x-Chapters, 4x.3, 16 more pages about TIAs

W

Winfield Hill

Guest
Announcing a useful x-Chapter DRAFT section.

Compensation of TIAs wasn't discussed much
in AoE III, 8.11, pages 537-555. Mentioned
briefly in 4.3.1.C, we assigned the topic to
Chapter 4x. Here's x-Chapter section 4x.3,
which adds 16 pages to 19 TIA pages in AoE3.

https://www.dropbox.com/s/11wp4nlumil1koq/4x.3_TIA_final-DRAFT.pdf?dl=1

(This is a partial repost in a new-thread,
from thread, "RF transistors for PD cascode"
where George Herold was considering using a
cascode input for TIA photodiode amplifier.
There I argued that when working to reduce
high-frequency e_n Cin noise in a TIA, the
cascode isolation approach works well only
at higher input current levels, where you
can maintain the cascode gain (fT) of the
transistor, end even add additional bias
current. But at very low currents, the
bootstrap approach can work better.) See
details in AoE III, 8.11, pages 537-555.

Beside discussing compensation, we show a
few useful tricks. And 4x.3.7 introduces
an amazing TIA configuration, which covers
a dynamic signal range of 10^7 or more, with
a single TIA op-amp. During discussions
here on s.e.d., two other approaches came up.
See 4x.3.9 using a bootstrap, including a
1-meg TIA with 1MHz bandwidth. And 4x.3.10
with a cascode BJT. There we see again the
struggle to maintain wide amplifier bandwidth
when using a cascode at currents below 1 to
10uA, also see fT discussion in 2x.9 to 2x.11

https://www.dropbox.com/s/br9caixbtderl44/2x.9-11_BJT_beta_fT_DRAFT.pdf?dl=1


--
Thanks,
- Win
 
On 13 Sep 2019 07:08:19 -0700, Winfield Hill <winfieldhill@yahoo.com>
wrote:

Announcing a useful x-Chapter DRAFT section.

Compensation of TIAs wasn't discussed much
in AoE III, 8.11, pages 537-555. Mentioned
briefly in 4.3.1.C, we assigned the topic to
Chapter 4x. Here's x-Chapter section 4x.3,
which adds 16 pages to 19 TIA pages in AoE3.

https://www.dropbox.com/s/11wp4nlumil1koq/4x.3_TIA_final-DRAFT.pdf?dl=1

(This is a partial repost in a new-thread,
from thread, "RF transistors for PD cascode"
where George Herold was considering using a
cascode input for TIA photodiode amplifier.
There I argued that when working to reduce
high-frequency e_n Cin noise in a TIA, the
cascode isolation approach works well only
at higher input current levels, where you
can maintain the cascode gain (fT) of the
transistor, end even add additional bias
current. But at very low currents, the
bootstrap approach can work better.) See
details in AoE III, 8.11, pages 537-555.

Beside discussing compensation, we show a
few useful tricks. And 4x.3.7 introduces
an amazing TIA configuration, which covers
a dynamic signal range of 10^7 or more, with
a single TIA op-amp. During discussions
here on s.e.d., two other approaches came up.
See 4x.3.9 using a bootstrap, including a
1-meg TIA with 1MHz bandwidth. And 4x.3.10
with a cascode BJT. There we see again the
struggle to maintain wide amplifier bandwidth
when using a cascode at currents below 1 to
10uA, also see fT discussion in 2x.9 to 2x.11

https://www.dropbox.com/s/br9caixbtderl44/2x.9-11_BJT_beta_fT_DRAFT.pdf?dl=1
Click to expand...

One trick that I've used for gain switching is to have two cascode
transistors. Both emitters go to the photodiode, but the collectors
drive separate amps with different gains. Wiggle the transistor base
voltages to decide which path is active.
 
jlarkin@highlandsniptechnology.com wrote...
On 13 Sep 2019 07:08:19 -0700, Winfield Hill <winfieldhill@yahoo.com
wrote:

Announcing a useful x-Chapter DRAFT section.

Compensation of TIAs wasn't discussed much
in AoE III, 8.11, pages 537-555. Mentioned
briefly in 4.3.1.C, we assigned the topic to
Chapter 4x. Here's x-Chapter section 4x.3,
which adds 16 pages to 19 TIA pages in AoE3.

https://www.dropbox.com/s/11wp4nlumil1koq/4x.3_TIA_final-DRAFT.pdf?dl=1

(This is a partial repost in a new-thread,
from thread, "RF transistors for PD cascode"
where George Herold was considering using a
cascode input for TIA photodiode amplifier.
There I argued that when working to reduce
high-frequency e_n Cin noise in a TIA, the
cascode isolation approach works well only
at higher input current levels, where you
can maintain the cascode gain (fT) of the
transistor, end even add additional bias
current. But at very low currents, the
bootstrap approach can work better.) See
details in AoE III, 8.11, pages 537-555.

