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

[amal banerjee]

Could some electronics guru please help ? I am looking for a very low(few 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 advance.

 

[John Larkin]

On Wed, 20 Sep 2023 08:08:08 -0700 (PDT), amal banerjee
<dakupoto@gmail.com> wrote:

Could some electronics guru please help ? I am looking for a very low(few 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 advance.

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.

 

[John Smiht]

On Wednesday, September 20, 2023 at 10:21:50 AM UTC-5, John Larkin 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(few 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 advance.
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.

VTO: Vertical Take Off

 

[piglet]

On 20/09/2023 16:21, John Larkin wrote:

On Wed, 20 Sep 2023 08:08:08 -0700 (PDT), amal banerjee
dakupoto@gmail.com> wrote:

Could some electronics guru please help ? I am looking for a very low(few 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 advance.

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.

I think they meant V-turn-on?

Strange sub threshold behaviors exist but I know nothing about them.

piglet

 

[jeroen]

On 2023-09-20 17:08, amal banerjee wrote:

Could some electronics guru please help ? I am looking for a very low(few 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 advance.

That\'s what amplifiers are for.

Jeroen Belleman

 

[Tabby]

On Wednesday, 20 September 2023 at 18:10:44 UTC+1, John Smiht wrote:

On Wednesday, September 20, 2023 at 10:21:50 AM UTC-5, John Larkin 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(few 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 advance.
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.
VTO: Vertical Take Off

I\'ve seen transistors do that. Just apply 100x rated power

 

[John Smiht]

On Wednesday, September 20, 2023 at 7:57:41 PM UTC-5, Tabby wrote:

On Wednesday, 20 September 2023 at 18:10:44 UTC+1, John Smiht wrote:
On Wednesday, September 20, 2023 at 10:21:50 AM UTC-5, John Larkin 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(few 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 advance.
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.
VTO: Vertical Take Off
I\'ve seen transistors do that. Just apply 100x rated power

A TO92 is what I think of as a transistor-on-the-half-shell.

 

[John Smiht]

On Wednesday, September 20, 2023 at 12:37:46 PM UTC-5, piglet wrote:

On 20/09/2023 16:21, John Larkin 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(few 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 advance.

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.

I think they meant V-turn-on?

Strange sub threshold behaviors exist but I know nothing about them.

piglet

Or maybe V-turn-off?

 

[amal banerjee]

On Wednesday, September 20, 2023 at 8:51:50 PM UTC+5:30, John Larkin 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(few 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 advance.
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 dark current
is 12 pA.

 

[Jan Panteltje]

On a sunny day (Wed, 20 Sep 2023 21:28:49 -0700 (PDT)) it happened amal
banerjee <dakupoto@gmail.com> wrote in
<21592d6c-93a9-4852-a6d9-285c75bbd202n@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

 

[John Larkin]

On Thu, 21 Sep 2023 05:24:34 GMT, Jan Panteltje <alien@comet.invalid>
wrote:

On a sunny day (Wed, 20 Sep 2023 21:28:49 -0700 (PDT)) it happened amal
banerjee <dakupoto@gmail.com> wrote in
21592d6c-93a9-4852-a6d9-285c75bbd202n@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

Or drive a logic-level mosfet. Add a gate-source resistor.

One might get 440 mV using the pd in photovoltaic mode, but it will
make many volts in reverse-bias mode.

------------------------ +
| |
--- R1 a few k
/ \\ |
| |------------ out, negative going on light input
| d
|----g nfet
| s
R9 |
| ----------------- GND

Measure the pd current when illuminated and pick R9 suitably.

 

[legg]

On Wed, 20 Sep 2023 08:08:08 -0700 (PDT), amal banerjee
<dakupoto@gmail.com> wrote:

Could some electronics guru please help ? I am looking for a very low(few 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 advance.

Advanced Linear Devices make mos discretes with turn-on voltages
dialable down to zero.

http://www.aldinc.com/

RL

 

[amal banerjee]

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.

 

[amal banerjee]

On Thursday, September 21, 2023 at 7:45:16 PM UTC+5:30, John Larkin wrote:

On Thu, 21 Sep 2023 05:24:34 GMT, Jan Panteltje <al...@comet.invalid
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
Or drive a logic-level mosfet. Add a gate-source resistor.

