Pulse frequency multiplication. Frequency multiplier (MF). Review of methods for solving similar problems

A frequency multiplier is such a GVV, the oscillation frequency, the output of which is 2, 3,..., n times higher than the input.

The frequency multiplier circuit is similar to that of a conventional radio frequency amplifier. A multiplier differs from an amplifier in that the output circuit of the multiplier is tuned to second, third or p-y harmonic of the input voltage. Therefore, the load releases the power of the harmonic to which the output circuit is configured.

From the analysis of the mode of oscillations of the second kind, it is known that with an increase in the harmonic number, the amplitude of the harmonic components decreases: I n =α n, Imah- Therefore useful power and the efficiency of the multiplier is less than that of the amplifier. The multiplication mode is used in low-power transmitter stages, the low efficiency of which practically does not reduce the transmitter efficiency in practice.

The principle of constructing transistor frequency multipliers is based on the use of two physical processes: the selection of the desired harmonic from the collector current pulse and the nonlinear nature of the change in the collector capacitance from changes in the collector voltage.

Transistor frequency multipliers, operating on the principle of isolating the desired harmonic from a pulse, provide multiplication by a relatively low frequencies. This happens because with increasing operating frequency, the collector current pulse expands (up to 180°) and the content of higher harmonics in it sharply decreases. In practice, multipliers based on this principle operate at frequencies up to 0.3 Ѡ t.

For multiplication at higher frequencies, the nonlinearity of the collector capacitance is used. This allows you to obtain a frequency at the output of the multiplier that is greater than the cutoff frequency of the transistor. In Fig. Figure 2.12 shows a diagram of a transistor frequency multiplier operating at both low and high frequencies. The input of the circuit is supplied with a voltage of the fundamental frequency, to which the circuit in the base circuit of the transistor is tuned. The collector circuit includes filters that isolate a given harmonic on the load.

Transistor oscillators operate at frequencies up to 10 GHz. To obtain power at higher frequencies, frequency multipliers based on semiconductor diodes - varicaps and varactors - are switched on after the transistor generator.

IN semiconductor devices The capacitance of a p-n junction consists of two components: barrier (1) - the main one when the junction is closed and diffusion (2) - the main one in an open transition.

Graphs of the dependence of the capacitances of the p-n junction on the voltage across it are shown in Fig. 2.13. Curve 3 reflects the resulting capacitance of the pn junction. To operate the multiplier on the characteristic C res =f(U) select the operating point A, by applying the appropriate bias voltage.

Diodes designed to operate at small amplitudes compared to the bias voltage are called varicaps. The properties of a varicap are determined only by the properties of the barrier capacitance of the gated junction.

Diodes designed to operate at large amplitudes are called varactors. In varactor multipliers, work occurs in both the closed and open transition regions.

The operating principle of a varactor frequency multiplier is based on the use of the nonlinearity of the p-n junction capacitance. When a harmonic voltage is applied to the p-n junction, the current through the junction will be non-harmonic (Fig. 2.13.6). This current contains higher harmonic components. The use of the open pn junction region leads to an increase in the level of higher harmonics.

A varactor can be connected to a multiplier circuit both in parallel (Fig. 2.14a) and in series (Fig. 2.14.6). The multiplier input circuit is tuned to the fundamental frequency, and the output circuit is tuned to the second or third harmonics. Such a frequency multiplier is passive, since the energy of output oscillations at the fno frequency is determined by the energy of only one input voltage source with a frequency co.

The advantage of a parallel multiplier circuit is that one terminal of the varactor is at zero potential. This makes it possible to place the varactor on a large radiator and improve the thermal conditions, which means increasing the useful power.

The sequential circuit (Fig. 2.14.6) provides better stability of operation, since the inductance of the leads and the capacitance of the housing are part of the oscillatory system of the multiplier. But in this scheme, the heat removal conditions become more complicated.

The best efficiency of power conversion in a varactor is achieved by selecting the optimal value of the bias voltage corresponding to a certain value of the input voltage. As the amplitude of the input voltage changes, the conversion efficiency also changes.

Auto bias ensures that the offset voltage changes as the input voltage changes, thus maintaining optimal conversion efficiency.

Varactor frequency multipliers are used to double or triple the frequency. To obtain multiplication of greater multiplicity, several doublers or triplers are connected in series.

