SU879782A2 - Device for automatic control of frequency - Google Patents

Description

one

The invention relates to radio engineering and- can be used, for example, in following filters or in devices for stabilizing a discrete set of frequencies.

According to the main author. St. No. 758522, a device for automatic frequency control is known, which contains two identical phase automatic frequency control (PLL) rings connected to the input, to the control input of each of which a corresponding modulating oscillator is connected, the first mixer, whose inputs are connected to the outputs of the adjustable oscillators of both PLL rings, the second mixer, the inputs of which are connected to the outputs of the corresponding modulating oscillators, the frequency ratio meter, the inputs of which are connected to the outputs of the first and the third mixer, one input of which is connected to the output of the adjustable oscillator of one of the PLL rings, and between the other input of which and the output of the modulating oscillator of the same PLL, a frequency multiplier with controllable multiplication factor is included. The equalization input is connected to

output meter frequency ratio. In this case, the frequencies of the modulating oscillators are chosen from the condition

five ,,

where F and Fg are the frequencies of the corresponding modulating oscillators; Other - frequency difference 1.1 J.

10 However, this device is critical.

and not sufficiently robust, since with the incomplete identity of the PLL rings, as well as under the influence of interference, false

5 circuit operation.

The purpose of the invention is to reduce the criticality of tuning and improving noise immunity.

The goal is achieved in that an automatic frequency control device containing two input-connected identical PLL rings to the control input of each of which is connected to the corresponding modulating oscillator, the first mixer, whose inputs are connected to the outputs of the adjustable oscillators of both PLL rings, the second mixer, inputs which are connected to the outputs of the corresponding 30 NCH modulating oscillators, a frequency ratio meter, the inputs of which are connected to the outputs of the first and second mixers, the third mixer, dyn turn is connected to the generator being adjusted vyhou one of the rings of the PLL, and between the other input and the output of the modulating otorrhea for generators of the same ring including The PLL frequency multiplier with control emy-. the multiplication factor, the control input of which is connected to the output of the frequency ratio meter, while the frequencies of the modulating oscillators are chosen from

F-F2 - AF “F, 2,

where F and Fg are the frequencies of the corresponding modulating oscillators;

AF is the frequency difference, a key is connected to the combined inputs of both PLL loops; a high-pass filter, an amplitude detector, a threshold device and a time relay are connected in series between the output of the first mixer and the control input of the key.

The drawing shows a structural electrical circuit of the device described.

The automatic frequency control device contains identical first and second PLL rings 1 and 2, consisting of phase detector 3, low pass filter 4, adjustable oscillator 5, phase modulator b, modulating oscillators 7 and 8, first mixer 9, second mixer 10, a third mixer 11, a frequency ratio meter 12, a frequency multiplier 13 with a controlled multiplication factor, as well as a key 14, a time relay 15, a high-pass filter 16, an amplitude detector 17, a threshold device 18,

JacTOTbi modulating generators 7 and 8 are selected from the conditions

R,,

where F is the frequency of the modulating oscillator 7

fy is the frequency of the modulating oscillator 8.

The operation of the described device is as follows

The initial state of the INPUT signal is absent, the key 14 is closed, the frequencies of the adjustable oscillators are approximately equal and the following conditions are fulfilled:

 i, .2,

where f, f are the frequencies of adjustable oscillators 5 rings 1 and 2 of the PLL, At the outputs of phase modulators 6

signals with a line spectrum will be present, with the distance between adjacent spectral components of each signal being equal to the frequency of the corresponding modulating oscillator. Since the frequencies F and differ by the value of Lp, the spectral components of the signal at the outputs of the modulators of the 6 PLL rings do not coincide, and the detuning between them increases with increasing order numbers of the spectral component.

The cut-off frequency of the high-pass filter 16 is selected from the conditions;

Vaqkc media

where w., „,,,, is the maximum order

AAOKS

the number of the spectral component used; initial detuning between frequencies of tunable 1 oscillators 5.

In this case, the output of the filter 16

The high frequency and amplitude detector 17 have no signal, the threshold device 18 is in the zero state, the time relay 15 is open, and the key control signal is absent.

