Radio frequency amplifier. Radio frequency amplifier (yrt). UPUs with focused selection filter

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.

Basic requirements and qualitative indicators

1. Resonant voltage gain coefficient

Or by power

where G. in G. N - active components of the conductors of the input and load of the amplifier.

2. Frequency selectivity - mainly on the mirror channel of superhyterodyne receivers (
).

3. Noise coefficient yrwhich largely determines the ability of the receiver to reproduce useful information at low levels of the received signal. From the point of view of the minimum level of noise, it is enough to ensure that the reinforcement coefficient for yrth power was at the level of 10-100, so the required number of cascades usually does not exceed two.

4. Sustainability, characterizes the absence of self-excitation of the amplifier.

In addition, yrch in its indicators should ensure the amplification of signals in a certain dynamic range with distortions that do not exceed the specified level.

Considering that the URR operates in the amplification mode of weak signals, we will consider an amplifying device with a linear active 4-pin.

Resonance amplifying cascade of moderately high frequencies

In the range of moderately high frequencies ( f. < 300 MHz) To describe the properties of amplifying cascades, it is convenient to use the system Y.-Parameters in which the equation of the linear 4-pole is recorded in the form (5.1)

(5.1)

where , and ,- voltages and currents at the inlet and outlet of the 4-poles, respectively,

- Parameters in short circuit mode at the input and output of the 4-pole.

The most general scheme of the resonant cascade can be presented in the form (Fig. 5.1).

The figure shows the scheme of the resonant amplifier in which to the contour L.C. partially connected as a transistor output Vt. 1, so the entrance of the next cascade on the transistor Vt. 2 . In both cases, autotransformer communication is used. However, in such an amplifier, these links can be implemented by another known method, for example, transformer.

Elements R. 1 , R. 2 , ,used to set the operation mode of the operation Vt. 1 dC. Required filtration for nutrition is carried out by filter R. F. , C. F. . The calculation of these elements is made similarly as it is done for aperiodic amplifiers. Therefore, the questions of the working point of the resonant amplifiers are not considered here.

Regardless of the type of connection of the amplifying device with a resonant circuit, the resonance amplifier can be represented as the following equivalent circuit (Fig. 5.2).

From the equivalent scheme presented it follows that

(5.2)

When using double autotransformer communication, the conductivity of the load can be represented as

, (5.3)

where,
.

The voltage gain coefficient can be obtained if you use expressions (5.1) and (5.2). Taking into account these expressions, you can get

(5.4)

From the last expression you can get

(5.5)

Where do you get

, (5.6)

where - complete equivalent performance of the contour.

The resonant properties of the cascade are determined by the frequency response
, and the latter corresponds to the resonant characteristic of the oscillating circuit LC. The equivalent resistance of the oscillatory circuit included in the collector circuit of the transistor can be represented as follows.

Full equivalent contour resistance
can be represented

, (5.8)

where
-Beed contour frustration.

The coefficient of amplification of the cascade on the resonant frequency can be represented as

, (5.9)

where
.

- The transformation coefficient from the output of the first active element before the input of the following.

Taking into account this, for the resonant cascade, we obtain the following expression for the gain.

(5.10)

According to the structure, the resulting formula corresponds to the formula to determine the coefficient of amplification of the aperiodic cascade, only a resonant contour is used as the load in the latter.

Since the radio frequency amplifier is at the input of the radio receiver, then its noise characteristics and dynamic range are mainly determined by the characteristics of the entire device as a whole. It is the noise coefficient of the radio frequency amplifier determines the sensitivity of the radio.

The gain of signals in the receiver can occur to the frequency converter, i.e. At the received frequency, and after the converter - at an intermediate frequency. The gain at the frequency of the received signal is carried out using radio frequency amplifiers (yrts). In addition to gain, frequency selectivity should be provided. Rangery must have circuits with variable settings. They are most often performed by one-contact. An active element of the amplifier is a field or bipolar transistor in a discrete or integral version. In an intermediate frequency amplifiers, preference is given to bipolar transistors due to the provision of a higher gain coefficient. Radio Frequency Amplifiers are raising selectivity on the mirror channel and the sensitivity of the receiver. According to the circuit structure of the URR, can be aperiodic or resonant.

Aperiodic yrch Only the ratio of the SIG-DOW / noise and sensitivity of the receiver increase. The most commonly applied in transistor receivers of direct gain on two and bonds. As a load of aperiodic yrt, a throttle, a resistor or transformer can be served. The CAS-CAS CAM is simple in execution and configuration. In the transformer yarch) facilitates the coordination of the output of one thing cascade with the subsequent entrance. In addition, the transformer cascade of yrts can be easily remade into reflex.

Resonant yrchprovide a signal amplification and are in-out not only real sensitivity, but also selectivity on the mirror channel Transistor resonance yrts in DV bands, BC and KB are collected according to the scheme with OE A in the VHF band - according to the scheme with about.

Cascades of the URR may contain one or two resonant constructions. The radio frequency amplifier with one contour gives a smaller power, but more simple in manufacturing and configuring. Schemes with inductive contour links allow you to change the connection and get the greatest gain or better selectivity. By changing the connection over the range, you can somewhat compensate for the non-uniformity of the co-emission of the input circuits.

Radio frequency amplifiers of the VHF range are performed by cascading schemes. They have the best characteristics than ordinary yrts. The first trans-zistor is included according to the OE scheme, due to which the small input conductivity of the amplifier is achieved, and the second V2 - according to the scheme with the scheme, which ensures a large coefficient of stable gain. According to the per-junc current, the transistors are included in series, which causes the need to increase the power supply voltage.

By strengthening a cascoid amplifier is equivalent to a single-stage amplifier with a direct transmission conductivity of the first transistor and the load of the second. The cascading scheme is used in the strength of the range of meter waves. The first cascade of the scheme is beneficial to be fulfilled on the field of transistor, which has a low noise level and small "anti-input conductivity, the electoral receiver selective system will be shortened, is included at the inlet of the cascading amplifier. In the second stage, it is preferred by a drift transistor, included according to the scheme with respectively and providing the greatest steady gain. With this execution of the amplifier's cascading scheme, its coefficient of stable amplification increases, the level of noise is significantly reduced, the selectivity of the receiver's radio signal path increases, which is their advantage.

Similar advantages have cascading schemes (low noise levels and high coefficient, stable strengthening) on \u200b\u200belectronic lamps, usually the total cathode included in the circuit - the overall grid.

Radio Frequency Amplifiers and Intermediate Radio Receiver Frequency

Name of parameter	Value
Theme of article:	Radio Frequency Amplifiers and Intermediate Radio Receiver Frequency
Rubric (thematic category)	Communication

Strengthening received radio signals in the receiving device is carried out in its preset, ᴛ.ᴇ. On radio frequency, and after the frequency converter - at an intermediate frequency. Accordingly, radio frequency amplifiers (yrts) and an intermediate frequency amplifiers (UPCs) are distinguished. In these amplifiers, the frequency selectivity of the receiver should be ensured together with the gain. For this, the amplifiers contain resonant chains: single oscillatory circuits, filters on linked contours, various types of filters of focused selectivity. Radio frequency amplifiers with variable settings are usually performed with a selective system similar to the receiver in the input chain, more often this is one-contact election chains.

In the intermediate frequency amplifiers, complex types of electoral systems, having accommodation, are close to rectangular, such as electromechanical filters (EMF ), quartz filters (CF), filters on surface (volumetric) acoustic waves (surfactants), etc.

Most modern receivers use single-circuit yrts. Less often, with high selection requirements and noise ratio, yrch may contain up to three cascades.

The basic electrical characteristics of amplifier include:

1. Resonance voltage gain coefficient .

At ultra-high frequencies (microwave), the concept of power gain is more often used, where - active component of the input conductivity of the amplifier; - active component of the conductivity of the load.

2. Painful selectivity amplifier Shows a relative reduction in gain with a given detachment.

Sometimes selectivity is characterized by a rectangulation coefficient, for example,.

3.Ceefficient Noise Defines the noise properties of the amplifier.

4. Signal in Amplifier: amplitude-frequency, phase, nonline.

5. Resistance to the work of the amplifier It is determined by its ability to maintain the main characteristics during operation (usually to O and ACH), as well as the lack of a tendency to self-excitation.

Figure 1-3 shows the basic schemes of the URR, and in Fig. 4, the execution scheme with a selective focus filter (FSI) in the form of an electromechanical filter.

Fig.1. Yrt on the field transistor

Fig.2. Yrt on bipolar transistor

Fig.3. Urch with inductive communication with the electoral system

Fig.4. UPUs with filter focused selectivity

In radio frequency and intermediate frequency amplifiers, two options for inclusion of an amplifying device are mainly used: with a common emitter (common source) and a cascading circuit on transistors.

Figure 1 shows the amplifier scheme on the field transistor with a common source. In the drain circuit included the oscillating circuit L to C C.The outline is configured by a capacitor with TO (Can be used to adjust the circuit of a varicap or a varicapable matrix).

In the amplifier, used sequential power supply through the filter R3C3.Shifting voltage VT1.determined by the voltage drop from the source current on the resistor R2. Resistor R1is the drainage resistance of the transistor VT1.and serves to transmit the bias voltage to the transistor's shutter.

In fig. 2 shows a similar yrket diagram on a bipolar transistor. A double incomplete inclusion of the circuit with transistors VT1, VT2 is applied here, which makes it possible to provide it extremely important e contour by the outlet side of the VT1 transistor output from the entry side of the VT2 transistor . The supply voltage to the transistor collector is served through the R4C4 filter, the turnout of the coil contour L K.DC mode and temperature stabilization is provided with resistors R1, R2 and R3. Capacity C2.eliminates negative feedback on variable current.

In fig. 3 shows a diagram with a transformer circuit with a transistor collector and an autotransformer communication with the next stage input. Usually, in this case, use, "extended" circuit setting (see Lab. Work No. 1).

In fig. 4 shows the scheme of the Cascade of the OSCE with the FSI, made on the microcircuit 265 of UVZ . The microcircuit is a Cascian amplifier OE - about.

Intermediate frequency amplifiers provide the main strengthening and detectivity of the receiver on the SOS. Their important feature is that they work at a fixed intermediate frequency and have a big strengthening, order.

When using various types of FSI, the required increase in the OEX is achieved by using broadband cascades.

Common for all circuits is the double incomplete inclusion of the electoral system. (Complete inclusion can be considered as a special case when the transformation coefficients M and N are equal to one). For this reason, one generalized equivalent amplifier substitution scheme can be used to analyze (see Fig. 5).

Fig.5. Generalized equivalent chart of resonant amplifier

The transistor on the output side is replaced by an equivalent current generator with parameters, and a current, and from the entry side of the next cascade conductivity ,. R4 leak resistor (Fig. 1) or divider (Fig. 2) is replaced by conductivity (or).

Usually the amount of conductivity is considered conduction of the load GN, ᴛ.ᴇ.

An analysis of the equivalent scheme allows you to get the estimated relationships to determine the characteristics of the cascade.

Thus, the complex coefficient of amplification of the cascade is determined by the expression

equivalent contour resonant conductivity;

Generalized contour disorder.

From this ratio it is easy to define the coefficient module

strengthening

and resonant gain of the urch cascade

The resonant gain reaches its maximum value with the same contour shunting from the output side of the active instrument and on the load side (the input of the next cascade), ᴛ.ᴇ. when

The proposed ratios allow to obtain the equation of the resonant amplifier curve. So, with low disorders ,. From where, the bandwidth of the yrh brief 0.707 (- 3dB) is equal

The resonant coefficient of strengthening of the OSCE aluminum cascade is the same as the one-circuit yarch

For UPUs with a two-circuit strip filter, the resonant coefficient of amplification of the cascade is determined by the expression

where - communication factor between contours, and the communication coefficient between contours.

The gain (voltage) coefficient of ECUs with any FSI when applying the filter at the input and output should be calculated by the formula

Here, - characteristic (wave) FSI resistance in the input and output, respectively;

Filter transmission coefficient in transparency (transparency).

In the event that if you know the filter attenuation in the transparency of the transparency of the vadizibelch, then

Inclusion coefficients M.and n.calculate from the condition for matching the filter at the entrance and output

The resonant characteristic of the CSC Cascade with the FSI is fully determined by the change coefficient change curve FS.from frequency. Separate points of the resonant curve FS.set in reference books.

The gain of the selective amplifier should not exceed the value of the sustainable gain coefficient. In general, it can be estimated from an expression

If a cascading scheme is used as an amplifying element, then it is extremely important to substitute the corresponding conductivity values \u200b\u200bfor the cascading scheme for example, for the OE scheme

In the case of using field transistors of the active component of conductivity, you can neglected and

Radio frequency amplifiers and intermediate frequency radios - concepts and types. Classification and features of the category "Radio Frequency Amplifiers and Intermediate Radio Receiver" 2017, 2018.