| Author |
Message |
Guest
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 Posted:
Sat Nov 26, 2005 9:35 am Post subject:
a low leakage (<1pA) electrical switch? |
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Hi,
I'm looking for a low leakage (<1pA) electrical switch, SPST or SPDT.
The only I can find is MAX326/7, but they have about 1000 ohms
restitance at ON condition. Who knows such a switch with lower Ron (<10
ohm)?
Many thanks!
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Robert Baer
Guest
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| Posted:
Sat Nov 26, 2005 9:35 am Post subject:
Re: a low leakage (<1pA) electrical switch? |
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zhenzhongwang@gmail.com wrote:
| Quote: | Hi,
I'm looking for a low leakage (<1pA) electrical switch, SPST or SPDT.
The only I can find is MAX326/7, but they have about 1000 ohms
restitance at ON condition. Who knows such a switch with lower Ron (<10
ohm)?
Many thanks!
You were damn lucky to get anything that Maxim/Dallas advertises! |
That aside, at 1pA, who cares about the on resistance - even 1meg is
an almost short.
And any FET-based device is going to have temerature leakage doubling
(per 10C) problems.
Try a 2N7000 which is a small MOSFET. |
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Mike Harrison
Guest
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| Posted:
Sat Nov 26, 2005 5:35 pm Post subject:
Re: a low leakage (<1pA) electrical switch? |
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On 26 Nov 2005 03:43:15 -0800, Winfield Hill <Winfield_member@newsguy.com> wrote:
| Quote: | Robert Baer wrote...
zhenzhongwang@gmail.com wrote:
I'm looking for a low leakage (<1pA) electrical switch, SPST or SPDT.
The only I can find is MAX326/7, but they have about 1000 ohms
restitance at ON condition. Who knows such a switch with lower Ron
(<10 ohm)?
Many thanks!
|
Relay ?
Seriously.
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Winfield Hill
Guest
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| Posted:
Sat Nov 26, 2005 5:35 pm Post subject:
Re: a low leakage (<1pA) electrical switch? |
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Winfield Hill wrote...
| Quote: |
Robert Baer wrote...
zhenzhongwang@gmail.com wrote:
I'm looking for a low leakage (<1pA) electrical switch, SPST or SPDT.
The only I can find is MAX326/7, but they have about 1000 ohms
restitance at ON condition. Who knows such a switch with lower Ron
(<10 ohm)?
Many thanks!
You were damn lucky to get anything that Maxim/Dallas advertises!
DigiKey has several hundred max326 parts in stock, DIP and soic.
|
However, not meant to detract from the truth of Robert's remark.
| Quote: | I agree, discrete FETs (rather than ICs with their substrate
leakage, etc.) are best for the under 10pA region.
|
One CMOS switch IC with good-looking datasheet leakage
curves (under 10pA) is Vishay's 16-year-old DG417 series,
http://www.vishay.com/analog-switches/list/product-70051/
They also have the newer DG417B series with lower Qinject,
http://www.vishay.com/analog-switches/list/product-72107/
--
Thanks,
- Win |
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Winfield Hill
Guest
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| Posted:
Sat Nov 26, 2005 5:35 pm Post subject:
Re: a low leakage (<1pA) electrical switch? |
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|
Robert Baer wrote...
| Quote: |
zhenzhongwang@gmail.com wrote:
I'm looking for a low leakage (<1pA) electrical switch, SPST or SPDT.
The only I can find is MAX326/7, but they have about 1000 ohms
restitance at ON condition. Who knows such a switch with lower Ron
(<10 ohm)?
Many thanks!
You were damn lucky to get anything that Maxim/Dallas advertises!
|
DigiKey has several hundred max326 parts in stock, DIP and soic.
| Quote: | That aside, at 1pA, who cares about the on resistance - even 1meg
is an almost short.
|
Right.
| Quote: | And any FET-based device is going to have temerature leakage
doubling (per 10C) problems. Try a 2N7000 which is a small
MOSFET.
|
I agree, discrete FETs (rather than ICs with their substrate
leakage, etc.) are best for the under 10pA region. WRT the
5-ohm 2n7000, I'd say even that's not quite small enough,
*very* small MOSFETs are best for sub pA use. zhenzhongwang
should know that low Ron is the result of a large active area,
which is not compatible with very low leakage.
There are switch circuit configurations that can help. E.g.,
the "T" form can be used to improve the 1/Ron vs leakage-current
tradeoff. A set of three sd210 lateral DMOS fets can be used
(with an inverting opamp, similar to AoE fig 4.50) to achieve
an Ron of about 70 ohms with under 1pA of effective leakage.
