TAPR TICC boxed
I thought about using the clamp diodes as protection but was a bit worried about power supply noise leaking through the diodes and adding some jitter to the input signals... I'm probably just being paranoid. The TICC doesn't have the resolution for it to matter or justify a HP5370 or better quality front end. I'll probably go with a fast comparator to implement the variable threshold input.
As protection circuit I have used a 51ohm from the front panel input to the TICC input than two diodes one from TICC input to gnd , other from TICC input to +5V.
Mark wrote:
I thought about using the clamp diodes as protection but was a bit worried about power supply noise leaking through the diodes and adding some jitter to the input signals...
It is a definite worry even with a low-noise, 50 ohm input, and a
potential disaster with a 1Mohm input. Common signal diodes (1N4148,
1N914, 1N916, 1N4448, etc.) are specified for 5-10nA of reverse current.
Even a low-leakage signal diode (e.g., 1N3595) typically has several
hundred pA of leakage. Note that the concern isn't just power supply
noise -- the leakage current itself is quite noisy.
For low-picoamp diodes at a decent price, I use either (1) the B-C diode
of a small-signal BJT, or (2) the gate diode of a small-geometry JFET.
A 2N5550 makes a good high-voltage, low-leakage diode with leakage
current of ~30pA. Small signal HF transistors like the MPSH10 and
2N5179 (and their SMD and PN variants) are good for ~5pA, while the gate
diode of a PN4417A JFET (or SMD variant) has reverse leakage current of
~1pA (achieving this in practice requires a very clean board and good
layout).
I posted some actual leakage test results to Didier's site, which can be
downloaded at
http://www.ko4bb.com/getsimple/index.php?id=download&file=03_App_Notes_-_Proceedings/Reverse_leakage_of_diode-connected_BJTs_and_FETs_measurement_results.pdf.
This document shows the connections I used to obtain the data.
The TICC doesn't have the resolution for it to matter or justify a HP5370 or better quality front end. I'll probably go with a fast comparator to implement the variable threshold input.
Properly applied, a fast comparator will have lower jitter than the rest
of the errors, and is an excellent choice. Bruce suggested the LTC6752,
which is a great part if you need high toggle speeds (100s of MHz) or
ultra-fast edges. But you don't need high toggle rates and may not need
ultra-fast edges. Repeatability and stability are more important than
raw speed in this application. The LT1719, LT1720, or TLV3501 may work
just as well for your purpose, and they are significantly less fussy to
apply.
Note that the LTC6752 series is an improved replacement for the ADCMP60x
series, which itself is an improved replacement for the MAX999. Of
these three, the LTC6752 is the clear winner in my tests. If you do
choose it (or similar), make sure you look at the transitions with
something that will honestly show you any chatter at frequencies up to
at least several GHz. It only takes a little transition chatter to
knock the potential timing resolution of the ultra-fast comparator way
down. Do make sure to test it with the slowest input edges you need it
to handle.
Best regards,
Charles
FJH1100
Ultra Low Leakage Diode
Alex
On 3/31/2017 6:00 PM, Charles Steinmetz wrote:
Mark wrote:
I thought about using the clamp diodes as protection but was a bit
worried about power supply noise leaking through the diodes and
adding some jitter to the input signals...
It is a definite worry even with a low-noise, 50 ohm input, and a
potential disaster with a 1Mohm input. Common signal diodes (1N4148,
1N914, 1N916, 1N4448, etc.) are specified for 5-10nA of reverse
current. Even a low-leakage signal diode (e.g., 1N3595) typically has
several hundred pA of leakage. Note that the concern isn't just power
supply noise -- the leakage current itself is quite noisy.
For low-picoamp diodes at a decent price, I use either (1) the B-C
diode of a small-signal BJT, or (2) the gate diode of a small-geometry
JFET. A 2N5550 makes a good high-voltage, low-leakage diode with
leakage current of ~30pA. Small signal HF transistors like the MPSH10
and 2N5179 (and their SMD and PN variants) are good for ~5pA, while
the gate diode of a PN4417A JFET (or SMD variant) has reverse leakage
current of ~1pA (achieving this in practice requires a very clean
board and good layout).
