JPS596531B2 - automatic frequency control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic frequency control device for matching a transmission frequency to a target frequency (modulated frequency of a pulse-modulated received signal) with required accuracy in a microwave transmitter/receiver or the like.

FIG. 1 shows an example of a conventional device of this type.

In the figure, reference numeral 1 denotes a mixer to which a received signal such as a pulse-modulated microwave signal is applied, and in this mixer 1, the modulated frequency of the received signal, that is, the target frequency fl, and the transmission frequency f2 are mixed and intermediated. Frequency 1F (=f1
~f2). 2 is intermediate frequency 1
3 is a detector that detects the output of the intermediate frequency amplifier 2; 4 is a frequency discriminator that converts the intermediate frequency 1F into a voltage signal; 5 is intermittently output from the frequency discriminator 4. The pulse amplifier 6 that amplifies the voltage signal is a sample hold circuit that catches the voltage signal output from the pulse amplifier 5 when the detector 3 is outputting and holds it for a predetermined time.

7 is a DC amplifier, 8 is a low-pass loop filter that suppresses the closed loop system from oscillating, 9 is a driver, 1
0 is a voltage controlled oscillator that is controlled by the driver 9 and converts a voltage signal into a frequency to create a transmission frequency f2.

This transmission frequency f2 is applied to the mixer 1 and the transmission side. In the case of such an automatic frequency control device, there is a drawback that if the characteristics of the frequency discriminator 4, which serves as a reference, fluctuate due to temperature changes or the like, the fluctuation is taken into account in the transmission frequency.

In order to avoid this, there were various disadvantages such as the need for very expensive parts with excellent stability in the frequency discriminator. SUMMARY OF THE INVENTION An object of the present invention is to provide an automatic frequency control device that can compensate for variations in the characteristics of a frequency discriminator.

A specific example of the present invention will be explained in detail below with reference to FIG.

In the figure, 11 is an antenna, and this antenna has a pulse-modulated frequency (target frequency) fl
A reception signal of f is received, and a transmission signal of a transmission frequency f, which is controlled to match this datemark frequency, is transmitted. 12 is a circulator that controls the passage of the transmitted signal and the received signal; 13 is a local oscillator that generates a sublocal signal with a sublocal frequency f3; 14
is a submixer that mixes the transmission frequency f2 and the sublocal frequency f3 and outputs a local signal of the local frequency (F2+F3).

15 is a main mixer, which mixes the target frequency f1 and the local frequency (F2+F3), or mixes the transmission frequency F2.
and local frequency (F2+F3) to form an intermediate frequency signal of intermediate frequency FIF.

16 is an intermediate frequency amplifier that amplifies the intermediate frequency signal, and 17 is a frequency discriminator that converts the intermediate frequency FIF of the amplified intermediate frequency signal into a voltage signal and outputs it.

This frequency discriminator 17 has a center frequency selected to be F3 in particular, and is structured such that the output voltage is zero when the input frequency is F3. Reference numeral 18 is a detector for detecting an intermediate frequency signal, and reference numeral 19 is a control circuit for controlling various parts based on the detection output as described later.

Reference numeral 20 indicates a sample and hold circuit at the time of transmission, which is controlled by the control circuit 19 and stores the voltage signal of the frequency discriminator 17 only at the time of transmission; and 21, the frequency discriminator 1 which is controlled by the control circuit 19;
This is a high-speed sample-and-hold circuit that stores a new voltage signal only when receiving it every time a voltage signal is output from 7.

22 is an adder circuit, 23 is a first sample-and-hold circuit for output feedback, and 24 is a second sample-and-hold circuit for output feedback. These three circuits input each output at the time of reception to the input side. A human output repetitive addition circuit 25 is formed which repeatedly performs the operation of returning the input data and adding it to a new input.