--
Thanks,
- Win |
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John Larkin
Guest
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| Posted:
Sun Nov 27, 2005 1:04 am Post subject:
Re: a low leakage (<1pA) electrical switch? |
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On Sat, 26 Nov 2005 16:11:41 GMT, Mike Harrison <mike@whitewing.co.uk>
wrote:
| Quote: | On 26 Nov 2005 03:43:15 -0800, Winfield Hill <Winfield_member@newsguy.com> wrote:
Robert Baer wrote...
zhenzhongwang@gmail.com wrote:
I'm looking for a low leakage (<1pA) electrical switch, SPST or SPDT.
The only I can find is MAX326/7, but they have about 1000 ohms
restitance at ON condition. Who knows such a switch with lower Ron
(<10 ohm)?
Many thanks!
Relay ?
Seriously.
|
Relays are wonderful. You can get a sealed DPDT latching relay, <0.1
ohms on, >1T ohm off, 1500 volt standoff, zero thermal EMF, tiny
surface mount, isolated logic-level drive, for under $3. Most of these
tiny relays stand a bit off the board, so wash nicely... no trapped
flux.
John |
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Winfield Hill
Guest
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| Posted:
Sun Nov 27, 2005 1:35 am Post subject:
Re: a low leakage (<1pA) electrical switch? |
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John Larkin wrote...
| Quote: | Mike Harrison wrote:
Winfield Hill wrote:
Robert Baer wrote...
zhenzhongwang@gmail.com wrote:
I'm looking for a low leakage (<1pA) electrical switch, SPST or SPDT.
The only I can find is MAX326/7, but they have about 1000 ohms
restitance at ON condition. Who knows such a switch with lower Ron
(<10 ohm)?
Relay? Seriously.
Relays are wonderful. You can get a sealed DPDT latching relay,
0.1 ohms on, >1T ohm off, 1500 volt standoff, zero thermal EMF, tiny
surface mount, isolated logic-level drive, for under $3. Most of these
tiny relays stand a bit off the board, so wash nicely... no trapped
flux.
|
I agree.
I see in my work email that Zhenzhong Wang also wrote a scientist
here at the Institute, asking about a drawing for an STM preamp I
designed some years ago for this fellow. I'm not sure which one
that was right now, but most of my STM preamp designs (if they had
the dual-feedback resistor feature), used NAiS Aromat TN2 relays.
http://pewa.panasonic.com/pcsd/product/sign/pdf_cat/tn.pdf The
100M resistor and relay pins were soldered in air or on a teflon
standoff, as was the opamp's negative input and the protection
components. There may be better small relays to use, but these
worked well for us. The relay activates to invoke the lower-gain
mode, and gets its coil operating power from a filtered source.
--
Thanks,
- Win |
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Guest
|
| Posted:
Sun Nov 27, 2005 1:35 am Post subject:
Re: a low leakage (<1pA) electrical switch? |
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<zhenzhongwang@gmail.com> wrote in message
news:1132989442.754581.250830@o13g2000cwo.googlegroups.com...
| Quote: | Hi,
I'm looking for a low leakage (<1pA) electrical switch, SPST or SPDT.
The only I can find is MAX326/7, but they have about 1000 ohms
restitance at ON condition. Who knows such a switch with lower Ron (<10
ohm)?
Many thanks!
|
What leakage is it that concerns you? Are you worried about leakage from
the input to the output or from input to ground, or from switching signal to
output? Also, are you concerned with leakage in the on condition or the off
condition? Give us some idea of where the problem is.
If you just need isolation between input and output, I'd suggest a
3-terminal switch, rather than a 2-terminal one.
Norm Strong |
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Joerg
Guest
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| Posted:
Sun Nov 27, 2005 1:35 am Post subject:
Re: a low leakage (<1pA) electrical switch? |
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Hello Win, Hello Zhenzhong,
| Quote: | ... There may be better small relays to use, but these
worked well for us. The relay activates to invoke the lower-gain
mode, and gets its coil operating power from a filtered source.
|
Reed relays may be an option here but they are pretty expensive
nowadays. IIRC even the regular Coto 9800 series lists 10^12 ohms
insulation.
Digikey has lots of them.
Regards, Joerg
http://www.analogconsultants.com |
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wang
Guest
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| Posted:
Sun Nov 27, 2005 1:35 am Post subject:
Re: a low leakage (<1pA) electrical switch? |
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Hill, many thanks.
I'm a student of Prof. DongminChen, and use lots of boxes named RIS***,
which you designed several years ago. Sometimes they work not really
well. |
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Robert Baer
Guest
|
| Posted:
Sun Nov 27, 2005 9:35 am Post subject:
Re: a low leakage (<1pA) electrical switch? |
|
|
Mike Harrison wrote:
| Quote: | On 26 Nov 2005 03:43:15 -0800, Winfield Hill <Winfield_member@newsguy.com> wrote:
Robert Baer wrote...
zhenzhongwang@gmail.com wrote:
I'm looking for a low leakage (<1pA) electrical switch, SPST or SPDT.
