JP3029342B2 - Receiver circuit of wireless communication device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio communication device used in a mobile radio communication system such as a portable / automobile telephone system and a cordless telephone device, and more particularly to a radio communication device employing a dual mode as a radio communication system. Related to a receiving circuit.

[0002]

2. Description of the Related Art In recent years, a system employing a dual mode wireless communication system has been proposed as one of mobile wireless communication systems. The dual mode is a system using both the analog mode and the digital mode.
The analog mode is a method in which a carrier is modulated by, for example, FM with a voice signal and data on a transmission side and transmitted, and a reception side receives a modulated carrier transmitted from the transmission side and performs FM demodulation to reproduce voice and data. It is. On the other hand, in the digital mode, a voice signal and data are encoded on a transmission side, a carrier is modulated by the encoded signal according to, for example, a π / 4 shift DQPSK system, and transmitted. In this method, after receiving and demodulating a modulated carrier, the demodulated signal is decoded to reproduce an audio signal and data. In the wireless communication in the digital mode, a method is generally used in which a plurality of time slots are time-division multiplexed and transmitted by one radio frequency.

FIG. 2 shows a configuration of a receiving circuit of a radio communication device used in a system employing such a dual mode. In FIG. 1, a radio signal arriving via a radio line is received by an antenna 1 and then input to a high-frequency amplifier 3 via a duplexer (DUP) 2, and is amplified by the high-frequency amplifier 3 and then to a first mixer. 4 is input. In the first mixer 4, the received radio signal is mixed with a local oscillation signal generated from a first local oscillator 5, and thereby frequency-converted into a first intermediate frequency signal. Note that, for example, a frequency synthesizer 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, the signal 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 to be demodulated.

That is, in the case of the analog mode, the second intermediate frequency signal is limited in amplitude by an amplitude limiter (LIM) 11 and then input to a 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 demodulated signal to a speaker (not shown).

On the other hand, in the digital mode, the second intermediate frequency signal is gain-controlled by an automatic gain control circuit (AGC) 21 and then input to a third mixer 22. Then, in the third mixer 22, the signal is mixed with the local oscillation signal generated from the third local oscillator 23 to become a baseband signal, and the digital demodulator (DEM) 2
4 is input. In the digital demodulator 24, the baseband signal is demodulated by digital signal processing, and the resulting digital demodulated signal is supplied to a decoder (not shown) for error correction decoding and voice decoding. .

In the above-mentioned radio communication apparatus, when a high-power radio signal is received, for example, when a radio communication apparatus of a communication partner is nearby, the high-frequency amplifier 3 of the receiving circuit and each mixer 4, 4 7 has a high gain, so that the second intermediate frequency signal is distorted. When this distortion occurs, the following problems occur in the conventional receiving circuit.

That is, in a mobile wireless communication system,
In general, since wireless channels used for communication are arranged at a fixed frequency interval, if unnecessary waves are radiated from a wireless communication device during communication, adverse effects such as interference may occur on other adjacent wireless channels, which may cause a serious problem. Not preferred. Therefore, as described above, the receiving circuit of the wireless communication device includes band-pass filters 6, 9 in the first and second intermediate frequency stages, respectively.
Are provided, and the filters 6 and 9 limit the band of the received intermediate frequency signal. In the digital mode, a band occupied by one radio channel is wider than that in the analog mode. Therefore, a band limiting filter called a Nyquist filter is always inserted into the baseband section of the digital demodulation circuit. I have. However, with such a configuration, a high-power radio signal is received in the digital mode as described above,
As a result, when distortion occurs in the second intermediate frequency signal, the code error rate of the digital demodulated signal is significantly degraded due to the influence of the band limitation by the band-pass filter 9 of the second intermediate frequency stage, thereby lowering the communication quality.

On the other hand, in order to improve the bit error rate of the digital demodulated signal, it is conceivable 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, and as a result, the reception quality deteriorates.

[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 occurs or sufficient channel selectivity cannot be obtained in the analog mode.