2.10. Connection diagrams for transistor generators

To increase the output power of the hot water supply, several transistors are connected in parallel or in series to operate on one common load.

When transistors are connected in parallel to operate on one common load, the same electrodes of the transistors are connected to each other in parallel. In this case, the currents of individual transistors in the common wire add up and the total power is released in the output circuit.

Transistors connected in parallel must have the same parameters, otherwise one of the transistors will bypass the other transistor and the load. A significant spread in the parameters of transistors leads to the need to use additional circuit solutions to equalize the operating modes of individual transistors. However, this leads to complexity of the circuit, and therefore reduces the reliability of its operation. Therefore, they are limited to connecting no more than two or three transistors in parallel.

Due to the complexity of setup and reduced reliability, circuits with parallel connection of transistors are rarely used.

Low-power push-pull generators (tens of watts) at frequencies of 1-10 MHz can be performed on magnetically coupled transformers, as shown in Fig. 2.15. The transistors in this circuit operate in class B mode, i.e., with a cutoff angle of 0 = 90°. When an alternating excitation voltage is applied to the input in the collector circuits, the collector current pulses are shifted in phase by 180°. According to the first harmonic current, the transistors are connected in series.

VT1 leaks from the collector VT1 via transistor VT1, then the emitter - collector section of the transistor VT2, through load T2 to the collector of the transistor VT1.

Collector current of the first harmonic of the transistor VT2 leaks from the collector VT2 through the collector - emitter section VT2, through emitter - collector VT1, through the load and to the collector VT2.

Through load T2 The collector currents of the first harmonic flow in one direction and therefore add up. In the common power supply wire, the first harmonic currents are directed towards each other and cancel each other out.

At the output of this circuit, with its good symmetry, there are no higher harmonics, since the even harmonics of the collector currents of both transistors in the output transformer are compensated, and odd harmonics in pulses with a cutoff of 0 = 90° are practically absent.

2.11. Diagrams of output stages of radio transmitters

The radio frequency oscillations created by the generator are transmitted to the antenna for radiation. To do this, the transmitter antenna must be connected to the output circuit of the last stage of the transmitter. The antenna-loaded stage is called the output stage. The transmitter output stage is the most powerful stage and draws the most energy from the power supplies. Therefore, the energy performance of the output stage mainly determines the energy performance of the transmitter as a whole. Therefore, the output stage should have the highest possible efficiency. In addition, the output stage operates in the mode of oscillations of the second kind, “higher harmonic components of the current of its output circuit can be transmitted to the antenna and emitted by it, creating interference with other radio stations. To eliminate this, the output stage must provide sufficiently good harmonic filtering.

The operating mode and energy performance of the output stage depend on electrical parameters antenna and the method of connecting it to the output circuit of the generator.

Depending on the method of connecting the antenna, there are two output schemes - simple and complex.

A simple output circuit is one in which the antenna is directly connected to the generator output circuit, as shown in Fig. 2.16, a. In this circuit, the antenna, together with the tuning and communication elements, is part of the output circuit, which is the load of the generator. The output circuit here is called an antenna circuit. It must be tuned to a given frequency and have a resistance equal to the optimal equivalent load resistance of the generator.

It is known that the most complete transfer of oscillatory power to the antenna occurs when the input impedance of the antenna is matched with the output impedance of the generator. In a simple circuit, the antenna circuit is tuned to a given frequency using a tuning coil L n, and the load resistance is selected by changing the inductance or coupling capacitance.

If the transmitter operates on one fixed wave, then the conditions for implementing the most advantageous generator mode and the most complete transfer of energy to the antenna are achieved as follows. First, tune the antenna circuit to the operating frequency of the generator, and then, without changing the circuit settings, select the value of the circuit’s equivalent resistance to ensure optimal operation of the generator.

When the antenna is directly connected to the output circuit of the generator, the energy is transferred to the antenna most fully and this achieves a higher efficiency of the generator, which is an advantage of a simple output circuit.

The disadvantage of a simple circuit is low harmonic filtering and unreliable operation in the event of antenna breaks. If the antenna breaks, the load resistance decreases and the generator may find itself in an undervoltage mode. In this case, power losses on an electronic device can exceed permissible limits and destroy the device.

