In the process of building various electronic circuits, it is often necessary to generate oscillations of various shapes. This task can be solved in different ways. Most often, various generators are used for this, which is a positive feedback amplifier. You can also use an element with negative resistance.
One of these elements is a tunnel diode, the current-voltage characteristic (VAC) of which is schematically shown in Figure 1. In the same place, dotted lines mark the area with negative AC resistance, i.e. the falling part of the I - V characteristic for which dI / dU <0.
Basic properties of a tunnel diode
The tunnel diode, the schematic of which is shown in Figure 2, was developed in 1957 by the Japanese physicist Leo Esaki, who became a Nobel laureate 15 years later.
It differs from other solid-state electronic devices in a very high concentration of dopants, as a result of which they begin to have a decisive influence on its parameters in terms of conductivity, i.e. the original semiconductor (most often Ge or GsAs) becomes degenerate. For this reason, some researchers even single out such materials in a special group of semimetals.
Additionally, in comparison with classical semiconductor diodes, it has several times smaller thickness of the pn junction region and increased by about two times the so-called. potential barrier, which allows quantum mechanical tunneling effect.
The strengths of the component are mainly determined by the extremely simple structure and small width its working area, which makes it possible to reduce the potential of the control action to a few millivolts. These features provide noticeably less inertia compared to transistors and the ability to function normally at frequencies of tens of GHz.
Along with this, the element is characterized by low power consumption and is capable of fully functioning at the minimum voltage of the power supply.
The tunnel diode is highly resistant to ionizing radiation.
The main disadvantages are considered to be the rapid degradation of parameters during operation and low resistance to overheating. In addition, the diode requires very careful handling during circuit setup and troubleshooting. may fail even with a normal continuity with a multimeter.
Main parameters and fields of application
The list of passport characteristics of an element usually includes:
- maximum permissible current, peak current and trough current of the I – V characteristic;
- bias voltage;
- own capacity;
- direct active resistance.
In semiconductor microwave circuitry, a tunnel diode is used in:
- high-speed switches;
- circuits for generating and amplifying oscillations in the millimeter wavelength range.
As an example, Figure 3 shows a diagram of the simplest generator based on this element.
The operating frequency of the circuit is set by the LC circuit, and the VD tunnel diode acts as a key element that compensates for energy losses in the circuit during the generation process. The output signal is taken from the resistor Rн.