That is, the adder circuit 22 adds the output of the high-speed sample-and-hold circuit 21, the output of the transmitting sample-and-hold circuit 20, and the output of the second sample-and-hold circuit 24 for output feedback, and adds the output of the high-speed sample-and-hold circuit 21, the output of the transmitting sample-and-hold circuit 20, and the output of the second sample-and-hold circuit 24 for output feedback. The circuit 23 is configured to store a new memory each time. The second sample and hold circuit 24 for output feedback is configured to store the stored contents of the current time and provide the stored contents to the adder circuit 22 before the first sample and hold circuit 23 performs new storage.
The control circuit 19 includes each sample hold circuit 21, 23, 2
A control signal is issued so that the storage of 4 is performed sequentially at predetermined time intervals upon reception. 26 is a driver, 27 is a high frequency voltage controlled oscillator that is controlled by the driver 26 and converts a voltage signal into a frequency to create a transmission signal of transmission frequency F2, and 28 is a divider that divides the transmission signal into two.

One transmission signal is given to the sub-mixer 14, and the other transmission signal is given to the high frequency amplifier 29 and amplified. 30
is a transmission control switch that is controlled by the control circuit 19 and allows the transmission signal to pass only during the transmission time period.

In such an automatic frequency control device, during the transmission time period, when the transmission frequency F2 follows the target frequency f1 with the required accuracy as described later, the transmission control switch 30 is turned on by a transmission command from the control circuit 19. A transmission signal of frequency F2, which is the output of the high frequency voltage controlled oscillator 27, is amplified by the high frequency amplifier 29, passes through the circulator 12, and is radiated from the antenna 11.

Since the transmission output, that is, the output of the high frequency amplifier 29, is large,
The transmitted signal of frequency F2 enters the receiving system as a leakage signal, reduced by the amount of isolation of the circulator 12. Therefore, a part of the transmission signal of frequency F2 is input as a signal input to the main mixer 15, and a local signal of frequency (F2+F3) is input as a local input.
Therefore, the intermediate frequency FIF of the intermediate frequency output is F3. As mentioned above, the center frequency of the frequency discriminator 17 is selected to be F3, so if there is an error of 1 ΔF3 in the center frequency of this frequency discriminator 17, which is the reference, a voltage ΔV3 corresponding to the error will appear. . If this voltage ΔF3 is stored in the sample and hold circuit 20 at the time of transmission according to a command from the control circuit 19 and added to the automatic control loop at the time of transmission, the error of the frequency discriminator 17 will be automatically corrected. That is, as shown in FIG. 2, when the frequency discrimination characteristic of the frequency discriminator 17 is normal, the center frequency is F3 as a solid line A, and when an error of ΔF3 has occurred as a broken line B, then the frequency The frequency discriminator 17 to which F3 is input is -Δ
If an error occurs in F3, an output of ΔV3 is output. ΔF
When error 3 occurs, the intermediate frequency FIF is automatically controlled to converge to the frequency of (F3 - ΔF3) at the time of reception, so the output of the frequency discriminator 17 appears to be Δ■3 smaller than the normal state. become. In other words, the transmission frequency F2 is accompanied by an error of ΔF3 compared to the normal state. Therefore, if ΔV3 is applied from the sample-and-hold circuit 20 to the adder circuit 22 during reception, the error will be automatically corrected. Next, the operation during the reception time period will be explained.