Beside discussing compensation, we show a
few useful tricks. And 4x.3.7 introduces
an amazing TIA configuration, which covers
a dynamic signal range of 10^7 or more, with
a single TIA op-amp. During discussions
here on s.e.d., two other approaches came up.
See 4x.3.9 using a bootstrap, including a
1-meg TIA with 1MHz bandwidth. And 4x.3.10
with a cascode BJT. There we see again the
struggle to maintain wide amplifier bandwidth
when using a cascode at currents below 1 to
10uA, also see fT discussion in 2x.9 to 2x.11

https://www.dropbox.com/s/br9caixbtderl44/2x.9-11_BJT_beta_fT_DRAFT.pdf?dl=1

One trick that I've used for gain switching is
to have two cascode transistors. Both emitters
go to the photodiode, but the collectors drive
separate amps with different gains. Wiggle the
transistor base voltages to decide which path
is active.
Click to expand...

Yessir. Fleshed out in detail in 4x.3.10, but
I didn't know (or remember?) you had also come
up with the idea. I combined it with a JFET
bootstrap; BJT e_n gets high at low currents.

Your unusual diode scheme is explored in 4x.3.9,
where we show a 1M-ohm 1MHz version. That's not
possible with the super-wide-range simultaneous-
outputs scheme in 4x.3.7, due to JFET capacitance.

Lots of good reading for you in there, John.


--
Thanks,
- Win
 
jlarkin@highlandsniptechnology.com wrote...
Here's an emitter-switched version:

https://www.dropbox.com/s/jod3tbuowdgtxcs/J712_Amp.jpg?raw=1

We designed this for a big semiconductor-equipment company.
It worked great, so they stole it and did it themselves.
Turns out they are notorious, even proud, of doing that.
Click to expand...

What was the capacitance of the PD in that unit?
I see you paralleled two BF862 bootstraps.


--
Thanks,
- Win
 
On 13 Sep 2019 08:07:01 -0700, Winfield Hill <winfieldhill@yahoo.com>
wrote:

jlarkin@highlandsniptechnology.com wrote...

On 13 Sep 2019 07:08:19 -0700, Winfield Hill <winfieldhill@yahoo.com
wrote:

Announcing a useful x-Chapter DRAFT section.

Compensation of TIAs wasn't discussed much
in AoE III, 8.11, pages 537-555. Mentioned
briefly in 4.3.1.C, we assigned the topic to
Chapter 4x. Here's x-Chapter section 4x.3,
which adds 16 pages to 19 TIA pages in AoE3.

https://www.dropbox.com/s/11wp4nlumil1koq/4x.3_TIA_final-DRAFT.pdf?dl=1

(This is a partial repost in a new-thread,
from thread, "RF transistors for PD cascode"
where George Herold was considering using a
cascode input for TIA photodiode amplifier.
There I argued that when working to reduce
high-frequency e_n Cin noise in a TIA, the
cascode isolation approach works well only
at higher input current levels, where you
can maintain the cascode gain (fT) of the
transistor, end even add additional bias
current. But at very low currents, the
bootstrap approach can work better.) See
details in AoE III, 8.11, pages 537-555.

Beside discussing compensation, we show a
few useful tricks. And 4x.3.7 introduces
an amazing TIA configuration, which covers
a dynamic signal range of 10^7 or more, with
a single TIA op-amp. During discussions
here on s.e.d., two other approaches came up.
See 4x.3.9 using a bootstrap, including a
1-meg TIA with 1MHz bandwidth. And 4x.3.10
with a cascode BJT. There we see again the
struggle to maintain wide amplifier bandwidth
when using a cascode at currents below 1 to
10uA, also see fT discussion in 2x.9 to 2x.11

https://www.dropbox.com/s/br9caixbtderl44/2x.9-11_BJT_beta_fT_DRAFT.pdf?dl=1

One trick that I've used for gain switching is
to have two cascode transistors. Both emitters
go to the photodiode, but the collectors drive
separate amps with different gains. Wiggle the
transistor base voltages to decide which path
is active.

