RU2280321C2 - Phase locked loop circuit for radio-electronic equipment - Google Patents

Abstract

FIELD: radio-electronics; transceiving equipment for measurement technology.

SUBSTANCE: proposed circuit designed for generating two high-stability waves by applying reference signal across PLL input functions as follows. Applying voltage of output signal arriving from reference oscillator of high-frequency-stability generator and converted voltage of generator being adjusted to mixer inputs sets up voltage across this mixer which is amplified in intermediate-frequency amplifier and supplied to signal input of phase detector whose reference input is supplied with voltage from shift generator. In the process periodic voltage is built up across phase detector output, constant component of this voltage passed through dc amplifier acts upon frequency control of generator being adjusted through low-pass filter thereby bringing its frequency closer to input signal frequency. With frequencies of reference oscillator and generator under adjustment being equal, intermediate frequency becomes equal to shift generator frequency and beat frequency equals zero, that is, circuit functions in lock-on mode. High-power wave at frequency equal to that of reference signal is built up across output of generator under adjustment and low-power waves of upper side band appear at output of single-band amplitude modulator. With phase-modulated signal applied to mixer signal input PPL functions as phase-modulated detector and respective signal is picked off dc amplifier output.

EFFECT: enhanced sensitivity in receiving weak phase- or frequency-modulated signal.

1 cl, 1 dwg

Description

The invention relates to the field of electronics and is intended for use in radio receivers and radio transmitting devices and radio measuring equipment.

Known electrical circuit phase locked loop (PLL) [see Shahgildyan V.V., Lyakhovkin A.A. Phase locked loop systems. - M .: Svyaz, 1972, p.23-24], the input of which receives the oscillation of a highly stable frequency (ω _c ) of a signal generator, consisting of a tunable generator (with a frequency (ω _pg ), a mixer, an intermediate frequency amplifier, a phase detector, a reference generator (with a frequency ω _e ), a direct current amplifier (there are special cases where a direct current amplifier may be absent) and a low-pass filter. In the capture mode, the intermediate frequency (ω _p ) in the known ring is equal to the reference frequency (ω _e , t .e. ω _n = ω _m -ω _c = ω _e). Thus, ca Toth being adjusted in a known ring oscillator is equal to the sum of the input frequency and a highly stable reference oscillator signal frequency (i.e., ω = ω _m + ω _{to e).} The main drawback of the known PLL ring when it is used in the system is the inability to stabilize the frequency of oscillation being adjusted forming generator with a frequency equal to the highly stable frequency of the input oscillation Another disadvantage is the possibility of forming only one frequency of its output oscillation equal to the sum of the frequencies of the input high tabilnogo oscillation frequency and a reference generator (ω _m = ω _c + ω _e).

Closest to the technical nature of the claimed invention is a phase-locked loop (PLL) of electronic equipment, made in the form of a ring FAL [see Shahgildyan V.V., Lyakhovkin A.A. Phase locked loop systems. - M .: Svyaz, 1972, p.15-20], in which a highly stable frequency oscillation of the reference generator is fed to the signal input of a phase detector connected to a DC amplifier (there are special cases where a DC amplifier may be absent). In turn, the DC amplifier is connected by a low-pass filter, and the low-pass filter is connected to the control input of the tunable generator, which is connected to the reference input of the phase detector. This circuit, on the basis of the fact that the oscillation of the reference oscillator is highly stable in frequency, is fed to the signal input of the phase detector, and the frequency of the tunable oscillator in the capture mode is equal to the highly stable frequency of the reference oscillator, which is also taken as a prototype for most of the features. This well-known PLL can already generate, in the capture mode, the output oscillation of a tunable generator with a frequency ω _pg equal to the highly stable frequency ω _{from a} reference generator, and can also be used as a detector of phase-modulated (FM) or frequency-modulated (FM) oscillations. However, the disadvantages of the known PLL are: low sensitivity of reception of weak FM (FM) oscillations and the ability to form only one output oscillation with a frequency equal to the highly stable frequency of the output oscillation (i.e., ω _pr = ω _s ). Moreover, the low sensitivity of receiving FM (FM) oscillations is due to the low slope of the phase detector, proportional to the amplitude of the weak input oscillation.