A target frequency (reception frequency) f1 is received by the antenna 11, passes through the circulator 12, and is applied to the main misaki 15. In the main mixer 15, the target frequency f1 and the local frequency (F2+F3) are mixed to produce an intermediate frequency FI.
It is converted into F (=F2+F3-f1) and applied to the intermediate frequency amplifier 16. The intermediate frequency signal whose frequency is (F2+F3-f1) amplified by the intermediate frequency amplifier 16 is applied to the frequency discriminator 17. The intermediate frequency signal is detected by a detector 18 and becomes a trigger signal for a control circuit 19, and a control signal is given to a high speed sample and hold circuit 21. Target wave number f
1 and the transmission frequency F2 is converted into a voltage Δv by the frequency discriminator 17, stored in the high speed sample and hold circuit 21, and applied to the adder circuit 22. The addition output of the addition circuit 22 is sent to the first sample and hold circuit 23 for output feedback.
The stored contents are then transferred to the second sample-and-hold circuit 24 for output feedback, and fed back to the adder circuit 22. Sample hold circuit 21, 23
, 24 are sample timings of 21, 23, 2
4, every pulse repetition period T of the target frequency f1. The input of the adder circuit 22 is connected to the output signal of the one-loop loop of the automatic frequency control system via the high-speed sample-and-hold circuit 21, as well as the input-output repeat adder circuit 25 via the second sample-and-hold circuit 24 for output feedback. The output of is given as a feedback signal. Furthermore, an output signal is also provided from the sample and hold circuit 20 during transmission for error correction. The adder circuit 22 adds these three input signals. The addition output is sequentially transferred to the first and second sample and hold circuits 23 and 24, and then transferred to the addition circuit 22 again.
It is fed back to the human power side and added to the new input. Such operations are repeated, and the output of the circuit 25 is increased. The output of the input/output repeat adder circuit 25 is given to a driver 26, which controls a high frequency voltage controlled oscillator 27, and is converted into a transmission frequency F2 according to the output. Assuming that the loop gain is K, the control amount of the high frequency voltage controlled oscillator 27, which is the controlled object, is the pulse repetition period T during the reception time.
Assuming that is n times, then In other words, the gain of the system is N
It is equivalent to K. Generally, the reception time is sufficiently longer than the pulse repetition period T, so it is sufficient that the system open loop gain K is 1 or less. The output of the high-frequency voltage controlled oscillator 27, that is, the transmission output with a frequency of F2, is divided into two parts by a divider 28, one of which is given to the sub-mixer 14, and the other to the high-frequency amplifier 29.
given to.

When the transmission time comes, a transmission command is issued from the control circuit 19, the transmission control switch 30 is turned on, and the transmission signal is radiated from the antenna 11 via the circulator 12.

Note that the input/output repeating addition circuit 25 may perform analog-to-digital conversion of its input to perform digital processing.

The output is converted into an analog quantity by a digital-to-analog conversion circuit and is then applied to the driver 26. As explained above, in the automatic frequency control device according to the present invention, the local frequency of the main mixer is obtained by mixing the sub-local frequency and the transmission frequency, and this local frequency is mixed with the target frequency f1 or the transmission frequency, and The frequency discriminator has its center frequency matched with the sublocal frequency F3 and is controlled to converge to this frequency F3, and the output voltage signal of the frequency discriminator is connected to the downstream stage of the frequency discriminator at the time of transmission. Since a transmitting sample-hold circuit for storing data and an adding circuit for adding the output voltage signal of the frequency discriminator and the voltage signal from the transmitting sample-and-hold circuit are provided, an error occurs in the reference frequency discriminator. However, this can be corrected automatically.

Therefore, according to the present invention, it is possible to provide an automatic frequency control device with excellent frequency tracking performance. Further, according to the present invention, there is no need to use very expensive parts with excellent stability in the frequency discriminator, and the frequency discriminator can be manufactured at low cost.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional device, FIG. 2 is a characteristic diagram of a frequency discriminator, and FIG. 3 is a block diagram showing an example of a device according to the present invention. 11...Antenna, 12...Circulator, 13...Local oscillator, 14...
・Sub mixer, 15...Main mixer, 17・
...Frequency discriminator, 19...Control circuit,
20...Sample and hold circuit during transmission, 22.
... Addition circuit, 27 ... Voltage controlled oscillator, 30 ... Transmission control switch.

Claims (1)

[Claims] 1. A local oscillator that generates a sublocal frequency, a submisaki that mixes the sublocal frequency and the transmission frequency to form a local frequency, and a submisaki that mixes the target frequency and the local frequency during reception and mixes the transmission frequency and the a main mixer that mixes local frequencies to form an intermediate frequency; a frequency discriminator whose center frequency is selected as the sublocal frequency and converts the intermediate frequency into a voltage signal; and an output voltage of the frequency discriminator during transmission. a transmitting sample-and-hold circuit that stores the frequency discriminator, an adding circuit that adds the voltage signal from the frequency discriminator side and the voltage signal from the transmitting sample-and-hold circuit, and an adding circuit that adds the added voltage signal to the transmitting signal of the transmitting frequency. An automatic frequency control device comprising: a voltage controlled oscillator that converts the frequency into a voltage controlled oscillator and supplies the converted signal to the sub-mixer side and the transmission side.