 Analog switch on-resistance

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, $R_{\mathrm{on}}=\Delta v/i$. 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.^[ref]

An original example drives a $1.0\mathrm{k\Omega }$ load from an ideal source through $R_{\mathrm{on}}=30\Omega$. The voltage divider givesIf 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 $0.10\mu \mathrm{s}$ and requires $\tau \log 100\approx 0.461\mu \mathrm{s}$ 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.