I posted some actual leakage test results to Didier's site, which can
be downloaded at
http://www.ko4bb.com/getsimple/index.php?id=download&file=03_App_Notes_-_Proceedings/Reverse_leakage_of_diode-connected_BJTs_and_FETs_measurement_results.pdf.
This document shows the connections I used to obtain the data.
The TICC doesn't have the resolution for it to matter or justify a
HP5370 or better quality front end. I'll probably go with a fast
comparator to implement the variable threshold input.
Properly applied, a fast comparator will have lower jitter than the
rest of the errors, and is an excellent choice. Bruce suggested the
LTC6752, which is a great part if you need high toggle speeds (100s of
MHz) or ultra-fast edges. But you don't need high toggle rates and
may not need ultra-fast edges. Repeatability and stability are more
important than raw speed in this application. The LT1719, LT1720, or
TLV3501 may work just as well for your purpose, and they are
significantly less fussy to apply.
Note that the LTC6752 series is an improved replacement for the
ADCMP60x series, which itself is an improved replacement for the
MAX999. Of these three, the LTC6752 is the clear winner in my tests.
If you do choose it (or similar), make sure you look at the
transitions with something that will honestly show you any chatter at
frequencies up to at least several GHz. It only takes a little
transition chatter to knock the potential timing resolution of the
ultra-fast comparator way down. Do make sure to test it with the
slowest input edges you need it to handle.
Best regards,
Charles
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
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03/31/17
Fwiw, for a precision comparator you'll probably want a bipolar front end
for a lower flicker corner and better offset stability over cmos. For
high-speeds the diffpair is going to be biased fairly rich for bandwidth.
So you will more than likey have input bias currents of 100's of nA to uA
on your comparator. Which is not great with a 1 megohm source.
On Fri, Mar 31, 2017 at 9:08 PM Charles Steinmetz csteinmetz@yandex.com
wrote:
Mark wrote:
I thought about using the clamp diodes as protection but was a bit
worried about power supply noise leaking through the diodes and adding some
jitter to the input signals...
It is a definite worry even with a low-noise, 50 ohm input, and a
potential disaster with a 1Mohm input. Common signal diodes (1N4148,
1N914, 1N916, 1N4448, etc.) are specified for 5-10nA of reverse current.
Even a low-leakage signal diode (e.g., 1N3595) typically has several
hundred pA of leakage. Note that the concern isn't just power supply
noise -- the leakage current itself is quite noisy.
For low-picoamp diodes at a decent price, I use either (1) the B-C diode
of a small-signal BJT, or (2) the gate diode of a small-geometry JFET.
A 2N5550 makes a good high-voltage, low-leakage diode with leakage
current of ~30pA. Small signal HF transistors like the MPSH10 and
2N5179 (and their SMD and PN variants) are good for ~5pA, while the gate
diode of a PN4417A JFET (or SMD variant) has reverse leakage current of
~1pA (achieving this in practice requires a very clean board and good
layout).
I posted some actual leakage test results to Didier's site, which can be
downloaded at
<
http://www.ko4bb.com/getsimple/index.php?id=download&file=03_App_Notes_-_Proceedings/Reverse_leakage_of_diode-connected_BJTs_and_FETs_measurement_results.pdf
.
This document shows the connections I used to obtain the data.
The TICC doesn't have the resolution for it to matter or justify a
HP5370 or better quality front end. I'll probably go with a fast
comparator to implement the variable threshold input.
Properly applied, a fast comparator will have lower jitter than the rest
of the errors, and is an excellent choice. Bruce suggested the LTC6752,
which is a great part if you need high toggle speeds (100s of MHz) or
ultra-fast edges. But you don't need high toggle rates and may not need
ultra-fast edges. Repeatability and stability are more important than
raw speed in this application. The LT1719, LT1720, or TLV3501 may work
just as well for your purpose, and they are significantly less fussy to
apply.
Note that the LTC6752 series is an improved replacement for the ADCMP60x
series, which itself is an improved replacement for the MAX999. Of
these three, the LTC6752 is the clear winner in my tests. If you do
choose it (or similar), make sure you look at the transitions with
something that will honestly show you any chatter at frequencies up to
at least several GHz. It only takes a little transition chatter to
knock the potential timing resolution of the ultra-fast comparator way
down. Do make sure to test it with the slowest input edges you need it
to handle.
