= Amplifier output headroom
\b[Amplifier output headroom] is the <electric potential difference> reserved between a usable output limit and its corresponding supply rail. If the supply potentials are $V_-,V_+$ and the specified <amplifier output range> is $[V_{\rm lo},V_{\rm hi}]$, define
$$
h_-=V_{\rm lo}-V_-,\qquad h_+=V_+-V_{\rm hi}.
$$
These two margins can differ and depend on load and operating conditions. The switched-integrator datasheet lists supply conditions, output range and output-current limits separately.<ACF2101 Low Noise, Dual Switched Integrator datasheet>[Electrical Specifications, pp2–3, Output and Power Supply]{ref}
For an original chosen $0$–$5\,\mathrm V$ circuit with usable limits $0.25$ and $4.55\,\mathrm V$, the lower and upper margins are $0.25$ and $0.45\,\mathrm V$. A signal centered at $V_0$ has maximum symmetric peak excursion
$$
A_{\max}=\min(V_0-V_{\rm lo},V_{\rm hi}-V_0).
$$
At $V_0=2.50\,\mathrm V$ this is $2.05\,\mathrm V$. Centering instead at $(V_{\rm lo}+V_{\rm hi})/2=2.40\,\mathrm V$ permits $2.15\,\mathrm V$. Thus centering on the supply midpoint need not maximize the usable symmetric swing.
An output sweep into the actual load identifies where the specified gain or distortion tolerance fails. Changing the load tests whether the limit comes from output-current demand. These measurements concern static headroom; a fast pulse also tests <frequency response> and overload recovery. More final-stage headroom does not cure an internal violation of the <amplifier input common-mode range>.
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