[time-nuts] ? phase comparison or other device

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Sun Jul 1 10:10:35 EDT 2007


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




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