE simulations. The candidate photodiode I have in mind is BPW31|34(the Google query
for BPW31 datasheet returns the one for BPW34). The datasheet for BPW34 states that the open
circuit voltage is 440 mV -i.e., the reverse biased diode case.

 

[amal banerjee]

On Friday, September 22, 2023 at 4:01:34 PM UTC+5:30, Phil Hobbs wrote:

amal banerjee <daku...@gmail.com> wrote:
On Thursday, September 21, 2023 at 10:54:43/AM UTC+5:30, Jan Panteltje wrote:
On a sunny day (Wed, 20 Sep 2023 21:28:49 -0700 (PDT)) it happened amal
banerjee <daku...@gmail.com> wrote in
21592d6c-93a9-4852...@googlegroups.com>:

On Wednesday, September 20, 2023 at 8:51:50/PM UTC+5:30, John Larki> >n wrote:
On Wed, 20 Sep 2023 08:08:08 -0700 (PDT), amal banerjee
daku...@gmail.com> wrote:

Could some electronics guru please help ? I am looking for a very low(fe=
w milliVolts) VTO commercially available NMOS, and its corresponding PMOS.=

I am trying to use a reverse biased photodiode(very low output current) =
to
trigger a PMOS. The output voltage could then be used to trigger ideally=
a
BJT. Any hints, suggestiosn would be greatly appreciated. Thanks in adva> >nce.
What is VTO?

I don\'t think such a part exists. A photodiode might just barely turn
on a high-beta bipolar transisor.

What\'s the open-circuit voltage of the photodiode? What\'s the current?
Is a power supply available? If the pd is back-biased by a supply,
you\'d have lots of voltage available to turn on a mosfet.

A lithium battery might power a micropower comparator for decades.

Sorry for the confusion. \'VTO\' means threshold voltage for the mosfet..
The candidate photodiode is BPW31|34. The datasheet contains the following
data:
Open circuit voltage : 440 mV
In reverse bias, the diode is open circuit, so current should flow. The da=
rk current
is 12 pA.

Think \'current\'
the reverse photo-diode could drive the base of for exampe a NPN directly
photo diode current amplified by beta * R1 is output.
Note leakage etc..

------------------------ +
| |
--- R1 a few k
/ \\ |
--- |------------ out, negative going on light input
| c
---- b NPN beta 200
e
|
----------------- GND
I have tested your suggestion with SPICE simulations using an ordinary
BJT(BC547) and two RF BJTs
(BFR92A, BFQ790) each biased(as per Vce, Ic values listed in their
respective datasheets) for beta
values(150-200). I am using a GaAs photodiode SPICE model, which uses a
third input node for an
input voltage for the incident light. The light is pulsed, @ 1.5 MHz,
15.0 MHz and 150.0 MHz with pulse
amplitudes in the low milliVolt(1-2) range. Of the three transistors
BFQ790 performs best, but like each
of the other two, the output voltage at the output 50.0 Ohm resistor is
in the tenths of milliVolt range.

If you don’t know how much light you’ve got, you’re probably doomed. That
needs to be in optical terms, like “1.2 ns full width at half maximum, 1-2
picojoules, 950 nm”.

It also matters whether the light is spatially coherent, because that
governs how small a photodiode you can use.

If you tell us what you’re actually trying to do, we can be a lot more
helpful. Generating a sync signal from a laser beam is much easier than
detecting scattered light from a matte-textured object at a distance, but
there are tricks to make both easier.

Something like, “I need to detect laser pulses bouncing off a microscope
sample so that I can do lock-in measurements of the photoacoustic response”
or “I’m going to bounce laser pulses off my cat” would help a lot.

Cheers

Phil Hobbs

Cheers

Phil Hobbs

For instance
Find that out, first

--
Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC /
Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics

So far all my results are based on SPICE simulations. The candidate photodiode is BPW34 whose datasheet
states that it is for high speed light detection for visible and near infra red with half angle of sensitivity +/-65
degree. Reverse light current is 75 mA(typical).
I am experimenting with line of sight light detection at high frequency. No I would not want to bounce light
off my kitty, esepecially now that it has a kitten to take care of.