In a complex output circuit, there are two circuits in the generator output circuit (Fig. 2.16.6). One of them is connected directly to the output circuit of the generator and is called intermediate. The second circuit is created by the antenna elements and is called the antenna circuit. Both circuits are tuned to the operating frequency of the generator. The optimal load resistance in a complex circuit is selected by selecting the connection between the intermediate circuit and the antenna (using the successive approximation method).

The advantage of a complex circuit is better harmonic filtering. In addition, a complex circuit is more reliable, since if the antenna breaks, the generator goes into overvoltage mode and power losses due to heating of the electronic device are reduced. The disadvantage of a complex circuit is low efficiency due to energy losses on the communication elements and the intermediate circuit.

Complex output circuitry is used in large and medium power, in which better harmonic filtering is of great importance and large overall dimensions of the circuit and its complexity are allowed.

In low-power communication transmitters, for which their small overall dimensions, weight and simplicity of the circuit, as well as efficiency are of decisive importance, it is used simple circuit exit.

To control the operating mode of the electronic device and tune the circuit to resonance, a device for measuring currents in the output and input circuits of the generator is included in the output stage of the transmitter.

Chapter 3. AUTO GENERATORS

3.1. Self-excitation principle

To create radio frequency oscillations in radio transmitting devices, the phenomenon of the occurrence of electrical oscillations in an oscillatory circuit is used, into which a certain amount of energy is introduced from the outside, i.e., the primary source of electrical oscillations in radio transmitting devices is the oscillatory circuit.

If in the electrical circuit L.C. introduce a certain amount of energy from the outside, for example, by charging capacitor C, then free damped oscillations of radio frequency arise in the circuit.

In order for the oscillations to be undamped, that is, their amplitude does not decrease, it is necessary to periodically, in time with the free oscillations, replenish the energy in the circuit. This can be done periodically by connecting an EMF source to the circuit, which will recharge the circuit capacitor. When the amount of energy entering the circuit is sufficient to compensate for all energy losses in it, the oscillations in the circuit will be undamped.

To create continuous oscillations in the circuit, it is necessary to replenish energy once per period. And since the oscillation frequency is high (hundreds and thousands of kilohertz), only a special high-speed device - a vacuum tube or transistor - can connect a source of electrical energy to the circuit to replenish the energy in it.

In order for energy replenishment to enter the circuit in time with free oscillations (with its own oscillations), it is necessary that the oscillations themselves control the current of the power source. For this purpose, the generator circuit has feedback (OS) of the output circuit with the input circuit. Thus, a self-excited generator consists of an oscillatory circuit, an electronic device, a power source and positive elements feedback. /

The energy of the generated oscillations is released in the oscillatory circuit, the frequency of which is determined by the circuit parameters L and C. Electronic device acts as a regulator of energy consumption of the power source. The feedback elements can be an inductor or a capacitor. The power supply replenishes energy in the circuit. Thus, a self-excited generator is

_____________________________________________________________

Fig.3.1. block diagram of a self-oscillator

1-OS circuit; 2-reinforcing element; 3-oscillatory circuit;

4-power supply.

a device that creates radio frequency oscillations using an oscillating circuit and feedback elements. And since oscillations in such a generator occur automatically, immediately after turning on the power sources, it is called a self-oscillator (Fig. 3.1).

Shaping a frequency that is a multiple of a fixed input frequency is one of the most common applications of a PLL. In frequency synthesizers, the output signal frequency is formed by multiplying the frequency stabilized by a quartz resonator by the number n; the number n can be specified digitally, i.e. You can get a flexible signal source that can even be controlled using a computer or a simple controller.

IN in this example Let's try to use a PLL to get a fairly high frequency of the UHF range, stabilized by a low-frequency quartz resonator. So we have quartz resonator at a frequency of 6.8 MHz, the KR193IE6 microcircuit (divider by 64, operates at frequencies up to 1000 MHz), as well as the KR1564LP5 microcircuit, which we will use as a phase detector.

Let's start with a standard PLL circuit, in which a counter-divider by - n is connected between the VCO output and the phase detector (Fig. 1).

In this diagram, the transfer coefficient is indicated for each functional block. When calculating the PLL loop, these coefficients are used to perform stability calculations. There are special formulas for calculating each of the transmission coefficients. The overall gain of the PLL loop will be equal to the product of the gains of all the functional blocks of the loop.