Best regards,
Charles
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Attempting sub nanosecond timing with an actual 1Mohm source is an exercise in futility. There are very few cases where one would want to attempt precision timing measurements with such a high impedance source. The 1M pulldown on the TICC input is merely intended to maintain a valid logic input should the user leave that input disconnected. In actual use with PPS signals the source impedance is in most cases a few tens of ohms. If one wishes to have a 1Mohm input impedance for use with AC coupled signals then a low noise FET input buffer preceding the comparator is required.
Protection diodes in this application not only need to have low leakage, they also need to turn on and off fast enough to be useful.
The propagation delay dispersion (both vs common mode and vs overdrive) also need to be considered along with the comparator jitter.
Bruce
and overdrive (both vs overdrive and vs input common modeOn 01 April 2017 at 15:34 Scott Stobbe <scott.j.stobbe@gmail.com> wrote:
Fwiw, for a precision comparator you'll probably want a bipolar front end
for a lower flicker corner and better offset stability over cmos. For
high-speeds the diffpair is going to be biased fairly rich for bandwidth.
So you will more than likey have input bias currents of 100's of nA to uA
on your comparator. Which is not great with a 1 megohm source.
On Fri, Mar 31, 2017 at 9:08 PM Charles Steinmetz <csteinmetz@yandex.com>
wrote:
Mark wrote:
I thought about using the clamp diodes as protection but was a bit
worried about power supply noise leaking through the diodes and adding some
jitter to the input signals...
It is a definite worry even with a low-noise, 50 ohm input, and a
potential disaster with a 1Mohm input. Common signal diodes (1N4148,
1N914, 1N916, 1N4448, etc.) are specified for 5-10nA of reverse current.
Even a low-leakage signal diode (e.g., 1N3595) typically has several
hundred pA of leakage. Note that the concern isn't just power supply
noise -- the leakage current itself is quite noisy.
For low-picoamp diodes at a decent price, I use either (1) the B-C diode
of a small-signal BJT, or (2) the gate diode of a small-geometry JFET.
A 2N5550 makes a good high-voltage, low-leakage diode with leakage
current of ~30pA. Small signal HF transistors like the MPSH10 and
2N5179 (and their SMD and PN variants) are good for ~5pA, while the gate
diode of a PN4417A JFET (or SMD variant) has reverse leakage current of
~1pA (achieving this in practice requires a very clean board and good
layout).
I posted some actual leakage test results to Didier's site, which can be
downloaded at
<
http://www.ko4bb.com/getsimple/index.php?id=download&file=03_App_Notes_-_Proceedings/Reverse_leakage_of_diode-connected_BJTs_and_FETs_measurement_results.pdf http://www.ko4bb.com/getsimple/index.php?id=download&file=03_App_Notes_-_Proceedings/Reverse_leakage_of_diode-connected_BJTs_and_FETs_measurement_results.pdf
.
This document shows the connections I used to obtain the data.
The TICC doesn't have the resolution for it to matter or justify a
HP5370 or better quality front end. I'll probably go with a fast
comparator to implement the variable threshold input.
Properly applied, a fast comparator will have lower jitter than the rest
of the errors, and is an excellent choice. Bruce suggested the LTC6752,
which is a great part if you need high toggle speeds (100s of MHz) or
ultra-fast edges. But you don't need high toggle rates and may not need
ultra-fast edges. Repeatability and stability are more important than
raw speed in this application. The LT1719, LT1720, or TLV3501 may work
just as well for your purpose, and they are significantly less fussy to
apply.
Note that the LTC6752 series is an improved replacement for the ADCMP60x
series, which itself is an improved replacement for the MAX999. Of
these three, the LTC6752 is the clear winner in my tests. If you do
choose it (or similar), make sure you look at the transitions with
something that will honestly show you any chatter at frequencies up to
at least several GHz. It only takes a little transition chatter to
knock the potential timing resolution of the ultra-fast comparator way
down. Do make sure to test it with the slowest input edges you need it
to handle.
Best regards,
Charles
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Also for interest the 53131a schematic is available at
http://bee.mif.pg.gda.pl/ciasteczkowypotwor/HP/53131.pdf
HP used a low input bias current bjt opamp, the Lt1008 to bias/dc servo a
custom JFET buffer driving an AD96687 comparator.
