On Sun, 22 Sep 2013 14:37:18 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:
>On Sun, 22 Sep 2013 15:31:57 -0400, Phil Hobbs
><pcdhSpamMeSenseless@electrooptical.net> wrote:
>
>>On 9/21/2013 9:06 PM, Jim Thompson wrote:
>>> On Sat, 21 Sep 2013 10:51:06 -0700, John Larkin
>>> <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
>>>
>>>> On Sat, 21 Sep 2013 10:26:40 -0700, Jim Thompson
>>>> <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:
>>>>
>>>>> Here's a way to do capacitor multiplication...
>>>>>
>>>>>
>>>>> <http://www.analog-innovations.com/SED/CapMultiplier_JT_2013-09-21.pdf>
>>>>>
>>>>> limited only by OpAmp GBW product, and no resistive components until
>>>>> the OpAmps run out of steam.
>>>>>
>>>>> Mathematically, this is the same way I did behavioral models for
>>>>> crummy capacitors such as X7R and Y5U, except I had ideal amplifiers,
>>>>> and equations and/or tables to describe the changes versus voltage and
>>>>> temperature.
>>>>>
>>>>> Larkin's "Maybe I'll do this:"
>>>>>
>>>>>
>>>>> <https://dl.dropboxusercontent.com/u/53724080/Parts/Caps/Trim_Cap.JPG>
>>>>>
>>>>> does not fare so well. Do the math.
>>>>>
>>>>> ...Jim Thompson
>>>>
>>>>
>>>> 2.5x the parts (including a GHz opamp), maybe 50x the noise. It would destroy
>>>> the low-noise transimpedance amp that I'm doing. You have just invented the
>>>> world's noisiest capacitor. Well, you probably "invented" it 40 years ago.
>>>>
>>>> And I need a floating capacitor, not a grounded one. And I need about 0.4 pF,
>>>> which would call for a capacitance divider, not a multiplier.
>>>>
>>>
>>> Larkinus Bloviatus Fartus Maximus:
>>>
>>>> Net idiotic.
>>>
>>> I asked, "Do the math."
>>>
>>> Larkin didn't.
>>>
>>> I did.
>>>
>>> Though any kid fresh out of school would look at this...
>>>
>>> <http://www.analog-innovations.com/SED/Larkin_Trim_Cap_Folly.jpg>
>>>
>>> And note, by simple observation, several things...
>>>
>>> It's not a two terminal network.
>>>
>>> The impedance looking into the node on the left (marked arrow-style by
>>> Larkin) looks like that resistor from the arrow to IN- of the OpAmp
>>> (until the OpAmp runs into the GBW stop).
>>>
>>> The impedance looking into the right arrow is, in essence, a voltage
>>> source, zero AC impedance, again until the OpAmp runs into the GBW
>>> stop.
>>>
>>> If that's a _floating_ capacitor, I'm the King of Siam.
>>>
>>> But Larkin's sickophants should be happy, their low-information
>>> mentality, and need for name-calling, has been satisfied. They will
>>> now face toward San Fransicko and chant... >:-}
>>>
>>> ...Jim Thompson
>>>
>>
>>I thought you were trying not to dish that stuff out?
>>
>>Using a voltage divider on a small compensation cap is a pretty common
>>approach in TIAs, though IME it's usually a capacitive divider rather
>>than a resistive one. It works OK up to the point where the summing
>>junction loading is important. You clearly don't want to try
>>synthesizing 1 pF using a 1000:1 voltage divider and a nanofarad in
>>series.(*)
>>
>>Using a pot, you have to worry about the current noise of the low
>>resistances getting into the summing junction. (I posted a TIA fragment
>>a week or two back where I had to short out a 1G resistor with a relay
>>to avoid its Johnson noise current dominating the circuit performance
>>above a few hundred hertz.)
>>
>>However, given that the input capacitance is probably nearly 2 pF to
>>begin with, something like 0.5 pF and a low-value pot isn't necessarily
>>a silly way of making an adjustable 0.3 pF for that sort of use.
>
>Actually defining the total problem would have been a more useful
>exercise.
