Tunnel diode: detailed in simple language. Generators on diodes Microwave generator design circuit on a tunnel diode

Semiconductor diodes are rarely used as the main elements of generator and amplifier units. Being mostly purely passive components, they simply cannot act as a source of current or voltage needed for any oscillator or amplifier. However, there are a fairly small number of cases when, when using semiconductor diodes of certain types (tunnel diodes, Gunn diodes, avalanche diodes, parametric diodes), it is possible to construct diode amplifier and generator circuits.

Semiconductor devices such as tunnel diodes, Gunn diodes, and avalanche diodes share one property - the presence on the I-V characteristic of the device under certain conditions of a section with a negative differential resistance. In each of the above-mentioned devices, the physical effects that cause the appearance of such a section are different. In a tunnel diode, this is a sharp decline in the tunnel effect with an increase in the electric field strength in the semiconductor above a certain critical value; in a Gunn diode, this is the specificity of the band structure of gallium arsenide; in an avalanche-transit diode, this is the specificity of avalanche breakdown at high frequencies of the applied voltage. It should be noted that these cases are not the only ones. An example is the widely known and popular in the 30s. Kristadin Loseva, which was also a semiconductor diode introduced into a special breakdown mode.

Today, diode self-oscillators in the microwave range are most widespread. They use Gunn diodes and avalanche transit diodes. Under certain conditions, such generators can be converted into amplifiers and used for resonant amplification of microwave signals. However, due to the increased noise level and practical irrationality, amplifiers based on Gunn diodes and avalanche diodes are used extremely rarely.

A special type of microwave amplification devices is the so-called. parametric amplifiers. They are built on the basis of special parametric diodes. The operating principle of such amplifiers is very close to how the diode mixers described above work. The parametric diode, as in mixers, receives two signals. With a certain coordination of these signals and the correct choice of the diode operating mode, it is possible to redistribute the power of the incident signals in favor of one of them (the useful one) on the nonlinear conductivity or capacitance of the diode. At the same time, it is possible to convert the frequency of this signal. Parametric microwave amplifiers are very difficult to set up and are quite unstable. Their main advantage is their uniquely low noise level. Therefore, they are most often used in radio telescopes and deep space communication systems.

Tunnel diodes may be of greatest interest and practical value. Generator and amplifier devices based on them can be used in radio receivers, radio microphones, measuring equipment, etc.

A simplified circuit of a self-oscillator using a tunnel diode is shown in Fig. 3.6-42.

Rice. 3.6-42. Simplified circuit of a self-oscillator using a tunnel diode

Since the I-V characteristic of the tunnel diode has a section with a negative resistance that is stable in voltage, when a parallel oscillatory circuit is connected to it, it can generate. In this case, the negative resistance of the diode will compensate for the losses, and undamped oscillations can arise and be maintained in the circuit. Modern tunnel diodes can generate at frequencies up to 1 GHz or more. However, due to the small size of the section of the current-voltage characteristic of a diode with negative resistance, the power it delivers at any frequency is a fraction of a milliwatt. To prevent the shape of the generated oscillations from being distorted, as a rule, a partial inclusion of a diode in the generator circuit is used. The main condition for generation is that the circuit loss resistance exceeds the negative resistance of the tunnel diode. Considering that the parallel resistance of losses in real oscillatory circuits significantly exceeds the negative resistance of a tunnel diode, partial inclusion of the diode in the circuit (through the tap of the coil) is used.

Some of the power of the generated oscillations will be released at the internal resistance of the bias source, so it should be as small as possible. Since the required bias voltage is very small (for example, for germanium tunnel diodes of the order of 0.1...0.15 V), tunnel diodes are usually powered from a voltage divider (Fig. 3.6-43). However, this can lead to wasted power consumption of the power supply (which is important for subminiature devices). Therefore, to power tunnel diodes, sources with the lowest possible output voltage should be used. The output resistance of the voltage divider is selected within the range of 5...10 Ohms, and only in devices where the greatest efficiency is required, it can be increased to 20...30 Ohms. The negative resistance of the tunnel diode must exceed the resistance of the divider by 5...10 times. It is not advisable to bypass such small resistances with capacitors to reduce losses of high-frequency energy, since in some cases this can lead to unstable operation of the generator, especially if its mode was selected according to the maximum output power. It should be taken into account that for stable operation of the generator it is necessary to maintain a stable position of the diode operating point. If the supply voltage changes by at least 10% (for example, due to the discharge of a chemical battery), the normal operation of the generator may be disrupted. Sometimes it is advisable to use a pre-stabilized voltage or use nonlinear resistances in the divider (stabilizing the current in the upper arm, and voltage in the lower arm). So, if in the self-oscillator circuit (Fig. 3.6-43) instead of resistance R2 we use a low-power germanium diode in direct connection, as shown in Fig. 3.6-44, the stability of the generator will improve, and when the supply voltage changes within 1...1.5 V, no additional adjustments will be required.

