[time-nuts] ? phase comparison or other device

[Dr Bruce Griffiths]

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