JPH05235643A - Receiver - Google Patents

Abstract

PURPOSE:To obtain an excellent reception characteristic even when the receiver receives undesired radiation from a local oscillator by providing a high pass filter having a prescribed attenuation within a shift frequency band of the local oscillator in a stage between a frequency converter and a demodulator. CONSTITUTION:A ratio D/U of a desired wave level D to an interference wave level U is maximum being nearly 7dB and at least 3dB or over when the wave of the U is overlapped with a maximum frequency shift frequency of frequency modulation of the D wave. The cut-off frequency of high pass filters 108,109 in use is set to 30% of the maximum frequency shift, when the frequency difference between both the waves is 25% of the maximum frequency shift of the frequency modulation signal used for the system, the result of the calculation of the required D/U is -2dB. This shows improvement of nearly 5dB from the result of calculation (3dB), and then the receiver with immunity against undesired radiation via the local oscillator from other station is obtained without revision of other sections of the receiver.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver used in mobile communication systems such as mobile phones, car phones and pagers.

[0002]

2. Description of the Related Art Generally, a direct conversion receiving method and a superheterodyne receiving method are known as receiving methods in mobile communication systems such as mobile phones, car phones, and pagers. Hereinafter, these two methods will be described.

The direct conversion receiving system is a receiving system in which a received high frequency RF signal is mixed with a local oscillator signal having the same frequency as that of the received high frequency RF signal and the frequency is directly converted into a base band for detection. FIG. 7 shows a configuration example of the direct conversion receiver. In the figure, the RF signal received from the antenna 201 is R
After passing through the F filter 202, it is amplified by the RF amplifier 203, divided into two channels, and mixed by a mixer (frequency converter) 2
At 04 and 207, from the local oscillator 206,
It is mixed with a carrier having the same frequency as the RF signal. This local oscillator includes first mixers 204 and 9
Each of them is connected to the second mixer 207 via the 0 ° phase shifter 205.

The received RF signal is converted into a baseband signal having a 90 ° phase relationship by the first and second mixers, passed through lowpass filters 210 and 211, and then amplified by baseband amplifiers 212 and 213. For example, it is detected by a detector such as the flip-flop detector 214. In addition, the AC coupling 2 in the latter stage of the mixer
08 and 209 are inserted for the purpose of removing the DC component in order to prevent the filters 210 and 211 and the amplifiers 212 and 213 from being saturated by the DC component generated in the mixer.

On the other hand, the super-heterodyne receiving system mixes a received radio frequency (RF) signal with a signal having a first reference frequency to obtain a difference or sum of frequencies of the radio frequency (RF) signal and the first reference frequency. Intermediate frequency (IF)
To get Further, this is a receiving system in which the IF signal is mixed with a second reference frequency, the frequency is converted into a base band, and detection is performed. FIG. 13 shows a configuration example of a super heterodyne receiver. In the figure, the RF signal received from the antenna 23 passes through the image suppression RF filter 24,
The signal is amplified by the RF amplifier 25 and mixed by the mixer 26 with the first reference signal from the local oscillator 27.

After passing through the image suppressing filter 28, the output signal of the mixer 26 is mixed with the unmodulated wave of the second reference frequency from the local oscillator 30 in the mixer 29. Then, after removing unnecessary frequency components from the output of the mixer 29 through the channel selection filter 31,
Further, it is input to the detector 33 and demodulated.

The above-described direct conversion receiving system is used for the superheterodyne system RF stage because it does not have an intermediate frequency and does not have an image response in principle because it directly converts the frequency of the RF signal to baseband. With the advance of LSI in recent years, downsizing of the receiver can be realized for the reasons that a sharp filter for image removal which is already required is unnecessary, a filter for baseband channel selection can be LS1. It is receiving attention as a reception method.

In an actual direct conversion receiver, since the isolation between the RF ports of the mixers 204 and 207 and the local port (L0) is not perfect, the carrier wave from the local oscillator 206 leaks to the RF section (215). , 216), is transmitted through the RF amplifier 203 and the RF filter 202 (217) and is radiated into the air from the antenna 201. This leakage also occurs from the common bias power supply line for the RF circuit.

