= Analog switch on-resistance
{title2=$R_{\rm on}$}
\b[Analog switch on-resistance] is the conducting path's effective <electrical resistance> at a specified signal level, supply and <temperature>. In a locally resistive model, $R_{\rm on}=\Delta v/i$. It is neither an ideal short circuit nor necessarily constant as the signal moves. Complementary switch devices reduce signal-dependent resistance variation, as the manufacturer's circuit and curves illustrate.<MT-088: Analog Switches and Multiplexers Basics>[pp2–3, Figures1–3; p5, Figure6]{ref}
An original example drives a $1.0\,\mathrm{k\Omega}$ load from an ideal source through $R_{\rm on}=30\,\Omega$. The <voltage divider> gives
$$
\frac{v_o}{v_i}=\frac{1000}{1000+30}=0.97087.
$$
If the <analog switch on-resistance> rises to $50\,\Omega$ elsewhere in the signal range, the ratio becomes $0.95238$, about $1.90\%$ below its first value. One gain correction cannot make both ratios exact. <Switch on-resistance flatness> therefore matters separately from the minimum resistance; variation with the signal can create <nonlinearity>.
The same resistance affects dynamics. A stipulated constant $50\,\Omega$ discharging $2.0\,\mathrm{nF}$ has <RC circuit> <time constant> $0.10\,\mathrm{\mu s}$ and requires $\tau\log100\approx0.461\,\mathrm{\mu s}$ to reduce an initial residual to one percent. This is a chosen single-pole model; amplifier dynamics can extend the actual <integrator reset settling time>.
On a bench, measure the terminal drop at known <electric current> while sweeping the signal level within the permitted range. Separate a nearly constant series loss from its signal-dependent variation. The source resistance and load belong in that measurement; the switch's control propagation delay is not its conducting-path resistance.
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