JP2000022580A - Radio equipment and filter changeover method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To constitute two filters at a low cost and to prevent characteristics from being degraded due to the temperature change in a transmitter-receiver for performing transmission and reception by switching two high frequency filters. SOLUTION: The correction for a changeover frequency to a temperature is stored in a ROM 11. A control part 9 reads the correction corresponding to the temperature of the high frequency filters 5 and 6 detected by a thermistor 10 from the ROM 11, adds it to a reference changeover frequency and obtains the correction of the changeover frequency. Then, which one of the high frequency filters 5 and 6 is to be used is decided depending on whether a transmission/reception frequency is larger or smaller than the corrected changeover frequency and changeover circuits 3 and 4 are controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio and a filter switching method thereof, and more particularly to a radio in which a frequency channel of a transmission / reception signal changes and a filter switching method thereof.

[0002]

2. Description of the Related Art In a mobile telephone system or the like, there are many frequency channels allocated to the system, and it is necessary to provide a radio device with a high-frequency filter that covers all the frequency channels. On the other hand, in particular, in the case of a wireless device having a low first intermediate frequency, the frequency is set to 倍 times the intermediate frequency and 2
It is necessary to sufficiently suppress the double spurious sensitivity, and a high-frequency filter having a sharp attenuation characteristic is required.
However, it is difficult to realize a high-frequency filter having a large band and a sharp attenuation characteristic as described above.

For this purpose, two high-frequency filters having different pass bands from each other are prepared, and are switched according to the frequency channel for transmitting and receiving. FIG.
Shows an example of characteristics when two filters are used, and a high-frequency filter having characteristics FC1 and FC2 at room temperature is prepared. The required bandwidth B in FIG. 2 is a band covering a frequency channel used in the system, and a switching frequency fs is set near the center thereof.
If the high frequency filter of C2 is equal to or lower than the switching frequency fs, the high frequency filter of the characteristic FC1 is switched to be used. According to this method, the pass bandwidth of one high-frequency filter may be smaller than the required bandwidth B, so that a sharp attenuation characteristic can be easily obtained.

[0004]

The characteristics of a filter change with temperature. For example, when a SAW filter commonly used in wireless devices is used, a negative frequency deviation occurs with respect to temperature. The characteristics FL1 and FL2 indicated by the dotted lines in FIG. 2 are examples of the characteristics FC1 and FC2 of the two high-frequency filters at room temperature when the temperature is lower than room temperature, and the pass band is shifted to a higher frequency. FIG. 3 shows an example when the temperature rises, and the characteristics FC1 and FC
2 have characteristics FH1 and FH which are shifted toward lower frequencies.
H2. With such high-frequency filter temperature characteristics, the characteristics FC1, FC
Depending on the choice of 2 and the size of the deviation due to temperature, FIG.
As shown in the example, the switching frequency fs may come to a place where the frequency characteristic FL2 at the time of low temperature falls in the attenuation range. At a high temperature, the frequency characteristic FL1 as illustrated in FIG.
In the attenuation range, the switching frequency fs may come. Further, the frequency at the end of the required bandwidth B may also affect the attenuation range of each filter.

In such a state, the high-frequency filter gives unnecessary attenuation to the frequency channels near the switching frequency or near the end of the required bandwidth. To prevent this, it is sufficient to provide each high-frequency filter with a bandwidth that does not cause the above-mentioned attenuation even if the filter characteristics change in temperature. It is not preferable because it accompanies. In particular, large temperature changes are unavoidable in mobile devices and base stations of mobile radio systems, and the use of advanced filters is difficult in terms of miniaturization and cost reduction of the devices themselves, and the above-mentioned problems occur. Cheap.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a radio apparatus which does not use a high-frequency filter having particularly good characteristics and which does not increase the loss in a high-frequency filter to be used even when a large temperature change occurs. It is to provide a filter switching method.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a radio apparatus having a variable transmission / reception frequency and uses different passbands which are switched according to the transmission / reception frequency. A filter switching method for switching between two high-frequency filters, comprising detecting a temperature of the high-frequency filter, and changing a predetermined correction value corresponding to the detected temperature to a reference switching determined with respect to a reference temperature. Calculating a corrected switching frequency in addition to the frequency, and determining which of the two high-frequency filters to use depending on whether the transmission / reception frequency is higher or lower than the calculated switching frequency. Provide a way.

The present invention also relates to a radio apparatus comprising two high-frequency filters whose transmission / reception frequencies are variable and which are switched according to the transmission / reception frequencies and have different pass bands from each other. Temperature detection means for detecting the temperature of the filter, switching frequency correction means for correcting a predetermined reference switching frequency corresponding to the detected temperature when the temperature detected by the means is given; High frequency filter switching control means for determining which of the two high frequency filters is to be used depending on whether the transmission / reception frequency is higher or lower than the switching frequency corrected by the means. Provide a radio.

Further, the invention is characterized in that the switching frequency correction means stores a correction value of the reference switching frequency for each of the detected temperatures in a predetermined ROM, and stores the correction value in the ROM when the detected temperature is given. And a calculating means for reading the correction value to be added and adding the read correction value to the reference switching frequency to obtain a corrected switching frequency.

