packages of two WWVB watches: $20 at www.woot.com while they last <EOM>
John Miles wrote:
The output of an opamp is always referenced to its power supply,
regardless of the configuration. If the power supply is noisy,
the output is noisy.
Beyond a few kHz this may be true, but at lower frequencies
even a low-grade
opamp has excellent rejection of power supply noise. A good opamp data
sheet will characterize the PSRR versus frequency.
-- john, KE5FX
John
Only when the opamp is operating within its linear region, not when the
output is saturated.
Opamp saturation has been proposed as a good method of reducing the
output noise of an opamp when an amplifier is overdriven.
This is clearly not true when power supply noise is significant, as is
almost always the case.
Sure; I was mainly objecting to use of the term "always." The statement
that "the output of an opamp is always referenced to its power supply" is
simply not a good model of the situation near DC, unless (as you note) the
output is saturated.
-- john, KE5FX
On Saturday 30 June 2007 10:15, Dr Bruce Griffiths wrote:
Not true, there's nothing magic about amplifier saturation, any means
that limits the amplifier output whilst dropping the small signal gain
to a low value will have exactly the same effect.
"The AD8036 and AD8037, from Analog Devices, are wide bandwidth, low distortion clamping amplifiers.
The AD8036 is unity gain stable. The AD8037 is stable at a gain of two or greater.
These devices allow the designer to specify a high (VCH) and low (VCL) output clamp voltage.
The output signal will clamp at these specified levels."
http://www.analog.com/en/prodDesc/0,2895,AD8036%255F0,00.html
AN-402: Replacing Output Clamping Op Amps with Input Clamping Amps (pdf, 57,313 bytes)
http://www.analog.com/UploadedFiles/Application_Notes/374941256AN-402.pdf
"So far most clamping amplifiers have relied upon an output clamping architecture and are called output clamp amps (OCAs).
A new architecture called an input clamp amp (ICA) offers superior clamping accuracy and lower distortion."
A diode clamp in the feedback path will cut the noise gain to 1 when
either diode turns on. The following diode clamp across the filter
capacitor will reduce the noise gain to a very small value when it turns on.
Both diode clamps and internal saturation will still produce some output
noise although not from the amplifier input stages.
Improperly done diode clamps can significantly increase harmonics.
--
http://www.wearablesmartsensors.com/
http://www.softwaresafety.net/ http://www.designer-iii.com/
http://www.unusualresearch.com/
Bob Paddock wrote:
On Saturday 30 June 2007 10:15, Dr Bruce Griffiths wrote:
Not true, there's nothing magic about amplifier saturation, any means
that limits the amplifier output whilst dropping the small signal gain
to a low value will have exactly the same effect.
"The AD8036 and AD8037, from Analog Devices, are wide bandwidth, low distortion clamping amplifiers.
The AD8036 is unity gain stable. The AD8037 is stable at a gain of two or greater.
These devices allow the designer to specify a high (VCH) and low (VCL) output clamp voltage.
The output signal will clamp at these specified levels."
http://www.analog.com/en/prodDesc/0,2895,AD8036%255F0,00.html
AN-402: Replacing Output Clamping Op Amps with Input Clamping Amps (pdf, 57,313 bytes)
http://www.analog.com/UploadedFiles/Application_Notes/374941256AN-402.pdf
"So far most clamping amplifiers have relied upon an output clamping architecture and are called output clamp amps (OCAs).
A new architecture called an input clamp amp (ICA) offers superior clamping accuracy and lower distortion."
A diode clamp in the feedback path will cut the noise gain to 1 when
either diode turns on. The following diode clamp across the filter
capacitor will reduce the noise gain to a very small value when it turns on.
Both diode clamps and internal saturation will still produce some output
noise although not from the amplifier input stages.
Improperly done diode clamps can significantly increase harmonics.
Bob
These devices are a little noisy below 100Hz.
Also any noise at the input clamp level inputs appears at the output.
Since these devices actually set the maximum input voltage before
clamping occurs they are unsuitable when the gain is high.
