JPS598087B2 - Automatic frequency control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for receiving high frequency signals with large frequency drift,
This invention relates to an automatic frequency control method that obtains a desired constant intermediate frequency.

Frequency sweep operations in conventional automatic frequency control systems have been performed based on one carrier signal detection circuit or one pilot signal detection circuit.

Therefore, this sweep operation must sweep the entire intermediate frequency fluctuation range related to the frequency drift range of the high-frequency received signal, and if the input S/N is poor, the sweep time becomes extremely long, and the receiving system The drawback was that it significantly affected the synchronization time delay.

SUMMARY OF THE INVENTION The present invention aims to provide an automatic frequency control method that eliminates the above-mentioned drawbacks, and is intended to provide an automatic frequency control method that is designed to prevent frequency fluctuations caused by a mixer receiving a high-frequency received signal with frequency drift and an output due to the sweep operation of a local oscillator. Any one of a plurality of carrier wave signal detection circuits that output an intermediate frequency within the range and are within the frequency fluctuation range and are arranged at appropriate frequency intervals responds to the mixer output and responds to the mixer output. The frequency of the local oscillator output is jumped by a preset jump frequency amount corresponding to each carrier signal detection circuit to be near the desired frequency, and from then on, P L
The mixer output is set to a desired constant intermediate frequency by L (Phase locked loop), and the frequency is set near the desired frequency by the sweep operation of the local oscillator following the frequency jump of the local oscillator output. This automatic frequency control method is characterized in that the output of the mixer is set to a desired constant frequency using a PLL, and therefore the sweep time is greatly shortened compared to the conventional method, and the above-mentioned drawbacks can be solved.

Examples of the present invention will be described below. 1 and 2 relate to one embodiment of the present invention, and this embodiment will be explained using the block diagram of FIG. 1 and the frequency allocation diagram of FIG. 2.

First, in FIG. 1, 1 is a high frequency received signal frequency f accompanied by frequency drift as an intermediate frequency f.

2 is a voltage-controlled local oscillator related to conversion to an intermediate frequency in mixer 1, 3 is a voltage addition circuit, 4 is a switch, 5 is a phase comparator,
6 collectively shows carrier wave signal detection circuits, and in this embodiment, there are five carrier wave signal detection circuits f2, f. ，
f. ,f-. , f −2 are arranged.

7 is a jump frequency amount output circuit, 8 is a jump frequency amount correction circuit, 9 is a D/A converter, 10 is a counter, 1
1 is a control circuit, and 12 is a carrier signal extraction circuit.

Note that the carrier wave signal extraction circuit 12 uses the reference signal frequency f.

In order to accurately match the frequency of the output of the mixer 1 to REF, a PLL is configured via the phase comparator 5, switch 4, voltage adder circuit 3, local oscillator 2, and mixer 1.

Next, in FIG. 2, Ω is the mixer 1 in FIG.
shows the frequency variation range of the output.

It should be noted that in the conventional method, a single carrier signal detection circuit or the like sweeps the entire frequency fluctuation range Ω.

f-2, f-1, fo, f1, f2 are frequency arrangements corresponding to the carrier signal detection circuits with the same symbols in Fig. 1, and as shown in the figure, appropriate frequency intervals are taken within the frequency fluctuation range Ω. , this f.

is also the desired intermediate frequency.

Also, f-2, . f. , f. , f.
, f2 indicate the sensitive range of each carrier signal detection circuit.

Other symbols shown in FIG. 2 will be explained below in the course of explaining the operation of the embodiment shown in FIG.

The operation of the embodiment shown in FIG. 1 will be explained with reference to FIG. 2. First, the switch 4 is turned OFF, the counter 10 is controlled by the control circuit 11, and the output of the counter 10 is transferred to the D/A converter. At step 9, the voltage is converted into an analog voltage, and the local oscillator 2 is controlled via the voltage adder circuit 3 to sweep the local oscillator 2.

That is, the frequency of the output signal of the mixer 1, indicated by fx in FIG. 2, is varied in the direction of the arrow ■.

Through this sweep operation, the output of the mixer 1, that is, the signal of the difference frequency between the high frequency reception signal frequency f and the local oscillator 2, is detected by the carrier wave signal detection circuit 6, f, for example (
2), the detection output DETf1 is supplied to the control circuit 11 via the jump frequency amount output circuit γ, and the control circuit 11 outputs a constant intermediate frequency f.

In this case, if
.

The frequency f is equal to the frequency difference of f1l.

In the direction of , the jump frequency amount output circuit 7 and the control circuit 11
, jump frequency amount correction circuit 8, and voltage addition circuit 3
Jump local oscillator 2 with the related operation (arrow ◎ in Figure 2)
direction).

This jump frequency amount correction circuit 8 is provided in consideration of the drift of the output of the local oscillator 2 and the setting error of the jump amount, etc., and thereby ensures that the search can be performed by re-sweeping after the jump. , the jump frequency amount is corrected to be slightly larger or smaller than the frequency difference 1 fo-ft I according to the relationship between the sweep direction and the jump direction.

For example, as shown in FIG. 2, when the carrier wave signal detection circuit 6
If the jump frequency is detected at f1, the jump frequency amount will be smaller than the set amount 1fo-ftl (the amount that fluctuates in the direction of the arrow ◎ in FIG. 2 and reaches the point ■).

Then, f of the carrier signal detection circuit 6 via the jump frequency amount output circuit 7.

