[sdiy] I don't get this documentation....

[Dave Manley]

mark verbos wrote:
> I'm looking at this page comparing Analog Devices' Sample & Hold chips 
> and the droop rate measurements don't seem to be rational to me. If the 
> AD781 has a droop rate of 0.1µV/µs and the PKD01 has a droop rate of 
> 0.07mV/ms, isn't the PKD01 better? Why are the changing the seconds 
> portion of this ratio? If the milli turns to micro on both sides of the 
> slash, isn't that cancelled out? wtf? Why don't they just put this in 
> V/S, since that would then be the same? This addition of the prefix 
> after the slash has to be a typo right? The SMP04 droops 2 volts/ 
> second, no way...
> 
> 
> http://www.analog.com/en/other/sampletrack-and-hold-amplifiers/AD781/products/product.html 

I'd guess the specs match the intended application (and maybe the actual 
performance tests done on the part).  The AD781 is intended to run at a 
higher sample rate than the PKD01, so the droop rates are scaled to 
match the intended sample rate.  The parts that have similar acquisition 
times have similar droop rate units.  (Although the values in the table 
for the SMP04 spec mv/ms while the datasheet for the SMP04 specs mv/S!)

The thing that is missing from these specs is for how long the droop 
rate is guaranteed after the sample is taken.

Regards "better".  What is better?  It depends on the application.

-Dave