Hi, all,
I'm in a bit of a rush, doing revs to a testing board for a prototype
lidar ASIC that turns out to be..., um..., well.... Let's just say it's
a _tiny_bit_delicate_ electrically. Yeah, just a little delicate,
that's it. (Not our design or our nickel, fortunately.)
It runs on a single supply, so the only sequencing issues are with the
signal pins. Thus the test board is going to bring up V_DD smoothly and
not too slowly: a monotonic edge of about 100 us. While that's going
on, all the inputs and outputs will see 100k ohms to ground. (All the
enables are positive-true, which makes this easier.)
The digital pins are all inputs, so they're just buffered with
SN74LVC1G125s (tri-state Schmitt noninverting), with the aforementioned
100k to ground on their outputs.
The analog outputs don't have much drive, but can go pretty fast if you
keep the capacitance down. There are a fair few of them, so I want to
mux them down before the op amp buffers (OPA2626es--surprisingly nice
chips).
Because we're not made of money, and the test boards aren't ITAR, we're >getting them made and stuffed at JLCPCB. Thus we care a lot about what
their tame distributor LCSC has in stock.
They're fairly light on analog muxes, it turns out. Going through what
they do have, I was reminded just how awful the capacitance of old-timey
mux parts is--way over 100 pF at the common pin of an 8-1, blech.
They do have these very nice-looking USB switches, type PI3USB14-A, for >pretty cheap ($0.45 @ 1ea) and in plentiful stock.
They look beautiful--6 ohms R_on, 4 pF C_off typical--but apart from one >crosstalk number, the datasheet gives only sketchy hints about their
actual analog performance--bandwidth and crosstalk, but nothing about
charge injection, switching times, make-before-break, resistance
linearity, or distortion.
Has any of you used them for actual analog stuff?
Thanks
Phil Hobbs
Hi, all,
I'm in a bit of a rush, doing revs to a testing board for a prototype
lidar ASIC that turns out to be..., um..., well.... Let's just say it's
a _tiny_bit_delicate_ electrically. Yeah, just a little delicate,
that's it. (Not our design or our nickel, fortunately.)
It runs on a single supply, so the only sequencing issues are with the
signal pins. Thus the test board is going to bring up V_DD smoothly and
not too slowly: a monotonic edge of about 100 us. While that's going
on, all the inputs and outputs will see 100k ohms to ground. (All the
enables are positive-true, which makes this easier.)
The digital pins are all inputs, so they're just buffered with
SN74LVC1G125s (tri-state Schmitt noninverting), with the aforementioned
100k to ground on their outputs.
The analog outputs don't have much drive, but can go pretty fast if you
keep the capacitance down. There are a fair few of them, so I want to
mux them down before the op amp buffers (OPA2626es--surprisingly nice
chips).
Because we're not made of money, and the test boards aren't ITAR, we're getting them made and stuffed at JLCPCB. Thus we care a lot about what their tame distributor LCSC has in stock.
They're fairly light on analog muxes, it turns out. Going through what
they do have, I was reminded just how awful the capacitance of old-timey
mux parts is--way over 100 pF at the common pin of an 8-1, blech.
They do have these very nice-looking USB switches, type PI3USB14-A, for pretty cheap ($0.45 @ 1ea) and in plentiful stock.
They look beautiful--6 ohms R_on, 4 pF C_off typical--but apart from one crosstalk number, the datasheet gives only sketchy hints about their
actual analog performance--bandwidth and crosstalk, but nothing about
charge injection, switching times, make-before-break, resistance
linearity, or distortion.
Has any of you used them for actual analog stuff?
Thanks
Phil Hobbs
On 26/04/2024 2:28 am, Phil Hobbs wrote:
Hi, all,
I'm in a bit of a rush, doing revs to a testing board for a prototype
lidar ASIC that turns out to be..., um..., well.... Let's just say
it's a _tiny_bit_delicate_ electrically. Yeah, just a little
delicate, that's it. (Not our design or our nickel, fortunately.)
It runs on a single supply, so the only sequencing issues are with the
signal pins. Thus the test board is going to bring up V_DD smoothly
and not too slowly: a monotonic edge of about 100 us. While that's
going on, all the inputs and outputs will see 100k ohms to ground.