The technical problem to be solved by the claimed invention is directed is to eliminate these drawbacks, namely, increasing the sensitivity of receiving a weak FM (FM) signal and the ability to increase the number of output highly stable in oscillation frequency. The problem is achieved by the fact that in the well-known phase-locked circuit of automatic frequency control of electronic equipment, containing a reference oscillator of a highly stable oscillation frequency and a phase detector, a DC amplifier, a low-pass filter and a tunable generator connected through a control input, in contrast to her, in the claimed additionally introduced a single-band amplitude modulator, a crystal oscillator, a mixer and an intermediate frequency amplifier s. The output of the tunable generator is connected to the high-frequency input of a single-band amplitude modulator, the modulating input of which is connected to the output of the quartz shift generator. The input of a single-band amplitude modulator is connected to the reference input of the mixer, and the signal input of the mixer is connected to the output of a reference oscillator with a highly stable oscillation frequency. The mixer output is connected through an intermediate frequency amplifier to the signal input of a phase detector, the reference input of which is connected to the output of a crystal shear generator. Moreover, the outputs of the DC amplifier, a tunable generator and a single-band amplitude modulator, each separately, additionally have their taps supplying the corresponding voltage outside the circuit.

The combination of the claimed restrictive and distinctive features allows us to achieve the technical task - to increase the sensitivity of receiving a weak FM (FM) signal and to increase the number of output oscillations highly stable in frequency.

In the inventive PLL, due to the introduction of a mixer, a single-band amplitude modulator, modulated by a quartz shear generator, which is both a generator of the reference voltage of the phase detector, and an intermediate frequency amplifier, while the frequency of the adjustable generator is continuously approaching by changing the DC voltage at the output of the DC amplifier to frequency of the reference generator, an effect is achieved when the frequencies of both generators are compared, and the frequencies of the voltages acting on cial and reference inputs of the phase detector are equal to each other, i.e., capture mode is set.

Thanks to the conversion of the input oscillation in the mixer and the amplification of the converted signal voltage in the intermediate frequency amplifier, the possibility of a significant increase in the voltage amplitude at the signal input of the phase detector is achieved, the value of which becomes much larger than the voltage amplitude at the similar input of the phase detector of the known solution - the prototype. Therefore, an effect is achieved in which the steepness of the phase detector is proportional to the amplitude of the signal voltage and, accordingly, the sensitivity of receiving a weak FM (FM) oscillation of the inventive PLL circuit is significantly higher than that of the well-known prototype solution circuit.

In addition, thanks to the introduction of a single-band amplitude modulator, the inputs of which are oscillations of a tunable generator with a frequency of ω _pg and the modulating voltage of a quartz shear generator with a frequency of ω _q , it is possible to form two oscillations of a highly stable frequency in the capture mode, one of which is the output oscillation of a tunable generator with a frequency of ω _pg = ω _s , and the other with an oscillation of a single-band amplitude modulator with a frequency of ω _OAM = ω _s + ω _q .

Thus, a solution to the problem is achieved.

The drawing shows a functional diagram of the inventive circuit phase automatic frequency adjustment of electronic equipment with an illustration of the voltage in the circuit.

The inventive PLL circuit of electronic equipment contains: a reference generator of a highly stable oscillation frequency - 1; tunable generator - 2 with control input I; single-band amplitude modulator - 3 with a high-frequency input I and with a modulating input II; mixer - 4 with reference I and signal II inputs; intermediate frequency amplifier - 5; quartz shear generator - 6; phase detector - 7 with signal I and reference II inputs; DC amplifier - 8; low pass filter - 9.

Moreover, in the circuit are connected in series: a phase detector 7, a DC amplifier 8, a low-pass filter 9, which is connected to the control input I of the adjustable oscillator 2. Moreover, the output of the adjustable generator 2 is connected to the high-frequency input I of a single-band amplitude modulator 3, modulating input II of which is connected to the output of the quartz shear generator 6; the output of a single-band amplitude modulator 3 is connected to the reference input I of the mixer 4, and the signal input II of the mixer 4 is connected to the output of the reference oscillator of a highly stable oscillation frequency 1. The output of the mixer 4 is connected via an intermediate frequency amplifier 5 to the signal input I of the phase detector 7, the reference input II which is connected to the output of the quartz shear generator 6. In addition, the outputs of the DC amplifier 8, the tunable generator 2 and the single-band amplitude modulator 3, each separately, additionally eyut their bends - outputs, respectively I, II, III, corresponding voltage supply outside the circuit.

The inventive PLL circuit of electronic equipment is used as follows:

1. In the case of using a PLL to receive a weak FM oscillation, a voltage is extracted at the tap - the output of I circuit.