The re-sweep (the second
(varies in the direction of the arrow ■ in the figure), the intermediate frequency f.

(point 0 in Figure 2) and stop the sweep.

Next, AFC operation is started as in the conventional method.

That is, by stopping the operation of the counter 10 according to the instruction from the control circuit 11, the output of the D/A converter 9 is kept constant and the frequency of the local oscillator 2 is held, so that while this sweep stop state is maintained, the operation of the counter 10 is stopped. , a carrier signal extraction circuit 12 outputs a carrier signal component, and the output is a reference signal frequency f.

The local oscillator 2 is controlled by the voltage generated by comparing RF and F with the phase comparator 5 via the switch 4 and the voltage adding circuit 3.

Therefore, the high frequency received signal frequency f with drift is a constant intermediate frequency f.

(point ◎ in Figure 2).

Note that in this AFC operation process, the switch is in the ON state, which means that the carrier wave signal extraction circuit 12 causes the control circuit 11 to turn on the switch 4 at the time when the carrier wave signal extraction circuit 12 outputs the carrier wave signal component. I was instructed to turn it on.

The configuration and operation of one embodiment have been described above with reference to FIG. 1 and FIG. 2. In this embodiment, the sweep time is reduced by 1.5% compared to the conventional method, and the time can be greatly shortened.

In other words, the jump and sweep operations of the present invention reduce the sweep width to approximately 1/1 compared to the frequency fluctuation range Ω.
It is clear that the number of carrier wave signal detection circuits can be set to (the number of carrier wave signal detection circuits arranged).

Although the jump frequency amount correction circuit 8 was used in the above embodiment, the automatic frequency control method of the present invention requires consideration of, for example, the drift of the output of the local oscillator 2 and the setting error of the jump amount in the configuration shown in FIG. If there is no means, the jump frequency amount output circuit 7 is made to correspond to the voltage addition circuit 3 and the control circuit 11 without using a means corresponding to the jump frequency amount correction circuit 8.

In this case, for example, the jump frequency amount is set so that the jump does not occur to the point ■ shown in FIG. 2, but jumps to the point ■ in the direction of the arrow ■.

Other configurations and operations are similar to those of the previous embodiment.

Note that due to the formation of the high frequency reception signal f, there may be cases where a pilot signal is obtained without a carrier signal being obtained from the output of the mixer 1. In this case, the carrier signal detection circuit 6, for example, f
-2,f-] 1fO, f1rf2 A circuit that receives a pilot signal and regenerates a carrier signal is adopted, and also receives a pilot signal on the input side of the carrier signal extraction circuit 120 and regenerates it into a carrier signal. It is sufficient to add a circuit or provide this reproduction function to the carrier wave signal extraction circuit 12.

According to the present invention, a plurality of carrier signal detection circuits are provided at appropriate frequency intervals, and the local oscillator jumps and sweeps only a predetermined amount of frequencies. intermediate frequency signals can be obtained in an extremely short time compared to conventional methods.

Therefore, the automatic frequency control method of the present invention is suitable for cases where the sweep speed has a large effect on the reception synchronization time, for example, in a spread frequency communication method where communication is often performed with a very poor input S/N ratio. This is effective in reducing synchronization time.

[Brief explanation of the drawing]

1 and 2 relate to one embodiment of the present invention, with FIG. 1 being a block diagram showing the configuration, and FIG. 2 being a frequency allocation diagram. 1...Mixer, 2...Local oscillator,
3...Voltage addition circuit, 4...Switch, 5...Phase comparator, 6...Carrier signal detection circuit, 7... Jump frequency amount output circuit, 8...Jump frequency amount correction circuit, 9...
...D/A converter, 10...Counter,
11...Control circuit, 12...Carrier signal extraction circuit, f...High frequency received signal frequency, f
o...Intermediate frequency, foRF, F...
Reference signal frequency, Ω...4 frequency fluctuation range (mixer output frequency range).

Claims (1)

[Claims] 1. In an automatic frequency control method that receives a high frequency signal with frequency drift and obtains a desired constant intermediate frequency,
A mixer receives the high frequency signal and the output from the sweep operation of the local oscillator and outputs an intermediate frequency within a predetermined frequency variation range, and a plurality of intermediate frequencies within the frequency variation range and arranged at appropriate frequency intervals. Any carrier wave signal detection circuit of the carrier wave signal detection circuits responds to the mixer output, and jumps the frequency of the local oscillator output by a preset jump frequency amount corresponding to each of the carrier wave signal detection circuits that responded. In the vicinity of the frequency, hereafter,
An automatic frequency control method characterized in that the output of the mixer is set to a desired constant intermediate frequency using a PLL. 2. In an automatic frequency control method that receives a high frequency signal with frequency drift and obtains a desired constant intermediate frequency,
A mixer receives the high frequency signal and the output from the sweep operation of the local oscillator and outputs an intermediate frequency within a predetermined frequency variation range, and a plurality of intermediate frequencies within the frequency variation range and arranged at appropriate frequency intervals. One of the carrier wave signal detection circuits responds to the mixer output, and the frequency of the local oscillator output is jumped by a preset jump frequency amount corresponding to each of the carrier wave signal detection circuits that responded. , then the local oscillator performs a sweep operation up to the vicinity of the desired frequency, and thereafter the PLL
An automatic frequency control method characterized in that the output of the mixer is set to a desired constant intermediate frequency.