(All the enables are positive-true, which makes this easier.)
The digital pins are all inputs, so they're just buffered with
SN74LVC1G125s (tri-state Schmitt noninverting), with the
aforementioned 100k to ground on their outputs.
The analog outputs don't have much drive, but can go pretty fast if
you keep the capacitance down. There are a fair few of them, so I
want to mux them down before the op amp buffers
(OPA2626es--surprisingly nice chips).
Because we're not made of money, and the test boards aren't ITAR,
we're getting them made and stuffed at JLCPCB. Thus we care a lot
about what their tame distributor LCSC has in stock.
They're fairly light on analog muxes, it turns out. Going through
what they do have, I was reminded just how awful the capacitance of
old-timey mux parts is--way over 100 pF at the common pin of an 8-1,
blech.
They do have these very nice-looking USB switches, type PI3USB14-A,
for pretty cheap ($0.45 @ 1ea) and in plentiful stock.
They look beautiful--6 ohms R_on, 4 pF C_off typical--but apart from
one crosstalk number, the datasheet gives only sketchy hints about
their actual analog performance--bandwidth and crosstalk, but nothing
about charge injection, switching times, make-before-break, resistance
linearity, or distortion.
Has any of you used them for actual analog stuff?
Thanks
Phil Hobbs
As long as you don't need the signals to swing near the positive rail, I suggest you google "H-mode mixer" as a lot of amateur radio enthusiasts
have built mixers using bus switches, basically just nmos fets with a
gate driver. For example: https://martein.home.xs4all.nl/pa3ake/hmode/switches.html
They may not be better than the PI3USB14-A but I have a better guess of
what is in them.
On 27/04/2024 1:01 am, Chris Jones wrote:
On 26/04/2024 2:28 am, Phil Hobbs wrote:
Hi, all,
I'm in a bit of a rush, doing revs to a testing board for a prototype
lidar ASIC that turns out to be..., um..., well.... Let's just say
it's a _tiny_bit_delicate_ electrically. Yeah, just a little
delicate, that's it. (Not our design or our nickel, fortunately.)
It runs on a single supply, so the only sequencing issues are with the
signal pins. Thus the test board is going to bring up V_DD smoothly
and not too slowly: a monotonic edge of about 100 us. While that's
going on, all the inputs and outputs will see 100k ohms to ground.
(All the enables are positive-true, which makes this easier.)
The digital pins are all inputs, so they're just buffered with
SN74LVC1G125s (tri-state Schmitt noninverting), with the
aforementioned 100k to ground on their outputs.
The analog outputs don't have much drive, but can go pretty fast if
you keep the capacitance down. There are a fair few of them, so I
want to mux them down before the op amp buffers
(OPA2626es--surprisingly nice chips).
Because we're not made of money, and the test boards aren't ITAR,
we're getting them made and stuffed at JLCPCB. Thus we care a lot
about what their tame distributor LCSC has in stock.
They're fairly light on analog muxes, it turns out. Going through
what they do have, I was reminded just how awful the capacitance of
old-timey mux parts is--way over 100 pF at the common pin of an 8-1,
blech.
They do have these very nice-looking USB switches, type PI3USB14-A,
for pretty cheap ($0.45 @ 1ea) and in plentiful stock.
They look beautiful--6 ohms R_on, 4 pF C_off typical--but apart from
one crosstalk number, the datasheet gives only sketchy hints about
their actual analog performance--bandwidth and crosstalk, but nothing
about charge injection, switching times, make-before-break, resistance
linearity, or distortion.
Has any of you used them for actual analog stuff?
Thanks
Phil Hobbs
As long as you don't need the signals to swing near the positive rail, I
suggest you google "H-mode mixer" as a lot of amateur radio enthusiasts
have built mixers using bus switches, basically just nmos fets with a
gate driver. For example:
https://martein.home.xs4all.nl/pa3ake/hmode/switches.html
They may not be better than the PI3USB14-A but I have a better guess of
what is in them.
Ah, I see they also tried ones with both NMOS and PMOS devices in the >switches. The FSA3157 seems to have somewhat more complete
specifications than the one you mentioned.