Rice. 3.6-43. Circuit of a self-oscillator based on a tunnel diode powered by a voltage divider

Rice. 3.6-44. Circuit of a self-oscillator based on a tunnel diode with nonlinear resistance in the power circuit

All of the above-mentioned methods of voltage stabilization somewhat complicate the circuits, and in some cases increase power consumption, so they are not widely used. In real equipment, tunnel diodes are most often used in conjunction with transistors. It is known that in a transistor, the emitter current depends relatively little on the collector supply voltage, especially if the transistor bias is stabilized in some way. Therefore, when feeding a diode with the emitter current of a transistor, you can gain not only in stability, but also in efficiency. The latter increases here due to the fact that losses on the upper arm of the divider are eliminated, and the additional power consumed by the tunnel diode is small.

In Fig. 3.6-45, 3.6-46, 3.6-47 present three examples of using a tunnel diode generator. When designing such generators, one should strive to obtain the maximum quality factor of the oscillating circuit in order to increase the power delivered to the load.

Rice. 3.6-45. The simplest tunnel diode transmitter

Rice. 3.6-46. Improved tunnel diode transmitter circuit

Rice. 3.6-47. Local oscillator on a tunnel diode

To increase power, you can also include two or more diodes in the generator circuit (Fig. 3.6-48). In this case, it is best to connect the diodes in series with direct current. Then the voltage at the lower resistance of the divider should be twice as high as for one tunnel diode, i.e. losses on the upper arm are reduced. It must be borne in mind that the resistance of the lower arm must necessarily consist of two identical resistances, and their midpoint must be connected via direct current to the midpoint of the two diodes. Otherwise, stable operation of two diodes connected in series is impossible. For alternating current, diodes can be connected in parallel or in series. In the diagram shown in Fig. 3.6-48 each diode is connected to a separate winding. To obtain the greatest power, the connection of each diode to the circuit should be adjusted individually.

Rice. 3.6-48. Self-oscillator based on two tunnel diodes

A tunnel diode generator can also be built using a quartz resonator that sets the oscillation frequency. An example of such a scheme is shown in Fig. 3.6-49.

Send your good work in the knowledge base is simple. Use the form below

Students, graduate students, young scientists who use the knowledge base in their studies and work will be very grateful to you.

Posted on http://www.allbest.ru/

BELARUSIAN NATIONAL TECHNICAL UNIVERSITY

FACULTY OF INSTRUMENT ENGINEERING

Department of Information and Measuring Equipment and Technologies

COURSE WORK

in the discipline: "Receiving and transmitting devices"

Topic: MASTER AUTO-GENERATOR ON A TUNNEL DIODE

Performer: Novik S. F.

Head: Vorobey R.I.

Essay

The course work contains 18 pages, 4 drawings, 1 appendix.

AUTO-GENERATOR, DIODE AUTO-GENERATORS, TUNNEL DIODE, CIRCUIT DIAGRAM.

The purpose of the course work is to develop a circuit diagram and calculate a master oscillator based on a tunnel diode, describe its operation, and calculate the elements included in the circuit diagram

The project presents: an electrical circuit diagram of a master self-oscillator based on a tunnel diode and its calculation.

Introduction

1. Analysis of the principle of operation of a self-oscillator based on a tunnel diode

1.1 General information about self-generators

1.2 Diode self-oscillators

1.3 Tunnel diode

2. Development of a self-oscillator circuit based on a tunnel diode

3. Calculation of a self-oscillator circuit based on a tunnel diode

3.1 Selecting a tunnel diode

3.2 Diode mode calculation

3.3 Power circuit calculation

3.4 Calculation of the resonator

3.5 Calculation of capacity Csv and C1

Conclusion

List of sources used

Introduction

During the course work, a master oscillator circuit based on a tunnel diode was developed and calculated.