In this case, the oscillation of the reference generator 1, simulating a weak FM (FM) oscillation, in V, equal to:

- среднее значение амплитуды колебания в В;Where

- the average value of the amplitude of the oscillations in In;

t is the time in s;

и ν_c(t) - соответственно средняя и модуляционная составляющие круговой частоты колебания эталонного генератора в рад/с;

and ν _c (t) are the average and modulation components of the circular oscillation frequency of the reference oscillator in rad / s, respectively;

φ _c (t) is the modulation component of the oscillation phase in rad, fed to the signal input II of mixer 4.

The oscillation of the tunable generator 2, in, equal

- среднее значение амплитуды колебания подстраиваемого генератора, в В;Where

- the average value of the amplitude of the oscillation of the tunable generator, in V;

и ν_пг(t) - соответственно средняя и модуляционная составляющие круговой частоты колебания подстраиваемого генератора в рад/с;

- модуляционная составляющая фазы подстраиваемого генератора в радианах,

and ν _pg (t) are the average and modulation components of the circular oscillation frequency of the tunable generator in rad / s;

- modulation component of the phase of the tunable generator in radians,

arrives at the high-frequency input I of a single-band amplitude modulator 3, and at its modulating input II - the voltage of the crystal shear generator, in V, equal to

и

- соответственно среднее значение амплитуды и круговой частоты напряжения u₆(t) кварцевого генератора сдвига 6, измеряемые соответственно в В и рад/с.Where

and

- respectively, the average value of the amplitude and the circular frequency of the voltage u ₆ (t) of the crystal shear generator 6, measured respectively in V and rad / s.

At the same time, at the output of a single-band amplitude modulator 3, an oscillation of the upper lateral frequency, in V, equal to

и

- соответственно среднее значение амплитуды и круговой частоты однополосного амплитудного модулятора 3, соответственно в В и рад/с. Это напряжение поступает на опорный вход I смесителя 4. При одновременной подаче на оба входа смесителя 4, моделируемого его типовым перемножающим устройством с коэффициентом передачи

(не показано), напряжений эталонного генератора 1 и однополосного амплитудного модулятора 3, на его выходе появляется напряжение u₄(t), содержащее составляющие суммарной

и разностной

круговых частот, в В, соответственно, равноеWhere

and

- respectively, the average value of the amplitude and circular frequency of a single-band amplitude modulator 3, respectively, in V and rad / s. This voltage is supplied to the reference input I of the mixer 4. When simultaneously fed to both inputs of the mixer 4, modeled by its typical multiplying device with a transmission coefficient

(not shown), the voltages of the reference generator 1 and a single-band amplitude modulator 3, the voltage u ₄ (t) appears on its output, containing the components of the total

and difference

circular frequencies, in V, respectively, equal

When this voltage u ₄ (t) arrives at the input of an intermediate frequency amplifier 5 tuned, as is known, to a differential intermediate frequency, the voltage of the differential intermediate frequency, in V, equal to

where K _UPCH is the dimensionless gain of the intermediate frequency amplifier;

- круговая разностная промежуточная частота, в рад/с.

- circular difference intermediate frequency, in rad / s.

(не показано), возникает напряжение, в В, равноеWhen simultaneously applying voltage to the phase detector 7 from the outputs of an intermediate frequency amplifier 5 and a quartz shift generator 6 at the output of a phase detector 7 modeled by a multiplier with a transmission coefficient

(not shown), there is a voltage, in V, equal to

The voltage U ₇ (t) from the output of the phase detector 7 through the DC amplifier 8 is fed to the input of the low-pass filter 9 of the PLL, where the voltage component of the total frequency is filtered out and the voltage u ₉ (t) with the average circular frequency acts on the control input of the tunable generator 2 beats measured in rad / s

,The instantaneous frequency of the tunable generator 2 changes as a result of the appearance of voltage at the input of its typical frequency controller (not shown) and will be:

,

- средняя круговая частота свободного подстраиваемого генератора в рад/с;Where

- average circular frequency of a free tunable generator in rad / s;

S _PG - the steepness of the modulation characteristics of the tunable generator, in rad / s · V.

