JPH0879145A - Automatic frequency control system for radio communication equipment - Google Patents

Abstract

PURPOSE: To provide radio communication equipment of a diversity system capable of effectively operating an AFC circuit in a high frequency area and obtaining a high S/N. CONSTITUTION: For this automatic frequency control(AFC) system of the radio communication equipment, the AFC circuit 1 is inserted to the radio communication equipment adopting the diversity system having two sets of reception systems A and B. Then, only the detection output fS of one side reception system B provided with the band filter circuits BPF2B and BPF3B of a wide frequency band width for covering the frequency fluctuation range of a used crystal oscillator is fixedly connected to the input of the automatic frequency adjustment circuit 1 and the effect of the automatic frequency control is fed back to both two sets of the reception systems A and B. The band filter circuits BPF2A and BPF3A of the reception system A not connected to the input of the automatic frequency control circuit 1 are made the band filter circuits of an optimum voice band width in a passing band narrower than the band filter circuits BPF2B and BPF3B of the wide frequency band width.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an operating system of an automatic frequency adjusting circuit (abbreviated as AFC circuit) for a diversity type wireless communication device, and particularly to a gigahertz region (UHF,
The present invention relates to an AFC operation method capable of obtaining a good signal-to-noise ratio (S / N ratio) and diversity effect in a high frequency band in the microwave region.

[0002]

2. Description of the Related Art Generally, diversity is prepared by preparing two or more systems having a small correlation with each other, that is, a probability of simultaneously degrading channel quality, and selecting or synthesizing their outputs to reduce the influence of fading. There are types such as space diversity (SD), frequency diversity, and route diversity.

Of these, space diversity is shown in FIG.
As shown in the block diagram of the super-heterodyne circuit which is a normal receiving device of the above, two sets of receiving systems A and B are built in,
This is a method of forming two propagation paths by spatially separating the respective receiving antennas ANTA and ANTB to reduce the correlation of the influence of propagation, and in the present mobile radio communication device, more stable call quality is obtained. Therefore, the signal strength of the detection output fS of the receiving system, which is in a better condition than the other one of the two receiving systems A and B, is set to the diversity changeover switch circuit D.
A method (so-called switching-type space diversity) that is selected by comparison with ivSW (comparator) is often used.

When the space diversity method is adopted, BPF2A, BPF2B and BPF3A, BP
Generally, F3B has the same band filter.

If the block diagram of FIG. 3 is outlined for the receiving system A, the incoming wave f received by the antenna (ANTA) is first amplified by a high frequency amplifier (HFA) through a high frequency band filter (BPF1A). This is the first local oscillator (L
The first intermediate frequency (fi1 = f-f01) is added to the output f01 of o1A) and the first mixer MIX called a mixer. Since fi1 is an inaudible sound, the second mixer MI together with the output f02 of the second local oscillator Lo2A is used to make the sound audible.
In addition to X, a second intermediate frequency (fi2 = fi-f02) is set, this is detected (DET), and the detected output fS is input to the diversity changeover switch circuit (DivSW).

Diversity changeover switch circuit (Div
SW) compares the signal of the other receiving system B input in the same manner as above, selects and outputs the one with higher sensitivity, low-frequency amplification (LFA), and sounds the speaker.

On the other hand, due to the increase in the number of channels accompanying the increase in the number of wireless communication users in recent years, the operating frequency is shifting to a higher frequency, but most of these high frequency management uses a crystal oscillator. There is.

However, it is approaching its limit, and UHF which is the currently used frequency or microwave (1G
However, the crystal oscillator has become a situation in which it cannot be said that the crystal oscillator is sufficient.

That is, a crystal oscillator used in a normal wireless communication device has an oscillation frequency variation due to a temperature change,
Stability within its allowable temperature range is ± 2PPM (1GH
z is about ± 2 KHz), and it is difficult to stably oscillate a frequency higher than that except using a constant temperature bath or the like.

In wireless communication in recent years, a smaller, lighter, and power-saving type is desired, so that the specifications of the above-described constant temperature bath do not meet the requirement.

