JPH05327536A - Receiving circuit for radio communication equipment - Google Patents

Abstract

PURPOSE:To attain the demodulating operation of a high quality in both a digital mode and an analog mode by preventing the generation of the deterioration of a code error ratio in the digital mode, and obtaining a sufficient channel selectivity in the analog mode, even at the time of the generation of the distortion of an intermediate frequency signal due to the reception of the radio signal of a large power. CONSTITUTION:This circuit is equipped with a first band pass filter 31 having a prescribed pass band width, and a second band pass filter 32 having the wider pass band width than the pass band width of the band pass filter 31. Then, in the analog mode, the received second intermediate frequency signal outputted from a second mixer 7 is band-limited by the first band pass filter 31, and supplied to an analog demodulating circuit 10. And also, in the digital mode, the received second intermediate frequency signal outputted from the second mixer 7 is band-limited by the second band pass filter 32, and supplied to a digital demodulating circuit 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless communication device used in a mobile wireless communication system such as a mobile / automobile phone system or a cordless phone device, and more particularly to a wireless communication device adopting a dual mode as a wireless communication system. Of the receiver circuit.

[0002]

2. Description of the Related Art Recently, a system adopting a dual mode wireless communication system has been proposed as one of mobile wireless communication systems. The dual mode is a system that uses both an analog mode and a digital mode.
The analog mode is a method in which a carrier wave is FM-modulated by a voice signal and data on the transmitting side and transmitted, and a modulated carrier wave sent from the transmitting side on the receiving side is received and FM demodulated to reproduce voice and data. Is. On the other hand, in the digital mode, a voice signal and data are encoded on the transmitting side, a carrier wave is modulated by the encoded signal by, for example, a π / 4 shift DQPSK system, and then transmitted, and the receiving side transmits from the transmitting side. In this system, a modulated carrier wave is received and demodulated, and then the demodulated signal is decoded to reproduce a voice signal and data. In the wireless communication in the digital mode, a method in which a plurality of time slots are time-division multiplexed by one radio frequency and transmitted is generally used.

FIG. 2 shows a configuration of a receiving circuit of a wireless communication device used in a system adopting such a dual mode. In the figure, a radio signal arriving via a radio line is received by an antenna 1, then input to a high frequency amplifier 3 via a duplexer (DUP) 2, amplified by the high frequency amplifier 3, and then a first mixer. Input to 4. In the first mixer 4, the received radio signal is mixed with the local oscillation signal generated from the first local oscillator 5, and thereby frequency-converted into the first intermediate frequency signal. A frequency synthesizer, for example, is used as the first local oscillator. The first mixer 4
The first intermediate frequency signal output from is subjected to band limitation by the band pass filter 6 and then input to the second mixer 7,
Here, it is mixed with a local oscillation signal generated from the second local oscillator 8 and frequency-converted into a second intermediate frequency signal. Then, the second intermediate frequency signal output from the second mixer 7 passes through the band pass filter 9, and then is input to the analog demodulation circuit 10 or the digital demodulation circuit 20 and demodulated.

That is, in the analog mode, the second intermediate frequency signal is amplitude-limited by the amplitude limiter (LIM) 11 and then input to the frequency discriminator (DISC) 12 where it is demodulated and demodulated. The output is amplified by an audio frequency amplifier (AFA) 13 and then output as an analog demodulation signal to a speaker (not shown).

On the other hand, in the digital mode, the second intermediate frequency signal is input to the third mixer 22 after being gain-controlled by the automatic gain control circuit (AGC) 21. The third mixer 22 mixes with the local oscillation signal generated from the third local oscillator 23 to form a baseband signal, and the digital demodulator (DEM) 2
Input to 4. In the digital demodulator 24, the baseband signal is demodulated by digital signal processing, and the digital demodulated signal obtained by this is supplied to a decoder (not shown) for error correction decoding processing and speech decoding processing. ..

By the way, when a high-power radio signal is received in the above-mentioned wireless communication device, for example, when a wireless communication device of a communication partner is present nearby, the high-frequency amplifier 3 of the receiving circuit and the mixers 4, 4. Since 7 has a high gain, distortion occurs in the second intermediate frequency signal. When this distortion occurs, the following problems occur in the above conventional receiving circuit.