>
>>
>>Cheers
>>
>>Phil Hobbs
>>
>>(*) Back in the early part of my career, I actually managed to make an
>>op amp integrator oscillate all by itself. Fast op amp with high Zout
>>and some phase funnies in its compensation, small R_in/large C_F.
>
>Nowhere in Larkin's multiple posts was "capacitor immersed in an
>integrator" mentioned.
>
>When I show a true capacitor multiplier, I get his usual ration of
>shit... and bloviations about "floating".
>
> ...Jim Thompson
Other people understood what I meant; I want a sub-pF variable cap to trim a
circuit, and neither end is grounded. I posted the actual circuit.
If you had posted "your" cap multiplier with some neutral comment, like "take a
look at this cap multiplier", you'd look somewhat less stupid. Or if the context
wasn't clear, you could have asked. But you misunderstood the situation and
posted a challenge. How did you get to be so rash and insecure?
You're sure not aging gracefully.
--
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
Reply by John Larkin●September 22, 20132013-09-22
On Sun, 22 Sep 2013 15:31:57 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
>On 9/21/2013 9:06 PM, Jim Thompson wrote:
>> On Sat, 21 Sep 2013 10:51:06 -0700, John Larkin
>> <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
>>
>>> On Sat, 21 Sep 2013 10:26:40 -0700, Jim Thompson
>>> <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:
>>>
>>>> Here's a way to do capacitor multiplication...
>>>>
>>>>
>>>> <http://www.analog-innovations.com/SED/CapMultiplier_JT_2013-09-21.pdf>
>>>>
>>>> limited only by OpAmp GBW product, and no resistive components until
>>>> the OpAmps run out of steam.
>>>>
>>>> Mathematically, this is the same way I did behavioral models for
>>>> crummy capacitors such as X7R and Y5U, except I had ideal amplifiers,
>>>> and equations and/or tables to describe the changes versus voltage and
>>>> temperature.
>>>>
>>>> Larkin's "Maybe I'll do this:"
>>>>
>>>>
>>>> <https://dl.dropboxusercontent.com/u/53724080/Parts/Caps/Trim_Cap.JPG>
>>>>
>>>> does not fare so well. Do the math.
>>>>
>>>> ...Jim Thompson
>>>
>>>
>>> 2.5x the parts (including a GHz opamp), maybe 50x the noise. It would destroy
>>> the low-noise transimpedance amp that I'm doing. You have just invented the
>>> world's noisiest capacitor. Well, you probably "invented" it 40 years ago.
>>>
>>> And I need a floating capacitor, not a grounded one. And I need about 0.4 pF,
>>> which would call for a capacitance divider, not a multiplier.
>>>
>>
>> Larkinus Bloviatus Fartus Maximus:
>>
>>> Net idiotic.
>>
>> I asked, "Do the math."
>>
>> Larkin didn't.
>>
>> I did.
>>
>> Though any kid fresh out of school would look at this...
>>
>> <http://www.analog-innovations.com/SED/Larkin_Trim_Cap_Folly.jpg>
>>
>> And note, by simple observation, several things...
>>
>> It's not a two terminal network.
>>
>> The impedance looking into the node on the left (marked arrow-style by
>> Larkin) looks like that resistor from the arrow to IN- of the OpAmp
>> (until the OpAmp runs into the GBW stop).
>>
>> The impedance looking into the right arrow is, in essence, a voltage
>> source, zero AC impedance, again until the OpAmp runs into the GBW
>> stop.
>>
>> If that's a _floating_ capacitor, I'm the King of Siam.
>>
>> But Larkin's sickophants should be happy, their low-information
>> mentality, and need for name-calling, has been satisfied. They will
>> now face toward San Fransicko and chant... >:-}
>>
>> ...Jim Thompson
>>
>
>I thought you were trying not to dish that stuff out?