On Fri, Mar 31, 2017 at 10:34 PM Scott Stobbe scott.j.stobbe@gmail.com
wrote:
Fwiw, for a precision comparator you'll probably want a bipolar front end
for a lower flicker corner and better offset stability over cmos. For
high-speeds the diffpair is going to be biased fairly rich for bandwidth.
So you will more than likey have input bias currents of 100's of nA to uA
on your comparator. Which is not great with a 1 megohm source.
On Fri, Mar 31, 2017 at 9:08 PM Charles Steinmetz csteinmetz@yandex.com
wrote:
Mark wrote:
I thought about using the clamp diodes as protection but was a bit
worried about power supply noise leaking through the diodes and adding some
jitter to the input signals...
It is a definite worry even with a low-noise, 50 ohm input, and a
potential disaster with a 1Mohm input. Common signal diodes (1N4148,
1N914, 1N916, 1N4448, etc.) are specified for 5-10nA of reverse current.
Even a low-leakage signal diode (e.g., 1N3595) typically has several
hundred pA of leakage. Note that the concern isn't just power supply
noise -- the leakage current itself is quite noisy.
For low-picoamp diodes at a decent price, I use either (1) the B-C diode
of a small-signal BJT, or (2) the gate diode of a small-geometry JFET.
A 2N5550 makes a good high-voltage, low-leakage diode with leakage
current of ~30pA. Small signal HF transistors like the MPSH10 and
2N5179 (and their SMD and PN variants) are good for ~5pA, while the gate
diode of a PN4417A JFET (or SMD variant) has reverse leakage current of
~1pA (achieving this in practice requires a very clean board and good
layout).
I posted some actual leakage test results to Didier's site, which can be
downloaded at
<
http://www.ko4bb.com/getsimple/index.php?id=download&file=03_App_Notes_-_Proceedings/Reverse_leakage_of_diode-connected_BJTs_and_FETs_measurement_results.pdf
.
This document shows the connections I used to obtain the data.
The TICC doesn't have the resolution for it to matter or justify a
HP5370 or better quality front end. I'll probably go with a fast
comparator to implement the variable threshold input.
Properly applied, a fast comparator will have lower jitter than the rest
of the errors, and is an excellent choice. Bruce suggested the LTC6752,
which is a great part if you need high toggle speeds (100s of MHz) or
ultra-fast edges. But you don't need high toggle rates and may not need
ultra-fast edges. Repeatability and stability are more important than
raw speed in this application. The LT1719, LT1720, or TLV3501 may work
just as well for your purpose, and they are significantly less fussy to
apply.
Note that the LTC6752 series is an improved replacement for the ADCMP60x
series, which itself is an improved replacement for the MAX999. Of
these three, the LTC6752 is the clear winner in my tests. If you do
choose it (or similar), make sure you look at the transitions with
something that will honestly show you any chatter at frequencies up to
at least several GHz. It only takes a little transition chatter to
knock the potential timing resolution of the ultra-fast comparator way
down. Do make sure to test it with the slowest input edges you need it
to handle.
Best regards,
Charles
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Also interesting the LTC6752 is rail-rail input. Any rail-rail input opamp
I've used ends up with an ugly bump in input offset voltage transitioning
from the nmos or npn diff pair to the pmos or nmos. I'm not sure how good
or bad a rail-rail comparator may behave when common-mode biased in that
region.
On Fri, Mar 31, 2017 at 11:22 PM Bruce Griffiths bruce.griffiths@xtra.co.nz
wrote:
Attempting sub nanosecond timing with an actual 1Mohm source is an
exercise in futility. There are very few cases where one would want to
attempt precision timing measurements with such a high impedance source.
The 1M pulldown on the TICC input is merely intended to maintain a valid
logic input should the user leave that input disconnected. In actual use
with PPS signals the source impedance is in most cases a few tens of ohms.
If one wishes to have a 1Mohm input impedance for use with AC coupled
signals then a low noise FET input buffer preceding the comparator is
required.
Protection diodes in this application not only need to have low leakage,
they also need to turn on and off fast enough to be useful.
The propagation delay dispersion (both vs common mode and vs overdrive)
also need to be considered along with the comparator jitter.