In this respect, deviation in frequency of ± 2 KHz or more is a fatal problem in wireless communication in which the used frequency exceeds 1 GHz. (Deterioration of communication sound, reduction of communication distance, worst case inability to start communication, etc.) In order to avoid these, an automatic frequency adjustment circuit (hereinafter also referred to as AFC circuit for short) has been devised, and a television receiver or FM radio It is used in receivers. (However,
It seems that there is no example adopted in mobile radio communication devices, so-called transceivers. 3) In FIG. 3, the AFC circuit (AFC) 1 detects the deviation of the center frequency of the detector DET output fS of the receiving system A or B selected by the diversity changeover switch circuit (DivSW) to detect both receiving systems A and B. Local oscillator frequency f01 to be fed back to the first and second local oscillators Lo1A, Lo2A, Lo1B, and Lo2B and synthesized by the mixer MIX,
Adjust f02.

[0012]

However, the current A
The FC circuit is not effective unless a filter circuit having a wider band than the possible frequency fluctuation is used in the receiving system.

That is, when the frequency of the crystal oscillator, which is the basis of the frequency management of the system, is deviated, even the presence or absence of the signal of the other party cannot be detected in the receiving system using the usual optimum band filter, and the AFC circuit It will not work properly.

For example, in the case where the frequency used is 1 GHz and the stability of the crystal oscillator used is ± 2.5 PPM, assuming that the audio bandwidth is ± 3.75 KHz, the fluctuation frequency ± 2.5 KHz that can occur in the crystal oscillator is added to this. And ±
The frequency becomes 6.25 KHz, and a filter circuit having a bandwidth larger than this is required. This originally means that a bandpass filter having an optimum bandwidth of about ± 4 KHz is sufficient when the frequency shift is zero, but it requires the use of a wider bandpass filter, which deteriorates the S / N ratio of reception. It ends up.

At frequencies of 1 GHz or higher, a filter circuit having a wider bandwidth must be adopted in order to effectively operate the AFC circuit 1.

The stability of the crystal oscillator is ± 2.5 PPM (1
It is generally about ± 2.5 KHz at GHz, and the one with stability (± 1.5 PPM or less) higher than that is very expensive and has a problem in cost, and this also requires a constant temperature bath at several GHz. become.

On the other hand, it is natural that the two sets of receiving systems A and B in the diversity type wireless communication device are designed to be equivalent including the bandwidth of the band-pass filter circuit, so that in the high frequency range. When incorporating the above AFC circuit, as a result, a wide bandpass filter is used for both of the two receiving systems, and the S / N ratio deteriorates.

The present invention has been made in view of the above circumstances, and it is possible to perform sufficient automatic frequency adjustment (A) without unnecessarily widening the bandwidth of the filter while utilizing diversity.
The present invention provides a new AFC circuit system that can obtain the (FC) effect and a good S / N ratio.

[0019]

According to the present invention, a wide frequency bandwidth covering a frequency variation range of a crystal oscillator to be used in an automatic frequency adjustment system for a wireless communication apparatus adopting a diversity system having two sets of receiving systems. With the band-pass filter circuit, only the detection output of one receiving system is fixedly connected to the input of the automatic frequency adjusting circuit, and the effect of the automatic frequency adjusting is fed back to the local oscillators of both receiving systems. The band filter circuit of the receiving system which is not connected to the input of the automatic frequency adjusting circuit is a band filter circuit having an optimum voice bandwidth with a narrower pass band than the band filter circuit having the wide frequency bandwidth. The above object is achieved by providing an automatic frequency adjustment method for a wireless communication device.

[0020]

In the normal diversity type wireless communication device, the two receiving systems A and B do not always have the same performance, but are unbalanced due to the difference in the signal system (as can be seen from FIG. 3). In addition, the transmission / reception switching circuit 3 (TX / RXSW) with the transmission system TX is additionally inserted on one side).

Conversely speaking, even if the two receiving systems A and B are slightly unbalanced, it can be said that the diversity function has been fulfilled if the other receiving system can supplement the other receiving system when the other enters the dead zone.