>
>Using a voltage divider on a small compensation cap is a pretty common
>approach in TIAs, though IME it's usually a capacitive divider rather
>than a resistive one. It works OK up to the point where the summing
>junction loading is important. You clearly don't want to try
>synthesizing 1 pF using a 1000:1 voltage divider and a nanofarad in
>series.(*)
>
>Using a pot, you have to worry about the current noise of the low
>resistances getting into the summing junction. (I posted a TIA fragment
>a week or two back where I had to short out a 1G resistor with a relay
>to avoid its Johnson noise current dominating the circuit performance
>above a few hundred hertz.)
>
>However, given that the input capacitance is probably nearly 2 pF to
>begin with, something like 0.5 pF and a low-value pot isn't necessarily
>a silly way of making an adjustable 0.3 pF for that sort of use.
>
>Cheers
>
>Phil Hobbs
>
>(*) Back in the early part of my career, I actually managed to make an
>op amp integrator oscillate all by itself. Fast op amp with high Zout
>and some phase funnies in its compensation, small R_in/large C_F.
Oscillation isn't an unusual event; stability is!
I sim'd the pot thing (yes, you prefer algebra) and it had an inconsequential
effect on noise. I'd only do this on the breadboard. I like being able to
calculate the effective capacitance after I twiddle the pot; I can't think of
any other trimmer that easily allows that.
--
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
Reply by Jim Thompson●September 22, 20132013-09-22
On Sun, 22 Sep 2013 15:31:57 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
>On 9/21/2013 9:06 PM, Jim Thompson wrote:
>> On Sat, 21 Sep 2013 10:51:06 -0700, John Larkin
>> <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
>>
>>> On Sat, 21 Sep 2013 10:26:40 -0700, Jim Thompson
>>> <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:
>>>
>>>> Here's a way to do capacitor multiplication...
>>>>
>>>>
>>>> <http://www.analog-innovations.com/SED/CapMultiplier_JT_2013-09-21.pdf>
>>>>
>>>> limited only by OpAmp GBW product, and no resistive components until
>>>> the OpAmps run out of steam.
>>>>
>>>> Mathematically, this is the same way I did behavioral models for
>>>> crummy capacitors such as X7R and Y5U, except I had ideal amplifiers,
>>>> and equations and/or tables to describe the changes versus voltage and
>>>> temperature.
>>>>
>>>> Larkin's "Maybe I'll do this:"
>>>>
>>>>
>>>> <https://dl.dropboxusercontent.com/u/53724080/Parts/Caps/Trim_Cap.JPG>
>>>>
>>>> does not fare so well. Do the math.
>>>>
>>>> ...Jim Thompson
>>>
>>>
>>> 2.5x the parts (including a GHz opamp), maybe 50x the noise. It would destroy
>>> the low-noise transimpedance amp that I'm doing. You have just invented the
>>> world's noisiest capacitor. Well, you probably "invented" it 40 years ago.
>>>
>>> And I need a floating capacitor, not a grounded one. And I need about 0.4 pF,
>>> which would call for a capacitance divider, not a multiplier.
>>>
>>
>> Larkinus Bloviatus Fartus Maximus:
>>
>>> Net idiotic.
>>
>> I asked, "Do the math."
>>
>> Larkin didn't.
>>
>> I did.
>>
>> Though any kid fresh out of school would look at this...
>>
>> <http://www.analog-innovations.com/SED/Larkin_Trim_Cap_Folly.jpg>
>>
>> And note, by simple observation, several things...
>>
>> It's not a two terminal network.
>>
>> The impedance looking into the node on the left (marked arrow-style by
>> Larkin) looks like that resistor from the arrow to IN- of the OpAmp
>> (until the OpAmp runs into the GBW stop).
>>
>> The impedance looking into the right arrow is, in essence, a voltage
>> source, zero AC impedance, again until the OpAmp runs into the GBW
>> stop.
>>
>> If that's a _floating_ capacitor, I'm the King of Siam.
>>
>> But Larkin's sickophants should be happy, their low-information
>> mentality, and need for name-calling, has been satisfied. They will
>> now face toward San Fransicko and chant... >:-}
>>
>> ...Jim Thompson
>>
>
>I thought you were trying not to dish that stuff out?