Based on the results of calculating the value of the general coefficient, the stable operation of a given circuit diagram is judged. The greatest difficulties in these calculations come from the calculation of low-pass filter elements. Most radio amateurs who do not have the opportunity to calculate stability have to select filter components until the circuit works. Let's try to look at the purpose of the filter elements. Figure 2 shows one of the possible low-pass filter circuits.

The product R1xC0 determines the contour smoothing time, and R0/R1 - damping, i.e. no overload in frequency hopping. The selection of values ​​can begin with R0 = 0.2 R1. Figure 2(b) shows a circuit with an additional capacitor C1. One of the possible options for this filter may have the following data: R1 = 10k, R0 = 10k, C0 = 1000 and C1 = 0.033 microns.

Let's consider the circuit diagram of a frequency multiplier with a PLL, which contains a quartz resonator with a frequency of 6.8 MHz, a KR193IE6 microcircuit (divider by 64, operates at frequencies up to 1000 MHz), as well as a KR1564LP5 microcircuit, which we will use as a phase detector. Figure 3 shows one of the possible fundamental electrical diagrams frequency multiplier by 64 using a PLL, which uses the components listed above.

Fig.3

This scheme is not worked out and is presented by me purely for illustrative purposes. possible option multiplier using PLL. The phase detector is made on MS DD1 74NS86 (564LP5). The element of this DD1.1 microcircuit is used to create a generator with a quartz resonator Z1. Element DD1.3, which operates in repeater mode, receives a signal from the MS VCO frequency divider.

The difference signal is detected at element DD1.2 and fed to an active low-pass filter made on transistors VT1 and VT2. R10 and C6 are additional low-pass filter elements. The difference signal is supplied to the varicap VD1 through R10. The VCO is made on transistor VT3, and on VT4 a buffer is assembled - a VCO frequency amplifier. From VT4, the signal c is fed through C14 to the output, and through the high-pass filter C13Dr1S15 to the VCO frequency divider, made on DD2. From the output of the frequency divider, the signal is fed to the phase detector through capacitor C16.

Capture process

To perform the frequency locking process a necessary condition is the sufficient voltage of the error signal after the low-pass filter. You should always remember that the low-pass filter on LC elements introduces a large attenuation of the signal. The first order loop will always synchronize because there is no attenuation of the error signal at low frequency.

Second-order loop timing depends on the type of phase detector and the bandwidth of the low-pass filter. In addition, the XOR phase detector has a limited acquisition range depending on the filter time constant.

Fig.4
The capture process takes place in the following way: When the phase error signal brings the VCO frequency closer to the reference frequency, its changes become slower and vice versa. The error signal is therefore asymmetrical and changes more slowly in the part of the cycle during which fgun approaches fon.

As a result, a non-zero average component appears, i.e. constant component, which brings the PLL into synchronism. If you graphically analyze the VCO control voltage during the capture process, you can get something similar to the signal shown in Fig. 4.
Every capture process is different and looks different every time.

Capture and tracking strip

When using an XOR phase detector, the capture bandwidth is limited by the time constant of the low-pass filter. This makes some sense, since if the difference in frequency is large, the error signal will be attenuated by the filter so much that the loop will never be able to capture. Obviously, increasing the filter time constant reduces the capture bandwidth, since this leads to a reduced loop gain.

Frequency multiplier on MS12179

Motorola produces serially the MC12179 type PLL chip, which already contains the following components necessary to create a full-fledged PLL circuit, namely:

All the elements necessary to organize the operation of an external generator with quartz frequency stabilization;
Phase detector;
Frequency divider by 256, which allows you to use this MS as a frequency multiplier up to frequencies of 2500 MHz;
There is an input for the VCO frequency and an error signal output to the low-pass filter.

Please note that there is no low-pass filter included in the microcircuit; in each individual case it should be designed in accordance with the individual requirements for the multiplier.

Fig.5 and 6

Figure 5 shows a schematic diagram of the PLL circuit with the MC12179 microcircuit. Quartz Z1 can be selected in the range from 5 to 11 MHz, while the output of the multiplier can obtain frequencies in the range from 2400 to 2800 MHz. Schemes of possible low-pass filters are shown in Fig. 6.

The frequency multiplier with PLL on the MS12179 creates noise many times less than the multiplier according to the circuit described above with a separate frequency divider.

