Forums

nice fA opamp

Started by John Larkin May 5, 2016
http://www.analog.com/en/products/amplifiers/operational-amplifiers/ada4530-1.html#product-overview

Input current is typically 0.1 fA at room temp. Noise and offset specs
are impressive for a fA opamp.

0.1 fA is 625 electrons per second.



-- 

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement 

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

Cute part--thanks. 

Cheers

Phil Hobbs
On Thu, 05 May 2016 17:11:36 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

> >http://www.analog.com/en/products/amplifiers/operational-amplifiers/ada4530-1.html#product-overview > >Input current is typically 0.1 fA at room temp. Noise and offset specs >are impressive for a fA opamp. > >0.1 fA is 625 electrons per second.
0.1fA is what the graph shows. Spec is +/- 20Fa. What am I missing? -- Boris --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus
On Fri, 06 May 2016 07:52:43 -0400, Boris Mohar
<borism_void_@sympatico.ca> wrote:

>On Thu, 05 May 2016 17:11:36 -0700, John Larkin ><jjlarkin@highlandtechnology.com> wrote: > >> >>http://www.analog.com/en/products/amplifiers/operational-amplifiers/ada4530-1.html#product-overview >> >>Input current is typically 0.1 fA at room temp. Noise and offset specs >>are impressive for a fA opamp. >> >>0.1 fA is 625 electrons per second. > >0.1fA is what the graph shows. Spec is +/- 20Fa. What am I missing?
Typ vs guaranteed, I guess. -- John Larkin Highland Technology, Inc lunatic fringe electronics
On Thursday, May 5, 2016 at 5:11:43 PM UTC-7, John Larkin wrote:
> http://www.analog.com/en/products/amplifiers/operational-amplifiers/ada4530-1.html#product-overview > > Input current is typically 0.1 fA at room temp. Noise and offset specs > are impressive for a fA opamp. > > 0.1 fA is 625 electrons per second.
Well, that's getting down there. A fifty-year old Cary 31 electrometer has about 1E-18 A input current, so there's only another decade or two before solid state catches up. To vacuum tubes. Gold-plated elecrodes, cast iron case, sapphire insulators... they say a lot of the cost is in the packaging. The chopper for that old amp operated with a 440 Hz (that's A above middle C, to a musician) tuning fork oscillator.
On Thu, 05 May 2016 17:11:36 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

> >http://www.analog.com/en/products/amplifiers/operational-amplifiers/ada4530-1.html#product-overview > >Input current is typically 0.1 fA at room temp. Noise and offset specs >are impressive for a fA opamp. > >0.1 fA is 625 electrons per second.
--- Wowie Zowie... Show your work. John Fields
On Fri, 6 May 2016 10:39:41 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

>On Thursday, May 5, 2016 at 5:11:43 PM UTC-7, John Larkin wrote: >> http://www.analog.com/en/products/amplifiers/operational-amplifiers/ada4530-1.html#product-overview >> >> Input current is typically 0.1 fA at room temp. Noise and offset specs >> are impressive for a fA opamp. >> >> 0.1 fA is 625 electrons per second. > >Well, that's getting down there. A fifty-year old Cary 31 electrometer >has about 1E-18 A input current, so there's only another decade or two >before solid state catches up. To vacuum tubes. > >Gold-plated elecrodes, cast iron case, sapphire insulators... they >say a lot of the cost is in the packaging.
ebay has at least one, but the shipping looks expensive.
> >The chopper for that old amp operated with a 440 Hz (that's A above >middle C, to a musician) tuning fork oscillator.
I looked for a manual for the Cary but didn't find one. I think maybe a vibrating reed acted like a variable capacitor and modulated the input voltage into an AC amplifier. Is that how it worked? If so, a vibrating reed with a solid-state amplifier would be at least as good as the tube version. -- John Larkin Highland Technology, Inc lunatic fringe electronics
On Saturday, May 7, 2016 at 1:07:31 PM UTC+10, John Larkin wrote:
> On Fri, 6 May 2016 10:39:41 -0700 (PDT), whit3rd <whit3rd@gmail.com> > wrote: > > >On Thursday, May 5, 2016 at 5:11:43 PM UTC-7, John Larkin wrote: > >> http://www.analog.com/en/products/amplifiers/operational-amplifiers/ada4530-1.html#product-overview > >> > >> Input current is typically 0.1 fA at room temp. Noise and offset specs > >> are impressive for a fA opamp. > >> > >> 0.1 fA is 625 electrons per second. > > > >Well, that's getting down there. A fifty-year old Cary 31 electrometer > >has about 1E-18 A input current, so there's only another decade or two > >before solid state catches up. To vacuum tubes. > > > >Gold-plated elecrodes, cast iron case, sapphire insulators... they > >say a lot of the cost is in the packaging. > > ebay has at least one, but the shipping looks expensive. > > >The chopper for that old amp operated with a 440 Hz (that's A above > >middle C, to a musician) tuning fork oscillator. > > I looked for a manual for the Cary but didn't find one. I think maybe > a vibrating reed acted like a variable capacitor and modulated the > input voltage into an AC amplifier. Is that how it worked? If so, a > vibrating reed with a solid-state amplifier would be at least as good > as the tube version.
A changing capacitance in an electric field generates an AC current. Analog Devices had a solid state competitor to the vibrating reed with a back-biased varactor bridge which worked much the same way. I once thought about building one of my own, but figured that I'd have needed very well matched diodes in the bridge and gave up at that point. The Cary would have needed a very low input capacitance amplifier, which would have been easier to realise with a valve/tube back then. -- Bill Sloman, Sydney
<bill.sloman@ieee.org> wrote in message 
news:06598350-1435-4e07-8082-b4bb61041265@googlegroups.com...
> The Cary would have needed a very low input capacitance amplifier, which > would have been easier to realise with a valve/tube back then. >
Not as much as you might think: the smallest triodes (like the "acorn" style 57, 0.3pF G-H, 1.2pF G-P) and "electrometer" types are comparable to what you'll get from smaller semiconductors, especially with bootstraps. Likewise the follower performance of a triode or pentode isn't very good, due to the lower gain. Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
On Sat, 7 May 2016 13:43:22 -0500, "Tim Williams"
<tiwill@seventransistorlabs.com> wrote:

><bill.sloman@ieee.org> wrote in message >news:06598350-1435-4e07-8082-b4bb61041265@googlegroups.com... >> The Cary would have needed a very low input capacitance amplifier, which >> would have been easier to realise with a valve/tube back then. >> > >Not as much as you might think: the smallest triodes (like the "acorn" style >57, 0.3pF G-H, 1.2pF G-P) and "electrometer" types are comparable to what >you'll get from smaller semiconductors, especially with bootstraps. > >Likewise the follower performance of a triode or pentode isn't very good, >due to the lower gain. > >Tim
I think there were tubes, used for tape head and mic inputs, that got close to 1 nV/rtHz noise levels. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com