>
>Using a voltage divider on a small compensation cap is a pretty common
>approach in TIAs, though IME it's usually a capacitive divider rather
>than a resistive one. It works OK up to the point where the summing
>junction loading is important. You clearly don't want to try
>synthesizing 1 pF using a 1000:1 voltage divider and a nanofarad in
>series.(*)
>
>Using a pot, you have to worry about the current noise of the low
>resistances getting into the summing junction. (I posted a TIA fragment
>a week or two back where I had to short out a 1G resistor with a relay
>to avoid its Johnson noise current dominating the circuit performance
>above a few hundred hertz.)
>
>However, given that the input capacitance is probably nearly 2 pF to
>begin with, something like 0.5 pF and a low-value pot isn't necessarily
>a silly way of making an adjustable 0.3 pF for that sort of use.
Actually defining the total problem would have been a more useful
exercise.
>
>Cheers
>
>Phil Hobbs
>
>(*) Back in the early part of my career, I actually managed to make an
>op amp integrator oscillate all by itself. Fast op amp with high Zout
>and some phase funnies in its compensation, small R_in/large C_F.
Nowhere in Larkin's multiple posts was "capacitor immersed in an
integrator" mentioned.
When I show a true capacitor multiplier, I get his usual ration of
shit... and bloviations about "floating".
...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Reply by Phil Hobbs●September 22, 20132013-09-22
On 9/21/2013 9:06 PM, Jim Thompson wrote:
> On Sat, 21 Sep 2013 10:51:06 -0700, John Larkin
> <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
>
>> On Sat, 21 Sep 2013 10:26:40 -0700, Jim Thompson
>> <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:
>>
>>> Here's a way to do capacitor multiplication...
>>>
>>>
>>> <http://www.analog-innovations.com/SED/CapMultiplier_JT_2013-09-21.pdf>
>>>
>>> limited only by OpAmp GBW product, and no resistive components until
>>> the OpAmps run out of steam.
>>>
>>> Mathematically, this is the same way I did behavioral models for
>>> crummy capacitors such as X7R and Y5U, except I had ideal amplifiers,
>>> and equations and/or tables to describe the changes versus voltage and
>>> temperature.
>>>
>>> Larkin's "Maybe I'll do this:"
>>>
>>>
>>> <https://dl.dropboxusercontent.com/u/53724080/Parts/Caps/Trim_Cap.JPG>
>>>
>>> does not fare so well. Do the math.
>>>
>>> ...Jim Thompson
>>
>>
>> 2.5x the parts (including a GHz opamp), maybe 50x the noise. It would destroy
>> the low-noise transimpedance amp that I'm doing. You have just invented the
>> world's noisiest capacitor. Well, you probably "invented" it 40 years ago.
>>
>> And I need a floating capacitor, not a grounded one. And I need about 0.4 pF,
>> which would call for a capacitance divider, not a multiplier.
>>
>
> Larkinus Bloviatus Fartus Maximus:
>
>> Net idiotic.
>
> I asked, "Do the math."
>
> Larkin didn't.
>
> I did.
>
> Though any kid fresh out of school would look at this...
>
> <http://www.analog-innovations.com/SED/Larkin_Trim_Cap_Folly.jpg>
>
> And note, by simple observation, several things...
>
> It's not a two terminal network.
>
> The impedance looking into the node on the left (marked arrow-style by
> Larkin) looks like that resistor from the arrow to IN- of the OpAmp
> (until the OpAmp runs into the GBW stop).
>
> The impedance looking into the right arrow is, in essence, a voltage
> source, zero AC impedance, again until the OpAmp runs into the GBW
> stop.
>
> If that's a _floating_ capacitor, I'm the King of Siam.
>
> But Larkin's sickophants should be happy, their low-information
> mentality, and need for name-calling, has been satisfied. They will
> now face toward San Fransicko and chant... >:-}
>
> ...Jim Thompson
>
I thought you were trying not to dish that stuff out?
Using a voltage divider on a small compensation cap is a pretty common
approach in TIAs, though IME it's usually a capacitive divider rather
than a resistive one. It works OK up to the point where the summing
junction loading is important. You clearly don't want to try
synthesizing 1 pF using a 1000:1 voltage divider and a nanofarad in
series.(*)
Using a pot, you have to worry about the current noise of the low
resistances getting into the summing junction. (I posted a TIA fragment
a week or two back where I had to short out a 1G resistor with a relay
to avoid its Johnson noise current dominating the circuit performance
above a few hundred hertz.)
