English: Block diagram of a negative resistance electronic oscillator, illustrating the "reference plane" analysis method. The circuit consists of a differential negative resistance device such as a Gunn diode or magnetron tube connected to a resonator such as a LC circuit, dielectric resonator, or cavity resonator. To determine the frequency and amplitude of oscillation, the circuit is thought of as divided by a plane (red) into two parts: the negative resistance device, and the resonator and load. The complex impedance "looking into" each part, Z_N(jω) and Z_L(jω), is calculated. The circuit will oscillate at the frequency ω and amplitude at which Z_N = -Z_L. Alternately the reflection coefficient Γ can be used. The circuit will oscillate when Γ_NΓ_L = 1.