A self-oscillator is a source of electromagnetic oscillations, the oscillations in which are excited spontaneously without external influence. Therefore, self-excited generators, in contrast to generators with external excitation (power amplifiers), are often called self-excited generators.

In radio transmitters, self-oscillators are used mainly as cascades that set the carrier oscillation frequency. Such generators are part of the transmitter exciter and are called master generators. The main requirement for them is high frequency stability. In some types of transmitters (especially in the microwave range), self-oscillators can be output stages. The requirements for such generators are similar to those for power amplifiers - to ensure high output power and efficiency.

A tunnel diode is a low-power generator diode with a narrow p-n junction, the active properties of which are manifested in a wide frequency range - from direct current to microwave.

1. Analysis of the principle of operation of a self-oscillator based on a tunnel diode

1.1 General information about self-generators

Master oscillators are designed in such a way that harmonic oscillations are excited in them. The main element of a harmonic oscillation generator is a resonator, the main property of which is the oscillatory nature of the transient process. The simplest resonator is an oscillatory circuit. If energy is introduced into the oscillatory circuit, then at a sufficiently high quality factor (Q " 1), current oscillations occur that decay over time. The decrease in the oscillation amplitude is explained by power losses in the circuit. Thus, to create a self-oscillator of harmonic oscillations, it is necessary to use a resonator with a sufficiently high quality factor and compensate for losses.

To fulfill the last condition, it is enough to periodically add portions of electromagnetic energy to the resonator synchronously with the excited oscillations. The source of energy can be a constant electric field; To convert its energy into vibration energy, an active element (AE) is required. The block diagram of the self-oscillator is shown in Figure 1. Feedback is needed here to synchronize the operation of the AE with the oscillations existing in the resonator.

Figure 1 - Block diagram of a self-oscillator

LC circuits and quartz plates are used as resonators in the high frequency range; for microwaves - segments of lines with distributed parameters, dielectric washers, ferrite spheres, etc. Active elements can be bipolar and field-effect transistors, as well as generator diodes - tunnel, avalanche-span, Gunn diodes, etc.

The mechanism of operation of the autogenerator is as follows. When the energy source is turned on, a transient oscillatory process occurs in the resonator, affecting the AE. The latter converts the source energy into oscillation energy and transfers it to the resonator. If the power supplied by the active element exceeds the power consumed by the resonator and load, i.e., the self-excitation condition is met, then the amplitude of the oscillations increases. As the amplitude increases, the nonlinearity of the AE appears; as a result, the growth of the output power slows down and at a certain oscillation amplitude, the output power turns out to be equal to the consumed power. If this energy balance is stable to small deviations, then a stationary oscillation mode is established in the self-oscillator.

Autogenerators differ significantly from other cascades of radio transmitters in that the frequency and amplitude of oscillations here are determined not by an external source, but by the parameters of their own oscillatory system and the active element.

1.2 Diode self-oscillators

Depending on the type of AE, transistor and diode self-oscillators are distinguished.

Diode self-oscillators provide stationary oscillations due to specific processes in generator diodes; feedback here is carried out automatically without the use of special elements.

1.3 Tunnel diode

A tunnel diode is a low-power generator diode with a narrow p-n junction, the active properties of which are manifested in a wide frequency range - from direct current to microwave. This allows you to build tunnel self-oscillators at a wide variety of frequencies. The output power of self-oscillators using tunnel diodes is usually hundreds of microwatts. An important advantage of a diode is the preservation of its properties as an active element under radiation conditions.

The equivalent circuit of a tunnel diode (Figure 2a) contains a current generator ia (uA), barrier capacitance of the p-l junction Sb ( uA), loss resistance in the semiconductor and contacts rs, and terminal inductance Lв. The dashed line in Figure 2b shows the static current-voltage characteristic of a conventional diode with a pn junction.

Figure 2. Equivalent circuit of a tunnel diode (a) and static current-voltage characteristic of a current generator (b)

2. Development of a self-oscillator circuit based on a tunnel diode

1. A tunnel diode is a device with an N-type current-voltage characteristic, therefore the oscillatory system, taking into account Lv n Sa at the connection points of the current generator ia (ua), must have a parallel resonance at a given frequency.

Figure 3. Principal electrical (a) and equivalent (b) power supply circuits of a tunnel diode.

2. A section of negative slope exists at very low voltages ua. In order for the diode to act as an active element of a self-oscillator, the supply voltage U0 must be within the limits of upeak< U0< uвп или 0,1 < U0 < 0,6 В. Так как напряжение стандартных источников питания Еп>1.5 V, then a voltage divider is required (Figure 3 a).