If you don't happen to need it to swing near the positive rail, you
might get less capacitance with a NMOS-only type like the venerable FST3125.
I hope the ones that also have PMOS devices in the switches keep the >backgates of the PMOS at the rail (like a 4016), and don't do the
horrible backgate switching trickery to reduce Ron like in the old 4066.
I think some of those might have been so bad that they could momentarily >short your signal to the rail, and even if not, they certainly had
another big charge injection mechanism.
On 27/04/2024 1:01 am, Chris Jones wrote:
On 26/04/2024 2:28 am, Phil Hobbs wrote:
Hi, all,
I'm in a bit of a rush, doing revs to a testing board for a prototype
lidar ASIC that turns out to be..., um..., well.... Let's just say
it's a _tiny_bit_delicate_ electrically. Yeah, just a little
delicate, that's it. (Not our design or our nickel, fortunately.)
It runs on a single supply, so the only sequencing issues are with
the signal pins. Thus the test board is going to bring up V_DD
smoothly and not too slowly: a monotonic edge of about 100 us. While
that's going on, all the inputs and outputs will see 100k ohms to
ground. (All the enables are positive-true, which makes this easier.)
The digital pins are all inputs, so they're just buffered with
SN74LVC1G125s (tri-state Schmitt noninverting), with the
aforementioned 100k to ground on their outputs.
The analog outputs don't have much drive, but can go pretty fast if
you keep the capacitance down. There are a fair few of them, so I
want to mux them down before the op amp buffers
(OPA2626es--surprisingly nice chips).
Because we're not made of money, and the test boards aren't ITAR,
we're getting them made and stuffed at JLCPCB. Thus we care a lot
about what their tame distributor LCSC has in stock.
They're fairly light on analog muxes, it turns out. Going through
what they do have, I was reminded just how awful the capacitance of
old-timey mux parts is--way over 100 pF at the common pin of an 8-1,
blech.
They do have these very nice-looking USB switches, type PI3USB14-A,
for pretty cheap ($0.45 @ 1ea) and in plentiful stock.
They look beautiful--6 ohms R_on, 4 pF C_off typical--but apart from
one crosstalk number, the datasheet gives only sketchy hints about
their actual analog performance--bandwidth and crosstalk, but nothing
about charge injection, switching times, make-before-break,
resistance linearity, or distortion.
Has any of you used them for actual analog stuff?
Thanks
Phil Hobbs
As long as you don't need the signals to swing near the positive rail,
I suggest you google "H-mode mixer" as a lot of amateur radio
enthusiasts have built mixers using bus switches, basically just nmos
fets with a gate driver. For example:
https://martein.home.xs4all.nl/pa3ake/hmode/switches.html
They may not be better than the PI3USB14-A but I have a better guess
of what is in them.
Ah, I see they also tried ones with both NMOS and PMOS devices in the switches. The FSA3157 seems to have somewhat more complete
specifications than the one you mentioned.
If you don't happen to need it to swing near the positive rail, you
might get less capacitance with a NMOS-only type like the venerable
FST3125.
I hope the ones that also have PMOS devices in the switches keep the backgates of the PMOS at the rail (like a 4016), and don't do the
horrible backgate switching trickery to reduce Ron like in the old 4066.
I think some of those might have been so bad that they could momentarily short your signal to the rail, and even if not, they certainly had
another big charge injection mechanism.
On Sat, 27 Apr 2024 01:12:13 +1000, Chris Jones
<lugnut808@spam.yahoo.com> wrote:
On 27/04/2024 1:01 am, Chris Jones wrote:
On 26/04/2024 2:28 am, Phil Hobbs wrote:
Hi, all,
I'm in a bit of a rush, doing revs to a testing board for a prototype
lidar ASIC that turns out to be..., um..., well.... Let's just say
it's a _tiny_bit_delicate_ electrically. Yeah, just a little
delicate, that's it. (Not our design or our nickel, fortunately.)
It runs on a single supply, so the only sequencing issues are with the >>>> signal pins. Thus the test board is going to bring up V_DD smoothly
and not too slowly: a monotonic edge of about 100 us. While that's
going on, all the inputs and outputs will see 100k ohms to ground.