Frequency synthesizer on LM7001

The frequency synthesizer circuit for the 145 MHz range is made on the LM7001J chip, used by various companies in household radios.

The synthesizer is designed to operate in FM transceiver devices with an intermediate frequency of 10.7 MHz. It provides signal formation with a frequency of 133.3...135.3 MHz in receiving mode and 144...146 MHz in transmitting mode with a frequency grid step of 25 kHz. It also provides the ability to scan in receive mode over the entire operating frequency range.

The synthesizer has non-volatile memory for three user frequencies. It also contains 9 repeater channels (R0...R8). In transmit mode, the synthesizer performs frequency modulation of the RF signal. The synthesizer is powered with a voltage of 8...15 V. Current consumption is no more than 50 mA. The RF signal level at its output at a load of 50 Ohms is at least 0.1 V. This very interesting design should be of interest to many radio amateurs.

Technical characteristics of MS LM7001J:

1. Rated voltage power supply, V........................................................ ......4.5...6.5.
2. Input voltage high level, V, at inputs CE, CL, Data 2.2...6.5.
3. Input voltage low level, V, at inputs CE, CL, Data ...0... 0.7.
4. The maximum permissible voltage supplied to the SC output, V.... 6.5.
5. Maximum permissible voltage supplied to the outputs BSoutl... BSout3, V........13.
6. Maximum permissible output current of the SC output, mA.................................... 3.
7. Maximum permissible input current of inputs BSoutl... BSout3, mA 3.
8. Frequency interval of input Amin1, MHz...................0.5...10.
9. Frequency interval of input Fmin, MHz, at frequency grid step
- 25,50,100 kHz.............45...130.
- 1,5,9,10 kHz............ 5...30.
10. Sensitivity for inputs Amin and Fmin, V (rms)..............0.1 ...1.5.
11. Typical value of input resistance for inputs Amin and Fmin, kOhm ............ 500.
12. Total current consumption, mA.................... 40.

The LM7001J and LM7001JM microcircuits are designed for building frequency synthesizers with a PLL system used in household radio receivers. Both microcircuits are identical in circuit and parameters and differ only in the design of the housing - the LM7001J has a DIP16 housing for conventional installation, LM7001JM -MFP20 for surface mounting (both chips are plastic). The assignment of the microcircuit pins is presented in the table below.

Pins Xout and Xin - output and input of the reference frequency signal amplifier; A quartz resonator is connected to these pins. Conclusion CE-input recording permission signal. CL - write clock input. Data - information input. SC - Syncro Control - control frequency output 400 kHz. BSoutl -BSout3 - band switching control outputs external devices(BSoutl output, in addition, is an 8 Hz frequency signal output); With the help of these signals, the ranges Amin and Fmin are switched - the inputs of the programmable frequency divider, in other words, the inputs of the AM and FM signals. Pdl and Pd2 are the outputs of the frequency-phase detector in FM and AM modes, respectively.

The functional diagram of the device is shown in Fig. 7. The control sequence of bits arriving at the receiving shift register determines the value of the frequency grid step of the synthesizer, the division coefficient of the programmable frequency divider, its operating mode and the state of the BSoutl...BSout3 outputs.

Fig.7

The microcircuit can operate with seven standard frequency grid step values ​​- 1, 5, 9, 10, 25, 50 or 100 kHz (with a standard oscillator frequency of 7200 kHz. The control bit sequence is introduced sequentially, starting with the least significant bit of the frequency division coefficient of the programmable divider, which can operate in two modes - AM and FM.

Phase-locked loops are often used for frequency multiplication. Previously, harmonic generator circuits were used for this purpose, followed by selecting the corresponding harmonic with a narrow-band filter.

A phase-locked loop circuit is much better suited for this purpose. In this circuit, it is relatively easy to change the multiplication coefficient of the circuit by changing the division coefficient in the feedback circuit. Frequency multiplication uses either digital or all-digital phase-locked loop circuitry.

Frequency multipliers are now commonly used to increase the internal clock speed of large integrated circuits. In these microcircuits digital circuit phase-locked loop is called an analog multiplier clock frequency, and the completely digital PLL circuit is called a digital frequency multiplier.

