JP2002057590A - Receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a receiver which can narrow a channel signal without using an antialiasing filter. SOLUTION: This receiver consists of a radio part 60 which multiplies the received radio signal by a 1st local oscillation frequency and outputs a 1st intermediate frequency signal, an A/D conversion part 70 which outputs the 1st intermediate frequency signal obtained by applying the A/D conversion to the 1st intermediate frequency signal outputted from the part 60 by a sampling system and a digital signal processing part 50 which multiplies the 1st intermediate frequency signal by a 2nd local oscillation frequency different for every channel signal for generating a 2nd intermediate frequency signal, narrows this frequency signal to a channel signal that is received via a band pass filter and demodulates the narrowed channel signal. The sampling frequency Fs of the part 70 has the value larger than that decided by subtracting the frequency band width of the channel signal from the triple frequency band width of the 1st intermediate frequency signal. In regard to the frequency band width of the 1st intermediate frequency signal, frequency interval between the least frequency value of frequency band width of the 1st intermediate and frequency 0 has a frequency interval larger than >=1/2 value decided by subtracting the frequency band width of the channel signal from the frequency band width of the 1st intermediate frequency signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio receiver used for radio communication such as mobile communication, and more particularly, to a circuit for demodulating a received signal, which is partially constituted by a digital signal processing device, and which has a receiving function. The present invention relates to a wireless receiver whose unit is realized by executing software on a digital signal processing device.

[0002]

2. Description of the Related Art In general, a receiver such as a conventional personal digital cellular (PDC) type portable telephone employs a double superheterodyne method. In a receiver of the double superheterodyne system, first, a first local oscillation frequency signal different for each channel is applied to a reception signal received by an antenna and whose frequency band is limited by a first band-pass filter (wide band). A first intermediate frequency signal of a channel to be multiplied and received (hereinafter, referred to as a target channel) is generated. Since the generated first intermediate frequency signal is output together with the extra frequency component from the first multiplier,
The excess frequency components other than the channel signal are removed by the band-pass filter (narrow band). Thereafter, the first intermediate frequency signal is multiplied by the second local oscillation frequency signal to generate a second intermediate frequency signal of the target channel. Since the generated second intermediate frequency signal is output from the second multiplier together with an extra frequency component, an extra frequency component other than the channel signal is removed by the third band-pass filter (narrow band). Thereafter, the second intermediate frequency signal is demodulated by the demodulation circuit into a data signal, an audio signal, or the like. In the above-mentioned conventional receiver, since the frequency interval between channels is narrowed in order to increase the number of channels, high frequency stability and accuracy are required as the first local oscillation frequency signal. The cost of the first local oscillator that generates the frequency signal has been expensive. Also, a first local oscillation frequency and a second band-pass filter (narrow band)
And the center error of the second local oscillation frequency and the center frequency of the third band-pass filter (narrow band). . In order to reduce the cost of the first local oscillator and reduce the frequency error in one step, a part of a circuit for demodulating a received signal is constituted by a digital signal processing device, and a part of a receiving function is replaced by the digital signal. 2. Description of the Related Art A wireless receiver (hereinafter, referred to as a digital receiver) realized by executing software on a processing device is known. Hereinafter, a conventional digital receiver will be described with reference to the drawings.

