Develop two rules of thumb as to when oscilloscope input resistance and function
ID: 1412986 • Letter: D
Question
Develop two rules of thumb as to when oscilloscope input resistance and function generator output resistance can be essentially ignored: (a) The oscilloscope’s input resistance may be ignored when: (b) The function generator’s output resistance may be ignored when: Develop two rules of thumb as to when oscilloscope input resistance and function generator output resistance can be essentially ignored: (a) The oscilloscope’s input resistance may be ignored when: (b) The function generator’s output resistance may be ignored when: Develop two rules of thumb as to when oscilloscope input resistance and function generator output resistance can be essentially ignored: (a) The oscilloscope’s input resistance may be ignored when: (b) The function generator’s output resistance may be ignored when:Explanation / Answer
a) The input resistance of the probe combined with the scope’s input resistance causes the measurement system
to act like a voltage divider. Ideally, Vmeas would equal Vsource because the signal at the test point would be
unchanged. In reality, the input resistance of the probe and scope will have some impact on the measured
amplitude. To minimize resistive loading, probes typically have a large input resistance, and for most applications,
the input
b) It depends. If you want to consider your function generator purely as a voltage source, then yes, the output
impedance should be as low as possible. It might be helpful to use a separate buffer amplifier for such
applications.
On the other hand, it is often useful to connect a function generator (especially an RF generator) to a transmission
line, in which case, you want the output impedance of the generator to match that of the line.
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