The use of tunnel diodes. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Radio amateur designer
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On fig. 1, 2 and 3 show three different circuit applications of the tunnel diode oscillator. The FM transmitter shown in Fig. 1 is very simple and provides reliable reception within a radius of 10-30 m when using a whip antenna and an FM receiver of medium sensitivity. Due to the fact that the transmitter modulation scheme is the simplest, the output signal is somewhat distorted, and, in addition to frequency modulation, obtained by changing the natural frequency of the generator synchronously with the microphone signal, there is significant amplitude modulation. It is impossible to greatly increase the output power of such a transmitter, since it is a source of interference. Such a transmitter can be used as a portable radio microphone, calling or intercom for short distances.
Rice. 1. The simplest tunnel diode transmitter.
Coil L contains 10 turns of PEL 0,2 wire.
The principle of operation of the local oscillator (Fig. 2) is the same as the previous transmitter. Its distinctive feature is the incomplete inclusion of the circuit. This is done in order to improve the shape and stability of the generated oscillations. An "ideal" sine wave can be obtained when in practice small non-linear distortions are unavoidable.
Rice. 2. Local oscillator on a tunnel diode L = 200 μH.
Shown in fig. 3 tuning fork generator can be used as a standard for tuning musical instruments or a telegraph buzzer. The generator can also operate on diodes with lower maximum currents. In this case, the number of turns in the coils must be increased, and the dynamic loudspeaker is turned on through an amplifier. For normal operation of the generator, the total ohmic resistance (r + r of the coil) must be less than ¦ - Rg ¦, and the position of the tuning fork legs relative to the magnetic core must be carefully adjusted.
Rice. 3. Audio frequency generator based on a tunnel diode
1 - tuning fork at a frequency of 440 Hz, 2 - magnetic core;
TD - gallium arsenide tunnel diode with current Imax=70mA; r = 9 ohm;
L1 \u2d L196 \uXNUMXd XNUMX μH - the inductance of the coil without a core;
K-key; GR-loudspeaker.
In order for the operating point of the diode to fall into the area with negative differential resistance, a voltage source with a very low internal resistance is required.
The value of this resistance in most cases ranges from several tens of ohms to several ohms. If the resistance connected in series with the tunnel diode turns out to be more than 2,5Rd, then the operating point cannot be stably located in the area with negative resistance.
To power devices on tunnel diodes, the circuit shown in Fig. 4 is used. The value of shunt resistance Rsh is selected from the condition Rsh=(0,2-0,3)Rd. Resistance R2 protects the diode and shunt Rsh from damage when the resistance R1 is fully removed.
Rice. 4 Tunnel diode DC bias scheme.
The power source can be accumulators or high capacity batteries. In this case, the selected operating point will be more stable over time.
Literature
- Radio No. 1, 1965
Publication: N. Bolshakov, rf.atnn.ru
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