(All the enables are positive-true, which makes this easier.)
The digital pins are all inputs, so they're just buffered with
SN74LVC1G125s (tri-state Schmitt noninverting), with the
aforementioned 100k to ground on their outputs.
The analog outputs don't have much drive, but can go pretty fast if
you keep the capacitance down. There are a fair few of them, so I
want to mux them down before the op amp buffers
(OPA2626es--surprisingly nice chips).
Because we're not made of money, and the test boards aren't ITAR,
we're getting them made and stuffed at JLCPCB. Thus we care a lot
about what their tame distributor LCSC has in stock.
They're fairly light on analog muxes, it turns out. Going through
what they do have, I was reminded just how awful the capacitance of
old-timey mux parts is--way over 100 pF at the common pin of an 8-1,
blech.
They do have these very nice-looking USB switches, type PI3USB14-A,
for pretty cheap ($0.45 @ 1ea) and in plentiful stock.
They look beautiful--6 ohms R_on, 4 pF C_off typical--but apart from
one crosstalk number, the datasheet gives only sketchy hints about
their actual analog performance--bandwidth and crosstalk, but nothing
about charge injection, switching times, make-before-break, resistance >>>> linearity, or distortion.
Has any of you used them for actual analog stuff?
Thanks
Phil Hobbs
As long as you don't need the signals to swing near the positive rail, I >>> suggest you google "H-mode mixer" as a lot of amateur radio enthusiasts
have built mixers using bus switches, basically just nmos fets with a
gate driver. For example:
https://martein.home.xs4all.nl/pa3ake/hmode/switches.html
They may not be better than the PI3USB14-A but I have a better guess of
what is in them.
Ah, I see they also tried ones with both NMOS and PMOS devices in the
switches. The FSA3157 seems to have somewhat more complete
specifications than the one you mentioned.
The 3157 is nice too, SPDT in a small package, with specified charge injection. We pay 7 cents.
On 2024-04-26 14:03, John Larkin wrote:
On Sat, 27 Apr 2024 01:12:13 +1000, Chris Jones
<lugnut808@spam.yahoo.com> wrote:
On 27/04/2024 1:01 am, Chris Jones wrote:
On 26/04/2024 2:28 am, Phil Hobbs wrote:
Hi, all,
I'm in a bit of a rush, doing revs to a testing board for a prototype >>>>> lidar ASIC that turns out to be..., um..., well.... Let's just say
it's a _tiny_bit_delicate_ electrically. Yeah, just a little
delicate, that's it. (Not our design or our nickel, fortunately.)
It runs on a single supply, so the only sequencing issues are with the >>>>> signal pins. Thus the test board is going to bring up V_DD smoothly
and not too slowly: a monotonic edge of about 100 us. While that's
going on, all the inputs and outputs will see 100k ohms to ground.
(All the enables are positive-true, which makes this easier.)
The digital pins are all inputs, so they're just buffered with
SN74LVC1G125s (tri-state Schmitt noninverting), with the
aforementioned 100k to ground on their outputs.
The analog outputs don't have much drive, but can go pretty fast if
you keep the capacitance down. There are a fair few of them, so I
want to mux them down before the op amp buffers
(OPA2626es--surprisingly nice chips).
Because we're not made of money, and the test boards aren't ITAR,
we're getting them made and stuffed at JLCPCB. Thus we care a lot
about what their tame distributor LCSC has in stock.
They're fairly light on analog muxes, it turns out. Going through
what they do have, I was reminded just how awful the capacitance of
old-timey mux parts is--way over 100 pF at the common pin of an 8-1, >>>>> blech.
They do have these very nice-looking USB switches, type PI3USB14-A,
for pretty cheap ($0.45 @ 1ea) and in plentiful stock.
They look beautiful--6 ohms R_on, 4 pF C_off typical--but apart from >>>>> one crosstalk number, the datasheet gives only sketchy hints about
their actual analog performance--bandwidth and crosstalk, but nothing >>>>> about charge injection, switching times, make-before-break, resistance >>>>> linearity, or distortion.
Has any of you used them for actual analog stuff?