Yessir. Fleshed out in detail in 4x.3.10, but
I didn't know (or remember?) you had also come
up with the idea. I combined it with a JFET
bootstrap; BJT e_n gets high at low currents.

Your unusual diode scheme is explored in 4x.3.9,
where we show a 1M-ohm 1MHz version. That's not
possible with the super-wide-range simultaneous-
outputs scheme in 4x.3.7, due to JFET capacitance.

Lots of good reading for you in there, John.
Click to expand...

Here's an emitter-switched version:

https://www.dropbox.com/s/jod3tbuowdgtxcs/J712_Amp.jpg?raw=1

We designed this for a big semiconductor-equipment company. It worked
great, so they stole it and did it themselves. Turns out they are
notorious, even proud, of doing that.
 
On Friday, September 13, 2019 at 10:08:30 AM UTC-4, Winfield Hill wrote:
Announcing a useful x-Chapter DRAFT section.

Compensation of TIAs wasn't discussed much
in AoE III, 8.11, pages 537-555.
Click to expand...

TIA = Transient Ischemic Attack

I can see why they wouldn't be mentioned in an electronics book.

--

Rick C.

- Get 2,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209
 
On 13 Sep 2019 09:26:28 -0700, Winfield Hill <winfieldhill@yahoo.com>
wrote:

jlarkin@highlandsniptechnology.com wrote...

Here's an emitter-switched version:

https://www.dropbox.com/s/jod3tbuowdgtxcs/J712_Amp.jpg?raw=1

We designed this for a big semiconductor-equipment company.
It worked great, so they stole it and did it themselves.
Turns out they are notorious, even proud, of doing that.

What was the capacitance of the PD in that unit?
I see you paralleled two BF862 bootstraps.
Click to expand...

Hey, Mouser has it now.

https://www.mouser.com/ProductDetail/First-Sensor/PS13-5B-TO5?qs=hIohqi1S7IocqsTNORsVIA%3D%3D

UV enhanced, to snoop a plasma discharge through a quartz window.

Fun while it lasted.
 
On 13/09/19 19:00, Winfield Hill wrote:
Rick C wrote...

TIA = Transient Ischemic Attack

The things we learn about as we get older.
Click to expand...

As I get older I begin to have a better idea of
what is going to kill /me/.

An idiot reporter once asked Michael Caine (the
actor) what it was like being 60. Caine, who is
pretty down-to-earth and sensible, merely said
"Better than the alternative".
 
On Friday, September 13, 2019 at 10:08:30 AM UTC-4, Winfield Hill wrote:
Announcing a useful x-Chapter DRAFT section.

Compensation of TIAs wasn't discussed much
in AoE III, 8.11, pages 537-555. Mentioned
briefly in 4.3.1.C, we assigned the topic to
Chapter 4x. Here's x-Chapter section 4x.3,
which adds 16 pages to 19 TIA pages in AoE3.

https://www.dropbox.com/s/11wp4nlumil1koq/4x.3_TIA_final-DRAFT.pdf?dl=1

(This is a partial repost in a new-thread,
from thread, "RF transistors for PD cascode"
where George Herold was considering using a
cascode input for TIA photodiode amplifier.
There I argued that when working to reduce
high-frequency e_n Cin noise in a TIA, the
cascode isolation approach works well only
at higher input current levels, where you
can maintain the cascode gain (fT) of the
transistor, end even add additional bias
current. But at very low currents, the
bootstrap approach can work better.) See
details in AoE III, 8.11, pages 537-555.

Beside discussing compensation, we show a
few useful tricks. And 4x.3.7 introduces
an amazing TIA configuration, which covers
a dynamic signal range of 10^7 or more, with
a single TIA op-amp. During discussions
here on s.e.d., two other approaches came up.
See 4x.3.9 using a bootstrap, including a
1-meg TIA with 1MHz bandwidth. And 4x.3.10
with a cascode BJT. There we see again the
struggle to maintain wide amplifier bandwidth
when using a cascode at currents below 1 to
10uA, also see fT discussion in 2x.9 to 2x.11

https://www.dropbox.com/s/br9caixbtderl44/2x.9-11_BJT_beta_fT_DRAFT.pdf?dl=1
Click to expand...
Again thanks, I can groove on the first figure. We use this diode
connected transistor as a temp sensor. I said, let's put in a current
range switch and then you can crudely calibrate the sensor
by measuring the forward voltage at different currents. (1-10-100 uA)
is the good range. The non-ideality is ~1%, And
I assume is related to current gain. Anyway, at low currents
(delta V between 10 nA and 100 nA) the non-ideality is worse.
~5% I think. (1.05)

George H.




