[SI-LIST] : Heisenberg's uncertainty principle and circuits

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From: Douglas C. Smith (doug@emcesd.com)
Date: Mon Apr 02 2001 - 19:43:17 PDT


Hi All,

Often, when making measurements, the loading on the signal by the
measurement is not taken into account. In addition to probe bandwidth,
its input impedance is just as important. Many high performance probes
on the market are useable to only a fraction of their stated bandwidth
because of very low input impedances, and this includes many FET probes.
That spec of less than a picofarad of input capacitance seems to imply
low circuit loading, but this is not always the case.

This month at http://www.dsmith.org the Technical Tidbit is on error
caused by probe loading. It is a real eye opener. But this is just the
"tip of the iceberg" on measurement limitations.

Doug

-- 
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