However, given that the input capacitance is probably nearly 2 pF to
begin with, something like 0.5 pF and a low-value pot isn't necessarily
a silly way of making an adjustable 0.3 pF for that sort of use.
Cheers
Phil Hobbs
(*) Back in the early part of my career, I actually managed to make an
op amp integrator oscillate all by itself. Fast op amp with high Zout
and some phase funnies in its compensation, small R_in/large C_F.
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510 USA
+1 845 480 2058
hobbs at electrooptical dot net
http://electrooptical.net
>On Sat, 21 Sep 2013 18:06:47 -0700, the renowned Jim Thompson
><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:
>
>>On Sat, 21 Sep 2013 10:51:06 -0700, John Larkin
>><jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
>>
>>>On Sat, 21 Sep 2013 10:26:40 -0700, Jim Thompson
>>><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:
>>>
>>>>Here's a way to do capacitor multiplication...
>>>>
>>>>
>>>><http://www.analog-innovations.com/SED/CapMultiplier_JT_2013-09-21.pdf>
>>>>
>>>>limited only by OpAmp GBW product, and no resistive components until
>>>>the OpAmps run out of steam.
>>>>
>>>>Mathematically, this is the same way I did behavioral models for
>>>>crummy capacitors such as X7R and Y5U, except I had ideal amplifiers,
>>>>and equations and/or tables to describe the changes versus voltage and
>>>>temperature.
>>>>
>>>>Larkin's "Maybe I'll do this:"
>>>>
>>>>
>>>><https://dl.dropboxusercontent.com/u/53724080/Parts/Caps/Trim_Cap.JPG>
>>>>
>>>>does not fare so well. Do the math.
>>>>
>>>> ...Jim Thompson
>>>
>>>
>>>2.5x the parts (including a GHz opamp), maybe 50x the noise. It would destroy
>>>the low-noise transimpedance amp that I'm doing. You have just invented the
>>>world's noisiest capacitor. Well, you probably "invented" it 40 years ago.
>>>
>>>And I need a floating capacitor, not a grounded one. And I need about 0.4 pF,
>>>which would call for a capacitance divider, not a multiplier.
>>>
>>
>>Larkinus Bloviatus Fartus Maximus:
>>
>>>Net idiotic.
>>
>>I asked, "Do the math."
>>
>>Larkin didn't.
>>
>>I did.
>>
>>Though any kid fresh out of school would look at this...
>>
>><http://www.analog-innovations.com/SED/Larkin_Trim_Cap_Folly.jpg>
>>
>>And note, by simple observation, several things...
>>
>>It's not a two terminal network.
>>
>>The impedance looking into the node on the left (marked arrow-style by
>>Larkin) looks like that resistor from the arrow to IN- of the OpAmp
>>(until the OpAmp runs into the GBW stop).
>>
>>The impedance looking into the right arrow is, in essence, a voltage
>>source, zero AC impedance, again until the OpAmp runs into the GBW
>>stop.
>>
>>If that's a _floating_ capacitor, I'm the King of Siam.
>
>Okay, maybe I'm wrong, but I thought the intent was simply to simulate
>a tiny variable cap across the feedback resistor. If that is the
>presumed intent, and Xc >> Rpot/4 ...
>
>
Right. Maybe a 500 ohm pot. The highest impedance the wiper looks is 125 ohms,
which is a 125 ps time constant, out of my range of interest. That 125 ohms adds
a teeny amount of Johnson noise to my breadboard, not a concern. Once I figure
out the best cap value, I can design that into the PCB, probably two caps in
series to give high tweaking resolution, like if I need 0.35 pF.
Saves a lot of soldering, and I can calculate the equivalent C, which I can't
with a gimmick. I could even use this, 1 pF cap + pot or two resistors, in
production, so I can hit small oddball values.