--
Thanks,
- Win
Click to expand...
 
On Friday, September 13, 2019 at 10:08:30 AM UTC-4, Winfield Hill wrote:
Announcing a useful x-Chapter DRAFT section.

Compensation of TIAs wasn't discussed much
in AoE III, 8.11, pages 537-555. Mentioned
briefly in 4.3.1.C, we assigned the topic to
Chapter 4x. Here's x-Chapter section 4x.3,
which adds 16 pages to 19 TIA pages in AoE3.

https://www.dropbox.com/s/11wp4nlumil1koq/4x.3_TIA_final-DRAFT.pdf?dl=1
Thanks Win, lots to read. I think you've posted some of that before.
Click to expand...

I've got to measure the low level response of the cascode.
At low currents, say 10 nA, does the transistor not turn on?
most of the photo current goes into the base?

George H.

(This is a partial repost in a new-thread,
from thread, "RF transistors for PD cascode"
where George Herold was considering using a
cascode input for TIA photodiode amplifier.
There I argued that when working to reduce
high-frequency e_n Cin noise in a TIA, the
cascode isolation approach works well only
at higher input current levels, where you
can maintain the cascode gain (fT) of the
transistor, end even add additional bias
current. But at very low currents, the
bootstrap approach can work better.) See
details in AoE III, 8.11, pages 537-555.

Beside discussing compensation, we show a
few useful tricks. And 4x.3.7 introduces
an amazing TIA configuration, which covers
a dynamic signal range of 10^7 or more, with
a single TIA op-amp. During discussions
here on s.e.d., two other approaches came up.
See 4x.3.9 using a bootstrap, including a
1-meg TIA with 1MHz bandwidth. And 4x.3.10
with a cascode BJT. There we see again the
struggle to maintain wide amplifier bandwidth
when using a cascode at currents below 1 to
10uA, also see fT discussion in 2x.9 to 2x.11

https://www.dropbox.com/s/br9caixbtderl44/2x.9-11_BJT_beta_fT_DRAFT.pdf?dl=1


--
Thanks,
- Win
Click to expand...
 
On Saturday, September 14, 2019 at 9:41:09 PM UTC-7, George Herold wrote:

We use this diode
connected transistor as a temp sensor. I said, let's put in a current
range switch and then you can crudely calibrate the sensor
by measuring the forward voltage at different currents. (1-10-100 uA)
is the good range. The non-ideality is ~1%, And
I assume is related to current gain. Anyway, at low currents
(delta V between 10 nA and 100 nA) the non-ideality is worse.
~5% I think. (1.05)
Click to expand...

What kind of transistor? For good logarithm conformance, the
low-noise types are preferred (like, BC550C).
 
On 13.09.19 3:08 PM, Winfield Hill wrote:
> https://www.dropbox.com/s/11wp4nlumil1koq/4x.3_TIA_final-DRAFT.pdf?dl=1

Looks like the second part number in footnote 18 should be CPH6904.
(Also, footnotes 18 and 30 are perhaps slightly repetitive.)

— David
 
George Herold wrote...
I've got to measure the low level response of
the cascode. At low currents, say 10 nA, does
the transistor not turn on?
Click to expand...

It'll be turned on.

> Most of the photo current goes into the base?

No. See AoE3 Figures 2.41 and 2.42 on page 92.
The latter shows a "typical" transistor with
beta = 350 at 10nA. See measured beta plots
in Figure 8.39, where traces 32, 35 and 38
show flat beta down to 1uA, and they will
continue to have plenty of gain, even down to
below 1nA. Or see Gummel plots in Figs 2x.72
and 2x.73, if you have it, with gain at 10pA.

Now see Figure 8.85, which shows the problems
with using a cascode connection, rather than a
JFET boostrap, to deal with high PD capacitance.
Trace 38 was a 2n5088, a good transistor to use
at low-currents. Its curve is on a trajectory
for fT=10MHz at 50uA. fT is proportional to Ic,
in that region, so we can estimate its fT would
be 2kHz at 10nA. Your PD amplifier would start
losing gain above 2kHz if the signal was 10nA.**

OTOH, with a say 10M feedback resistor, you'd
still have a 100mV signal, and keep your gain
out to the fc bandwidth, which could be 400kHz,
if you used a JFET bootstrap with a 50MHz opamp.