The unnecessary radiation of the local oscillator thus generated can be considered in the case of the super-heterodyne system, but in the super-heterodyne system, the carrier frequency of the received signal and the oscillation frequency of the local oscillator in the receiver are different (for example, 455 KHz), the power is radiated into the air to some extent because it is attenuated by the image suppression filter that normally uses the received signal as a pass band. On the other hand, in the direct conversion method,
Since the frequency of the desired wave and the oscillation frequency of the local oscillator of the receiver are the same, the RF filter has a perfect pass band against leakage from the local oscillator, and there is no part that attenuates unnecessary radiation power radiated from the antenna. Mixer (L
0-RF isolation) and RF amplifier (reverse characteristic) only. In this respect, the direct conversion method is disadvantageous as compared with the super heterodyne method.

Further, the output level of a local oscillator of a typical small receiver is usually required to be about -20 dBm to 0 dBm, and this value is considerably larger than that of an RF signal normally received, and the propagation loss of space is taken into consideration. However, the unnecessary radiation into the air of the local oscillator described above cannot be ignored. The radiation from the local oscillator to the air does not cause any trouble for the receivers having the same receiving frequency adjacent to each other because the receiving frequency and the local oscillator frequency are different in the super-heterodyne system, but in the case of the direct conversion system. Has the same frequency as the received signal, it becomes an interfering wave with respect to adjacent receivers that use the same frequency, causing radio wave interference between the receivers. In a wide area wireless communication system as well as when a direct conversion receiver is used in a relatively narrow place such as a local area wireless communication system, radio wave interference between the receivers becomes a serious problem.

FIG. 10 shows a reception spectrum when the local oscillator unnecessary radiation power radiated from such a direct conversion receiver is received by the direct conversion receiver using the same reception frequency in the system. It is a figure. Reception frequency 402 shown in FIG.
At, the local oscillator signal 403 radiated from the proximity receiver is received, overlapping the desired wave 401.
This oscillator signal 403 causes deterioration of reception sensitivity in the detector at the subsequent stage.

Next, another problem of the direct conversion receiver will be described. As mentioned above,
In the direct conversion receiver, when the L0-RF isolation is not perfect, the local oscillator 303 leaks into the RF port as shown in FIG. 8 (304).
However, at this time, a part of this signal is reflected (305) due to a mismatch or the like of the RF filter 301 and is mixed again with the local oscillator signal and the mixer 302, and the phase difference between the two signals at this time is There is a drawback in that a direct current output (DC component: 307 shown in FIG. 9) is generated in the band 306 to saturate the baseband active element 311 in the subsequent stage, resulting in sensitivity deterioration. To solve these problems, as shown in Japanese Patent Laid-Open No. 2-58948, a capacitor is inserted in series with the mixer output (AC couple: 310, 208, 209 in FIG. 7) and shown in 312 of FIG. By realizing such frequency characteristics, it was possible to remove the DC component, prevent saturation of the active element 311 in the subsequent stage, and prevent malfunction of the detector. Further, this AC couple was also effective in preventing malfunction of the circuit in the subsequent stage due to thermal noise 308 or 1 / f noise 309 in the low frequency range, which is peculiar to the dilent conversion receiver.

However, the AC couple (series capacitor) used in the conventional direct conversion receiver has a DC component of the mixer output, a thermal noise near DC,
The purpose is to remove 1 / f noise, which is insufficient for the purpose of attenuating the received local oscillator unnecessary radiation signal as described in FIG.

On the other hand, although the super-heterodyne receiver does not radiate an interference wave itself, it receives radio wave interference from an adjacent direct conversion receiver.

FIG. 14 shows a reception spectrum in the IF frequency band when the local oscillator unnecessary radiated power radiated from the direct conversion receiver is received by the super-heterodyne receiver using the same reception frequency in the system. It is the figure which showed. At the IF frequency 34, the local oscillator signal 35 having a frequency close to the frequency of the desired wave radiated from the proximity receiver is frequency-converted in the same manner as the desired wave 36, and appears overlapping the desired wave. This oscillator signal 35 causes deterioration of reception sensitivity in the subsequent detector.

