How opto-couplers operating as negative differential resistance devices can be used to generate stable RF oscillation circuits

The construction process of negative differential resistance (NDR) devices by using analogue opto-couplers is presented with their use to make a highly stable, radio-frequency oscillator. Analogue opto-couplers produce negative differential resistance when connected to a specific circuit design and offers a great benefits such as, differential parameters can be changed and controlled via changes to the optocoupler circuit design. The elements of an NDR circuit consists of an analogue optocoupler using a basic LED to emit light on to a photo-transistor base. The photo-transistor rapidly reaches saturation point due to the regenerative switching action of the optical positive feedback loop from the LED to the photo-transistor. The main benefit of using an opto-coupler as the NDR element is the ability to change NDR characteristics by replacing one opto-coupler with another.