A typical resistor's self capacitance might be
0.15pF, which would limit your fc bandwidth to
100kHz with 10M. To get to 400kHz, you can use
a feedback-resistor trick in Figure 8.80.C, and
set the trimpot with the fixture in Figure 8.91.
Or you could be satisfied with 100kHz, given that
your en-Cin noise will be rising in that region
anyway, plus you could get away with only a 5MHz
opamp, assuming Cin <= 8pF.

** You could help the cascode with an extra bias
current, but you'd need 2uA bias to get to 400kHz,
damaging your ability to measure to 10nA and below.
I don't see an advantage of the cascode over the
JFET boostrap, especially at currents below 1uA.

John used cascode with multiple opamps for gain
switching, but I show how to use a CMOS switch
instead; Figure 4x.29.B retains full bandwidth.


--
Thanks,
- Win
 
On Sunday, September 15, 2019 at 2:22:34 AM UTC-4, whit3rd wrote:
On Saturday, September 14, 2019 at 9:41:09 PM UTC-7, George Herold wrote:

We use this diode
connected transistor as a temp sensor. I said, let's put in a current
range switch and then you can crudely calibrate the sensor
by measuring the forward voltage at different currents. (1-10-100 uA)
is the good range. The non-ideality is ~1%, And
I assume is related to current gain. Anyway, at low currents
(delta V between 10 nA and 100 nA) the non-ideality is worse.
~5% I think. (1.05)

What kind of transistor? For good logarithm conformance, the
low-noise types are preferred (like, BC550C).
Click to expand...

TIP-32c (pnp TO-220) collector stuck to ground.

George H.
 
On Sunday, September 15, 2019 at 5:54:23 PM UTC-7, George Herold wrote:
On Sunday, September 15, 2019 at 2:22:34 AM UTC-4, whit3rd wrote:
On Saturday, September 14, 2019 at 9:41:09 PM UTC-7, George Herold wrote:

We use this diode
connected transistor as a temp sensor. ... at low currents
(delta V between 10 nA and 100 nA) the non-ideality is worse.
~5% I think. (1.05)

What kind of transistor? For good logarithm conformance, the
low-noise types are preferred (like, BC550C).

TIP-32c (pnp TO-220) collector stuck to ground.
Click to expand...

Probably low-ish lifetime for carriers in the base, you'd see
some emitter resistance at higher currents. That's typical
for power transistors. Good thermal time constant, easy attachment
through the tab, though.
 
On 15 Sep 2019 06:11:34 -0700, Winfield Hill <winfieldhill@yahoo.com>
wrote:

George Herold wrote...

I've got to measure the low level response of
the cascode. At low currents, say 10 nA, does
the transistor not turn on?

It'll be turned on.

Most of the photo current goes into the base?

No. See AoE3 Figures 2.41 and 2.42 on page 92.
The latter shows a "typical" transistor with
beta = 350 at 10nA. See measured beta plots
in Figure 8.39, where traces 32, 35 and 38
show flat beta down to 1uA, and they will
continue to have plenty of gain, even down to
below 1nA. Or see Gummel plots in Figs 2x.72
and 2x.73, if you have it, with gain at 10pA.

Now see Figure 8.85, which shows the problems
with using a cascode connection, rather than a
JFET boostrap, to deal with high PD capacitance.
Trace 38 was a 2n5088, a good transistor to use
at low-currents. Its curve is on a trajectory
for fT=10MHz at 50uA. fT is proportional to Ic,
in that region, so we can estimate its fT would
be 2kHz at 10nA. Your PD amplifier would start
losing gain above 2kHz if the signal was 10nA.**

OTOH, with a say 10M feedback resistor, you'd
still have a 100mV signal, and keep your gain
out to the fc bandwidth, which could be 400kHz,
if you used a JFET bootstrap with a 50MHz opamp.

A typical resistor's self capacitance might be
0.15pF, which would limit your fc bandwidth to
100kHz with 10M. To get to 400kHz, you can use
a feedback-resistor trick in Figure 8.80.C, and
set the trimpot with the fixture in Figure 8.91.
Or you could be satisfied with 100kHz, given that
your en-Cin noise will be rising in that region
anyway, plus you could get away with only a 5MHz
opamp, assuming Cin <= 8pF.

** You could help the cascode with an extra bias
current, but you'd need 2uA bias to get to 400kHz,
damaging your ability to measure to 10nA and below.
I don't see an advantage of the cascode over the
JFET boostrap, especially at currents below 1uA.