Bruce
and overdrive (both vs overdrive and vs input common modeOn 01 April 2017
at 15:34 Scott Stobbe scott.j.stobbe@gmail.com wrote:
Fwiw, for a precision comparator you'll probably want a bipolar front end
for a lower flicker corner and better offset stability over cmos. For
high-speeds the diffpair is going to be biased fairly rich for bandwidth.
So you will more than likey have input bias currents of 100's of nA to uA
on your comparator. Which is not great with a 1 megohm source.
On Fri, Mar 31, 2017 at 9:08 PM Charles Steinmetz csteinmetz@yandex.com
wrote:
Mark wrote:
I thought about using the clamp diodes as protection but was a bit
worried about power supply noise leaking through the diodes and adding some
jitter to the input signals...
It is a definite worry even with a low-noise, 50 ohm input, and a
potential disaster with a 1Mohm input. Common signal diodes (1N4148,
1N914, 1N916, 1N4448, etc.) are specified for 5-10nA of reverse current.
Even a low-leakage signal diode (e.g., 1N3595) typically has several
hundred pA of leakage. Note that the concern isn't just power supply
noise -- the leakage current itself is quite noisy.
For low-picoamp diodes at a decent price, I use either (1) the B-C diode
of a small-signal BJT, or (2) the gate diode of a small-geometry JFET.
A 2N5550 makes a good high-voltage, low-leakage diode with leakage
current of ~30pA. Small signal HF transistors like the MPSH10 and
2N5179 (and their SMD and PN variants) are good for ~5pA, while the gate
diode of a PN4417A JFET (or SMD variant) has reverse leakage current of
~1pA (achieving this in practice requires a very clean board and good
layout).
I posted some actual leakage test results to Didier's site, which can be
downloaded at
<
.
This document shows the connections I used to obtain the data.
The TICC doesn't have the resolution for it to matter or justify a
HP5370 or better quality front end. I'll probably go with a fast
comparator to implement the variable threshold input.
Properly applied, a fast comparator will have lower jitter than the rest
of the errors, and is an excellent choice. Bruce suggested the LTC6752,
which is a great part if you need high toggle speeds (100s of MHz) or
ultra-fast edges. But you don't need high toggle rates and may not need
ultra-fast edges. Repeatability and stability are more important than
raw speed in this application. The LT1719, LT1720, or TLV3501 may work
just as well for your purpose, and they are significantly less fussy to
apply.
Note that the LTC6752 series is an improved replacement for the ADCMP60x
series, which itself is an improved replacement for the MAX999. Of
these three, the LTC6752 is the clear winner in my tests. If you do
choose it (or similar), make sure you look at the transitions with
something that will honestly show you any chatter at frequencies up to
at least several GHz. It only takes a little transition chatter to
knock the potential timing resolution of the ultra-fast comparator way
down. Do make sure to test it with the slowest input edges you need it
to handle.
Best regards,
Charles
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
The common mode propagation delay dispersion is also likely to be significant unless one uses an SiGe ECL/CML comparator.
Calibrating this or actually the differential dispersion between channels is an interesting but not insoluble issue.
Bruce
On 01 April 2017 at 18:49 Scott Stobbe <scott.j.stobbe@gmail.com> wrote:
Also interesting the LTC6752 is rail-rail input. Any rail-rail input opamp
I've used ends up with an ugly bump in input offset voltage transitioning
from the nmos or npn diff pair to the pmos or nmos. I'm not sure how good
or bad a rail-rail comparator may behave when common-mode biased in that
region.
On Fri, Mar 31, 2017 at 11:22 PM Bruce Griffiths <bruce.griffiths@xtra.co.nz>
wrote:
Attempting sub nanosecond timing with an actual 1Mohm source is an
exercise in futility. There are very few cases where one would want to
attempt precision timing measurements with such a high impedance source.
The 1M pulldown on the TICC input is merely intended to maintain a valid
logic input should the user leave that input disconnected. In actual use
with PPS signals the source impedance is in most cases a few tens of ohms.
If one wishes to have a 1Mohm input impedance for use with AC coupled
signals then a low noise FET input buffer preceding the comparator is
required.
Protection diodes in this application not only need to have low leakage,
they also need to turn on and off fast enough to be useful.
The propagation delay dispersion (both vs common mode and vs overdrive)
also need to be considered along with the comparator jitter.