The distortion produced by a diode clamp is immaterial when one is only
interested in the zero crossing time.
Bruce
These devices are a little noisy below 100Hz.
Rather than constantly battle the "there is to much noise", what are
your thoughts on deliberately injecting out-of-band noise?
As an example:
http://www.analog.com/UploadedFiles/Application_Notes/319765654AN-410.pdf
"Overcoming Converter Nonlinearities with Dither"
The distortion produced by a diode clamp is immaterial when one is only
interested in the zero crossing time.
It depends on where the harmonics fall.
--
http://www.wearablesmartsensors.com/
http://www.softwaresafety.net/ http://www.designer-iii.com/
http://www.unusualresearch.com/
Bob Paddock wrote:
These devices are a little noisy below 100Hz.
Rather than constantly battle the "there is to much noise", what are
your thoughts on deliberately injecting out-of-band noise?
As an example:
http://www.analog.com/UploadedFiles/Application_Notes/319765654AN-410.pdf
"Overcoming Converter Nonlinearities with Dither"
The distortion produced by a diode clamp is immaterial when one is only
interested in the zero crossing time.
It depends on where the harmonics fall.
Bob
What is the application for which you want to use injected out of band
noise?
Since the performance of a well designed zero-crossing detector is
equivalent to a 25 bit ADC when locating the zero-crossing, it will be
difficult to replicate this performance using a lower resolution ADC
even combined with out of band dithering.
In practice, diode clamp circuit distortion in a zero-crossing detector
isn't an issue.
Bruce
From: Dr Bruce Griffiths bruce.griffiths@xtra.co.nz
Subject: Re: [time-nuts] ? phase comparison or other device
Date: Mon, 02 Jul 2007 10:02:44 +1200
Message-ID: 46882484.4030002@xtra.co.nz
Bob
What is the application for which you want to use injected out of band
noise?
Since the performance of a well designed zero-crossing detector is
equivalent to a 25 bit ADC when locating the zero-crossing, it will be
difficult to replicate this performance using a lower resolution ADC
even combined with out of band dithering.
In practice, diode clamp circuit distortion in a zero-crossing detector
isn't an issue.
We soon will have well-tested ZCDs of "sufficient" resolution at our hands
here on the list. They will be fairly easy to duplicate. As we combine findings
of different origins I think alot will be gained.
Now, would interferometric approaches lower our 1/f noise floor in the mixers?
I have been considering multiple insertion polyphase filters in order to
acheive the equalent of a 0/180 degree combiner network but for 10 MHz where
such approaches would be bulky unless built by coaxes, which certainly would be
possible to acheive. Any opinions?
Cheers,
Magnus
Bob Paddock wrote:
"The AD8036 and AD8037, from Analog Devices, are wide bandwidth, low distortion clamping amplifiers.
The AD8036 is unity gain stable. The AD8037 is stable at a gain of two or greater.
These devices allow the designer to specify a high (VCH) and low (VCL) output clamp voltage.
The output signal will clamp at these specified levels."
http://www.analog.com/en/prodDesc/0,2895,AD8036%255F0,00.html
AN-402: Replacing Output Clamping Op Amps with Input Clamping Amps (pdf, 57,313 bytes)
http://www.analog.com/UploadedFiles/Application_Notes/374941256AN-402.pdf
"So far most clamping amplifiers have relied upon an output clamping architecture and are called output clamp amps (OCAs).
A new architecture called an input clamp amp (ICA) offers superior clamping accuracy and lower distortion."
Bob
A significant issue with these clamping amplifiers is that although when
the clamp is active the signal gain is near very low, the amplifier
noise gain is the same as when the clamp isn't active.
In contrast with a simple diode clamp, the signal gain is low when the
clamp is conducting and the amplifier noise gain is at worst unity.
Surely this characteristic of a simple diode clamp reduces the noise
associated with the amplifier accumulated on the low pass filter
capacitor in a zero-crossing detector over the amplifier noise
contribution from an equivalent zero-crossing detector using such input
clamping amplifiers?
Bruce