3. The existence of a section of negative slope not only on the dynamic current-voltage characteristic (as with all active elements), but also on the static characteristic leads to the need to ensure the stability of the DC operating point.

Electrical circuit of a self-oscillator using a tunnel diode. Figure 4 shows one of the possible circuits of such a self-oscillator.

Figure 4. Schematic diagram of a self-oscillator based on a tunnel diode.

Here R1, R2 are the voltage divider in the power circuit;

Sbl, Lbl - elements blocking the power source from high frequency currents;

C1, C2, L - elements of the resonator that sets the generation frequency;

Ссв - communication capacity with the load. In order to simultaneously ensure high frequency stability and optimal energy conditions, an incomplete connection of the resonator to the diode is used.

3. Calculation of a self-oscillator circuit based on a tunnel diode

The calculation of a tunnel self-oscillator consists of 3 main stages: 1) selection of a diode; 2) calculation of the diode mode; 3) calculation of the resonator and power circuit.

3.1 Selecting a tunnel diode

When choosing a diode, you should take into account the required output power of the oscillator. To obtain high frequency stability, a weakened connection to the load should be used, selecting a sufficiently small capacitance Ssv. Then the power in the load Rn? (0,1 ... 0.2) P1, Where P1 , is the oscillatory power given off by the diode to the external circuit.

From the theory of tunnel self-oscillators it follows that the maximum oscillatory power of the diode is:

P1 max ? 0,2 ,

= ipeak-iVP;= upeak-uvp.

Since = ipeak;? 0,4 For gallium arsenide diodes, we obtain the following ratio for choosing a diode: ipeak? 100 Rn.

3.2 Diode mode calculation

The purpose of the calculation is to find the optimal load conductivity GTo, constant voltage U0 , on the diode, equivalent resistance of the power supply Rist. As a result of the calculation, the amplitude of oscillations becomes known Ua1 , oscillatory P1, and consumed P0 power, as well as the electronic efficiency of the autogenerator.

When calculating the diode mode, it is necessary to take into account the conditions for the existence of a stationary mode, self-excitation and DC stability. It is necessary to calculate the dependence of the real GA and imaginary Va conductivity parts Ya on the amplitude of oscillations Ua1. Main contribution to Va gives the barrier capacitance of the diode, i.e. Wha?wCb1, where Sb1 is the capacitance averaged over the first harmonic Co(uA). Calculations show that the value INa weakly depends on Ua1, therefore they consider the capacity Co constant, assuming Sat1 -- Sat (U0). Calculation | Ga|(Ua) can be done in the following order.

Figure 6. Normalization of the current-voltage characteristics of a tunnel diode based on gallium arsenide ( A) and dependence | Ga|/ ipeak on voltage amplitude ( b)

1. Let us approximate the static current-voltage characteristic of a tunnel diode with a suitable analytical expression.

2. Assuming that the voltage ua(t) on the diode has a harmonic form (this is true if the quality factor of the circuit at parallel resonance is sufficiently high), we substitute the voltage into the formula that approximates the current-voltage characteristic

ua(f) = U0+Ua1coswt

and find the dependence i a (t) .

3. Unfolding function i a (t) in the Fourier series, we find the amplitude of the first harmonic of the diode current Ia1 .

4. Calculate

|Ga| = Ia1/ Ua1 .

5. Repeat the calculations for different Ua1 And U0. As a result, we get a family of dependencies | Ga|(Ua1) at U0 as a parameter.

Since the current-voltage characteristics of tunnel diodes made from the same material are identical and differ only in the value of the peak current 1 "pyak", then in the calculations you can use some average characteristic normalized to i peak, which is valid for a certain semiconductor material (Figure 6).

As calculations using the described method showed and experiments confirmed, the optimal mode is obtained with the following parameters of the self-oscillator: U0= 0.37V; | Ga|/ ipeak=1.2 V-1. In this case, the amplitude of oscillations Ua1 = 0.33 V, and the excitation mode at U0= const turns out to be rigid.

3.3 Power circuit calculation

The diode power circuit performs the following main functions: 1) supplies the diode with the energy necessary to generate electromagnetic oscillations; 2) provides optimal displacement of the operating point on the static current-voltage characteristic.