--
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
Reply by Jim Thompson●September 21, 20132013-09-21
>On Sat, 21 Sep 2013 18:06:47 -0700, the renowned Jim Thompson
><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:
>
>>On Sat, 21 Sep 2013 10:51:06 -0700, John Larkin
>><jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
>>
>>>On Sat, 21 Sep 2013 10:26:40 -0700, Jim Thompson
>>><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:
>>>
>>>>Here's a way to do capacitor multiplication...
>>>>
>>>>
>>>><http://www.analog-innovations.com/SED/CapMultiplier_JT_2013-09-21.pdf>
>>>>
>>>>limited only by OpAmp GBW product, and no resistive components until
>>>>the OpAmps run out of steam.
>>>>
>>>>Mathematically, this is the same way I did behavioral models for
>>>>crummy capacitors such as X7R and Y5U, except I had ideal amplifiers,
>>>>and equations and/or tables to describe the changes versus voltage and
>>>>temperature.
>>>>
>>>>Larkin's "Maybe I'll do this:"
>>>>
>>>>
>>>><https://dl.dropboxusercontent.com/u/53724080/Parts/Caps/Trim_Cap.JPG>
>>>>
>>>>does not fare so well. Do the math.
>>>>
>>>> ...Jim Thompson
>>>
>>>
>>>2.5x the parts (including a GHz opamp), maybe 50x the noise. It would destroy
>>>the low-noise transimpedance amp that I'm doing. You have just invented the
>>>world's noisiest capacitor. Well, you probably "invented" it 40 years ago.
>>>
>>>And I need a floating capacitor, not a grounded one. And I need about 0.4 pF,
>>>which would call for a capacitance divider, not a multiplier.
>>>
>>
>>Larkinus Bloviatus Fartus Maximus:
>>
>>>Net idiotic.
>>
>>I asked, "Do the math."
>>
>>Larkin didn't.
>>
>>I did.
>>
>>Though any kid fresh out of school would look at this...
>>
>><http://www.analog-innovations.com/SED/Larkin_Trim_Cap_Folly.jpg>
>>
>>And note, by simple observation, several things...
>>
>>It's not a two terminal network.
>>
>>The impedance looking into the node on the left (marked arrow-style by
>>Larkin) looks like that resistor from the arrow to IN- of the OpAmp
>>(until the OpAmp runs into the GBW stop).
>>
>>The impedance looking into the right arrow is, in essence, a voltage
>>source, zero AC impedance, again until the OpAmp runs into the GBW
>>stop.
>>
>>If that's a _floating_ capacitor, I'm the King of Siam.
>
>Okay, maybe I'm wrong, but I thought the intent was simply to simulate
>a tiny variable cap across the feedback resistor. If that is the
>presumed intent, and Xc >> Rpot/4 ...
>
>
>Best regards,
>Spehro Pefhany
Depends on your definition of "floating" ;-)
...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Reply by John Larkin●September 21, 20132013-09-21
On Sat, 21 Sep 2013 18:06:47 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:
>On Sat, 21 Sep 2013 10:51:06 -0700, John Larkin
><jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
>
>>On Sat, 21 Sep 2013 10:26:40 -0700, Jim Thompson
>><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:
>>
>>>Here's a way to do capacitor multiplication...
>>>
>>>
>>><http://www.analog-innovations.com/SED/CapMultiplier_JT_2013-09-21.pdf>
>>>
>>>limited only by OpAmp GBW product, and no resistive components until
>>>the OpAmps run out of steam.
>>>
>>>Mathematically, this is the same way I did behavioral models for
>>>crummy capacitors such as X7R and Y5U, except I had ideal amplifiers,
>>>and equations and/or tables to describe the changes versus voltage and
>>>temperature.
>>>
>>>Larkin's "Maybe I'll do this:"
>>>
>>>
>>><https://dl.dropboxusercontent.com/u/53724080/Parts/Caps/Trim_Cap.JPG>
>>>
>>>does not fare so well. Do the math.
>>>
>>> ...Jim Thompson
>>
>>
>>2.5x the parts (including a GHz opamp), maybe 50x the noise. It would destroy
>>the low-noise transimpedance amp that I'm doing. You have just invented the
>>world's noisiest capacitor. Well, you probably "invented" it 40 years ago.