John used cascode with multiple opamps for gain
switching, but I show how to use a CMOS switch
instead; Figure 4x.29.B retains full bandwidth.
Click to expand...

One caution: the capacitance of a CMOS switch isn't all to ground,
some of it's to the supply rail. The V+ supply needs to be very quiet.

17 pF is kind of a lot of c to hang on the summing point of an opamp.
 
On Sunday, September 15, 2019 at 9:11:43 AM UTC-4, Winfield Hill wrote:
George Herold wrote...

I've got to measure the low level response of
the cascode. At low currents, say 10 nA, does
the transistor not turn on?

It'll be turned on.

Most of the photo current goes into the base?

No. See AoE3 Figures 2.41 and 2.42 on page 92.
The latter shows a "typical" transistor with
beta = 350 at 10nA. See measured beta plots
in Figure 8.39, where traces 32, 35 and 38
show flat beta down to 1uA, and they will
continue to have plenty of gain, even down to
below 1nA. Or see Gummel plots in Figs 2x.72
and 2x.73, if you have it, with gain at 10pA.

Now see Figure 8.85, which shows the problems
with using a cascode connection, rather than a
JFET boostrap, to deal with high PD capacitance.
Trace 38 was a 2n5088, a good transistor to use
at low-currents. Its curve is on a trajectory
for fT=10MHz at 50uA. fT is proportional to Ic,
in that region, so we can estimate its fT would
be 2kHz at 10nA. Your PD amplifier would start
losing gain above 2kHz if the signal was 10nA.**

OTOH, with a say 10M feedback resistor, you'd
still have a 100mV signal, and keep your gain
out to the fc bandwidth, which could be 400kHz,
if you used a JFET bootstrap with a 50MHz opamp.

A typical resistor's self capacitance might be
0.15pF, which would limit your fc bandwidth to
100kHz with 10M. To get to 400kHz, you can use
a feedback-resistor trick in Figure 8.80.C, and
set the trimpot with the fixture in Figure 8.91.
Or you could be satisfied with 100kHz, given that
your en-Cin noise will be rising in that region
anyway, plus you could get away with only a 5MHz
opamp, assuming Cin <= 8pF.

** You could help the cascode with an extra bias
current, but you'd need 2uA bias to get to 400kHz,
damaging your ability to measure to 10nA and below.
I don't see an advantage of the cascode over the
JFET boostrap, especially at currents below 1uA.

John used cascode with multiple opamps for gain
switching, but I show how to use a CMOS switch
instead; Figure 4x.29.B retains full bandwidth.


--
Thanks,
- Win
Click to expand...

Hi Win, wow thanks so much for the help and interest. I think i've finally got
my head around the transistor GBW (f_T) as a function of collector current.

I did the following series of experiments with big pin-44 PD, opa2192 opamp,
~15 V of bias on the PD and 10 Meg ohm TIA resistor.
I'm looking at the step response (blinking LED) and choose the output amplitude
to always be 600 mVp-p... three scale divisions on 'scope which lets me
guesstimate time constant (TC) as time to 2/3rds of max.

1.) straight TIA, ugly near turn on, ~200 us TC.

2.) with cascode (2n3904) ~300 us TC... linear rise of voltage with
time (not at all, a one pole response.)

3.) cascode with 100 Meg bias R. Sweet one pole response,
TC = 50 us.

4.) cascode, with bias and with bootstrap (of PD), better and better
one pole and ~10 us TC

5.) remove bias R, cascode and bootstrap. ~20 uS TC, slow turn-on
(not one pole.)

6.) bootstrap alone. Nice one pole, ~10 us TC (maybe a tinch faster
than the full cascode/ bias/ bootstrap.

This is all very encouraging, and I assume expected by all the PD-front end
experts.

I'm going to try the 'full monty' (cascode/bais/ bootstrap) with 1 meg FB.
fun stuff.

George H.
(who wonders why he didn't try the cascode years ago.)
 
Am 13.09.19 um 16:36 schrieb jlarkin@highlandsniptechnology.com:

One trick that I've used for gain switching is to have two cascode
transistors. Both emitters go to the photodiode, but the collectors
drive separate amps with different gains. Wiggle the transistor base
voltages to decide which path is active.
Click to expand...

I have used sth. similar for AGC in a Driscoll oscillator.
One of the 2 cascode transistors diverts some of the current
to /dev/nul.

cheers, Gerhard
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top