Frequency response of an amplifier
1) How does the test equipment influence the frequency response of the amplifier ?


Ideally, not at all. After all, that's the point, isn't it?

But you need to understand the input and output characteristics of the test equipment and how it will interact with the corresponding characteristics of the equipment being tested.

For example, your 100:1 voltage divider is a 40-dB attenuator only if you assume that it is driven with zero impedance and loaded with infinite impedance. A 40-dB attenuator designed for 50-&Omega; input and output impedances would use very different resistor values.

For example:







simulate this circuit &ndash; Schematic created using CircuitLab

In general, when you're interested in voltage measurements, the source impedance of any generator should be less than 1/10 the impedance of the circuit node you're connecting it to (less is better), and any measuring device should have at least 10&times; the impedance of the node that's driving it (more is better).


  2) Why is the output voltage measured using a 10:1 probe ?


Because the 10:1 probe has 10&times; the input impedance, which loads the device being tested 1/10 as much.