Tektronix 2A61 Instruction Manual page 12

Operating Instructions—-Type 2A61
If your application contains DC common-mode voltage
higher than the +5 volt maximum, or DC difference levels
greater than 100 mV, use blocking capacitors in series with
the inputs of the Type 2A61. If the dynamic signal amplitude
is large, a simple resistance divider may be needed to bring
the signal to a suitable level for measurement. However,
when using such dividers, the loading of the source by the
divider(s), the loading of the divider(s) by the Type 2A61
input resistance and capacitance, the amplitude error intro-
duced by inaccuracies in the divider components and the
noise generated by the divider(s) should all be taken into
account. Additionally, when using two such dividers in a
differential application, the resultant Common Mode Rejec-
tion Ratio depends on how accurately the dividers are
matched over the frequency range of interest.