it's a BC546, 10k collector resistor... I thought it was fast enough,
but also think the signal is inverted, since there's passive quenching
in this circuit, so the breakdown voltage of the APD is lowering too
slowly before next photon, causing this kind of positive edge.. if you
see well there's the same slope in all the signals. I'm currently
searching for an active quenching circuit that fits into my application.
Best Regards,
Ilia.
On 10/21/16 09:53, Adrian Godwin wrote:
What is the circuit driving that signal ? It appears to have too little
positive drive to overcome the capacitance. Perhaps it's an open collector
with too large a pull-up ?
On 21 Oct 2016 12:23 a.m., "Ilia Platone" <i...@iliaplatone.com> wrote:
sorry, no attachment, this mail contains two images, one is the previous
attempt, the second (IMG_003.JPG) was taken at 5us/div, 1v/div with a
different oscilloscope setup.
Best Regards,
Ilia.
On 10/20/16 18:12, Attila Kinali wrote:
On Thu, 20 Oct 2016 10:59:21 +0100
"David J Taylor" <david-tay...@blueyonder.co.uk> wrote:
Actually, of the 15 Raspberry Pi cards I have only one is used in a
graphics
application.
Yes, the rpi are used for all kind of stuff and there is a huge community
around them that helps with all kind of questions. Unfortunately, the
rpi is also used for all kind of stuff that it is a suboptimal choice
(to put it mildly), but people do not care or do not want to check
for alternatives. It kind of works, that's all they care about.
On the positive side they work very well with external devices for control
and measurement,
And for most of these applications a 32bit uC that uses a fraction of
the power would be the right choice. Often a clock of 1MHz would be
enough.
and have a huge amount of software and hardware support for
a vast range of devices which makes for fast and easy development.
That's the only plus side. But then, most of the code written in C
can be used on a uC just the same with little to no modification.
I will be interested to see what is recommended for a 100 kHz event rate.
This is actually a very tough question. 100kHz means that for each event
there is only 10µs available for detection, processing and output. Using
a uC that would be something in the order of 1000-2000 CPU cycles. On an
application processor (rpi and its cusins) that would be 2000 to 20'000
cycles.
While 1000 cycles on a uC is quite a lot, you cannot do any fancy
processing
with so few cycles.
On the application processor 20k cylces is plenty, but you have the
complex
OS that eats up a few thousand cycles itself. Addtionally there comes
the interrupt latency that the application processors suffer from, which
is in the order of 1-10µs... So they would need a kind of (hardware)
system
to queue up the events to process them in badges. Because of this, an rpi
wouldn't work at all (bitbanging takes several µs for each operation).
Going for an uC is easier in that regard as they have very little
interrupt
latency (usually just 5-10 cycles), but then you have problems with
getting the output out of the uC as their I/O subsystems are usually
optimized to work in a stand-alone fashion.
Maybe one way would be to use an arm9/cortex-a5 based uC (ie not an
application
processor) and use their high speed I/O.
For better answers, I would need to know what kind of events these are
and what exactly need to be done/measured.
Attila Kinali
--
Ilia Platone
via Ferrara 54
47841
Cattolica (RN), Italy
Cell +39 349 1075999
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--
Ilia Platone
via Ferrara 54
47841
Cattolica (RN), Italy
Cell +39 349 1075999
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