Bruce
and overdrive (both vs overdrive and vs input common modeOn 01 April 2017
at 15:34 Scott Stobbe <scott.j.stobbe@gmail.com> wrote:
Fwiw, for a precision comparator you'll probably want a bipolar front end
for a lower flicker corner and better offset stability over cmos. For
high-speeds the diffpair is going to be biased fairly rich for bandwidth.
So you will more than likey have input bias currents of 100's of nA to uA
on your comparator. Which is not great with a 1 megohm source.
On Fri, Mar 31, 2017 at 9:08 PM Charles Steinmetz <csteinmetz@yandex.com>
wrote:
Mark wrote:
I thought about using the clamp diodes as protection but was a bit
worried about power supply noise leaking through the diodes and adding some
jitter to the input signals...
It is a definite worry even with a low-noise, 50 ohm input, and a
potential disaster with a 1Mohm input. Common signal diodes (1N4148,
1N914, 1N916, 1N4448, etc.) are specified for 5-10nA of reverse current.
Even a low-leakage signal diode (e.g., 1N3595) typically has several
hundred pA of leakage. Note that the concern isn't just power supply
noise -- the leakage current itself is quite noisy.
For low-picoamp diodes at a decent price, I use either (1) the B-C diode
of a small-signal BJT, or (2) the gate diode of a small-geometry JFET.
A 2N5550 makes a good high-voltage, low-leakage diode with leakage
current of ~30pA. Small signal HF transistors like the MPSH10 and
2N5179 (and their SMD and PN variants) are good for ~5pA, while the gate
diode of a PN4417A JFET (or SMD variant) has reverse leakage current of
~1pA (achieving this in practice requires a very clean board and good
layout).
I posted some actual leakage test results to Didier's site, which can be
downloaded at
<
http://www.ko4bb.com/getsimple/index.php?id=download&file=03_App_Notes_-_Proceedings/Reverse_leakage_of_diode-connected_BJTs_and_FETs_measurement_results.pdf http://www.ko4bb.com/getsimple/index.php?id=download&file=03_App_Notes_-_Proceedings/Reverse_leakage_of_diode-connected_BJTs_and_FETs_measurement_results.pdf
.
This document shows the connections I used to obtain the data.
The TICC doesn't have the resolution for it to matter or justify a
HP5370 or better quality front end. I'll probably go with a fast
comparator to implement the variable threshold input.
Properly applied, a fast comparator will have lower jitter than the rest
of the errors, and is an excellent choice. Bruce suggested the LTC6752,
which is a great part if you need high toggle speeds (100s of MHz) or
ultra-fast edges. But you don't need high toggle rates and may not need
ultra-fast edges. Repeatability and stability are more important than
raw speed in this application. The LT1719, LT1720, or TLV3501 may work
just as well for your purpose, and they are significantly less fussy to
apply.
Note that the LTC6752 series is an improved replacement for the ADCMP60x
series, which itself is an improved replacement for the MAX999. Of
these three, the LTC6752 is the clear winner in my tests. If you do
choose it (or similar), make sure you look at the transitions with
something that will honestly show you any chatter at frequencies up to
at least several GHz. It only takes a little transition chatter to
knock the potential timing resolution of the ultra-fast comparator way
down. Do make sure to test it with the slowest input edges you need it
to handle.
Best regards,
Charles
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Hi
There are low(fish) leakage / low capacitance / high speed transient suppressor diodes out there.
The aren’t going to do anything good in a 1 megohm environment. They are quite
useful in lower impedance circuits.
Bob
On Apr 1, 2017, at 1:49 AM, Scott Stobbe scott.j.stobbe@gmail.com wrote:
Also interesting the LTC6752 is rail-rail input. Any rail-rail input opamp
I've used ends up with an ugly bump in input offset voltage transitioning
from the nmos or npn diff pair to the pmos or nmos. I'm not sure how good
or bad a rail-rail comparator may behave when common-mode biased in that
region.
On Fri, Mar 31, 2017 at 11:22 PM Bruce Griffiths bruce.griffiths@xtra.co.nz
wrote:
Attempting sub nanosecond timing with an actual 1Mohm source is an
exercise in futility. There are very few cases where one would want to
attempt precision timing measurements with such a high impedance source.