 

[Phil Hobbs]

amal banerjee <dakupoto@gmail.com> wrote:

On Friday, September 22, 2023 at 4:01:34 PM UTC+5:30, Phil Hobbs wrote:
amal banerjee <daku...@gmail.com> wrote:
On Thursday, September 21, 2023 at 10:54:43/AM UTC+5:30, Jan Panteltje wrote:
On a sunny day (Wed, 20 Sep 2023 21:28:49 -0700 (PDT)) it happened amal
banerjee <daku...@gmail.com> wrote in
21592d6c-93a9-4852...@googlegroups.com>:

On Wednesday, September 20, 2023 at 8:51:50/PM UTC+5:30, John Larki> >n wrote:
On Wed, 20 Sep 2023 08:08:08 -0700 (PDT), amal banerjee
daku...@gmail.com> wrote:

Could some electronics guru please help ? I am looking for a very low(fe=
w milliVolts) VTO commercially available NMOS, and its corresponding PMOS.=

I am trying to use a reverse biased photodiode(very low output current) =
to
trigger a PMOS. The output voltage could then be used to trigger ideally=
a
BJT. Any hints, suggestiosn would be greatly appreciated. Thanks in adva> >nce.
What is VTO?

I don\'t think such a part exists. A photodiode might just barely turn
on a high-beta bipolar transisor.

What\'s the open-circuit voltage of the photodiode? What\'s the current?
Is a power supply available? If the pd is back-biased by a supply,
you\'d have lots of voltage available to turn on a mosfet.

A lithium battery might power a micropower comparator for decades.

Sorry for the confusion. \'VTO\' means threshold voltage for the mosfet.
The candidate photodiode is BPW31|34. The datasheet contains the following
data:
Open circuit voltage : 440 mV
In reverse bias, the diode is open circuit, so current should flow. The da=
rk current
is 12 pA.

Think \'current\'
the reverse photo-diode could drive the base of for exampe a NPN directly
photo diode current amplified by beta * R1 is output.
Note leakage etc..

------------------------ +
| |
--- R1 a few k
/ \\ |
--- |------------ out, negative going on light input
| c
---- b NPN beta 200
e
|
----------------- GND
I have tested your suggestion with SPICE simulations using an ordinary
BJT(BC547) and two RF BJTs
(BFR92A, BFQ790) each biased(as per Vce, Ic values listed in their
respective datasheets) for beta
values(150-200). I am using a GaAs photodiode SPICE model, which uses a
third input node for an
input voltage for the incident light. The light is pulsed, @ 1.5 MHz,
15.0 MHz and 150.0 MHz with pulse
amplitudes in the low milliVolt(1-2) range. Of the three transistors
BFQ790 performs best, but like each
of the other two, the output voltage at the output 50.0 Ohm resistor is
in the tenths of milliVolt range.

If you don’t know how much light you’ve got, you’re probably doomed. That
needs to be in optical terms, like “1.2 ns full width at half maximum, 1-2
picojoules, 950 nm”.

It also matters whether the light is spatially coherent, because that
governs how small a photodiode you can use.

If you tell us what you’re actually trying to do, we can be a lot more
helpful. Generating a sync signal from a laser beam is much easier than
detecting scattered light from a matte-textured object at a distance, but
there are tricks to make both easier.

Something like, “I need to detect laser pulses bouncing off a microscope
sample so that I can do lock-in measurements of the photoacoustic response”
or “I’m going to bounce laser pulses off my cat” would help a lot.

Cheers

Phil Hobbs

Cheers

Phil Hobbs

For instance
Find that out, first

--
Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC /
Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics
So far all my results are based on SPICE simulations. The candidate
photodiode is BPW34 whose datasheet
states that it is for high speed light detection for visible and near
infra red with half angle of sensitivity +/-65
degree. Reverse light current is 75 mA(typical).
I am experimenting with line of sight light detection at high frequency.
No I would not want to bounce light
off my kitty, esepecially now that it has a kitten to take care of.

That’s way too vague for me to be able to help much, except to say that the
difficulty ranges from trivial to impossible, depending on the details.

The BPW34 isn’t great for bandwidths over 50 MHz or so, but with a better
detector and a decent front end it isn’t hard to reproduce nanosecond
pulses. Even op amps can have gain bandwidths in the gigahertz.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC /
Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics

 

[Jan Panteltje]

On a sunny day (Fri, 22 Sep 2023 05:00:49 -0700 (PDT)) it happened amal
banerjee <dakupoto@gmail.com> wrote in
<5dafb884-2b86-4c19-ad66-5985532e19c8n@googlegroups.com>:

What is the photo diode reverse current with light on say a 12V supply?
The \'heavy\' version that you have is somewhat congested. If you are saying =
TR3(the transistor whose base
is connected to the photodiode anode) be a Darlington pair, I have tried th=
at already in the SPICE simulation,
although without the 100k (R1). The simulation results were not good - both=
the output current through and
voltage across the 50 Ohm load were worse compared to the single transistor=
case. I will definitely try
out it out again with the 100k(R1). I did think about the emitter follower =
at the TR3 output, but after
I examined the single TR3 output(across the 50 Ohm) I did not pursue it. Th=
e last question
about the reverse bias current for photodiode I am not sure, because so far=
these are all based on
SPICE simulations. The candidate photodiode I have in mind is BPW31|34(the =
Google query
for BPW31 datasheet returns the one for BPW34). The datasheet for BPW34 sta=
tes that the open
circuit voltage is 440 mV -i.e., the reverse biased diode case.