That is, in the mobile wireless communication system,
In general, the wireless channels used for communication are arranged at fixed frequency intervals, so if an unwanted wave is radiated from the wireless communication device during communication, adverse effects such as interference will occur on other adjacent wireless channels. Not good for Therefore, in the receiving circuit of the wireless communication device, as described above, the bandpass filters 6 and 9 are provided in the first and second intermediate frequency stages, respectively.
Is provided and the band of the received intermediate frequency signal is limited by these filters 6 and 9. Further, particularly in the digital mode, the band occupied by one radio channel is wider than that in the analog mode, so that a band limiting filter called a Nyquist filter is always inserted in the base band part of the digital demodulation circuit. There is. However, with such a configuration, in the digital mode, a high-power radio signal is received as described above,
When the second intermediate frequency signal is distorted by this, the bit error rate of the digital demodulated signal is significantly deteriorated due to the effect of the band limitation by the band pass filter 9 of the second intermediate frequency stage, and the communication quality is deteriorated.

On the other hand, in order to improve the code error rate of the digital demodulated signal, it is possible to widen the pass band of the band pass filter 9 of the second intermediate frequency stage. However, in this case, the channel selectivity of the analog demodulation circuit cannot be sufficiently obtained in the analog mode, resulting in deterioration of reception quality.

[0009]

As described above, in the conventional receiving circuit, when a high power radio signal is received and the second intermediate frequency signal is distorted by this, the bit error rate in the digital mode is reduced. There is a problem that deterioration is caused or sufficient channel selectivity cannot be obtained in the analog mode.

The present invention has been made in view of the above circumstances, and an object of the present invention is to improve the code error rate in the digital mode even if the intermediate frequency signal is distorted by the reception of a high-power radio signal. It is an object of the present invention to provide a receiving circuit of a radio communication device which does not cause deterioration and which can obtain a sufficient channel selectivity in the analog mode and can perform high quality demodulation operation in the digital mode and the analog mode.

[0011]

In order to achieve the above object, the present invention provides a wireless communication system having an analog mode and a digital mode as a wireless communication system, and selectively using these modes for wireless communication. In the receiving circuit, in addition to frequency conversion means for receiving a radio signal and frequency-converting it into a predetermined intermediate frequency signal, a first filter means having a predetermined pass band width, and a first filter means of the first filter means. And a second filter means having a pass band width wider than the pass band width. In the analog mode, the received intermediate frequency signal output from the frequency conversion means is band-limited by the first filter means and subjected to analog demodulation, while in the digital mode,
The received intermediate frequency signal output from the frequency conversion means is band-limited by the second filter means and is used for digital demodulation.

[0012]

As a result, according to the present invention, in the analog mode, the received intermediate frequency signal is input to the analog demodulation circuit after being band-limited by the first filter means having a narrow pass band. On the other hand, in the state of the digital mode, the received intermediate frequency signal is input to the digital demodulation circuit after being band-limited by the second filter means whose pass band width is set to a wide band. That is, the narrow band first filter means is used in the analog mode, and the wide band second filter means is used in the digital mode. Therefore, even if the intermediate frequency signal is distorted due to the reception of a high-power radio signal in the digital mode, the effective frequency band of the intermediate frequency signal is almost completely used for digital demodulation. Error rate degradation is prevented. On the other hand, in the analog mode, the intermediate frequency signal is subjected to sufficient band limitation by the narrow band filter and then subjected to analog demodulation, so that sufficient channel selectivity can be obtained. Therefore, it is possible to obtain a high-quality demodulated signal in both the analog mode and the digital mode.

[0013]

1 is a circuit block diagram showing the configuration of a receiving circuit of a dual mode wireless communication apparatus according to an embodiment of the present invention. In the figure, the same parts as those in FIG. 2 are designated by the same reference numerals and detailed description thereof will be omitted.

A first bandpass filter 31 is interposed between the second mixer 7 and the analog demodulation circuit 10,
In addition, a second band pass filter 31 is provided between the second mixer 7 and the digital demodulation circuit 20.
Of these, the first band-pass filter 31 has a narrow-band band-pass characteristic set so that sufficient channel selectivity is obtained in the analog demodulation circuit 10. On the other hand, the second bandpass filter 32 has a wideband bandpass characteristic which is set in the digital demodulation circuit 20 so as to suppress the deterioration of the code error rate within a predetermined range.

With such a configuration, the radio signal received by the antenna 1 is amplified by the high frequency amplifier 3, and then the first local oscillation signal and the first local oscillation signal by the first mixer 4 and the second mixer 7, respectively. The two local oscillation signals are mixed and down-converted to a predetermined second intermediate frequency signal. Then, first in the state of the analog mode, the second
The second intermediate frequency signal output from the mixer 7 is subjected to a narrow band limitation by the first band pass filter 31 and then input to the analog demodulation circuit 10 and demodulated. Therefore, the analog demodulation circuit 10 can obtain sufficient channel selectivity.