The 1M pulldown on the TICC input is merely intended to maintain a valid
logic input should the user leave that input disconnected. In actual use
with PPS signals the source impedance is in most cases a few tens of ohms.
If one wishes to have a 1Mohm input impedance for use with AC coupled
signals then a low noise FET input buffer preceding the comparator is
required.
Protection diodes in this application not only need to have low leakage,
they also need to turn on and off fast enough to be useful.
The propagation delay dispersion (both vs common mode and vs overdrive)
also need to be considered along with the comparator jitter.
Bruce
and overdrive (both vs overdrive and vs input common modeOn 01 April 2017
at 15:34 Scott Stobbe scott.j.stobbe@gmail.com wrote:
Fwiw, for a precision comparator you'll probably want a bipolar front end
for a lower flicker corner and better offset stability over cmos. For
high-speeds the diffpair is going to be biased fairly rich for bandwidth.
So you will more than likey have input bias currents of 100's of nA to uA
on your comparator. Which is not great with a 1 megohm source.
On Fri, Mar 31, 2017 at 9:08 PM Charles Steinmetz csteinmetz@yandex.com
wrote:
Mark wrote:
I thought about using the clamp diodes as protection but was a bit
worried about power supply noise leaking through the diodes and adding some
jitter to the input signals...
It is a definite worry even with a low-noise, 50 ohm input, and a
potential disaster with a 1Mohm input. Common signal diodes (1N4148,
1N914, 1N916, 1N4448, etc.) are specified for 5-10nA of reverse current.
Even a low-leakage signal diode (e.g., 1N3595) typically has several
hundred pA of leakage. Note that the concern isn't just power supply
noise -- the leakage current itself is quite noisy.
For low-picoamp diodes at a decent price, I use either (1) the B-C diode
of a small-signal BJT, or (2) the gate diode of a small-geometry JFET.
A 2N5550 makes a good high-voltage, low-leakage diode with leakage
current of ~30pA. Small signal HF transistors like the MPSH10 and
2N5179 (and their SMD and PN variants) are good for ~5pA, while the gate
diode of a PN4417A JFET (or SMD variant) has reverse leakage current of
~1pA (achieving this in practice requires a very clean board and good
layout).
I posted some actual leakage test results to Didier's site, which can be
downloaded at
<
.
This document shows the connections I used to obtain the data.
The TICC doesn't have the resolution for it to matter or justify a
HP5370 or better quality front end. I'll probably go with a fast
comparator to implement the variable threshold input.
Properly applied, a fast comparator will have lower jitter than the rest
of the errors, and is an excellent choice. Bruce suggested the LTC6752,
which is a great part if you need high toggle speeds (100s of MHz) or
ultra-fast edges. But you don't need high toggle rates and may not need
ultra-fast edges. Repeatability and stability are more important than
raw speed in this application. The LT1719, LT1720, or TLV3501 may work
just as well for your purpose, and they are significantly less fussy to
apply.
Note that the LTC6752 series is an improved replacement for the ADCMP60x
series, which itself is an improved replacement for the MAX999. Of
these three, the LTC6752 is the clear winner in my tests. If you do
choose it (or similar), make sure you look at the transitions with
something that will honestly show you any chatter at frequencies up to
at least several GHz. It only takes a little transition chatter to
knock the potential timing resolution of the ultra-fast comparator way
down. Do make sure to test it with the slowest input edges you need it
to handle.
Best regards,
Charles
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Hi
The whole delay difference thing does get into a “do you care?” sort of category. The
testing process you are doing may well calibrate out (or ignore) an offset of this nature.
This is quite true in a number of TimeNut sort of tests.
Bob
On Apr 1, 2017, at 4:02 AM, Bruce Griffiths bruce.griffiths@xtra.co.nz wrote:
The common mode propagation delay dispersion is also likely to be significant unless one uses an SiGe ECL/CML comparator.
Calibrating this or actually the differential dispersion between channels is an interesting but not insoluble issue.
Bruce
On 01 April 2017 at 18:49 Scott Stobbe <scott.j.stobbe@gmail.com> wrote:
Also interesting the LTC6752 is rail-rail input. Any rail-rail input opamp
I've used ends up with an ugly bump in input offset voltage transitioning
from the nmos or npn diff pair to the pmos or nmos. I'm not sure how good
or bad a rail-rail comparator may behave when common-mode biased in that
region.