>>
>>And I need a floating capacitor, not a grounded one. And I need about 0.4 pF,
>>which would call for a capacitance divider, not a multiplier.
>>
>
>Larkinus Bloviatus Fartus Maximus:
>
>>Net idiotic.
>
>I asked, "Do the math."
>
>Larkin didn't.
>
>I did.
>
>Though any kid fresh out of school would look at this...
>
><http://www.analog-innovations.com/SED/Larkin_Trim_Cap_Folly.jpg>
>
>And note, by simple observation, several things...
>
>It's not a two terminal network.
>
>The impedance looking into the node on the left (marked arrow-style by
>Larkin) looks like that resistor from the arrow to IN- of the OpAmp
>(until the OpAmp runs into the GBW stop).
>
>The impedance looking into the right arrow is, in essence, a voltage
>source, zero AC impedance, again until the OpAmp runs into the GBW
>stop.
>
>If that's a _floating_ capacitor, I'm the King of Siam.
You somehow missed the point entirely. I have an opamp circuit that includes a
cap, roughly 0.4 pF, but I want to tweak it. I want to trim that cap up/down a
bit until the circuit works the way I want it to, in a breadboard. I could
solder in various caps, which has obvious problems. Or I could use a varicap
diode, a trimmer cap, or a gimmick.
Or I could use this circuit with a 1 pF cap and maybe a 500 ohm pot, replacing
the fixed capacitor. I can turn the pot and vary the opamp response without
bending anything or soldering. Even better, I can measure the resistances of the
turned pot with an ohmmeter and easily calculate the value of the equivalent
single capacitor, which none of the other methods do.
The pot is a "cap divider" that, in my circuit, adds trivial amounts of noise or
phase shift and really lets me simulate a ~~0.4 pF wideband variable capacitor.
Your circuit is cool, except for not being original, and having almost
everything wrong with it.
What is this "fresh kid out of school" obsession that you keep having? Make sure
they're at least 18.
--
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
Reply by Spehro Pefhany●September 21, 20132013-09-21
On Sat, 21 Sep 2013 18:06:47 -0700, the renowned Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:
>On Sat, 21 Sep 2013 10:51:06 -0700, John Larkin
><jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
>
>>On Sat, 21 Sep 2013 10:26:40 -0700, Jim Thompson
>><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:
>>
>>>Here's a way to do capacitor multiplication...
>>>
>>>
>>><http://www.analog-innovations.com/SED/CapMultiplier_JT_2013-09-21.pdf>
>>>
>>>limited only by OpAmp GBW product, and no resistive components until
>>>the OpAmps run out of steam.
>>>
>>>Mathematically, this is the same way I did behavioral models for
>>>crummy capacitors such as X7R and Y5U, except I had ideal amplifiers,
>>>and equations and/or tables to describe the changes versus voltage and
>>>temperature.
>>>
>>>Larkin's "Maybe I'll do this:"
>>>
>>>
>>><https://dl.dropboxusercontent.com/u/53724080/Parts/Caps/Trim_Cap.JPG>
>>>
>>>does not fare so well. Do the math.
>>>
>>> ...Jim Thompson
>>
>>
>>2.5x the parts (including a GHz opamp), maybe 50x the noise. It would destroy
>>the low-noise transimpedance amp that I'm doing. You have just invented the
>>world's noisiest capacitor. Well, you probably "invented" it 40 years ago.
>>
>>And I need a floating capacitor, not a grounded one. And I need about 0.4 pF,
>>which would call for a capacitance divider, not a multiplier.
>>
>
>Larkinus Bloviatus Fartus Maximus:
>
>>Net idiotic.
>
>I asked, "Do the math."
>
>Larkin didn't.
>
>I did.
>
>Though any kid fresh out of school would look at this...
>
><http://www.analog-innovations.com/SED/Larkin_Trim_Cap_Folly.jpg>
>
>And note, by simple observation, several things...
>
>It's not a two terminal network.