Therefore, it is necessary to somehow remove the local oscillator signal 35.

[0017]

As described above, in the conventional direct conversion receiver, the leakage power is radiated from the antenna when the local oscillator is in an operating state, and this unnecessary radiation is generated between the receivers. It was causing mutual interference.

That is, in the system using the direct conversion receiving system, it becomes difficult to receive a desired wave due to unnecessary radiation of the local oscillator from other direct conversion receivers in the system.
Therefore, there is a problem that a stable service cannot always be provided. Therefore, in order to effectively apply the direct conversion receiver to the wireless communication system, the emission of the local oscillator output is suppressed, or the leakage local oscillator power received by the receiving side is not affected in some way in reception. Need to decline to a level.

Further, in the conventional super-heterodyne receiver, the reception sensitivity is deteriorated by the interference wave having a frequency close to the reception frequency. Such an interference wave having a frequency close to the reception frequency cannot be ignored particularly when a direct conversion receiver is included as a slave station used in a wireless system.

For example, in the paging system, a method of simultaneously communicating with slave stations belonging to a certain group in the same time slot is adopted. In such a case, all the stations belonging to the same group are The local oscillator of the receiver is activated. Therefore, there is a problem that a plurality of slave stations that use the same carrier frequency that are close to each other cause radio interference and cause a decrease in reception sensitivity. In addition, even when the direct conversion method is adopted for the receiving unit of a mobile phone or the like, in the case of control information communication or broadcast communication, the receiving units of the slave stations in the zone are in the operating state at the same time. There is a problem that radio wave interference occurs between a plurality of terminals using the carrier frequency.

Therefore, in order to effectively apply the direct conversion receiver to the wireless communication system, the leaked local oscillator power received by the superheterodyne receiver in the same system does not affect reception in some way. Need to decline to a level.

The present invention has been made in order to solve such a conventional problem, and an object thereof is to achieve a good result even when the local oscillator unnecessary radiation is received from an adjacent direct conversion receiver. It is to provide a receiver capable of realizing reception characteristics.

[0023]

To achieve the above object, the present invention provides a local oscillator for generating a reference signal having a frequency substantially equal to the center frequency of a digitally or analogically amplitude-modulated or frequency-modulated high-frequency signal. A phase shifter for obtaining first and second reference signals whose phases are orthogonal to each other with respect to the reference signal from the local oscillator, the high frequency signal, and the first and second phase shifters from the phase shifter.
Of the first reference signal and the second reference signal of
First and second frequency converters for obtaining the baseband signal of the above, and a first frequency converter having the output of the frequency converter as an input signal
And a second low-pass filter, first and second amplifiers for amplifying the output of the low-pass filter, and a demodulator for demodulating the amplifier output signal. Between the first and second frequency converters and the demodulator, the low cutoff frequency is the deviation frequency of the local oscillator allowed by the specifications of the wireless communication system, and the frequency modulation used in the wireless system. It is characterized in that it has a high-pass filter that is set between the maximum frequency shift frequency of the signal and has a predetermined amount of attenuation outside the band.

Further, in a receiver for obtaining received data by mixing a predetermined reference signal with a high frequency signal frequency-modulated by a digital or analog signal to convert it into an intermediate frequency, and demodulating this by a demodulator to obtain received data. A band cutoff filter is provided in the front stage of the device, and the band cutoff filter has a center frequency that matches the center frequency of the reception frequency signal or the intermediate frequency signal, and the cutoff frequency is allowed by the specifications of the wireless communication system. It is characterized in that it is set to a width between the shift frequency and the maximum frequency shift frequency of the frequency modulation signal and has a predetermined amount of attenuation within the band.