I am looking at the BWP34 datasheet fig 3 reverse light current vesus irradiance
it is as much as 100 uA for 2 mW / cm^2

For a beta of even as low as 100 that gives 10 mA Ic in the first transistor
With say a 220 Ohm resistor that makes 2.2V
Add an emitter follower or any other buffer (PNP reverse is better) to get 50 Ohm driving capability,
and it should work.
Less light less output, higher collector resistor more output, higher beta more output.
The collector resistor of the first stage should not be too high if you want 100 MHz (effects of Cce Ccb).
You will need to specify light source , pulse width, etc
The only spices I use are pepper, chili and salt.

Mr Hobbs who post here has written a book IIRC about driving an opamp into the invering input
using feedback?
Whatever you do, you need a low impedance termination for your photo-diode in reverse mode
as the impedance is high and any capacitance will limit speed.

You can also type
BWP34 circuit diagram
in google, then select \'pictures\' from top screen,
and plenty of examples and I even see the circuit I described

Often faster than waiting here for replies.

 

[amal banerjee]

On Friday, September 22, 2023 at 6:19:12 PM UTC+5:30, Phil Hobbs wrote:

amal banerjee <daku...@gmail.com> wrote:
On Friday, September 22, 2023 at 4:01:34 PM UTC+5:30, Phil Hobbs wrote:
amal banerjee <daku...@gmail.com> wrote:
On Thursday, September 21, 2023 at 10:54:43/AM UTC+5:30, Jan Panteltje wrote:
On a sunny day (Wed, 20 Sep 2023 21:28:49 -0700 (PDT)) it happened amal
banerjee <daku...@gmail.com> wrote in
21592d6c-93a9-4852...@googlegroups.com>:

On Wednesday, September 20, 2023 at 8:51:50/PM UTC+5:30, John Larki> >n wrote:
On Wed, 20 Sep 2023 08:08:08 -0700 (PDT), amal banerjee
daku...@gmail.com> wrote:

Could some electronics guru please help ? I am looking for a very low(fe=
w milliVolts) VTO commercially available NMOS, and its corresponding PMOS.=

I am trying to use a reverse biased photodiode(very low output current) =
to
trigger a PMOS. The output voltage could then be used to trigger ideally=
a
BJT. Any hints, suggestiosn would be greatly appreciated. Thanks in adva> >nce.
What is VTO?

I don\'t think such a part exists. A photodiode might just barely turn
on a high-beta bipolar transisor.

What\'s the open-circuit voltage of the photodiode? What\'s the current?
Is a power supply available? If the pd is back-biased by a supply,
you\'d have lots of voltage available to turn on a mosfet.

A lithium battery might power a micropower comparator for decades.

Sorry for the confusion. \'VTO\' means threshold voltage for the mosfet.
The candidate photodiode is BPW31|34. The datasheet contains the following
data:
Open circuit voltage : 440 mV
In reverse bias, the diode is open circuit, so current should flow. The da=
rk current
is 12 pA.

Think \'current\'
the reverse photo-diode could drive the base of for exampe a NPN directly
photo diode current amplified by beta * R1 is output.
Note leakage etc..

------------------------ +
| |
--- R1 a few k
/ \\ |
--- |------------ out, negative going on light input
| c
---- b NPN beta 200
e
|
----------------- GND
I have tested your suggestion with SPICE simulations using an ordinary
BJT(BC547) and two RF BJTs
(BFR92A, BFQ790) each biased(as per Vce, Ic values listed in their
respective datasheets) for beta
values(150-200). I am using a GaAs photodiode SPICE model, which uses a
third input node for an
input voltage for the incident light. The light is pulsed, @ 1.5 MHz,
15.0 MHz and 150.0 MHz with pulse
amplitudes in the low milliVolt(1-2) range. Of the three transistors
BFQ790 performs best, but like each
of the other two, the output voltage at the output 50.0 Ohm resistor is
in the tenths of milliVolt range.

If you don’t know how much light you’ve got, you’re probably doomed. That
needs to be in optical terms, like “1.2 ns full width at half maximum, 1-2
picojoules, 950 nm”.

