Experiments with an analog tunnel diode

Original author: Ted Yapo
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In addition to the tunneling diode , it is interesting to conduct a series of experiments with its functional analogue, known for several decades. It is similar to a slow-iron emulator: there are no real quantum effects, and performance is not that. But the I – V characteristic is similar, as is the behavior of the device in the circuit.

From KDPV we can conclude that the analog is a two-terminal network, inside of which there is a certain simple circuit. Here it is:

The author tried to use transistors 2N3904 and 2N2222, but it turned out that 2N4401 work better. The properties of the analog can be varied, choosing the resistor R6. The scheme of an impromptu characterographer is the same:

And still, it measures the total voltage on the "diode" and the resistor on one channel, and on the resistor only on the other. The voltage drop only on the "diode" can be determined by subtraction. And knowing the voltage across the resistor, you can calculate the current.

The characterograph works the same regardless of the shape of the oscillations generated by the generator. The author set the frequency to about 100 Hz. The analogue is much "stronger" than a real tunneling diode: you can not be afraid to disable it by static, slightly exceeded voltage from the generator, too long soldering. The characteristic is as follows:

The negative resistance on that almost linear portion of the I – V characteristic where it exists (from 1.55 to 3.0 V) is approximately -64 Ohms. With increasing voltage in this range, the current drops from 27.2 to 4.4 mA. With a further increase in voltage, the current increases slightly.

The generator on the analog of the tunneling diode is obtained if you just turn on the oscillatory circuit in series with it and apply power:

The calculated frequency turned out to be 5.033 kHz, the real - 5.11 kHz. The generator operates in the range of supply voltages from 1.6 to 3.6 V, the best form of oscillation is obtained at 3.6 V. But at a voltage above 2.6 V, the generator does not self-start, that is, you must first start it with a lower voltage, which then gradually increase to optimal. The amplitude of the oscillations exceeds the supply voltage: at 3.5 V it is 4.3 V.

A capacitor in parallel with the power supply at such a low frequency is optional.

The voltage amplifier on the analogue of the tunneling diode is quite unusual: it is powered by an amplified signal, and the amplitude at the output is slightly larger than at the input. To obtain such an amplifier, it is enough to add two resistors to the device: 51-ohm reduces the output resistance of the generator to 25 Ohms, 30-ohm - load:

We feed rectangular pulses, adjust the amplitude, and suddenly we see: The

input amplitude is 1.26 V, at the output is 1.84 V.

Of course, a miracle did not happen, the author added to the input signal and adjusted a certain “offset”. Obviously, the generator he has has a function of shifting the signal up by adding a constant component to it. Due to this, the output amplitude turned out to be larger than the input, although in the circuit there are no capacitances and inductances other than spurious ones. But the gain in the variable component is obvious.

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