[0025]

In the direct conversion receiver according to the present invention, in order to attenuate the unnecessary radiated power from the direct conversion receiver in the vicinity, the cutoff frequency between the frequency converter and the demodulator is set according to the specifications of the wireless communication system. A high-pass filter that is set between the allowed deviation frequency of the local oscillator and the maximum frequency deviation frequency of the frequency-modulated signal used in the wireless communication system and has a certain amount of attenuation outside the band. Since it is provided, even if unnecessary radiated power from a direct conversion receiver in the vicinity is received, this unnecessary radiated power can be removed, and good wireless communication can be achieved without causing radio wave interference between adjacent slave stations. Will be able to do.

Also, in the superheterodyne receiver of the present invention, similarly, in order to attenuate unnecessary radiation power from the direct conversion receiver adjacent thereto, the cutoff frequency is provided in the preceding stage of the demodulator according to the specifications of the wireless communication system. It is set to the width between the allowable deviation frequency of the local oscillator and the maximum frequency deviation frequency of the frequency modulation signal, and since it has a band stop filter with a certain amount of attenuation in the band. , Does not cause radio wave interference.

[0027]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a direct conversion receiver to which the present invention is applied. In the figure, the order of the RF filter 202 and the RF amplifier 203 may be reversed.

The direct conversion receiver shown in the figure has a high level for attenuating this signal to the preceding stage of the detector 114 when the local oscillator output radiated from the direct conversion receiver of another adjacent station is received. The bandpass filters 108 and 109 are provided. First, the characteristics of these filters will be described.

First, focusing on the out-of-band attenuation characteristic of this high-pass filter, the desired wave level (D) and the local oscillator output radiated from an adjacent receiver to satisfy a predetermined reception error rate. It is necessary to find the relationship (required D / U) with the reception level (U) of (interference wave). here,
Assuming the conventional receiver shown in FIG. 7, a result of a computer experiment performed on a digital frequency modulation signal (NRZ-FSK) will be described.

FIG. 2 shows a reception error rate of 10 ^-2 for a direct conversion receiver with a transmission rate: maximum frequency deviation of R FSK: Dev 2 * Dev / R (modulation index of FSK) = 6. Is a calculation result showing the relationship (D / U) between the desired wave level (D) and the interference wave level (U) for As a result, due to the frequency difference between the D wave and the U wave,
The desired D / U is different, and the required D / U becomes the largest when the U wave overlaps the maximum frequency shift frequency of the frequency modulation of the D wave.
It can be seen that D / U of B or more is required. This required D
Note that / U is the D / U at the input of demodulator 114.

In the receiver of this embodiment, this required D
In order to realize / U, it is characterized by having a wide-pass filter having a characteristic of passing only the main spectrum component of the D wave and attenuating the U wave.
Therefore, the high-pass filter to be used does not necessarily have to be inserted only after the filters 108 and 109 shown in FIG. 1, and is appropriately divided so as to satisfy the required D / U at the stage before the demodulator. It may be inserted and inserted.

FIG. 3 shows the required D / U when the cutoff frequency of the high-pass filters 108 and 109 is set to 30% of the maximum frequency deviation in the receiver shown in FIG. Is the calculation result of. When the frequency difference between the U wave and the D wave is 25% of the maximum frequency deviation of the frequency modulation signal used in the system, the required D / U is -2 dB, which is a conventional receiver. Comparing with the calculation result (FIG. 2), it can be seen that it is improved by about 5 dB as compared with 3 dB. Therefore, as compared with the conventional direct conversion receiver, it is possible to realize a receiver resistant to unnecessary radiation of the local oscillator from other stations without changing the other parts of the receiver.

From the above description, the lower limit frequency of the cutoff frequency of the high-pass filter to be inserted is the shift frequency of the local oscillator allowed by the specifications of the radio communication system in which the present receiver is used ( It is obvious that the frequency shift due to the normal temperature change) may be used. As a result, it becomes possible to attenuate the received leakage local oscillator output of another station.

