Miller effect oscillator
The Miller effect oscillator uses the Miller effect to create an oscillator . The inductance L2 at the output of the amplifier ensures a negative differential resistance at the input of the amplifier via the gain in the transistor . Quote from
- When the load is inductive the input impedance can .. be represented as a negative resistance.
Energy is supplied to the resonant circuit through this negative resistance. With a suitable design of the components, there is an oscillation at the oscillating circuit frequency. The signal of the oscillator is coupled out at the output of the amplifier via C2.
An oscillation caused by the Miller effect usually occurs unintentionally due to an excessive inductive load on a high-frequency amplifier. Only with certain components such as an avalanche diode or Gunn diode is a negative differential resistance intentionally used to generate signals. For a tuning oscillator in the superhet receiver, better circuits such as Hartley circuit or Clapp circuit are used, which get by with a single resonant circuit.
The data from coil L1 and capacitor C1 of the resonant circuit essentially define the generated frequency via Thomson's oscillation equation . The additional capacities of the remaining components reduce this calculated frequency by a few percent.
Equivalent circuit diagram
The left side shows the external wiring of the triode with cathode F, grid G and anode P. The right side shows the internal capacitances of the triode as well as the amplifier equivalent circuit diagram, consisting of voltage source kE g and internal resistance. The voltage source in the tube supplies k times the voltage of E g . E g is the input voltage. The load resistance Z p consists of an ohmic component and an inductive and capacitive component.
credentials
- ↑ John M. Miller, Dependence of the input impedance of a three-electrode vacuum tube upon the load in the plate circuit (PDF; 3.1 MB), Scientific Papers of the Bureau of Standards , vol. 15, no. 351, pages 367-385 (1920).