равна

, в рад/с, окажется в данном случае использования заявляемой схемы больше полосы удержания Ω_у (как известно, полосой удержания Ω_y является такое значение разности частот

при котором происходит срыв слежения за частотой

, приводящий к потере синхронизации в системе ФАПЧ, т.е. к потере работоспособности системы), то в схеме наступит режим биений, для которого характерно неравенство частот подстраиваемого и эталонного генераторов:

.Moreover, if the initial detuning of the generators

is equal to

, in rad / s, it turns out in this case, the use of the claimed scheme is greater than the bandwidth Ω _y (as is known, the bandwidth Ω _y is such a value of the frequency difference

at which there is a breakdown in tracking the frequency

leading to loss of synchronization in the PLL system, i.e. loss of system performance), then the beat mode will occur in the circuit, which is characterized by the frequency inequality of the tuned and reference generators:

.

по отношению к начальной расстройке генераторов по частоте

.In this mode, the phase difference between the two generators is continuously increasing, and the voltage u ₇ (t) at the input of the phase detector 7 periodically changes. In this case, the durations of positive and negative half-waves turn out to be different, which leads to the appearance of a constant component of the voltage at the output of the phase detector 7, which changes the average beat frequency

in relation to the initial detuning of the generators in frequency

.

всегда меньше начальной расстройки генераторов на частоте

. При этом, если среднюю частоту биений еще непрерывно уменьшать, известным путем изменения величины постоянного управляющего напряжения, например изменением величины коэффициента усиления усилителя постоянного тока 8, то при

в дальнейшем произойдет автоматическое приближение частоты подстраиваемого генератора к частоте эталонного генератора, что, в конечном счете, приводит к нулевому значению средней частоты биений

, т.е. наступит необходимый для работы режим захвата, в котором частоты подстраиваемого 2 и эталонного 1 генераторов становятся одинаковыми

, а средняя частота выходного напряжения усилителя промежуточной частоты 5 равна средней частоте напряжения кварцевого генератора сдвига 6

.In a closed PLL, the average beat frequency

always less than the initial detuning of the generators at the frequency

. Moreover, if the average beat frequency is still continuously reduced, by known changes in the constant control voltage, for example, by changing the gain of the DC amplifier 8, then

in the future, the frequency of the tuned generator will automatically approximate to the frequency of the reference generator, which, ultimately, leads to a zero value of the average beat frequency

, i.e. the capture mode necessary for operation will come, in which the frequencies of the tunable 2 and reference 1 generators become the same

and the average frequency of the output voltage of the intermediate frequency amplifier 5 is equal to the average frequency of the voltage of the crystal shear generator 6

.

, на выходе усилителя постоянного тока 8, в В, составляетVoltage acting when

, at the output of the DC amplifier 8, in V, is

не учтена, так как эта составляющая отфильтровывается в фильтре нижних частот 9 кольца ФАПЧ и в соответствующем блоке обработки принимаемого сигнала (не показано), подключаемого в этом случае к выводу I схемы и состоящего обычно из типовых фильтра нижних частот, усилителя нижних частот и регистрирующего устройства.In this expression, the voltage u ₈ (t) is the component of the total average frequency

not taken into account, since this component is filtered out in the low-pass filter 9 of the PLL ring and in the corresponding processing unit of the received signal (not shown), connected in this case to the output of I circuit and usually consisting of typical low-pass filters, a low-frequency amplifier, and a recording device .

, и напряжение, действующее на входе соответствующего блока обработки принятого сигнала, в В, составитIn the capture mode, as noted, the average voltage frequencies of blocks 5 and 6 are equal, i.e.

, and the voltage acting at the input of the corresponding processing unit of the received signal, in V, will be

равенThe output voltage spectrum of the DC amplifier 8, acting at the input of the corresponding plug-in signal processing unit, in

is equal to

- крутизна фазового детектора, в В/рад;Where

- slope of the phase detector, in V / rad;

To the _{low-pass filter} (j Ω) is the dimensionless transfer function of the low-pass filter;

 Ω is the circular frequency, in rad / s;

j is the imaginary number;

φ _s (j Ω) is the spectrum of the phase modulation of the reference generator, in

- крутизна фазового детектора кольца - ФАПЧ, в В/рад;

и

- соответственно средние значения амплитуд напряжений входного эталонного генератора 1 подстраиваемого генератора 2, в В.For the PLL ring of the traditional solution - the prototype, the expression for the output voltage spectrum of the DC amplifier will be similar, but in it the steepness of the phase detector is a different value, namely

- slope of the phase detector of the ring - PLL, in V / rad;

and

- respectively, the average values of the voltage amplitudes of the input reference generator 1 of the tunable generator 2, in V.