To increase the clock frequency of digital microcircuits, a completely digital frequency multiplier circuit is often used, and for mixed circuits or circuits intended for digital signal processing, the use of an analog frequency multiplier is preferable. This is due to the spectral purity of the output signal. The analog circuit provides a more stable oscillation, but is slower to reach operating mode.

An example of a circuit diagram of an analog clock multiplier is shown in Figure 1.

Picture 1. Schematic diagram analog frequency multiplier.

In this circuit, a reference oscillator with quartz frequency stabilization is implemented on logical elements D4 and D6. The voltage-controlled generator is implemented on elements D1 and D3. Considering that this is an RC oscillator, it has a very large frequency tuning range. Field-effect transistor VT1 is used as a control element. It can change the channel resistance within several thousand. (The VCO frequency will be adjusted the same number of times.) The phase comparator is implemented on chips D7, D8 and D10. The capture band of the phase-locked loop circuit is determined by a low-pass filter implemented on capacitor C4.

This frequency multiplier allows only sixteen steps of clock frequency adjustment. The code that determines the multiplication coefficient is entered through a simplified serial port assembled on the shift register D2. Depending on the code, the output frequency changes 16 times.

In more complex frequency multiplier circuits, dividers are introduced between the reference oscillator and the phase comparator. This allows the implementation of fractional frequency multiplication factors.

an electronic (less often electromagnetic) device designed to increase the frequency of periodic electrical oscillations supplied to it by an integer number of times. Attitude f out / f in( f input and f out - oscillation frequencies, respectively, at the input and output of the AC) is called the frequency multiplication factor m(m ≥ 2; can reach several dozen). Feature U. h. – constancy T when changing (in some finite area) f input , as well as parameters of the ultrasonic frequency (for example, resonant frequencies of oscillatory circuits (See Oscillatory circuit) or Resonators , included in the U. part). It follows that if f input for some reason received an increment Δ f in (sufficiently small), then the increment Δ f output frequencies f output is such that Δ f input/ f in = Δ f out / f out, i.e. the relative instability of the oscillation frequency during multiplication remains unchanged. This important property of ultrasonic frequencies allows them to be used to increase the frequency of stable oscillations (usually obtained from a quartz master oscillator (see Master oscillator)) in various radio transmitting, radar, measuring, and other installations.

The most common AC units are those consisting of a nonlinear device (for example, a transistor , Varactor, or Varicapa , ferrite core coils; a vacuum tube (See Electron tube)) and an electric filter (See Electric filter) (one or more). A nonlinear device changes the shape of input oscillations, as a result of which components with frequencies that are multiples of f input These complex oscillations are fed to the input of a filter, which selects a component with a given frequency mf input , suppressing (not letting through) the rest. Since such suppression in real filters is not complete, undesirable (so-called side) components remain at the output of the amp, i.e., harmonics with numbers different from m. The task becomes easier if the nonlinear device generates almost only m- th harmonic f in - in this case, sometimes they do without a filter (similar ultrasonic filters are known on tunnel diodes (See Tunnel diode) and special electron beam devices). At m> 5 It may be energetically more advantageous to use multi-stage amplifiers (in which the output oscillations of one stage serve as input to the other).

Also used are ultrasonic units, the operation of which is based on the synchronization of a self-oscillator (see . Generation of electrical vibrations). In the latter, oscillations are excited with a frequency f 0 = mf input , which becomes exactly equal mf input under the influence of oscillations arriving at its input with a frequency f input The disadvantage of such control units is a relatively narrow band of values f inputs at which synchronization is possible. In addition to those mentioned above, radio-pulse ultrasonic frequencies have become somewhat widespread, in which radio pulses of a certain shape are supplied to the input of an electric filter, generated under the influence of input oscillations with a frequency f input

The main problem in creating an AC frequency is reducing the phase instability of output oscillations (due to the random nature of changes in their phase), leading to an increase in the relative instability of the output frequency compared to the corresponding value at the input. Rigorous calculation of equations involves the integration of nonlinear differential equations.

Lit.: Zhabotinsky M. E., Sverdlov Yu. L., Fundamentals of the theory and technology of frequency multiplication, M., 1964; Rizkin I. Kh., Frequency multipliers and dividers, M., 1966; Bruevich A.N., Frequency multipliers, M., 1970; Radio transmitting devices based on semiconductor devices, M., 1973.