It also matters whether the light is spatially coherent, because that
governs how small a photodiode you can use.

If you tell us what you’re actually trying to do, we can be a lot more
helpful. Generating a sync signal from a laser beam is much easier than
detecting scattered light from a matte-textured object at a distance, but
there are tricks to make both easier.

Something like, “I need to detect laser pulses bouncing off a microscope
sample so that I can do lock-in measurements of the photoacoustic response”
or “I’m going to bounce laser pulses off my cat” would help a lot.

Cheers

Phil Hobbs

Cheers

Phil Hobbs

For instance
Find that out, first

--
Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC /
Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics
So far all my results are based on SPICE simulations. The candidate
photodiode is BPW34 whose datasheet
states that it is for high speed light detection for visible and near
infra red with half angle of sensitivity +/-65
degree. Reverse light current is 75 mA(typical).
I am experimenting with line of sight light detection at high frequency..
No I would not want to bounce light
off my kitty, esepecially now that it has a kitten to take care of.


That’s way too vague for me to be able to help much, except to say that the
difficulty ranges from trivial to impossible, depending on the details.

The BPW34 isn’t great for bandwidths over 50 MHz or so, but with a better
detector and a decent front end it isn’t hard to reproduce nanosecond
pulses. Even op amps can have gain bandwidths in the gigahertz.

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC /
Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics

I know that the BPW34 is inappropriate for very high frequencies, but since I have
not worked with optoelectronic circuits for a while, I am trying to get my \"feet wet\"
before plunging into the real stuff. Yes, I have seen documentation on GHz op-amps,
but have not used them before.

 

[amal banerjee]

On Saturday, September 23, 2023 at 11:02:03 AM UTC+5:30, Jan Panteltje wrote:

On a sunny day (Fri, 22 Sep 2023 05:00:49 -0700 (PDT)) it happened amal
banerjee <daku...@gmail.com> wrote in
5dafb884-2b86-4c19...@googlegroups.com>:
What is the photo diode reverse current with light on say a 12V supply?
The \'heavy\' version that you have is somewhat congested. If you are saying =
TR3(the transistor whose base
is connected to the photodiode anode) be a Darlington pair, I have tried th> >at already in the SPICE simulation,
although without the 100k (R1). The simulation results were not good - both> > the output current through and
voltage across the 50 Ohm load were worse compared to the single transistor> > case. I will definitely try
out it out again with the 100k(R1). I did think about the emitter follower > >at the TR3 output, but after
I examined the single TR3 output(across the 50 Ohm) I did not pursue it. Th=
e last question
about the reverse bias current for photodiode I am not sure, because so far> > these are all based on
SPICE simulations. The candidate photodiode I have in mind is BPW31|34(the =
Google query
for BPW31 datasheet returns the one for BPW34). The datasheet for BPW34 sta> >tes that the open
circuit voltage is 440 mV -i.e., the reverse biased diode case.
I am looking at the BWP34 datasheet fig 3 reverse light current vesus irradiance
it is as much as 100 uA for 2 mW / cm^2

For a beta of even as low as 100 that gives 10 mA Ic in the first transistor
With say a 220 Ohm resistor that makes 2.2V
Add an emitter follower or any other buffer (PNP reverse is better) to get 50 Ohm driving capability,
and it should work.
Less light less output, higher collector resistor more output, higher beta more output.
The collector resistor of the first stage should not be too high if you want 100 MHz (effects of Cce Ccb).
You will need to specify light source , pulse width, etc
The only spices I use are pepper, chili and salt.

Mr Hobbs who post here has written a book IIRC about driving an opamp into the invering input
using feedback?
Whatever you do, you need a low impedance termination for your photo-diode in reverse mode
as the impedance is high and any capacitance will limit speed.

You can also type
BWP34 circuit diagram
in google, then select \'pictures\' from top screen,
and plenty of examples and I even see the circuit I described

Often faster than waiting here for replies.

Which Web site did you find the circuit diagram for the BWP34 ? I got my datasheet from \"www.alldatasheets.com\"
I have used the op-amp based transimpedance amplifier(with resistive feedback) some years ago for a low
frequency(3.5 MHz) automotive application. A low value capacitor(some pF), parallel to the feedback resistor, curbs
the effects of the capacitance of the reversed biased photodiode.