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

[0011]

According to the present invention, there is provided a radio communication apparatus comprising an analog mode and a digital mode as radio communication systems, and performing radio communication by selectively using these modes. In the receiving circuit, in addition to frequency conversion means for receiving and converting the frequency of the radio signal into a predetermined intermediate frequency signal, a first filter means having a predetermined pass bandwidth, Second filter means having a pass band wider than the pass band. In the state of the analog mode, the received intermediate frequency signal output from the frequency conversion means is band-limited by the first filter means for analog demodulation, while in the state of the digital mode,
The reception intermediate frequency signal output from the frequency conversion means is band-limited by a second filter means and is subjected to 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 subjected to band limitation by the first filter having a narrow pass band. On the other hand, in the digital mode, the received intermediate frequency signal is input to the digital demodulation circuit after being subjected to band limitation by the second filter means having a wide pass band. That is, in the analog mode, the narrow band first filter means is used, and in the digital mode, the wide band second filter means is used. Therefore, in the digital mode, even if the intermediate frequency signal is distorted due to the reception of a high-power radio signal, the intermediate frequency signal is subjected to digital demodulation with almost all of its effective band. Error rate degradation is prevented. On the other hand, in the analog mode, the intermediate frequency signal is subjected to analog demodulation after being subjected to sufficient band limitation by a narrow-band filter, so that sufficient channel selectivity can be obtained. Therefore, it is possible to obtain a high-quality demodulated signal both in the analog mode and in the digital mode.

[0013]

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

A first band-pass filter 31 is interposed between the second mixer 7 and the analog demodulation circuit 10,
A second band-pass filter 31 is interposed between the second mixer 7 and the digital demodulation circuit 20.
First, the first band-pass filter 31 has a narrow-band band-pass characteristic set so that a sufficient channel selectivity can be obtained in the analog demodulation circuit 10. On the other hand, the second bandpass filter 32 has a wideband bandpass characteristic set in the digital demodulation circuit 20 so as to suppress the deterioration of the bit 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 oscillator signal and the second local oscillator signal are respectively amplified by the first mixer 4 and the second mixer 7. The signal is mixed with the two local oscillation signals and down-converted into a predetermined second intermediate frequency signal. 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 a 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. For this reason, the effective band of the second intermediate frequency signal is supplied to the digital demodulation circuit 20 as it is with almost no band limitation. Therefore,
Even if a high-power radio signal is received and the second intermediate frequency signal is distorted due to the reception, the digital demodulation circuit 2 is almost kept without removing the entire band including the distortion.
Therefore, the digital demodulation circuit 20 can obtain a high-quality demodulated digital signal without deteriorating 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 the present embodiment, since the band pass filter 31 for the analog mode and the band pass filter 32 for the digital mode are separately provided, a sufficient channel selectivity in the analog mode is provided. 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 the distortion is not cut off 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 and 31 are used for the analog mode and the digital mode.
Although 32 is provided, it is also possible to form a filter having a variable pass band by using an active filter or the like, and to variably set the band pass characteristics of the filter between the analog mode and the digital mode.

Further, in the above-described embodiment, a case where a so-called superheterodyne type receiving circuit for down-converting a radio signal in two stages is used has been described as an example. 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 without departing from the gist 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 into a predetermined intermediate frequency signal, a first filter having a predetermined pass bandwidth is provided. Means, and second filter means having a pass band 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 converted to the first signal. (1) In the digital mode, the intermediate frequency signal output from the frequency conversion means is band-limited by the second filter means for digital demodulation. It is.

Therefore, according to the present invention, even if distortion occurs in the intermediate frequency signal due to reception of a high-power radio signal, the bit error rate does not deteriorate 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 apparatus capable of performing a high-quality demodulation operation in both the digital mode and the analog mode.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram illustrating 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]

Reference Signs List 1 antenna, 2 duplexer (DUP), 3 high frequency amplifier, 4 first mixer, 5 first local oscillator, 6 first
Band pass filter of intermediate frequency stage, 7 second mixer, 8
... second 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 ... third mixer, 23 ... third local oscillator, 24 ... digital demodulator, 31 ... first band-pass filter, 32 ...
Second bandpass filter.

Claims (1)

(57) [Claims] An analog mode and a digital mode are provided as a wireless communication system, and a receiving circuit of a wireless communication apparatus for performing wireless communication by selectively using these modes receives a wireless signal and receives a predetermined intermediate frequency. Frequency conversion means for converting a frequency into a signal; and in the analog mode state, the reception intermediate frequency signal output from the frequency conversion circuit is band-limited in accordance with a predetermined first band-pass characteristic and subjected to analog demodulation. First
And in the digital mode state, the received intermediate frequency signal output from the frequency conversion circuit is converted in accordance with a second band-pass characteristic having a wider pass band width than the first band-pass characteristic. A receiving circuit for a wireless communication apparatus, comprising: second filter means for performing band demodulation for digital demodulation.