In this case, it is not necessary that the band filters inserted in the receiving systems A and B have the same bandwidth.
The band-pass filter of one reception system (for example, A) obtains a high S / N ratio as an optimum narrow bandwidth (passes only the voice bandwidth) in a state where there is no frequency shift, and the other reception system (for example, B). The band filter of) is configured to secure a wide bandwidth and to detect and detect a voice signal on a deviated frequency without fail after detecting it. If only the detected output is input to the AFC circuit, The AFC circuit can be effectively operated even at the used frequency.

The frequency adjustment by the AFC circuit is fed back to both of the two sets of receiving systems A and B, and both receiving systems A and B are fed back.
The frequency shift of B is likewise adjusted to zero shift in the same way.

Generally, in the state where the frequency shift is zero, the receiving system A having good receiving sensitivity is selected by the diversity changeover switch circuit, and the receiving sensitivity is improved. (Depending on the radio wave propagation state, the reception system A may be in a poor reception state, and the reception system B having a wide band filter may be selected instead.) As a result, it becomes possible to increase the overall reception sensitivity,
In addition, the AFC can work well.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An automatic frequency adjustment system for a wireless communication device according to the present invention will be described in detail below with reference to the drawings.
It should be noted that the same components as those of the above-described conventional device are represented by the same reference numerals in the drawings.

FIG. 1 is a block diagram showing an automatic frequency adjustment method in a diversity type wireless communication apparatus according to the present invention.

FIG. 2 is a diagram for explaining the relationship between the pass band of the band filter circuit of the wireless communication apparatus according to the present invention, the voice bandwidth and the frequency shift of the crystal oscillator.

In FIG. 1, the automatic frequency adjustment method of the radio communication apparatus 10 is used by inserting the AFC circuit 1 into the radio communication apparatus adopting the diversity method having two sets of receiving systems A and B. Only the detection output fS of one receiving system B having bandpass filter circuits BPF2B and BPF3B having a wide frequency bandwidth covering the frequency fluctuation range of the crystal oscillator is fixedly connected to the input of the automatic frequency adjustment circuit 1 to perform the automatic frequency adjustment. The receiving system A is configured to feed back the effect to both of the two sets of receiving systems A and B, and is not connected to the input of the automatic frequency adjustment circuit 1.
The band-pass filter circuits BPF2A and BPF3A of the above-mentioned band-pass filter circuits BPF2B and BPF having a wide frequency band width.
The feature is that the block circuit configuration is a bandpass filter circuit having an optimum reception bandwidth in a pass band narrower than 3B.

A bandpass filter BPF for a high frequency range is usually used.
Since the bandwidths of 1A and BPF1B have a sufficiently wide bandwidth for the received signal, they can be ignored with respect to the operation of AFC and are equivalent to the conventional one.

As described above, in the present invention, the AFC
The circuit 1 is operated only by the detection output of one reception system B, and the bandpass filter BPF2B is generated even when the center frequency shift f0 → f0 ′ occurs so that the AFC normally operates as shown in FIG. 2 (a). , BPF3B are displaced from each other, the first intermediate frequency f
i1 'and the second intermediate frequency fi2' are always passed through to detect the detection circuit DE.
The filter has a relatively wide bandwidth (pass band BP) so that it can be detected at T and input to the AFC circuit 1.

The adjustment of the frequency shift by the AFC circuit 1 is performed by the local oscillators Lo1A and Lo1 of both the receiving systems A and B.
B, Lo2A, Lo2B.

On the other hand, in the other receiving system A which is not related to the AFC operation, there is no need to unnecessarily widen the bandwidth of the band filter for AFC, and there is no frequency shift as shown in FIG. 2 (b). As a premise, a narrow band filter optimal for passing the first and second intermediate frequencies fi1 and fi2 can be used, and a reception system with a good S / N ratio can be obtained. (It goes without saying that the wider the pass band BP, the more noise will pass, and the S / N ratio will deteriorate.) In the state where the frequency shift is zero, the receiving system A having this optimum filter and having good receiving sensitivity It is selected by the diversity switch circuit DivSW.