On the contrary, since the upper limit frequency of the cutoff frequency attenuates the leakage oscillator power mixed in the reception band, it is desirable to be able to attenuate the unnecessary radiation power from other stations in the widest possible band. From a point of view, it is clear that a higher cutoff frequency is better.
However, if the cutoff frequency of this high-pass filter is set too high, the portion of the signal component of the desired wave that is lost will increase, and this will degrade the normal reception sensitivity. In particular, when the frequency offset of the local oscillator occurs, when the cutoff frequency of the high-pass filter to be inserted is high, the lost portion of the signal component of the desired wave increases significantly, so that the reception error rate Deterioration becomes severe. This state is shown in FIG. In the figure, (a) shows a signal component 904 lost when the high-pass filter 903 is applied to the signal component 902 after frequency conversion (DC 901).
Is shown. On the other hand, when there is a frequency offset of the local oscillator (reference oscillator) of FIG. 6B, the center frequency of the signal component 906 of the frequency converter output is offset from the direct current 901 by the amount indicated by 909. For frequency modulated signals with few signal components in the center frequency part of the signal,
The number of signal components 908 lost when the high-pass filter 907 is applied is larger than that in the case of no frequency offset 904, which leads to deterioration of the reception error rate.

FIG. 4 is a diagram for explaining the upper limit of the cutoff frequency of the high-pass filter with respect to the above problems. When the cutoff frequency of the high-pass filter is changed, the frequency offset of the local oscillator is It shows the deterioration of the reception error rate at a certain time. In this calculation, it is assumed that there is no interference wave (leakage local oscillator power from another station). Here, in FIG. 4A, the cutoff frequency of the high-pass filter is 0 Hz (ideal case),
(B) shows the frequency offset of the local oscillator and the deterioration of reception sensitivity when the cutoff frequency of the high-pass filter is 50% of the maximum frequency deviation of FSK and (c) is 75%. ..

In FIG. 4, the cutoff frequency in (a) is 0H.
For z, until the local oscillator frequency offset is about 60% of the maximum frequency deviation of the frequency modulated signal,
While the deterioration of the reception error rate is about 3 dB, it is about 5 dB in (b) and 7 dB in (c). This is deterioration due to the loss of frequency components near the maximum frequency shift that includes a large amount of power (information). From the above, it can be seen that the upper limit of the cutoff frequency of the high-pass filter needs to be set at least equal to or lower than the maximum frequency deviation of the signal used in the system.

The purpose of the AC couple (804 in FIG. 5) used in the conventional direct conversion is to attenuate the thermal noise of the DC component and the frequency around it, and the cutoff frequency is near DC (about 50 Hz). On the other hand, the high-pass filter according to the present invention uses the local oscillator unnecessary radiation power 8 radiated from another adjacent station.
However, the frequency characteristic is as shown by 805, and is generally set higher than the cutoff frequency in the conventional case. It should be noted that depending on the amount of band attenuation required, this high-pass filter is simply A
It is also possible to realize with only C couple.

In the above description, although the high-pass filters 108 and 109 are connected in cascade to the low-pass filters 110 and 111 in the subsequent stage shown in FIG. 1, they are combined with the low-pass filters 110 and 111. It is obvious that the whole may be realized as a bandpass filter.

Further, the high-pass filter and AC coupling having the characteristics shown here are not realized by only one stage, but many stages are provided between stages such as a baseband filter, an amplifier, and a limiting amplifier. You may also insert separately.

The present invention also relates to the RF amplifier 1 shown in FIG.
It can also be applied to a receiver having a configuration in which a mixer 115 and an oscillator 116 as shown in FIG.

FIG. 12 is a block diagram showing a second embodiment of the present invention, showing a super-heterodyne receiver. The receiver shown in the figure is provided with a band stop filter 17 for attenuating this signal up to the preceding stage of the detector 22 when the local oscillator output radiated from the direct conversion receiver of another adjacent station is received. There is. First, the characteristics of these filters will be described.

First, the relationship between the desired wave level (D) and the reception level (U) of the local oscillator output (interference wave) radiated from an adjacent receiver to satisfy a predetermined reception error rate (required) D / U). The desired D / U differs depending on the frequency difference between the D wave and the U wave, and the most necessary D is when the U wave overlaps the maximum frequency shift frequency of the frequency modulation of the D wave.
/ U becomes large. It should be noted that this required D / U is the D / U at the input of demodulator 22. Usually, this D / U has a value of 3 to 7 dB.