Thanks
Phil Hobbs
As long as you don't need the signals to swing near the positive rail, I >>>> suggest you google "H-mode mixer" as a lot of amateur radio enthusiasts >>>> have built mixers using bus switches, basically just nmos fets with a
gate driver. For example:
https://martein.home.xs4all.nl/pa3ake/hmode/switches.html
They may not be better than the PI3USB14-A but I have a better guess of >>>> what is in them.
Ah, I see they also tried ones with both NMOS and PMOS devices in the
switches. The FSA3157 seems to have somewhat more complete
specifications than the one you mentioned.
The 3157 is nice too, SPDT in a small package, with specified charge
injection. We pay 7 cents.
The onsemi FSA3157 is obsolete, unfortunately. There are TI and Diodes
Inc versions that you can still get,
Cheers
Phil Hobbs
On Fri, 26 Apr 2024 19:30:58 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
On 2024-04-26 14:03, John Larkin wrote:
On Sat, 27 Apr 2024 01:12:13 +1000, Chris Jones
<lugnut808@spam.yahoo.com> wrote:
On 27/04/2024 1:01 am, Chris Jones wrote:
On 26/04/2024 2:28 am, Phil Hobbs wrote:
Hi, all,
I'm in a bit of a rush, doing revs to a testing board for a prototype >>>>>> lidar ASIC that turns out to be..., um..., well.... Let's just say >>>>>> it's a _tiny_bit_delicate_ electrically. Yeah, just a little
delicate, that's it. (Not our design or our nickel, fortunately.)
It runs on a single supply, so the only sequencing issues are with the >>>>>> signal pins. Thus the test board is going to bring up V_DD smoothly >>>>>> and not too slowly: a monotonic edge of about 100 us. While that's >>>>>> going on, all the inputs and outputs will see 100k ohms to ground. >>>>>> (All the enables are positive-true, which makes this easier.)
The digital pins are all inputs, so they're just buffered with
SN74LVC1G125s (tri-state Schmitt noninverting), with the
aforementioned 100k to ground on their outputs.
The analog outputs don't have much drive, but can go pretty fast if >>>>>> you keep the capacitance down. There are a fair few of them, so I >>>>>> want to mux them down before the op amp buffers
(OPA2626es--surprisingly nice chips).
Because we're not made of money, and the test boards aren't ITAR,
we're getting them made and stuffed at JLCPCB. Thus we care a lot >>>>>> about what their tame distributor LCSC has in stock.
They're fairly light on analog muxes, it turns out. Going through >>>>>> what they do have, I was reminded just how awful the capacitance of >>>>>> old-timey mux parts is--way over 100 pF at the common pin of an 8-1, >>>>>> blech.
They do have these very nice-looking USB switches, type PI3USB14-A, >>>>>> for pretty cheap ($0.45 @ 1ea) and in plentiful stock.
They look beautiful--6 ohms R_on, 4 pF C_off typical--but apart from >>>>>> one crosstalk number, the datasheet gives only sketchy hints about >>>>>> their actual analog performance--bandwidth and crosstalk, but nothing >>>>>> about charge injection, switching times, make-before-break, resistance >>>>>> linearity, or distortion.
Has any of you used them for actual analog stuff?
Thanks
Phil Hobbs
As long as you don't need the signals to swing near the positive rail, I >>>>> suggest you google "H-mode mixer" as a lot of amateur radio enthusiasts >>>>> have built mixers using bus switches, basically just nmos fets with a >>>>> gate driver. For example:
https://martein.home.xs4all.nl/pa3ake/hmode/switches.html
They may not be better than the PI3USB14-A but I have a better guess of >>>>> what is in them.
Ah, I see they also tried ones with both NMOS and PMOS devices in the
switches. The FSA3157 seems to have somewhat more complete
specifications than the one you mentioned.
The 3157 is nice too, SPDT in a small package, with specified charge
injection. We pay 7 cents.
The onsemi FSA3157 is obsolete, unfortunately. There are TI and Diodes
Inc versions that you can still get,
Cheers
Phil Hobbs
My MAX record shows OnSemi NLASB3157DFT2G as an acceptable sub. They
hires sadists to make up part numbers.
I like HH Smith, with part numbers like 101.
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