.Тогда для сравниваемых схем ФАПЧ достигается равенство

т.e крутизна фазового детектора 7 заявляемой схемы ФАПЧ в «К_упч» раз больше крутизны фазового детектора схемы ФАПЧ традиционного решения - прототипа.Selecting to compare the amplitudes of the voltage of a single-band amplitude modulator 3 of the claimed circuit, it is possible to achieve a situation in which the equality

Then, for the compared PLLs, equality is achieved

that is, the steepness of the phase detector 7 of the inventive PLL circuit is “K _upch ” times the steepness of the phase detector of the PLL circuit of the traditional solution - the prototype.

Thus, in the inventive scheme, the sensitivity of reception of a weak FM oscillation, proportional to S _fd , increases by a _{factor of} “K _upch ” (20 ÷ 30) dB.

For undistorted phase detection set parameters PLL rings such that _m S S K _PD K _{ynm LPF} (j Ω) / j Ω «1, and then reaches approximately matching the spectrum of the output voltage value of the dc amplifier 8 u ₈ (j Ω) ≅S _PD K _ynm φ _c (j Ω).

2. In the case of using the PLL to receive weak FM oscillations, a voltage u ₉ (t) is emitted at the output of the low-pass filter 9.

The output voltage of the low-pass filter u ₉ (t) is input to the corresponding plug-in processing unit of the received signal, as in the case of receiving an FM signal, and consisting of a typical low-pass filter, a low-frequency amplifier and a recording device (not shown in the drawing).

равен

,The voltage spectrum u ₉ (t) at the output of the low-pass filter 9, in

is equal to

,

where ν _c (j Ω) is the frequency modulation spectrum, in

For undistorted frequency detection set parameters PLL rings such that _m S S K _PD K _{ynm LPF} (j Ω) / j Ω »1 and then reaches approximately matching values of the output voltage range

3. In the case of using the PLL as a servo filter, use the voltage released at the output of the II circuit supplied to the input of the connected corresponding unit of the recording device (for example, a typical high-frequency analyzer) (not shown in the drawing).

. При этом, спектр модуляций частоты колебания подстраиваемого генератора

в

составитIn capture mode, the voltage at the output of the tunable generator 2 is

. In this case, the spectrum of modulations of the oscillation frequency of the tunable generator

at

will make

ν _pg (j Ω) = B (j Ω) ν _s (j Ω),

- безмерный коэффициент преобразования.Where

- immense conversion coefficient.

To avoid distortion frequency modulation spectrum signal set parameters ring PLL such that S _m S _PD K _ynm K _LPF (j Ω) / j Ω »1, and then reached the approximate ratio value of the frequency spectrum modulation oscillations being adjusted generator ν _m (j Ω) ≅ν _c (j Ω).

4. In the case of using the PLL to generate two highly stable oscillation frequencies, use the voltages allocated respectively to the inputs II and III of the circuit to a typical recording device (for example, a frequency meter) (not shown in the drawing).

In the capture mode, the voltages allocated at the outputs II and III of the circuit, respectively, will be

и

- формируемые высокостабильные средние круговые частоты в рад/с, так как средние круговые частоты

и

формируются на базе высокостабильных по частоте кварцевых эталонов частоты.Where

and

- formed highly stable average circular frequencies in rad / s, since the average circular frequencies

and

formed on the basis of highly stable frequency quartz frequency standards.

The results of a pilot test of the claimed invention, with the determination of the technical characteristics of the circuit confirm the achievement of the above effects of the claimed invention.

Claims (1)

A phase-locked loop circuitry for electronic equipment containing a reference oscillator of a highly stable oscillation frequency and a phase detector, a DC amplifier, a low-pass filter and a control input, an adjustable oscillator, characterized in that a single-band amplitude modulator is additionally introduced into it , quartz shear generator, mixer, intermediate frequency amplifier, while the output of the adjustable generator is connected to a high-frequency the input input of a single-band amplitude modulator, the modulating input of which is connected to the output of a quartz shear generator, the output of a single-band amplitude modulator is connected to the reference input of the mixer, and the signal input of the mixer is connected to the output of a highly stable oscillation reference generator; the output of the mixer is connected through an intermediate frequency amplifier to the signal input of a phase detector, the reference input of which is connected to the output of a quartz shear generator, the outputs of a DC amplifier, a tunable generator and a single-band amplitude modulator, each separately, additionally having their taps supplying the corresponding voltage outside the circuit .