To obtain the optimal mode of the diode with soft excitation of oscillations, it is advisable, as in the case of transistor oscillators, to use automatic bias. It is formed when a direct current flows from the diode I0 through parallel connected resistors R1 And R2 . You can choose resistance like this R1 And R2 that at the moment of excitation of oscillations the constant voltage on the diode will correspond to soft excitation, and in stationary mode - to the optimal value U0= 0.37 V. The possibility of such a choice is explained by the fact that with soft excitation of oscillations, direct current I0(0)( it is somewhat smaller ipeak) turns out to be greater than the current I0 in stationary mode. If there are fluctuations, the current I0 is no longer determined by the static current-voltage characteristic of the diode, but corresponds to some curve depending on the load GH(shaded area in Figure 6, a). This is explained by the fact that the time dependence ia(t) non-harmonic.

In the stationary oscillation mode, the constant voltage Uо will be equal to the optimal value of 0.37 V in the case when the change in voltage across the resistance Rist when the direct current I0 decreases to I0 is equal to the difference in the constant voltages on the diode in the optimal mode and at the moment of excitation. From here we get (Figure 6, a):

Rist?(U0-upk)/(ipeak-I0) (1)

In maximum efficiency mode:

From Figure 6, it is clear that in the optimal mode it is 0.3, so Rist? 0.4 V/ipeak; Then: electromagnetic tunnel diode generator

0.37 V + 0.27 A *0.4 Ohm = 0.47 V (3)

= (0.4 Ohm * 1.5 V) / 0.47 V = 1.27 Ohm (4)

) = 0.4 Ohm * 1.5 V / (1.5 V - 0.47 V) = 0.58 Ohm (5)

3.4 Resonator calculation

Selecting the circuit inductance L= 5 µH with quality factor QL= 110. We consider th

O Q0 QL.

Let's calculate the parameters of the resonator elements:

With = schRL = 2 pfpL= 2 * 3.14 * 0.5 Hz * 106 * 5 * 10-6 H = 15.7 Ohm (6)

WITHU= = ? 2072 pF (7)

Rp = WithQ0 = 15.7 Ohm * 110 1.72 kOhm (8)

C"1= C?/s = 2072 pF/15.7 Ohm = 132 pF (9)

C2? C"1 ? 132 pF (10)

3.5 Calculation of capacity Csv and C1

Shall we accept Rн? 300 Ohm, then:

Ssv == 60 pF (11)

60 pF (12)

132 - 60 = 72 pF (13)

The resistance of the input circuit should be much greater than the resonator circuit (). Let's take n=10, then:

Lbl=10L = 10 * 5 * 10-6 = 50 μH (14)

Cbl=Cbl/10 = 60 * 10-12 / 10 = 5 pF (15)

Conclusion

During the course work, a description of the operation of a self-oscillator based on a tunnel diode was given, a circuit diagram was developed, and the elements included in the circuit diagram were calculated.

List of sources used

1. Petrov B. E., Romanyuk V. A., Radio transmitters

Devices on semiconductor devices: Proc. manual for radio engineering. specialist. call/ M.: Higher. school, 1989 - 232 p.

2. Handbook of electric capacitors / M. N. Dyakonov, V. I. Karabanov, V. I. Prisnyakov, etc.; Under general ed. I. I. Chetvertkova and V. F. Smirnova. - M.: Radio and communication, 1983 - 576 p.

3. Resistors: Directory / V. V. Dubrovsky, D. M. Ivanov, N. Ya. Pratusevich and others; Ed. I. I. Chetvertkova and V. M. Terekhova. - 2nd ed., - M.: Radio and Communication, 1991 - 528 p.

Posted on Allbest.ru

Operating principle of a tunnel diode

The potential required to cause a tunnel diode to conduct, whether in forward or reverse bias mode, is very small, typically in the millivolt range. This is why tunnel diodes are known as low-resistance devices. They very weakly oppose the movement of current in the circuit.

The most unique feature of tunnel diodes is their voltage-to-current ratio when they are forward biased. When a tunnel diode is forward biased (from point A to point B on the graph) as the voltage increases, the current also increases to a certain amount. Once this value is reached, a further increase in the forward bias voltage causes the current to decrease to a minimum value (from point B to point C). In the region between the maximum and minimum current flows on the graph, the tunnel diode has negative resistance. In this region of negative resistance, the current flowing through the tunnel diode actually decreases as the voltage increases. The exact opposite of the usual voltage-current relationship occurs. However, when the voltage beyond point C increases, this device exhibits the usual voltage-current relationship.