One might get 440 mV using the pd in photovoltaic mode, but it will
make many volts in reverse-bias mode.
------------------------ +
| |
--- R1 a few k
/ \\ |
| |------------ out, negative going on light input
| d
|----g nfet
| s
R9 |
| ----------------- GND

Measure the pd current when illuminated and pick R9 suitably.

I agree that logic level mosfets might be best. I did a SPICE simulation with BSIM 4.8.2 level=54
NMOS-PMOS pair for an inverter. Even without a gate-source resistor, the output was 150.0 - 200 mV
range for pulsed input to my GaAs photodiode model(please check my previous response to Jan\'s
message). The pulses were at 1.5, 15 and 150 MHz respectively.

 

[whit3rd]

On Thursday, September 21, 2023 at 8:17:31 AM UTC-7, legg 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(few 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 advance.
Advanced Linear Devices make mos discretes with turn-on voltages
dialable down to zero.

http://www.aldinc.com/

Yes, but the turn-on is trimmed, not made abrupt, so \'down to zero\'
is more of a gain specification than a full switch threshold. JFETs have
been available for zero-threshold for years, and were quite useful for
low-leakage input applications.

 

[Jan Panteltje]

On a sunny day (Thu, 21 Sep 2023 23:20:09 -0700 (PDT)) it happened amal
banerjee <dakupoto@gmail.com> wrote in
<e1f8fc46-a40d-4fb8-beda-bd960b476c44n@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?

 

[whit3rd]

On Wednesday, September 20, 2023 at 8:08:14 AM UTC-7, amal banerjee wrote:

Could some electronics guru please help ? I am looking for a very low(few 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 advance.

Your signal (a photocurrent) is fast? And you want to switch according to that current?

There\'s very little voltage gain in a single MOS device, and what you want might be to avoid current lost to
charging the photodiode stray capacitance (i.e. you want near-zero dV/dt); a good receiver for a photodiode
with low current output is an op amp with resistor negative feedback, i.e. a transimpedance amplifier.
That way, there\'s negligible delta-V.

 

[Phil Hobbs]

amal banerjee <dakupoto@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

 

[John Larkin]

On Thu, 21 Sep 2023 23:28:56 -0700 (PDT), amal banerjee
<dakupoto@gmail.com> wrote:

On Thursday, September 21, 2023 at 7:45:16?PM UTC+5:30, John Larkin wrote:
On Thu, 21 Sep 2023 05:24:34 GMT, Jan Panteltje <al...@comet.invalid
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
Or drive a logic-level mosfet. Add a gate-source resistor.

One might get 440 mV using the pd in photovoltaic mode, but it will
make many volts in reverse-bias mode.
------------------------ +
| |
--- R1 a few k
/ \\ |
| |------------ out, negative going on light input
| d
|----g nfet
| s
R9 |
| ----------------- GND

Measure the pd current when illuminated and pick R9 suitably.
I agree that logic level mosfets might be best. I did a SPICE simulation with BSIM 4.8.2 level=54
NMOS-PMOS pair for an inverter. Even without a gate-source resistor, the output was 150.0 - 200 mV
range for pulsed input to my GaAs photodiode model(please check my previous response to Jan\'s
message). The pulses were at 1.5, 15 and 150 MHz respectively.

I don\'t understand this. What photodiode are you using?

What\'s the optical pulse width?

 

[amal banerjee]

On Friday, September 22, 2023 at 2:47:37 PM UTC+5:30, whit3rd wrote:

On Wednesday, September 20, 2023 at 8:08:14 AM UTC-7, amal banerjee wrote:
Could some electronics guru please help ? I am looking for a very low(few 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 advance.
Your signal (a photocurrent) is fast? And you want to switch according to that current?

There\'s very little voltage gain in a single MOS device, and what you want might be to avoid current lost to
charging the photodiode stray capacitance (i.e. you want near-zero dV/dt); a good receiver for a photodiode
with low current output is an op amp with resistor negative feedback, i.e.. a transimpedance amplifier.
That way, there\'s negligible delta-V.

Totally in agreement about the op-amp transimpedance amplifier. However, the gain-bandwidth-product of
even high end op-amps certainly would not extend beyond some 10s of MHz.