In the receiver according to the present invention, in order to realize the required D / U, only a main spectrum component of the D wave is passed and a band cutoff having a characteristic of attenuating the U wave is provided. It is characterized by having a filter. Therefore, the band stop filter in the present invention does not necessarily need to be inserted only at the position 17 shown in FIG. 12, and the required D
It suffices if they are appropriately divided and inserted so as to satisfy / U. As a result, compared with the conventional direct conversion receiver, it is possible to realize a receiver that is resistant to the unwanted radiation of the local oscillator from other stations without changing the other parts of the receiver. ..

FIG. 15 shows the characteristics of the band stop filter.
In the characteristic 51 of the band stop filter to be inserted, the lower limit value of the width between the stop frequency and the center frequency 49 of the stop band of the filter is the local oscillator allowed by the wireless communication system specification in which the present receiver is used. It is obvious that the deviation frequency (normally, frequency deviation due to temperature change) may be used. As a result, it becomes possible to attenuate the received leakage local oscillator output of another station.

On the contrary, since the upper limit means that the leakage oscillator power mixed in the reception band is attenuated, it is desirable to be able to attenuate the unnecessary radiation power from other stations in a band as wide as possible. Obviously, the higher the cutoff frequency is, the better. However, if the stop band of this band stop filter is set too wide, the desired wave 52
This results in a loss of normal reception sensitivity, since more of the signal component of is lost. In particular, when the frequency offset of the local oscillator occurs, when the stop band of the band stop filter to be inserted is wide, the lost part of the signal component of the desired wave is significantly increased, which deteriorates the reception error rate. Becomes fierce. This state is shown in FIG.

FIG. 7A shows the result after frequency conversion (center frequency 5).
The signal component 53 lost when the band stop filter 55 is applied to the signal component 56 of 4) is shown. On the other hand, when there is a frequency offset of the local oscillator (reference oscillator) of FIG. 6B, the center frequency of the signal component 62 of the frequency converter output is 5 times the maximum attenuation frequency of the filter.
Offset from 8 by the amount indicated by reference numeral 60. A frequency-modulated signal having a small number of signal components in the center frequency portion of the signal is lost as a signal component 57 when the band stop filter 61 is applied.
Is larger than 53 when there is no frequency offset, which leads to deterioration of the reception error rate.

Therefore, in consideration of the temperature characteristics of the reference oscillator used in the actual communication system, the upper limit of the absolute value of the cutoff frequency of the band stop filter is at least the maximum frequency deviation of the signal used in the system. It turns out that it needs to be set to:

Further, the band stop filter having the characteristics shown here is not realized by only one stage, but may be inserted into the RF stage or each intermediate frequency stage in many stages.

Further, in FIG. 12, a receiver having two intermediate frequencies has been described, but one intermediate frequency or 3
The same is true for one or more intermediate frequency receivers.

[0050]

As described above, in the direct conversion and superheterodyne receiver according to the present invention, when the unnecessary radiation of the local oscillator output, which is a problem in the conventional direct conversion receiver, is received. Received unwanted radiation power (interference wave)
Since it has a function of attenuating the signal to the extent that it does not affect the reception characteristic, it is possible to obtain a good reception characteristic even when the direct conversion receiving terminal is used in close proximity.

Further, if the receiving side is provided with the function of attenuating the interference wave as shown in the present invention, the amount of attenuation required for the radiated power is small on the side that radiates the local oscillator signal. The required isolation value between the (L0) -RF port and the required shield value of the housing can be relaxed, and the manufacturing of the receiver becomes easier than before. As a result, it is possible to provide an effect that it is possible to provide a wireless communication system that can always perform good communication even if a direct conversion receiver is adopted as a slave station.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a direct conversion receiver that is a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a required D / U of a receiver.

FIG. 3 is an explanatory diagram showing an effect of improving required D / U.

FIG. 4 is an explanatory diagram showing deterioration of a reception error rate when there is a frequency offset of a reference oscillator.

FIG. 5 is an explanatory diagram showing a cutoff frequency of the high pass filter according to the first embodiment.

