[time-nuts] Build my own dist. amp ??

Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed Dec 17 03:58:37 UTC 2008


Brian

What frequency sources other than those in cell phones (for which this
device is intended) have an output signal level of -14dBm?

Very few OCXOs and other frequency standards have outputs lower than +4dBm.
Most have outputs in the +7dBm to +15dBm range.
Thus for frequency distribution systems using such sources the device is
unsuitable for use at least in a well designed system at least.

High reverse isolation and low unit cost are irrelevant if the device
isn't a good fit.
Why compromise the system performance just so one can utilise such a
device??
Its not that much more expensive to do it properly.

Using an unnecessarily  wide band device in a frequency distribution
system isn't usually a particularly good idea.

No one in their right mind would attempt to use an opamp in a frequency
distribution system where the input signal level is around -14dBm unless
the phase noise performance is of little consequence.

The only way to find out what the close in phase noise characteristics
are is to construct an amplifier using such a device and measure it.
Its unlikely to be stellar given the small device geometries and the
likely biasing techniques employed.

At 10MHz the noise figure is likely to be closer to 15dB than 8dB.


Bruce

BriMDavis at aol.com wrote:
> Bruce Griffiths wrote:   
>   
>> Very noisy, too much gain and not enough output for use in a 10MHz
>> distribution amplifier with +7dbM - +15dBm input signal.
>>
>>     
>  Given that I mentioned both Pout and Noise Figure of the MAX2471 in
> my original post, I am obviously aware of those device specifications.
>  
>   I was attempting to ascertain whether anyone on the list had
> direct measurements, or other insight, into the close in residual
> phase noise performance of these parts, as I could not find any
> further specifications or internal circuit info in the associated
> datasheet and application notes.
>  
>   I have absolutely no aspirations of reaching a wideband noise floor
> of -178 dBc/Hz whilst using a device with 0 dBm output power and
> a noise figure of 8 dB.  But I suspect I can do as well as, or better
> than, the op-amp designs, over a wider input bandwidth.
>  
>  Yes, if I need more than 0 dBm of output power, there will need
> to be another output buffer or gain stage in the design, hence the
> phrase  "... as part of a reference distribution design ..."
>  
>   If you know of anything else with comparable reverse isolation, 
> usable from at least 10-200 Mhz, in such a tiny package, that
> costs a buck a channel, please let me know!
>  
> Brian
>  
>  
>  




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