I. Kh. Rizkin.

• - traction multiplier, - electronic device to enhance the flow of electrons based on secondary electron emission...
• - a special transformer that increases the frequency alternating current generated by the generator, or a special tube circuit used to produce high-frequency currents...

  Marine dictionary

• - an electronic device for amplifying the current of primary electrons based on secondary electron emission. The EU is either part of certain electric vacuum devices, or is used as an independent...

  Natural science. encyclopedic Dictionary

• - photomultiplier, - amplifier of weak photocurrents, action to-poro main. on secondary electron emission; a type of photoelectronic device. Basic PMT units: photocathode emitting electrons under the influence of optical...

  Big Encyclopedic Polytechnic Dictionary

• - see Secondary electron multiplier...

  Big Encyclopedic Polytechnic Dictionary

• - an electronic device designed to increase the frequency of periodic electrical oscillations supplied to it by an integer number of times. The ratio fout/fin is called the frequency multiplication factor m...
• - an electric vacuum device in which the flow of electrons emitted by the Photocathode under the influence of optical radiation is amplified in the multiplying system as a result of secondary electron emission...

  Great Soviet Encyclopedia

• - an electronic device for enhancing the flow of electrons based on secondary electron emission...

  Great Soviet Encyclopedia

• - radio-electronic device to increase by an integer factor the frequency of periodic electrical oscillations supplied to it...
• - an amplifier of weak photocurrents, the action of which is based on secondary electron emission. PMT structural units: photocathode, dynodes and anode-collector...

  Large encyclopedic dictionary

• - multiply/tel-det/ctor,...

  Together. Apart. Hyphenated. Dictionary-reference book

• - MULTIPLIER, multiplier, husband. In the expression: a frequency multiplier is a transformer that increases the frequency of an alternating...

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• - ...

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Chapter Six High Frequency Currents. Resonance transformer. Is electric current safe? Tesla's lecture on high frequency currents

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From the book Security Encyclopedia author Gromov V I

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Frequency multiplier

author Team of authors

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Photomultiplier tube

From the book Great Encyclopedia of Technology author Team of authors

Photomultiplier Photomultiplier A photomultiplier is an electric vacuum device in which the flow of electrons emitted by the photocathode under the influence of optical radiation is enhanced in the multiplying system as a result of secondary electron emission; circuit current

Frequency deviation

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1.3.2. Frequencies

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SEMICONDUCTOR FREQUENCY MULTIPLIERS

Communication, communication, radio electronics and digital devices

SEMICONDUCTOR FREQUENCY MULTIPLIERS 17. Transistor frequency multiplier 17. Diode frequency multipliers 17. Purpose operating principle and main parameters Frequency multipliers in the block diagram of the radio transmitter, see.

Lecture 1 7 . SEMICONDUCTOR FREQUENCY MULTIPLIERS

1 7 .2. Transistor frequency multiplier

1 7 . 4 . Control questions

17.1. Purpose, principle of operation and main parameters

Frequency multipliers in the block diagram of a radio transmitter (see Fig. 2.1) are located in front of the power amplifiers of RF or microwave oscillations, increasing the frequency of the exciter signal by the required number of times. Frequency multipliers can also be part of the exciter or frequency synthesizer itself. For the input and output signal of the frequency multiplier we write:

(17.1)

where n frequency multiplication factor by an integer number of times.

Classification of frequency multipliers is possible according to two main criteria: the principle of operation, or the method of implementing the function (17.1), and the type of nonlinear element. According to the principle of operation, multipliers are divided into two types: based on synchronization of the frequency of the self-oscillator external signal(see section 10.3), in P times lower in frequency (Fig. 17.1, a), and using a nonlinear element that distorts the input sinusoidal signal, and isolating the required harmonic from the resulting multi-frequency spectrum (Fig. 17.1, b).

Rice. 17.1. Frequency multipliers.

Based on the type of nonlinear element used, frequency multipliers of the second type are divided into transistor and diode.

The main parameters of the frequency multiplier are: frequency multiplication factor n ; output power nth harmonic Р n, 1st harmonic input power R 1, conversion factor K pr = P n / P 1 ; efficiency = Р n / Р 0 (in the case of a transistor multiplier), the level of suppression of spurious components.