On Fri, Mar 31, 2017 at 11:22 PM Bruce Griffiths <bruce.griffiths@xtra.co.nz>
wrote:
Attempting sub nanosecond timing with an actual 1Mohm source is an
exercise in futility. There are very few cases where one would want to
attempt precision timing measurements with such a high impedance source.
The 1M pulldown on the TICC input is merely intended to maintain a valid
logic input should the user leave that input disconnected. In actual use
with PPS signals the source impedance is in most cases a few tens of ohms.
If one wishes to have a 1Mohm input impedance for use with AC coupled
signals then a low noise FET input buffer preceding the comparator is
required.
Protection diodes in this application not only need to have low leakage,
they also need to turn on and off fast enough to be useful.
The propagation delay dispersion (both vs common mode and vs overdrive)
also need to be considered along with the comparator jitter.
Bruce
and overdrive (both vs overdrive and vs input common modeOn 01 April 2017
at 15:34 Scott Stobbe <scott.j.stobbe@gmail.com> wrote:
Fwiw, for a precision comparator you'll probably want a bipolar front end
for a lower flicker corner and better offset stability over cmos. For
high-speeds the diffpair is going to be biased fairly rich for bandwidth.
So you will more than likey have input bias currents of 100's of nA to uA
on your comparator. Which is not great with a 1 megohm source.
On Fri, Mar 31, 2017 at 9:08 PM Charles Steinmetz <csteinmetz@yandex.com>
wrote:
Mark wrote:
I thought about using the clamp diodes as protection but was a bit
worried about power supply noise leaking through the diodes and adding some
jitter to the input signals...
It is a definite worry even with a low-noise, 50 ohm input, and a
potential disaster with a 1Mohm input. Common signal diodes (1N4148,
1N914, 1N916, 1N4448, etc.) are specified for 5-10nA of reverse current.
Even a low-leakage signal diode (e.g., 1N3595) typically has several
hundred pA of leakage. Note that the concern isn't just power supply
noise -- the leakage current itself is quite noisy.
For low-picoamp diodes at a decent price, I use either (1) the B-C diode
of a small-signal BJT, or (2) the gate diode of a small-geometry JFET.
A 2N5550 makes a good high-voltage, low-leakage diode with leakage
current of ~30pA. Small signal HF transistors like the MPSH10 and
2N5179 (and their SMD and PN variants) are good for ~5pA, while the gate
diode of a PN4417A JFET (or SMD variant) has reverse leakage current of
~1pA (achieving this in practice requires a very clean board and good
layout).
I posted some actual leakage test results to Didier's site, which can be
downloaded at
<
http://www.ko4bb.com/getsimple/index.php?id=download&file=03_App_Notes_-_Proceedings/Reverse_leakage_of_diode-connected_BJTs_and_FETs_measurement_results.pdf http://www.ko4bb.com/getsimple/index.php?id=download&file=03_App_Notes_-_Proceedings/Reverse_leakage_of_diode-connected_BJTs_and_FETs_measurement_results.pdf
.
This document shows the connections I used to obtain the data.
The TICC doesn't have the resolution for it to matter or justify a
HP5370 or better quality front end. I'll probably go with a fast
comparator to implement the variable threshold input.
Properly applied, a fast comparator will have lower jitter than the rest
of the errors, and is an excellent choice. Bruce suggested the LTC6752,
which is a great part if you need high toggle speeds (100s of MHz) or
ultra-fast edges. But you don't need high toggle rates and may not need
ultra-fast edges. Repeatability and stability are more important than
raw speed in this application. The LT1719, LT1720, or TLV3501 may work
just as well for your purpose, and they are significantly less fussy to
apply.
Note that the LTC6752 series is an improved replacement for the ADCMP60x
series, which itself is an improved replacement for the MAX999. Of
these three, the LTC6752 is the clear winner in my tests. If you do
choose it (or similar), make sure you look at the transitions with
something that will honestly show you any chatter at frequencies up to
at least several GHz. It only takes a little transition chatter to
knock the potential timing resolution of the ultra-fast comparator way
down. Do make sure to test it with the slowest input edges you need it
to handle.
Best regards,
Charles
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_______________________________________________
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To unsubscribe, go to
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and follow the instructions there.
_______________________________________________
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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.