The only I can find is MAX326/7, but they have about 1000 ohms
restitance at ON condition. Who knows such a switch with lower Ron
(<10 ohm)?
Many thanks!
Relay ?
Seriously.
I think only if you make it yourself..reed capsule carefully cleaned |
and then not contaminated by pinkies, coil shorter than capsule length
and preferably not touching the glass envelope. |
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Robert Baer
Guest
|
| Posted:
Sun Nov 27, 2005 9:35 am Post subject:
Re: a low leakage (<1pA) electrical switch? |
|
|
Winfield Hill wrote:
| Quote: | Winfield Hill wrote...
Robert Baer wrote...
zhenzhongwang@gmail.com wrote:
I'm looking for a low leakage (<1pA) electrical switch, SPST or SPDT.
The only I can find is MAX326/7, but they have about 1000 ohms
restitance at ON condition. Who knows such a switch with lower Ron
(<10 ohm)?
Many thanks!
You were damn lucky to get anything that Maxim/Dallas advertises!
DigiKey has several hundred max326 parts in stock, DIP and soic.
However, not meant to detract from the truth of Robert's remark.
I agree, discrete FETs (rather than ICs with their substrate
leakage, etc.) are best for the under 10pA region.
One CMOS switch IC with good-looking datasheet leakage
curves (under 10pA) is Vishay's 16-year-old DG417 series,
http://www.vishay.com/analog-switches/list/product-70051/
They also have the newer DG417B series with lower Qinject,
http://www.vishay.com/analog-switches/list/product-72107/
You are right, i forgot about the DG series (been ages..). |
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Winfield Hill
Guest
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| Posted:
Sun Nov 27, 2005 5:35 pm Post subject:
Re: a low leakage (<1pA) electrical switch? |
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wang wrote...
| Quote: |
Hill, many thanks.
I'm a student of Prof. Dongmin Chen, and use lots of boxes named
RIS***, which you designed several years ago. Sometimes they work
not really well.
|
Sometimes they don't work well?
--
Thanks,
- Win |
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Winfield Hill
Guest
|
| Posted:
Sun Nov 27, 2005 5:35 pm Post subject:
Re: a low leakage (<1pA) electrical switch? |
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Joerg wrote...
| Quote: |
Hello Win, Hello Zhenzhong,
... There may be better small relays to use, but these
worked well for us. The relay activates to invoke the lower-gain
mode, and gets its coil operating power from a filtered source.
Reed relays may be an option here but they are pretty expensive
nowadays. IIRC even the regular Coto 9800 series lists 10^12 ohms
insulation.
|
http://pewa.panasonic.com/pcsd/product/sign/pdf_cat/tn.pdf
Taking one of these NAiS TN2 type relays apart shows they're
a real miracle of miniaturization. I appreciate having their
DPDT functionality in a very small size. For example, I use
the second section to make a T-type switching network, with
nearly-perfect capacitive isolation.
But I sometimes wonder if using a pair of reed relays instead
would have some advantage over the TN2 "conventional" relay.
Yes, glass reed relays have vacuum contacts, but the TN2's
gold-clad silver contacts in air continue to work well, even
though at 10pA it's certainly a classic case of "dry" switching.
--
Thanks,
- Win |
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martin griffith
Guest
|
| Posted:
Sun Nov 27, 2005 5:35 pm Post subject:
Re: a low leakage (<1pA) electrical switch? |
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|
On 27 Nov 2005 04:26:32 -0800, in sci.electronics.design Winfield Hill
<Winfield_member@newsguy.com> wrote:
| Quote: | Joerg wrote...
Hello Win, Hello Zhenzhong,
... There may be better small relays to use, but these
worked well for us. The relay activates to invoke the lower-gain
mode, and gets its coil operating power from a filtered source.
Reed relays may be an option here but they are pretty expensive
nowadays. IIRC even the regular Coto 9800 series lists 10^12 ohms
insulation.
http://pewa.panasonic.com/pcsd/product/sign/pdf_cat/tn.pdf
Taking one of these NAiS TN2 type relays apart shows they're
a real miracle of miniaturization. I appreciate having their
DPDT functionality in a very small size. For example, I use
the second section to make a T-type switching network, with
nearly-perfect capacitive isolation.
But I sometimes wonder if using a pair of reed relays instead
would have some advantage over the TN2 "conventional" relay.
Yes, glass reed relays have vacuum contacts, but the TN2's
gold-clad silver contacts in air continue to work well, even
though at 10pA it's certainly a classic case of "dry" switching.
in |
http://pewa.panasonic.com/pcsd/product/sign/pdf_cat/tn.pdf
fig14, what is a wire spring relay?
martin |
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