Suppose that in this state the key 14 is closed. Then, if you fulfill the conditions:

gahv-0 2,

where yyf, Q, PLL ring capture band in the absence of modulation, after the input signal enters the input device, the first and second PLL rings 1 and 2 are captured and the system establishes the equal frequencies of the input signal and the nearest spectral component at the outputs of phase modulators 6 In the case of proper operation of the device, i.e. with a small initial detuning between the frequencies of the adjustable generators 5 rings 1 and 2 of the PLL, as well as in the absence of interference on the control circuit of the two PLL rings, the sequence numbers of the spectral components on which the capture occurred are the same. Those. equality fgy {, (+ r-F- for the first PLL 1 ring

and equality Vi Vi Fg for the second ring of the PLL (Vi is the sequence number of the spectral component on which the capture occurred)

Then, using mixers 9-11, a frequency ratio meter 12 and a frequency multiplier 13 with a controlled multiplication factor, the output signal is synthesized with a frequency equal to the frequency of the input signal. It happens as follows.

The mixer 9 extracts the frequency difference of the adjustable oscillators 5 of the rings 1 and 2 of the PLL to Hu.F, the second mixer 10 extracts the difference of the modulating frequencies ,r, the frequency ratio meter 12 of these signals forms the logical control signal corresponding to the frequency ratio And which is then used to set the multiplication factor of the multiplier 13 frequency equal to VI. At the output of the frequency multiplier 13, there will be a sinal with a frequency AND F-f, which is then fed to one of the inputs of the third mixer 11. The second input of the third mixer 11 receives a signal with a frequency -,. - therefore at its output there will be a total signal with frequency {0ts. When the frequency of the input signal changes within the confinement band of the PLL rings, the equal frequencies of the input and output signals are maintained by the PLL system, and when the frequency of the input signal exceeds the confinement band, the first and second PLL loops over the adjacent harmonic component and the frequency is again equal input and output signal.

Under the influence of interference on the control circuits of the PLL rings, as well as with a large mismatch between the frequencies of tunable oscillators 5 (due to inaccurate initial installation or aging of elements of the oscillators, temperature drift, etc.), the initial initial locking or re-capturing of the PLL 1 and 2 may occur. those. capture for spectral components with different sequence numbers, for example, y and (Y + 1), In this case, cTBoigj f + иР /) for the first PLL 1 ring and f in 2 2 + + (I4--1) P, the second ring of the PLL.

At the output of the first mixer 9, a differential signal with

frequency, therefore, at the output of the device the frequency will be synthesized, not equal to the input. Since the cut-off frequency of the high-pass filter 16 is chosen to be less than, this signal passes through it, is detected by the amplitude detector 17 and is fed to a threshold device 18, which is triggered by its influence. In this case, a time relay 15 triggers, which opens the key 14 for some time, the input signal ceases to arrive at the inputs of rings 1 and 2 of the PLL, the capture of the rings disappears, and the circuit returns to its initial state. The duration of the pulse Lt time relay 18

a slightly longer transient time in the PLL rings is selected. After the end of the pulse D-L key 14 is closed, the input signal is fed to the inputs of the rings 1 and 2 of the PLL and a re-capture occurs. The process described above is repeated until the correct operation of the circuit, i.e. capture by spectral components with the same order number. A sign of the correct operation of the circuit is the low frequency of the signal at the output of the first mixer 9, which satisfies the condition

..

five

Thus, the key 14 and its control circuit, consisting of a consistently included high-pass filter 16; the amplitude detector 17, the threshold device 18, and a time relay 15 connected to the output of the mixer 9, precludes the incorrect operation of the frequency-control loop.

The described device has

5 increased noise immunity, since, after the failure of his work under the influence of interference, it has the ability to restore the correct grip, and it is also less critical to

0 tuning accuracy and stability of individual nodes (tunable oscillators, phase detectors, phase demodulators, low-frequency filters), the possibility of continuous capture, which allows the use of high order numbers of spectral components, which leads to an expansion of the capture band of the device.

0

Claims (1)

1. USSR author's certificate 758529, cl. H 03 W 3/04, 1978 (prototype).