[0010]

Embodiments of the present invention will be described below. FIG. 1 shows a configuration example of a portion related to the present invention of a wireless device according to the present invention, and shows a receiving circuit. Of course, the same applies to the transmission circuit, but is omitted here for simplicity. In FIG. 1, the high frequency signal R received by the antenna
F is amplified by an amplifier 2 via a high frequency filter 1 and then switched by high frequency filters 5
6, the frequency is converted by the local signal from the local oscillator 7 by the mixer 8, and the intermediate frequency signal IF
Is output to the following circuit. The control unit 9 is a CPU unit provided in the wireless device, and the control unit 9 determines which high-frequency filter is used in the switching circuits 3 and 4 according to the frequency channel with which the wireless device communicates. Is controlling. Here, the frequency characteristics of the high frequency filters 5 and 6 are as described with reference to FIG. 2 and both cover the required bandwidth B. Conventionally, a high-frequency filter is determined based on whether a frequency channel is higher or lower than a preset switching frequency.

According to the present invention, a thermistor 10 for detecting the temperature inside the wireless device, particularly, the high-frequency filters 5 and 6,
A ROM 11 storing a table for providing a switching frequency correction value Δfs corresponding to the temperature detected by the thermistor 10 is provided. The characteristics of this table are as shown in FIG. 4, for example.
s = 0, the correction value Δfs becomes negative as the temperature increases, and the correction value Δfs increases as the temperature decreases, and this characteristic is stored in the ROM at appropriate temperature intervals. ing. The characteristic shown in FIG. 4 corresponds to a negative temperature characteristic in which the shift of the pass band frequency with respect to the temperature is reversed in the positive and negative directions as in the SAW filter. If the filter has a positive temperature characteristic, FIG. Line.

In the above configuration, when the control section 9 captures the temperature t detected by the thermistor 10, the control section 9 refers to the ROM 11 to obtain a value Δ corresponding to the temperature t of the switching frequency correction value Δfs.
read fs (t),

## EQU1 ## With the frequency fsx determined by fsx = fs + .DELTA.fs (t) as the switching frequency, it is determined which of the high frequency filters 5 and 6 is to be selected, and the switching circuits 3 and 4 are controlled. However, fs is the switching frequency at normal temperature, and corresponds to the switching frequency (constant value) in the conventional method.

Assuming that the frequency fsx defined by (Equation 1) is a switching frequency, Δfs> 0 at a low temperature, so that the switching frequency fsL at this time is to the right of the frequency fs as shown in FIG. Move to the higher side,
This matches the moving directions of the characteristics FC1 and FC2 of the high frequency filters 5 and 6. Conversely, when the temperature becomes higher than the normal temperature, Δfs <0, and the switching frequency f at this time becomes
The moving direction of the sH from the frequency fs is determined by the high-frequency filters 5 and 6.
And the moving direction of the characteristic. Therefore, if the characteristics to be given to the ROM 11 are appropriately selected, the switching frequency is corrected in accordance with the temperature change without using a particularly wide pass band as the two high-frequency filters. Can also realize good reception characteristics (the same applies to transmission).

In the configuration example shown in FIG. 1, the table of the switching frequency correction value Δfs with respect to the detected temperature is linear as shown in FIG. 4, but is determined according to the temperature characteristic of the filter. Needless to say, there is no problem. If the characteristics shown in FIG. 4 can be expressed by a function, an algorithm for calculating the function may be incorporated in the control unit without using a ROM. In FIG. 1, the filter to be switched is an inter-stage filter that is located downstream of the amplifier 2. However, it goes without saying that the present invention can be applied to a filter having a similar function such as an antenna filter.

[0015]

According to the present invention, there is an effect that a transceiver capable of forming an inexpensive transmission / reception circuit of a filter switching system and having no characteristic deterioration due to a temperature change can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of a portion related to the invention of a wireless device according to the present invention.

FIG. 2 is an example of two filter characteristics (at low temperature) of a filter switching receiving circuit.

FIG. 3 is an example of two filter characteristics (at high temperature) of the filter switching receiving circuit.

FIG. 4 is an example of a switching frequency correction value versus temperature characteristic.

[Explanation of symbols]

 3, 4 switching circuit 5, 6 high frequency filter 9 control unit 10 thermistor 11 ROM

Claims (3)

[Claims] 1. A filter switching method for switching between two high-frequency filters having different passbands, which is provided in a wireless device having a variable transmission / reception frequency and switched according to the transmission / reception frequency, Detecting the temperature of the high-frequency filter, calculating a corrected switching frequency by adding a predetermined correction value corresponding to the detected temperature to a reference switching frequency determined for the reference temperature, and thus calculating A filter switching method, comprising: determining which of the two high-frequency filters is to be used depending on whether a transmission / reception frequency is higher or lower than a switching frequency. 2. A radio apparatus comprising two high-frequency filters whose transmission and reception frequencies are variable and have different pass bands which are switched according to the transmission and reception frequencies. Temperature detection means for detecting; switching frequency correction means for correcting a predetermined reference switching frequency corresponding to the detected temperature when the temperature detected by the means is given; And a high-frequency filter switching control means for determining which of the two high-frequency filters is to be used depending on whether the transmission / reception frequency is higher or lower than the switching frequency. 3. The switching frequency correction means stores a predetermined correction value of the reference switching frequency for each of the detected temperatures in a ROM, and stores a corresponding correction value from the ROM when the detected temperature is given. 3. The wireless device according to claim 2, further comprising: a calculation unit for reading and adding the read correction value to the reference switching frequency to obtain a corrected switching frequency.