Under normal conditions, tunnel diodes operate in the region of their negative resistance. In this area, a slight decrease in voltage turns the device on, and a slight increase turns it off. As such a unique switch, a tunnel diode can be used either as a generator or as a high-speed switch: a specific feature of the device, low resistance, allows you to change the internal resistance almost instantly. Tunnel diodes can also be used as amplifiers, where upward changes in the applied voltage cause proportionally larger changes in current in the circuit.

Rice. 1. The simplest transmitter using a tunnel diode.
Coil L contains 10 turns of PEL 0.2 wire.

The operating principle 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 vibrations. An "ideal" sinusoid can be obtained, but in practice small nonlinear distortions are inevitable.

Rice. 2. Local oscillator on a tunnel diode L=200 μH.

Shown in Fig. 3 tuning fork audio frequency 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 must be connected 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 - tunnel diode made of gallium arsenide with current Imax = 70 mA; r = 9 ohm;
L1=L2=196 μH—inductance of the coil without a core;
K—key; Gr—loudspeaker.

In order for the operating point of the diode to fall on the area with negative differential resistance, a voltage source with 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 is greater than 2.5Rd, then the operating point cannot be stably located in the area with negative resistance.

To power devices using tunnel diodes, the circuit shown in Fig. 4 is used. The value of the 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 resistance R1 is completely removed.

Rice. 4 DC bias circuit of a tunnel diode.

The power source can be rechargeable batteries or high-capacity batteries. In this case, the selected operating point will be more stable over time.

Historically, tunnel diodes appeared much later than transistors and lamps. Small dimensions and weight, high reliability and cost-effectiveness have led to a rapid expansion of their scope of application. Current-voltage characteristic of a tunnel diode - type N(Fig. 7). Therefore, the oscillator circuit is simple: a parallel AC circuit is connected to the diode (Fig. 8.44 b), and the DC mode is selected so that the operating point O is in the falling section of the characteristic (Fig. 7).

Fig.7. Current-voltage characteristic and generator circuit using a tunnel diode

DC mode must be ensured taking into account the internal resistance of the source R i. To do this, it is necessary to solve a system of two equations:

A graphical solution of the system is shown in Figure 8.44 a.

Let's consider two cases.

In the first case, with a steep slope of the characteristic | S(U 0)| > 1/R i, there are three possible states that satisfy the equations of the system - points A, O, B. Analysis, taking into account the capacitance of the diode itself, shows that only points A and B, located on the increasing sections of the characteristic, are stable. If the rest point (point O) is located in the characteristic section with a negative slope, then the state of the circuit will be unstable and the operating point will spontaneously shift to one of the extreme positions (to point A or point B).

In the second case, with a steep slope of the characteristic | S(U 0)| < 1/R i, there is only one state that satisfies the equations - point O. It turns out to be stable and therefore the operating point can be set at any section of the current-voltage characteristic with a negative slope, therefore, the phase condition of self-excitation is satisfied. The amplitude condition for self-excitation will be satisfied if | S(U 0)| > G Uh, where G E is the conductivity of the circuit at the diode connection points.

The oscillation frequency is

and can be changed using WITH K. The amplitude of oscillations changes by changing the point at which the diode is connected to the oscillatory circuit. If the coils L 1 and L 2 are not connected by a single magnetic field, then the circuit switching coefficient is equal to

If the coils L 1 and L 2 form a single coil with a common magnetic field, then the diode is connected to the inductive branch with a switching coefficient equal to

Where n 1 and n 2 - the number of turns in the parts of the coil indicated in the diagram L 1 and L 2 .

Blocking capacity WITH B is selected from the condition

Advantages of the scheme:

ability to operate in a very wide frequency range (from a few kilohertz to tens of gigahertz);

high stability of parameters when temperature changes over a wide range;

low level of own noise;

low energy consumption from power sources;

long service life;

low sensitivity to radiation.

The disadvantage of the circuit is the low output power, which is due to small intervals of currents and voltages within the falling portion of the characteristic (with a negative slope). For example, a generator based on one tunnel diode with a peak current of up to 10 mA provides power not exceeding a few milliwatts. To obtain more power, it is necessary to use diodes with high peak currents.

Tunnel diode: detailed in simple language. Generators on diodes Microwave generator design circuit on a tunnel diode

Send your good work in the knowledge base is simple. Use the form below

Similar documents

Operating principle of a tunnel diode