In-amp Diamond Plot — Analog Intuition

Key point: the shape is every internal rail. Inside it, the in-amp is still linear.

Amp type

Scenario

V+ V− Gain G G2 RR/RF VREF

Your signal

Vcm from to Vdiff from to

Vdiff is Vin+ − Vin−. The same number in both boxes is one point.

Headroom

Volts short of that rail. 0 means the node can sit on the rail. Negative lets it go past the rail.

Input, below V+ Input, above V− Link A1 and A2 A1, below V+ A1, above V− A2, below V+ A2, above V− Inner out, below V+ Inner out, above V− Output, below V+ Output, above V− A3 input, below V+ A3 input, above V−

Node voltages

Node	Now	Allowed	Room

\( V_1 = V_{\mathrm{cm}} - \dfrac{V_{\mathrm{out}}-V_{\mathrm{REF}}}{2G_2} \)

\( V_2 = V_{\mathrm{cm}} + \dfrac{V_{\mathrm{out}}-V_{\mathrm{REF}}}{2G_2} \)

\( V_{\mathrm{A3}} = \dfrac{G_2 V_{\mathrm{cm}} + (V_{\mathrm{out}}+V_{\mathrm{REF}})/2}{1+G_2} \)

\( G = 1 + \dfrac{R_R}{R_F} + 2\dfrac{R_R}{R_g} \)

\( V_{\mathrm{int}} = \left(1+\dfrac{R_F}{R_R}\right) V_{\mathrm{cm}} - \dfrac{R_F}{2R_R}(V_{\mathrm{out}}+V_{\mathrm{REF}}) \)

Why the shape

1 of 8

How to read this plot in 20 seconds

The shade is every output and common-mode pair that keeps every internal node off its rail.
Vertical lines are the output swing. Slanted lines are an input pin or an internal amp running out of room.
Horizontal lines are the output swing. Slanted lines are an input pin or an internal amp running out of room.
Your signal is the dot or the box. Green is still linear. Red is the part that clips. The banner names the node.

Hover the plot.