FIG. 6 shows a case where there is a frequency offset of a reference oscillator,
It is explanatory drawing which shows the deterioration of a reception error rate.

FIG. 7 is a block diagram showing a conventional direct conversion receiver.

FIG. 8 is an explanatory diagram showing a DC offset generated in a receiver.

FIG. 9 is an explanatory diagram showing a DC offset generated in a receiver.

FIG. 10 is an explanatory diagram showing received local oscillator unwanted radiation.

FIG. 11 is an explanatory diagram showing a modified example of the first embodiment.

FIG. 12 is a configuration diagram showing an embodiment of a super heterodyne receiver that is a second embodiment of the present invention.

FIG. 13 is a configuration diagram showing a conventional super-heterodyne receiver.

FIG. 14 is a diagram for explaining an interference wave close to an intermediate frequency.

FIG. 15 is a diagram for explaining the characteristics of a band cutoff filter.

FIG. 16 is a diagram for explaining deterioration of a reception error rate when there is a frequency offset of a local oscillator.

[Explanation of symbols]

 12 high frequency filter 13 high frequency amplifier 14 frequency converter 15 local oscillator 16 band pass filter 17 band stop filter 18 frequency converter 19 local oscillator 22 demodulator 101 antenna 102 high frequency filter 103 high frequency amplifier 104, 107 mixer 105 π / 2 transporter 106 Local oscillator 108,109 High pass filter 112,113 Baseband amplifier 114 Demodulator

Claims (9)

[Claims] 1. A local oscillator for generating a reference signal having a frequency substantially equal to the center frequency of a high frequency signal digitally or analogically frequency-modulated, and a first reference signal from the local oscillator whose phases are orthogonal to each other. And a phase shifter for obtaining a second reference signal, the high frequency signal, and the first and second reference signals from the phase shifter, respectively, to mix the first and second baseband signals. First and second frequency converters for obtaining, first and second low-pass filters using the frequency converter output as an input signal, and first and second for amplifying the low-pass filter output In a receiver including a second amplifier and a demodulator for demodulating the amplifier output signal, a low cutoff frequency is provided between the first and second frequency converters and the demodulator. Communication A high frequency band that is set between the deviation frequency of the local oscillator allowed by the system specifications and the maximum frequency deviation frequency of the frequency modulation signal used in the wireless system, and that has a certain amount of attenuation outside the band. A receiver having a pass filter. 2. The bandpass filter comprises first and second bandpass filters.
The receiver according to claim 1, wherein the receiver is realized by inserting one or more capacitors between the frequency converter and the demodulator. 3. The out-of-band attenuation of the high-pass filter is such that the level of the received local oscillator signal of the other station is higher than the reception sensitivity level of the desired wave in the preceding stage of the demodulator.
The receiver according to claim 1, wherein the receiver is set smaller by at least a predetermined value. 4. The predetermined value is a receiver error rate of 10
The receiver according to claim 3, which is set to be ^-2 or less. 5. The receiver according to claim 1, wherein the high pass filter is integrated with the low pass filter and is realized as a band pass filter. 6. A receiver in which a predetermined reference signal is mixed with a high-frequency signal frequency-modulated by a digital or analog signal to convert it into an intermediate frequency, and this is demodulated by a demodulator to obtain received data. A band cutoff filter is provided in the front stage of the device, and the band cutoff filter has a center frequency that matches the center frequency of the reception frequency signal or the intermediate frequency signal, and the cutoff frequency is allowed by the specifications of the wireless communication system. A receiver characterized by being set to a width between the shift frequency of and the maximum frequency shift frequency of the frequency-modulated signal and having a predetermined amount of attenuation within the band. 7. The receiver according to claim 6, wherein a plurality of the band stop filters are installed before the demodulator. 8. The in-band attenuation amount of the high-pass filter is such that the level of the received local oscillator signal of another station is higher than the reception sensitivity level of the desired wave in the preceding stage of the demodulator.
The receiver according to claim 6 or 7, wherein the receiver is set smaller by at least a predetermined value. 9. The predetermined value is a receiver error rate of 10
The receiver according to claim 8, which is set to be ^-2 or less.