However, depending on the radio wave propagation state, the receiving system A may have a poor receiving state, and the receiving system B having a wide band filter may be selected instead.

If a large frequency shift suddenly occurs when the receiving system A is in the selected state, the receiving system A may be in the unreceivable state because of the narrow band filter.
Since the reception is possible even though the sensitivity is poor, the diversity changeover switch circuit 1 selects the reception system B, and AFC works to adjust the frequency shift. Then, the receiving system A is likely to be selected again and the receiving sensitivity becomes good.

As a result, it is possible to increase the receiving sensitivity of the entire wireless communication device, and further the AFC can be sufficiently operated.

As described above, it is necessary to use AFC when using a high frequency in the gigahertz region in a diversity type wireless communication device, but in this system, only one receiving system is used for AFC operation and the other side is used. 1G by adjusting the frequency deviation of the signal to zero and setting the other receiving system to have a bandpass filter with an optimum voice bandwidth.
Even in mobile communications with a high frequency of Hz or higher, it is possible to obtain good S / N ratio and diversity effects while eliminating problems due to frequency deviation of crystal oscillators, etc. Can cope with the shift of the used frequency to the high frequency region in the future.

It should be noted that the AFC function here does not have to be always operating, and there is no problem even if the operation is performed at the start of communication or at regular intervals after the start.

In the present invention, two sets of receiving systems A,
It does not matter which side of B performs AFC, it does not stipulate how to use the output of AFC, and one receiving system with a narrow band filter improves the receiving sensitivity and the AFC function normally. It is limited to the method of operating.

[0039]

According to the automatic frequency adjustment method for the wireless communication device adopting the diversity method according to the present invention, the automatic frequency adjustment circuit is effectively operated in the gigahertz region where the frequency deviation of the crystal oscillator becomes a problem, and the automatic frequency adjustment circuit is more effective than the conventional diversity method. Also has an excellent effect that a high S / N ratio is obtained and the receiving sensitivity as a whole is improved.

[Brief description of drawings]

FIG. 1 is a block diagram of a receiver circuit for explaining an automatic frequency adjustment method of a wireless communication device according to the present invention.

FIG. 2 is a diagram for explaining the relationship between the pass band of the band filter circuit of the wireless communication device according to the present invention, the voice bandwidth, and the frequency shift of the crystal oscillator.

FIG. 3 is a block diagram of a conventional diversity receiving circuit (super heterodyne circuit).

[Explanation of symbols]

 1 Automatic Frequency Adjustment (AFC) Circuit 3 Transmission / Reception Switching Circuit (TX / RXSW) 10 Radio Communication Equipment A, B Diversity Reception System (RX) ANTA, ANTB Antenna BPF1A, BPF1B First Band Filter BPF2A, BPF2B Second Band Filter BPF3A, BPF3B Third band filter Lo1A, Lo1B First local oscillation circuit Lo2A, Lo2B Second local oscillation circuit MIX mixer (mixer) DET detector DivSW diversity switching switch circuit HFA high frequency amplifier LFA low frequency amplifier TX transmission system f arrival system fi1 First intermediate frequency fi2 Second intermediate frequency f01 First local oscillation frequency f02 Second local oscillation frequency fS Detection output f0 Center frequency f0 'Deviation frequency BP Pass band

Claims (1)

[Claims] 1. An automatic frequency adjustment system for a wireless communication apparatus adopting a diversity system having two sets of receiving systems, wherein one of band filter circuits having a wide frequency bandwidth covers a frequency variation range of a crystal oscillator to be used. Only the detection output of the receiving system is fixedly connected to the input of the automatic frequency adjusting circuit so that the effect of the automatic frequency adjusting is fed back to the local oscillators of both of the two receiving systems, and the input of the automatic frequency adjusting circuit is provided. The automatic frequency of the wireless communication device, characterized in that the band filter circuit of the receiving system not connected to is a band filter circuit of an optimum voice bandwidth in a narrower pass band than the band filter circuit of the wide frequency band width. Adjustment method.