 

[John Larkin]

On Sat, 23 Sep 2023 00:17:58 -0700 (PDT), amal banerjee
<dakupoto@gmail.com> wrote:

On Friday, September 22, 2023 at 6:19:12?PM UTC+5:30, Phil Hobbs wrote:
amal banerjee <daku...@gmail.com> wrote:
On Friday, September 22, 2023 at 4:01:34?PM UTC+5:30, Phil Hobbs wrote:
amal banerjee <daku...@gmail.com> wrote:
On Thursday, September 21, 2023 at 10:54:43/AM UTC+5:30, Jan Panteltje wrote:
On a sunny day (Wed, 20 Sep 2023 21:28:49 -0700 (PDT)) it happened amal
banerjee <daku...@gmail.com> wrote in
21592d6c-93a9-4852...@googlegroups.com>:

On Wednesday, September 20, 2023 at 8:51:50/PM UTC+5:30, John Larki> >n wrote:
On Wed, 20 Sep 2023 08:08:08 -0700 (PDT), amal banerjee
daku...@gmail.com> wrote:

Could some electronics guru please help ? I am looking for a very low(fe=
w milliVolts) VTO commercially available NMOS, and its corresponding PMOS.=

I am trying to use a reverse biased photodiode(very low output current) =
to
trigger a PMOS. The output voltage could then be used to trigger ideally=
a
BJT. Any hints, suggestiosn would be greatly appreciated. Thanks in adva> >nce.
What is VTO?

I don\'t think such a part exists. A photodiode might just barely turn
on a high-beta bipolar transisor.

What\'s the open-circuit voltage of the photodiode? What\'s the current?
Is a power supply available? If the pd is back-biased by a supply,
you\'d have lots of voltage available to turn on a mosfet.

A lithium battery might power a micropower comparator for decades.

Sorry for the confusion. \'VTO\' means threshold voltage for the mosfet.
The candidate photodiode is BPW31|34. The datasheet contains the following
data:
Open circuit voltage : 440 mV
In reverse bias, the diode is open circuit, so current should flow. The da=
rk current
is 12 pA.

Think \'current\'
the reverse photo-diode could drive the base of for exampe a NPN directly
photo diode current amplified by beta * R1 is output.
Note leakage etc..

------------------------ +
| |
--- R1 a few k
/ \\ |
--- |------------ out, negative going on light input
| c
---- b NPN beta 200
e
|
----------------- GND
I have tested your suggestion with SPICE simulations using an ordinary
BJT(BC547) and two RF BJTs
(BFR92A, BFQ790) each biased(as per Vce, Ic values listed in their
respective datasheets) for beta
values(150-200). I am using a GaAs photodiode SPICE model, which uses a
third input node for an
input voltage for the incident light. The light is pulsed, @ 1.5 MHz,
15.0 MHz and 150.0 MHz with pulse
amplitudes in the low milliVolt(1-2) range. Of the three transistors
BFQ790 performs best, but like each
of the other two, the output voltage at the output 50.0 Ohm resistor is
in the tenths of milliVolt range.

If you don’t know how much light you’ve got, you’re probably doomed. That
needs to be in optical terms, like “1.2 ns full width at half maximum, 1-2
picojoules, 950 nm”.

It also matters whether the light is spatially coherent, because that
governs how small a photodiode you can use.

If you tell us what you’re actually trying to do, we can be a lot more
helpful. Generating a sync signal from a laser beam is much easier than
detecting scattered light from a matte-textured object at a distance, but
there are tricks to make both easier.

Something like, “I need to detect laser pulses bouncing off a microscope
sample so that I can do lock-in measurements of the photoacoustic response”
or “I’m going to bounce laser pulses off my cat” would help a lot.

Cheers

Phil Hobbs

Cheers

Phil Hobbs

For instance
Find that out, first

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Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC /
Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics
So far all my results are based on SPICE simulations. The candidate
photodiode is BPW34 whose datasheet
states that it is for high speed light detection for visible and near
infra red with half angle of sensitivity +/-65
degree. Reverse light current is 75 mA(typical).
I am experimenting with line of sight light detection at high frequency.
No I would not want to bounce light
off my kitty, esepecially now that it has a kitten to take care of.


That’s way too vague for me to be able to help much, except to say that the
difficulty ranges from trivial to impossible, depending on the details.

The BPW34 isn’t great for bandwidths over 50 MHz or so, but with a better
detector and a decent front end it isn’t hard to reproduce nanosecond
pulses. Even op amps can have gain bandwidths in the gigahertz.

Cheers

Phil Hobbs
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Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC /
Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics
I know that the BPW34 is inappropriate for very high frequencies, but since I have
not worked with optoelectronic circuits for a while, I am trying to get my \"feet wet\"
before plunging into the real stuff. Yes, I have seen documentation on GHz op-amps,
but have not used them before.

Phil\'s book, Designing Electro-Optical Systems, has a lot of good
stuff on the subject.