Off isolation is defined as the ratio of the signal at the drain pin (Dx) of the device when a signal is applied to the source pin (Sx) of an off-channel. The characteristic impedance, Z₀, for the measurement is 50 Ω. Figure 6-9 shows the setup used to measure off isolation. Use off isolation equation to compute off isolation.

Figure 6-9 Off Isolation Measurement Setup

Equation 1.