Lack of frequency multipliers (Fig. 17.1, A ) The first type consists in narrowing the synchronization band with increasing harmonic number P. For frequency multipliers of the second type, the conversion coefficient decreases To pr with increasing p. Therefore, they are usually limited to the value n = 2 or 3 and, if necessary, turn on several frequency multipliers in series, alternating them with amplifiers.

17.2. Transistor frequency multiplier

The circuit of a transistor frequency multiplier (Fig. 17.2) and the method of calculating it are practically no different from an amplifier.

It is only necessary to configure the generator output circuit to n th harmonic and select the cutoff angle value =120  / n , corresponding to the maximum value of the coefficient n ( ). When calculating the output circuit, the expansion coefficient of the cosine pulse in the 1st harmonic 1 ( ) should be replaced by the coefficient for nth harmonic  n ( ). A circuit in the output circuit tuned in resonance with n - and signal harmonics, must have satisfactory filtering properties.

Rice. 17.2. Transistor frequency multiplier circuit.

The multiplication factor of the circuit in Fig. 17.2 usually does not exceed 34 times with an efficiency of 1020%.

17.3. Diode frequency multipliers

The operation of diode frequency multipliers is based on the use of the nonlinear capacitance effect. The latter uses a reverse-biased barrier capacitance p - n -transition. Semiconductor diodes, specially designed for frequency multiplication are called varactors. At =0.5 and  0 =0.5 V for the nonlinear capacitance of the varactor we obtain:

, (17.2)

where and - reverse voltage applied to p - n junction.

The graph of the nonlinear function (17.2) is shown in Fig. 17.3.

Rice. 17.3. Graph of nonlinear function (17.2).

The charge accumulated by a nonlinear capacitance is related to voltage and current by the following dependencies:

, (17.3)

Two main circuits of diode frequency multipliers with varactors are shown in Fig. 17.4.

Rice. 17.4. Diode frequency multipliers with varactors.

In the parallel diode multiplier circuit (Fig. 17.4, A ) there are two circuits (or filters) of a series type, tuned in resonance accordingly with the frequency of the input and output n  signals. Such circuits have low resistance to resonant frequency and large - on all the others (Fig. 17.5).

Rice. 17.5. Dependence of circuit resistance on frequency.

Therefore, the first circuit, tuned to resonance with the input signal frequency o, passes only the 1st harmonic of the current, and the second circuit, tuned to resonance with the output signal frequency n  , - only n th harmonic. As a result, the current flowing through the varactor has the form:

, (17.4)

Since the varactor capacitance (17.2) is a nonlinear function, then according to (17.3) at current (17.4) the voltage on the varactor is different from the sinusoidal shape and contains harmonics.

One of these harmonics, to which the second circuit is tuned, passes into the load.

Thus, with the help of a nonlinear capacitance, the device converts signal power with frequency into a signal with frequency n , i.e. frequency multiplication.

The second sequential frequency multiplier circuit works in a similar way (Fig. 17.4, b), in which there are two circuits (or filters) of parallel type, tuned into resonance according to the frequency of the input and output n  signals. Such circuits have high resistance at the resonant frequency and low resistance at all others. Therefore, the voltage on the primary circuit, tuned in resonance with the frequency of the input signal , contains only the 1st harmonic, and on the second circuit, tuned to resonance with the frequency of the output signal n  , - only n th harmonic. As a result, the voltage applied to the varactor has the form:

, (17.5)

where U 0 - constant bias voltage on the varactor.

Since the varactor capacitance (17.2) is a nonlinear function, then according to (17.3) at voltage (17.5) the current flowing through the varactor is different from the sinusoidal shape and contains harmonics. One of these harmonics, to which the second circuit is tuned, passes into the load. Thus, with the help of a nonlinear capacitance in the circuit, the signal power is converted with a frequency into a signal with frequency n , i.e. frequency multiplication.

Varactor frequency multipliers in the DCV range at n =2 and 3 have a high conversion factor K pr = P n / P 1 = 0.6…0.7. For large values P in the microwave range value K pr decreases to 0.1 and below.

17.4. Control questions

1. How is the frequency of oscillations multiplied?

2. Draw a circuit of a transistor frequency multiplier.

3. Explain why it is possible to multiply the oscillation frequency using a nonlinear capacitance.

4. Draw circuits of diode frequency multiplier of series and parallel type. What are the differences between them?