On the other hand, in the digital mode, the second intermediate frequency signal output from the second mixer 7 is input to the digital demodulation circuit 20 after passing through the second band pass filter 32. At this time, the band pass characteristic of the second band pass filter 32 is set to a wide band as described above. Therefore, the effective band of the second intermediate frequency signal is supplied to the digital demodulation circuit 20 almost without any band limitation. Therefore,
Even if a high-power radio signal is received and the second intermediate frequency signal is distorted due to this, the entire band including the distortion is not deleted and the digital demodulation circuit 2 is almost unchanged.
As a result, the digital demodulation circuit 20 can obtain a high-quality demodulated digital signal without degrading the error rate. The channel selectivity in the digital mode can be sufficiently obtained by the Nyquist filter provided in the baseband circuit system.

As described above, according to this embodiment, since the bandpass filter 31 for the analog mode and the bandpass filter 32 for the digital mode are separately provided, the channel selectivity in the analog mode is sufficient. On the other hand, in the digital mode, even if a high-power radio signal is received and the second intermediate frequency signal is distorted, the effective band including this distortion is not removed and is used for digital demodulation. Therefore, a good code error rate can be obtained.

The present invention is not limited to the above embodiment. For example, in the above embodiment, separate band pass filters 31 for analog mode and digital mode,
Although 32 is provided, a pass band variable type filter may be configured by using an active filter or the like, and the band pass characteristic of this filter may be variably set in the analog mode and the digital mode.

In the above embodiment, the case where a so-called super-heterodyne type receiving circuit for down-converting a radio signal in two steps is used has been described as an example, but the present invention can be applied to a receiving circuit for down-converting in one step. it can.

In addition, the configurations of the frequency conversion circuit, the analog demodulation circuit and the digital demodulation circuit, and the types of the radio communication system and the radio communication device can be variously modified and implemented without departing from the scope of the present invention.

[0021]

As described above in detail, according to the present invention, in addition to the frequency conversion means for receiving a radio signal and converting the frequency of the radio signal into a predetermined intermediate frequency signal, the first filter having a predetermined pass band width is provided. Means and a second filter means having a pass band width wider than the pass band width of the first filter means. In the analog mode, the intermediate frequency signal output from the frequency conversion means is first In the digital mode, the intermediate frequency signal output from the frequency conversion means is band-limited by the second filter means to be used for digital demodulation. Is.

Therefore, according to the present invention, even if the intermediate frequency signal is distorted due to the reception of a high-power radio signal, the code error rate is not deteriorated in the digital mode, and the channel selectivity is sufficient in the analog mode. Therefore, it is possible to provide a receiving circuit of a wireless communication device capable of performing high-quality demodulation operation in both digital mode and analog mode.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing a configuration of a receiving circuit of a wireless communication device according to an embodiment of the present invention.

FIG. 2 is a circuit block diagram showing a configuration of a receiving circuit of a conventional wireless communication device.

[Explanation of symbols]

1 ... Antenna, 2 ... Duplexer (DUP), 3 ... High frequency amplifier, 4 ... First mixer, 5 ... First local oscillator, 6 ... First
Bandpass filter of intermediate frequency stage, 7 ... Second mixer, 8
... 2nd local oscillator, 10 ... Analog demodulation circuit, 11 ... Amplitude limiter, (LIM), 12 ... Frequency discriminator (DIS
C), 13 ... Audio frequency amplifier (AFA), 20 ... Digital demodulation circuit, 21 ... Automatic gain control circuit (AGC), 2
2 ... 3rd mixer, 23 ... 3rd local oscillator, 24 ... Digital demodulator, 31 ... 1st band pass filter, 32 ...
Second bandpass filter.

Claims (1)

[Claims] 1. A radio communication system comprising an analog mode and a digital mode, and a reception circuit of a radio communication device which selectively uses these modes to perform radio communication, receives a radio signal, and outputs a predetermined intermediate frequency. Frequency conversion means for frequency-converting into a signal, and in the state of the analog mode, the reception intermediate frequency signal output from the frequency conversion circuit is band-limited according to a predetermined first band-pass characteristic and provided for analog demodulation. First
In the digital mode, the received intermediate frequency signal output from the frequency conversion circuit is subjected to a second band pass characteristic whose pass band width is set wider than that of the first band pass characteristic. A receiver circuit of a wireless communication device, comprising: second filter means for band limiting and for digital demodulation.