>
>The impedance looking into the node on the left (marked arrow-style by
>Larkin) looks like that resistor from the arrow to IN- of the OpAmp
>(until the OpAmp runs into the GBW stop).
>
>The impedance looking into the right arrow is, in essence, a voltage
>source, zero AC impedance, again until the OpAmp runs into the GBW
>stop.
>
>If that's a _floating_ capacitor, I'm the King of Siam.
Okay, maybe I'm wrong, but I thought the intent was simply to simulate
a tiny variable cap across the feedback resistor. If that is the
presumed intent, and Xc >> Rpot/4 ...
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
Reply by Jim Thompson●September 21, 20132013-09-21
On Sat, 21 Sep 2013 10:51:06 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
>On Sat, 21 Sep 2013 10:26:40 -0700, Jim Thompson
><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:
>
>>Here's a way to do capacitor multiplication...
>>
>>
>><http://www.analog-innovations.com/SED/CapMultiplier_JT_2013-09-21.pdf>
>>
>>limited only by OpAmp GBW product, and no resistive components until
>>the OpAmps run out of steam.
>>
>>Mathematically, this is the same way I did behavioral models for
>>crummy capacitors such as X7R and Y5U, except I had ideal amplifiers,
>>and equations and/or tables to describe the changes versus voltage and
>>temperature.
>>
>>Larkin's "Maybe I'll do this:"
>>
>>
>><https://dl.dropboxusercontent.com/u/53724080/Parts/Caps/Trim_Cap.JPG>
>>
>>does not fare so well. Do the math.
>>
>> ...Jim Thompson
>
>
>2.5x the parts (including a GHz opamp), maybe 50x the noise. It would destroy
>the low-noise transimpedance amp that I'm doing. You have just invented the
>world's noisiest capacitor. Well, you probably "invented" it 40 years ago.
>
>And I need a floating capacitor, not a grounded one. And I need about 0.4 pF,
>which would call for a capacitance divider, not a multiplier.
>
Larkinus Bloviatus Fartus Maximus:
>Net idiotic.
I asked, "Do the math."
Larkin didn't.
I did.
Though any kid fresh out of school would look at this...
<http://www.analog-innovations.com/SED/Larkin_Trim_Cap_Folly.jpg>
And note, by simple observation, several things...
It's not a two terminal network.
The impedance looking into the node on the left (marked arrow-style by
Larkin) looks like that resistor from the arrow to IN- of the OpAmp
(until the OpAmp runs into the GBW stop).
The impedance looking into the right arrow is, in essence, a voltage
source, zero AC impedance, again until the OpAmp runs into the GBW
stop.
If that's a _floating_ capacitor, I'm the King of Siam.
But Larkin's sickophants should be happy, their low-information
mentality, and need for name-calling, has been satisfied. They will
now face toward San Fransicko and chant... >:-}
...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Reply by John Larkin●September 21, 20132013-09-21
On Sat, 21 Sep 2013 10:51:06 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
>On Sat, 21 Sep 2013 10:26:40 -0700, Jim Thompson
><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:
>
>>Here's a way to do capacitor multiplication...
>>
>>
>><http://www.analog-innovations.com/SED/CapMultiplier_JT_2013-09-21.pdf>
>>
>>limited only by OpAmp GBW product, and no resistive components until
>>the OpAmps run out of steam.
>>
>>Mathematically, this is the same way I did behavioral models for
>>crummy capacitors such as X7R and Y5U, except I had ideal amplifiers,
>>and equations and/or tables to describe the changes versus voltage and
>>temperature.
>>
>>Larkin's "Maybe I'll do this:"
>>
>>
>><https://dl.dropboxusercontent.com/u/53724080/Parts/Caps/Trim_Cap.JPG>
>>
>>does not fare so well. Do the math.
>>
>> ...Jim Thompson
>
>
>2.5x the parts (including a GHz opamp), maybe 50x the noise. It would destroy
>the low-noise transimpedance amp that I'm doing. You have just invented the
>world's noisiest capacitor. Well, you probably "invented" it 40 years ago.
It's just Miller capacitance, C' = C * (1+G) , so you never invented it.
--
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators