Amplifiers of electrical signals parametric amplification. Dual-circuit parametric amplifier

Parametric amplifier

an electronic device in which the power signal is amplified at the expense of energy external source(the so-called pump generator), periodically changing the capacitance or inductance of a nonlinear reactive element electrical circuit amplifier. P. at. used mainly in radio astronomy (see Radio astronomy), long-range space and satellite communications and radar (see Radar) as a low-noise amplifier weak signals, arriving at the input of the radio receiving device, mainly in the microwave range. Most often in P. at. A parametric semiconductor diode (PPD) is used as a reactive element. In addition, in the microwave range, P.U. is used. Operating on electron-beam lamps, and in the region of low (sound) frequencies, P. at. with a ferromagnetic (ferrite) element.

The most widespread are two-frequency (or double-circuit) P.U .: in the centimeter range - regenerative "reflective amplifiers with frequency preservation" ( rice. , a), at decimeter waves - amplifiers - frequency converters ( rice. , b) (see Parametric excitation and amplification of electrical oscillations). As a receiving oscillatory circuit and an oscillatory circuit tuned to an auxiliary, or "idle" frequency (which is most often equal to the difference or the sum of the frequencies of the signal and the pump generator), in the P. at. cavity resonators are usually used (see cavity resonator) , inside which the PPD is located. Avalanche-transit semiconductor diode, Gunn diode, varactor are used in pump generators.

ny Frequency multiplier and less often reflective Klystron. The pumping frequency and "idle" frequency are chosen in most cases close to the critical frequency f kp PPD (i.e., to the frequency at which the PA ceases to amplify); in this case, the signal frequency should be much lower f kp. To obtain the minimum noise temperatures (see Noise temperature) (10-20 K or less), P.C. is used, cooled to temperatures of liquid nitrogen (77 K), liquid helium (4.2 K), or intermediate temperatures (usually 15-20 TO); at uncooled P. at. noise temperature 50-100 K and more. The maximum achievable gain and bandwidth of the P. at. are mainly determined by the parameters of the reactive element. P. at. with power amplification factors of the received signal equal to 10-30 db, and bandwidths of 10-20% of the carrier frequency (see Carrier Frequency) of the signal.

Lit .: Etkin VS, Gershenzon EM, Parametric microwave systems on semiconductor diodes, M .. 1964; Lopukhin VM, Roshal AS, Electron-beam parametric amplifiers, M., 1968; Microwave - semiconductor devices and their application, trans. from English, M., 1972; Kopylova K.F., Terpugov N.V., Parametric capacitive amplifiers low frequencies, M., 1973; Penfield P., Rafuse R., Varactor applications, Camb. (Mass.), 1962.

V. S. Etkin.

Equivalent circuits of parametric amplifiers: a - regenerative; b - "with upward conversion"; u in - input signal with a carrier frequency f c, u n - "pumping" voltage; u out1 - output signal with carrier frequency f c; u out2 - output signal with carrier frequency (f c + f n); Tp 1 - input transformer; Tr 2 - output transformer; Tr 2 - transformer in the "pump" circuit; D - parametric semiconductor diode; L - inductance coil of the oscillatory circuit tuned to the frequency (f c + f n); F s, F sn, F n - electrical filters having low impedance, respectively, at frequencies f c, (f c + f n), f n and sufficiently large at all other frequencies.

Big Soviet encyclopedia... - M .: Soviet encyclopedia. 1969-1978 .

See what "Parametric amplifier" is in other dictionaries:

An electronic device, in which the signal is amplified in terms of power due to external energy. source (so-called pump generator), periodically changing the capacity or inductance of a nonlinear reactive element amplifier circuits ... Physical encyclopedia

Big Encyclopedic Dictionary

parametric amplifier- - Topics telecommunications, basic concepts EN parametric amplifier ...

An amplifier of electrical oscillations, in which the main (amplifying) element is most often a varicap. Compared with conventional amplifiers has a significantly lower level of intrinsic noise. Used to amplify weak signals ... ... encyclopedic Dictionary

parametric amplifier- parametrinis stiprintuvas statusas T sritis automatika atitikmenys: angl. parametric amplifier vok. Parameterverstärker, m; parametrischer Verstärker, m rus. parametric amplifier, m pranc. amplificateur paramétrique, m ... Automatikos terminų žodynas

parametric amplifier- parametrinis stiprintuvas statusas T sritis fizika atitikmenys: angl. parametric amplifier vok. parametrischer Verstärker, m rus. parametric amplifier, m pranc. amplificateur paramétrique, m ... Fizikos terminų žodynas

Amplifier electr. signals, in addition, the signal power increases due to the energy of the source, which periodically changes the value of the reactive parameter of the system (usually capacity). P. at. differs in a very small level of int. noise. Used in ... ... Big Encyclopedic Polytechnic Dictionary

parametric light amplifier- parametrinis šviesos stiprintuvas statusas T sritis radioelektronika atitikmenys: angl. light parametric amplifier vok. Lichtparameterverstärker, m rus. parametric light amplifier, m pranc. amplificateur paramétrique de lumière, m ... Radioelektronikos terminų žodynas

electron beam parametric amplifier- EPU A microwave device based on a fast cyclotron wave, in which the transverse kinetic energy of the electron beam is amplified in a pump resonator located between the input and output communication devices. [GOST 23769 79] Subjects devices ... ... Technical translator's guide

Electron beam parametric amplifier- 61. Electron beam parametric amplifier A microwave device based on a fast cyclotron wave, in which the transverse kinetic energy of the electron beam is amplified in a pump resonator, ... ... Dictionary-reference book of terms of normative and technical documentation

Consider a variable capacitor

,

varying under the action of the pump voltage u n(t) = U n cos ( w n t). Let an alternating voltage be applied to this capacitor u C(t) = U 1 cos ( w 1 t + j), then the capacitive current will be

Thus, the current spectrum contains components with frequencies w 1 , w n + w 1 and w n - w 1 . These frequencies can be distinguished using sufficiently high Q contours tuned to frequencies w 1 and w 2 = w n ± w 1 and connected by a common nonlinear capacitance (Fig. 65).

Impedance losses in the first circuit will be R 1 = R" 1 ||R i(where R i- internal resistance of the signal source). Let this circuit be tuned to a frequency close to the frequency of the amplified signal, i.e. n 1 " w 1 . Accordingly, the second circuit L 2 C 2 R 2 tuned to frequency w 2 = w n ± w 1 (n 2 " w 2). Consider the case when the partial frequencies n 1 and n The 2 contours are far from each other so that the connectivity is small. In this case, the normal frequencies are close to the partial ones (the shift between the partial and the corresponding normal frequencies is small and we can assume that it lies in the passband of the circuits, i.e., each circuit resonates at its own frequency). Thus, the circuit will sharply increase its frequency, and weaken the rest.

With a sufficiently high Q-factor of the circuits, the resistances of each circuit for frequencies far from its partial frequency are practically zero. Thus, the circuit is an active load only in a small frequency range near its partial frequency. In the scheme we are considering in the main circuit, active power can be released only at a frequency w 1, and in an additional one - at one of the frequencies w 2 = w n ± w 1 . Thus, since we can track only one frequency in each circuit, then for these frequencies we write down the harmonic balance equations

(7.20)

Let a varicap be taken as a nonlinear capacitance. Then, as you know,

.

Insofar as u C = u 1 + u n - u 2, then, within the framework of harmonic balance, we must put u n = A n cos ( w n t), u 1 = A 1 cos ( w 1 t + y 1), u 2 = A 2 cos ( w 2 t + y 2) (phases y 1 and y 2 are measured from the pump voltage). Substituting these expressions into the expression for the charge, we obtain the relations for the components of the charge on the container C at frequencies w 1 and w 2:

In this case, the harmonic balance equation (7.20) under the influence of a harmonic signal i 1 = I 1 cos ( w 1 t + j) takes the form:

Let's simplify these expressions a little by introducing the partial frequencies n 1 and n 2, detunings x 1 and x 2, Q factor Q 1 and Q 2 amplifier circuits:

,  ;  ,  ;

,  .

Then, in this notation, equation (7.21) takes the form

The resulting ratio must be fulfilled at any time, therefore, in it, the coefficients at cos ( w 1 t + y 1) and sin ( w 1 t + y 1). We put on the right side j = y 1 + (j - y 1); ± y 2 = y 1 + (± y 2 - y 1), then after simple trigonometric transformations of the right-hand side, we get

We square (7.25) and (7.26) and add, then we can get

Recall that the upper sign corresponds to the case w 2 = w n + w 1, and the lower one is w 2 = w n - w 1 . The resulting expression shows that the amplitude of the low-frequency pumped parametric amplifier ( w n = w 2 - w 1) significantly differs from the amplitude of the high-frequency pumped amplifier ( w n = w 2 + w 1). Let us now consider each of these cases separately.

In the first case (when converting upward), the exact maximum signal will be achieved as a result of fine tuning of the contours, i.e. x 1 = x 2 = 0. In this case, the amplitudes of oscillations in the first and second circuits:

,  .	(7.29)
Rice. 66. Dependence of amplitudes A 1 and A 2 on the pump amplitude A n when fine tuning the amplifier circuits.	In fig. 66 depicts dependence A 1 and A 2 from A n when fine tuning the amplifier circuits. It can be seen from the figure that the amplitude of oscillations in the first loop decreases monotonically as the pump amplitude increases. Thus, in this case, there is no signal amplification in the first loop. However, the amplitude of oscillations in the second loop is proportional to the amplitude of the input signal at A n< A 0 grows with growth A n... Therefore, in the system, amplification with frequency conversion upward is possible if, as

the output signal to use the oscillations in the second amplifier circuit. Such an amplifier is a non-regenerative parametric amplifier with frequency up conversion. Let's determine the coefficient of its power amplification. By the power gain we mean the ratio of the power at the amplifier output to the input signal power released at the matched load. If the losses of the primary circuit are small enough and R i << R"1, then R 1 " R i and input source i 1 supplies power to the matched load n 1 = n 2. Thus, the increase in power is associated only with an increase in the frequency of quanta, and not their number, so the noise of such an amplifier is minimal and it is quite stable.

Amplifier with frequency conversion down ( w 2 = w n - w 1) is a conventional regenerative amplifier and does not offer any advantages over the regenerative mode of a single-loop amplifier.

It was found that, under certain conditions, parametric elements are able to play the role of active elements in the circuit. This makes it possible to create on their basis parametric amplifiers, which have a low level of intrinsic noise, since there is no current noise in them due to the shot effect. Parametric amplifiers are mainly used in the microwave range as input stages of high-sensitivity radio receivers.

In the 50s of the 20th century, the first semiconductor parametric diodes ( varactors). Parametrically controlled nonlinear capacitances and inductances were studied in Section 2.3.

Single-loop parametric amplifier. A schematic diagram of such an amplifier is shown in Fig. 6.8, a, and the equivalent is in Fig. 6.8, b.

Dependence of the parametric capacitance on the harmonic pump signal at the frequency
:

Conductivity
is introduced into the equivalent circuit of the amplifier by a parametric change in the capacitance by a pump signal. Input signal - harmonic current generator with amplitude , frequency and internal conductivity
.,
- load conductivity. To implement parametric amplification with maximum power release on load conduction, the following conditions must be met:

(6.27)

where
;

(6.29)

since the voltage amplitude at the generator terminals is equal, and active power is released in the load
.

If there is no pump signal, then power is released in the load

(6.30)

moreover
, because
.

Nominal power gain parametric amplifier is called the quantity

(6.31)

for example if
Cm,
See then.

The critical value of the introduced negative conductance, when the parametric amplifier loses stability and self-excites,

(6.32)

Under conditions (6.32), the negative conductivity of the varactor fully compensates the sum of the conductivities of the input generator and the load. The parametric amplifier works stably if
, if
, then the amplifier is self-excited and turns into a parametric oscillator.

Let the phase relations of the oscillations of the input signal and pumping be optimal so that in (6.27)
... Then from (6.27) and (6.32) we find the critical modulation depth of the parametric capacitance by the pump signal:

(6.33)

Consider the parametric gain in detuning mode. Synchronism condition:
, it is almost impossible to accurately execute. Let be
is the frequency offset of the input signal, that is
... If
, then the amplifier works in asynchronous mode. Then the value of the phase shift
, which determines the conductivity introduced into the circuit, depends on the time: The introduced resistance changes as

(6.34)

periodically changing the sign to the opposite over time.

The result is a deep beating-like change in the output level. This disadvantage prevents the use of single-loop amplifiers in practice.

Dual-circuit parametric amplifier. Free from the indicated disadvantage dual-loop parametric amplifier, the diagram of which is shown in Fig. 6.9.

The amplifier consists of two oscillatory circuits, one of which is tuned to the frequency ... This circuit is called signal. Another circuit called single, tuned to idle frequency
... The connection between the circuits is achieved through the parametric capacitance of the varactor. The pump signal changes the parametric capacitance harmonically at the pump frequency
:

Both oscillatory circuits - signal and idle - are of high Q. Therefore, in the stationary mode, the voltages on these circuits are approximately harmonic:

(6.36)

According to fig. 6.9, tension on the varactor
... Then the current through the varactor

(6.37)

Since, the signal spectrum (6.37) contains components at the signal frequency
, at idle frequency
, as well as at combination frequencies
and
... A varactor and an idle loop connected in series to the signal loop can be replaced in an equivalent circuit by the conduction introduced into the signal loop. To find this conductivity, it is necessary to select in (6.37) the current component at the signal frequency:

In (6.38), the first term is shifted with respect to the voltage
in phase at
... Therefore, due to it, there is no active conduction in the signal circuit. The second term at the signal frequency proportional to the amplitude
open circuit voltage. Let's find the value
... To do this, select in the varactor current (6.37) the useful component at the idle frequency, proportional to
:

(6.39)

Let be
- resonant resistance of the idle circuit. The voltage across it caused by fluctuations at the frequency
,

whence, comparing with the second expression in (6.36), we obtain:

(6.41)

Substitute expressions (6.41) into the second term in (6.38). We obtain the expression of the useful current component at the signal frequency due to the influence of the varactor and the idle circuit:

Conductance introduced into the signal circuit by serial connection of the varactor and the idle circuit,

(6.43)

turns out to be active and negative.

Next, you can calculate the nominal gain of the dual-circuit parametric amplifier using the formula (6.31). The analysis of the stability of the operation of a double-circuit amplifier is carried out in the same way as for a single-circuit amplifier. Let's compare the expression

(6.27)

for a single-circuit amplifier and (6.43) - for a double-circuit amplifier, we find that in a double-circuit amplifier, the introduced conductance, in contrast to a single-circuit amplifier, does not depend on the initial phases of the input signal and pumping. In addition, a dual-loop amplifier, unlike a single-loop amplifier, is not critical to the choice of signal frequencies and pumping
... The introduced conductance will be negative if
.

Output.A double-loop amplifier is capable of operating at an arbitrary ratio of the signal and pump frequencies, regardless of the initial phases of these oscillations. This effect is due to the use of auxiliary vibrations arising at one of the combination frequencies.

Power balance in multi-circuit parametric systems. Phase insensitivity allows you to study: multi-circuit parametric systems based on energy relationships. An equivalent circuit of a two-circuit parametric amplifier is shown in Fig. 6.10.

Here parallel to nonlinear capacitance
included three bipolar. Two of them contain the signal and pump sources, and the third forms an idler circuit tuned to the combinational frequency
, where
and - whole numbers. Each of the three two-port networks contains a narrow-band filter tuned to frequencies ,
and
, respectively. Simplifying the problem, we assume that the signal and pump circuits have no ohmic losses. If one of the sources (signal or pump) is absent, then the components at the combination frequencies in the current flowing through the nonlinear capacitor are absent. The no-load circuit current is zero. The system behaves like a reactive system, that is, it does not consume the power of the source on average.

If both sources are present, then the current component appears at the combination frequency
... This current can be closed through an idle circuit. The load on the idle circuit consumes on average power. Active parts of the resistances appear in the signal and pump circuits. Their meanings and signs are determined by the redistribution of capacities between sources. Let us apply to an autonomous (closed) system in Fig. 6.10 law of conservation of energy: the average (over the periods of the corresponding oscillations) power of the signal, pump and combination oscillations are related as

(6.44)

Average power expressed in terms of energy allocated for the period:

where
- frequency.

where
,
and
, or

Execution (6.45) regardless of frequency selection and
is possible only when

(6.47)

In (6.47), we pass from energies to powers, we obtain Manley-Rowe equations:

(6.48)

The Manley-Rowe equations allow studying the laws of power conversion in multi-circuit parametric systems. Let us examine two typical cases.

Upconverted parametric gain. Let in (6.48)
... We have:

(6.49)

The power delivered to the load is positive, while the power delivered to the circuit by the generator is negative. Since in (6.49)
, then
and
(see fig. 6.11).

Output. If the idle circuit of the parametric amplifier is tuned to the combinational frequency
, then both sources - signal and pump, give power to the idle circuit, where it is consumed in the load. Because
, then the power gain is

(6.50)

The advantage of the system under study is such stability that it cannot be excited at any signal and pump power. Disadvantage - the frequency of the output signal is higher than the frequency of the input signal. In the microwave range, this leads to difficulties in signal processing.

Regenerative parametric gain. Let be
,
... Then the frequency of the idle circuit
, and
... The Manley-Rowe equations are:

(6.51)

From the first equation in (6.51) it follows that
and
... This means that some part of the power taken from the pump generator enters the signal circuit. That is, the system has regeneration at the signal frequency. The output power can be extracted from both the signal and the no-load circuit (see Fig. 6.12) ..

The system gain cannot be determined from equations (6.51). Since the power contains both the part consumed from the input generator and the part arising from the regeneration effect. Under certain conditions such amplifiers tend to self-excite. Then, power is released in the signal loop even in the absence of a useful signal at the input.

A schematic diagram of a two-frequency or, as it is often called, a two-loop amplifier is shown in Fig. 10.16. The first, signal, circuit is tuned to the central frequency of the signal spectrum (resonant frequency), and the second, "idle" circuit - to the litter frequency, which is quite different from.

The pumping frequency is selected from the condition

(10.43)

When choosing a frequency, it is assumed that the signal frequency is outside the transparency band of the auxiliary circuit. But the combination frequency must be outside the operating band of the signal loop.

When these conditions are met, only one frequency voltage will exist on the signal loop, and frequencies on the auxiliary loop. Considering the amplitudes of these voltages to be small in comparison with, it is possible to replace the nonlinear capacitance, together with the pump generator, with a linear parametric capacitance varying with frequency, as was done in § 10.5.

Rice. 10.16. Two-frequency parametric amplifier

Then, under the influence of the signal voltage in the variable capacitance circuit, a current arises (in addition to other components that are not of interest in this case)

[cm. 10.36)]. Here .

On the resistance of the open circuit, the current creates a voltage drop

We write down the equivalent EMF acting on the capacitance C, as in § 8.16 [see. (8.99)], in the form

The combination current due to this EMF, by analogy with the expression (10.44), will be

Note that the pump phase and frequency (it is absent in expression (10.45)).

Taking into account the above relation for the last equality can be written in the form

As you can see, with respect to the signal circuit, the nonlinear capacitance, together with the pump generator and the idle circuit, can be replaced by conductivity, taking into account the found current

The complex amplitude of this current

The complex amplitude of the voltage across the signal loop.Therefore, the conductance bypassing the signal loop will be

(10.46)

where is the complex conjugate function of the function

For resonance, when, therefore, the resistance of the auxiliary circuit will be and formula (10.46) takes the form

In the equivalent circuit shown in Fig. 10.17, the elements located to the left of the dashed line correspond to the signal circuit of the amplifier, and to the right - to the nonlinear capacitance together with the auxiliary circuit. The resulting circuit is essentially the same as the single-loop amplifier circuit (see Figure 10.15). The only difference is in the method of determining the equivalent negative conductivity.

Details related to the definition of combinational oscillations are given in order to draw attention to the following advantages of a dual-loop amplifier:

a) the equivalent negative conductance, and hence the power amplification, do not depend on the phase of the pump voltage.

b) compliance with a certain ratio between frequencies is not required

Both of these properties of the two loop amplifier are explained by the fact that the total phase of the combination current in expression (10.45), which determines the nature of the equivalent conductivity, is essentially the phase difference of the pump voltages. The first of them has the form and the second (excluding). When the difference is formed, it drops out, and the difference frequency in any case coincides with the signal frequency (since).

The gain of a double-loop amplifier at a resonant frequency can be determined from an expression similar to formula (10.40):

where is calculated by the formula (10.46), is the conductivity of the load of the signal circuit.

When the signal frequency deviates from the resonant frequency and, accordingly, the frequency from the resistance modulus decreases, which leads to a decrease in the modulus and, consequently, the power amplification factor.

Based on expression (10.46), you can calculate the frequency response and bandwidth of the dual-loop amplifier.

The stability condition for the amplifier in this case can be written in the form

Consider the energy balance in a two-frequency amplifier depending on the frequency ratio Let the frequency and power of the signal at the input of the amplifier be given. Since with an increase in the auxiliary frequency, the modulus of the negative value increases [see. (10.46)], then it also grows [see. (10.48)]. Signal power at the amplifier output

To determine the required power of the pump generator Pson, as well as the power released in the auxiliary circuit, we use the Manley-Rowe theorem. Based on expression (7.104), the following relations can be written:

(The minus sign in the last expression is omitted, since it is obvious that this power is taken from the pump generator.) The power ratio is illustrated in Fig. 10.18. It can be seen from this figure that more power is allocated on the auxiliary circuit than on the signal one. Thus, although the power increases with increasing frequency, the distribution of the power taken from the pump oscillator changes in favor of the frequency.Despite this, they often operate in the mode, since when amplifying a weak signal, it is not the degree of power utilization that matters, but the power ratio

To illustrate the quantitative relationships in a two-frequency parametric amplifier, we give the following example.

Let it be required to amplify a signal at a frequency with a spectrum width

Initial data of the first (signal) circuit: characteristic impedance Ohm; internal resistance of the signal source, bypassing the circuit,; load resistance.

Initial data of the second (idle) circuit: resonant frequency; characteristic impedance Ohm; load resistance.

Before calculating the required variation of the varicap capacitance, we find the limiting conductivity value that can be connected to the signal circuit for a given signal spectrum width

The maximum Q-factor of the signal circuit (when shunting with negative conductivity), obviously, should not exceed

When the resulting conductivity bypassing the first circuit must be at least

In conclusion, let us note the main advantages and disadvantages of the parametric amplifier.

An important advantage of a parametric amplifier is its relatively low noise level compared to transistor or tube amplifiers. In § 7.3 it was noted that the main source of noise in transistor and tube amplifiers is the shot effect caused by the chaotic transfer of discrete charges of electrons and holes (in a transistor). In a parametric amplifier, a similar effect takes place in a device that modulates a parameter. For example, a change in the capacitance of a varicap occurs due to the movement of electrons and holes. However, the intensity of the flow of electricity carriers in a varicap is many times less than in a transistor or lamp. In the latter, the flux intensity directly determines the power of the useful signal released in the load circuit, and in the varicap - just the effect of modulation of the parameter. The weakening of the effect of the shot effect is so significant that in a parametric amplifier the noise level is determined mainly by thermal noise. In this regard, parametric diode cooling to 5 ... 10 is often used.

The disadvantage of a parametric amplifier is the complexity of decoupling the pump and signal circuits.

In the circuit shown in Figure 10.14, a, typical for parametric amplifiers of the meter range, decoupling is carried out using isolation capacitors and blocking chokes. In the microwave range, in which parametric amplifiers are especially widely used, it is necessary to resort to very complex designs that combine in one node a two-frequency oscillatory circuit in the form of hollow resonators, varicap and special decoupling elements (circulator, directional coupler, absorber, barrier filter). These issues are covered in special courses.

PARAMETRIC AMPLIFIER- an electronic device, in which the amplification of the signal in terms of power is carried out at the expense of the energy ext. source (so-called generator pumping), periodically changing the capacity or inductance of the nonlinear reactive element electr. amplifier circuits. P. at. apply Ch. arr. in radio astronomy, distant space. and satellite communications and radar as a low-noise amplifier of weak signals arriving at the input of a radio receiver, mainly. in the microwave range. Most often in P. at. parametric is used as a reactive element. semiconductor diode (PPD). In addition, in the microwave range are used P. at. Operating on electron-beam lamps, in the region of low (sound) frequencies - P. at. with ferromagnet. (ferrite) element.
Naib. two-frequency (or double-circuit) P.U. have become widespread: in the centimeter range - regenerative amplifiers with frequency retention (Fig., a), at decimeter waves - amplifiers - frequency converters (Fig., b)(cm. Parametric generation and amplification of electromagnetic oscillations)... As a foster, they sway. contour and vibrate. circuit tuned to an auxiliary, or "idle" frequency (which is most often equal to the difference or the sum of the frequencies of the signal and the pump generator), in the P. at. usually use cavity resonators, inside to-rykh have PPD.

Equivalent circuits of parametric amplifiers: a- regenerative; b- with frequency conversion "up"; u in - input signal with carrier frequency f with; u c - pump voltage; u out - output signal with carrier frequency f with; other :: - output signal with carrier frequency ( f c + f n ); Tp 1 - input transformer; Tr 2 - output transformer; Tr n - transformer in the pump circuit; D - parametric semiconductor diode; L- the inductor coil of the oscillatory circuit tuned to the frequency ( f n - f with); Fs, F cn, F n - electric filters having low impedance, respectively, at frequencies f with, ( f with ± f n), f n and large enough for all other frequencies.

Pump generators use avalanche diode, Gunn diode, varactor frequency multiplier and less often reflect. klystron. The pumping frequency and "idle" frequency are chosen in most cases close to critical. frequency f cr PPD (that is, to the frequency at which the P. at. ceases to amplify); in this case, the signal frequency should be much lower f cr. To get min. noise temperatures (10 - 20 K and less) are used P. at. cooled to a temperature of liquid nitrogen (77 K), liquid helium (4.2 K) or intermediate (usually 15 - 20 K); at uncooled P. at. noise temperature 20 - 500 K and more. The maximum achievable odds. gain and bandwidth of P. at. are determined in the main. parameters of the reactive element. P. at. with coeff. amplification of the received signal power equal to 10 - 30 dB, and bandwidths of 10 - 20% of the signal carrier frequency.
P. at. are supplanted by transistor low-noise microwave amplifiers, both cooled and uncooled, but continue to be used in the millimeter-wave radio wave range, where they still outperform transistor amplifiers.