English: Negative resistance oscillator circuit used with voltage controlled negative differential resistance (VCNR) devices. VCNRs require low impedance DC bias, and are stable for load impedances less than their differential resistance r, so they are called short-circuit stable devices. Therefore they are often used in circuits like this, with a series voltage source V_bias to bias the device, and a parallel resonant circuit LC as a load. The parallel resonant circuit has a high impedance at its resonant frequency but a low impedance at all other frequencies, so the circuit will be unstable and oscillate only at the resonant frequency.