FIG. 3 is a block diagram showing a configuration of a conventional digital receiver. The conventional digital receiver 100 shown in FIG. 3 includes a receiving antenna 1 and a first intermediate frequency signal (analog) obtained by multiplying a radio signal connected to the receiving antenna 1 and received by a first local oscillation frequency signal. And an A / D converter 3 that converts the first intermediate frequency signal (analog signal) from analog (A) to digital (D) to output a first intermediate frequency signal composed of a digital signal. And the first intermediate frequency signal (digital signal)
A digital signal processing unit (DSP) 4 that multiplies the local oscillation frequency signal to generate a second intermediate frequency signal (digital signal), and further demodulates the second intermediate frequency signal to output a demodulated signal (digital signal); Consists of The radio unit 2 includes a first band-pass filter 21 for passing a frequency band (wideband) signal of all channels demodulated by a digital receiver including a target channel from a radio signal received by the antenna 1, A first local oscillator 22 for generating a first local oscillation frequency signal, a multiplier 23 for multiplying a frequency band (broadband) signal of all channels by the first local oscillation frequency and outputting a first intermediate frequency signal, A second band-pass filter for removing extra frequency components other than the desired first intermediate frequency signal from the output of the multiplier. The digital signal processor (DSP) 4 has a pass band depending on whether the target channel to be received is in the upper band or the lower band with respect to the center frequency in the frequency band of the first intermediate frequency signal. , A low-pass filter 42, a high-pass filter 43, and a switching unit 41. The digital signal processing unit 4 includes a second local oscillator 44 for generating a second local oscillation frequency signal different for each channel, and a signal of one of the low-pass filter 42 and the high-pass filter 43. And a second local oscillation frequency to output a second intermediate frequency signal, and a narrow band third signal for removing extra frequency components other than the desired second intermediate frequency signal from the multiplier output. A band-pass filter 46;
Demodulation unit 4 for demodulating the intermediate frequency signal and outputting the demodulated signal
And 7. It should be noted that all the signals are processed as digital signals inside the digital signal processing unit 4, and the second local oscillation frequency signal is also a digital signal. However, for the sake of simplicity, the description of the digital signal will be omitted below. .

[0004] A first intermediate frequency signal composed of a digital signal is supplied to a low-pass filter 42 or a high-pass filter 4.
According to No. 3, the reason that only the low band side or only the high band side of the bandwidth is used is that the first local oscillation frequency is a frequency in the middle (center) of the band. This includes an aliasing signal of the channel signal in addition to the received channel signal. For example, when there is a channel signal to be received on the lower side of the bandwidth of the first intermediate frequency signal, an aliasing signal of the channel signal is generated on the higher side of the bandwidth of the first intermediate frequency signal. ing. Conversely, if there is a channel signal to be received on the higher side of the bandwidth of the first intermediate frequency signal, an aliasing signal of the channel signal is generated on the lower side of the bandwidth of the first intermediate frequency signal. are doing. Therefore, the low-pass filter 42, the high-pass filter 43,
Is also called an anti-aliasing filter, and removes an aliasing signal.

FIGS. 4 (a) to 4 (d) are diagrams showing signals of respective sections in the digital signal processing section 4 of FIG. FIG. 4 (a)
Is a low-pass filter 42 or a high-pass filter 43
FIG. 4B is a diagram showing a first intermediate frequency signal of a wide band before being input to the first intermediate frequency signal, FIG. 4B is a diagram showing a first intermediate frequency signal passed through the high-pass filter 43, and FIG. 4
FIG. 4B is a diagram showing a second intermediate frequency signal obtained by multiplying the first intermediate frequency signal by a second local oscillation frequency signal in FIG.
(D) is a diagram illustrating a channel signal narrowed down by a narrow third bandpass filter. FIG.
The horizontal axis of (d) indicates the frequency, and the sampling frequency Fs
The scales are described for the values of Fs / 2 and Fs / 4 with respect to.
The vertical axis indicates the level of the digital signal. When quadrature detection is used, the relationship of Fs = 4 * Fc must be satisfied between the center frequency Fc of the channel signal to be demodulated and the sampling frequency Fs.
Therefore, the center frequency of the narrow band-pass filter 46 in FIG. 3 needs to be equal to the center frequency Fc of the channel signal to be demodulated, so that the center frequency of the band-pass filter 46 has a value of Fs / 4.

As shown in FIG. 4A, the first intermediate frequency signal 31 of the digital signal output from the A / D converter 3 includes a channel signal S0 to be received and a frequency of Fs / 4. An aliasing signal S1 generated at a frequency value symmetrical to the channel signal S0 about the value is included. If the aliasing signal S1 remains, the second
Since the intermediate frequency signal is adversely affected, the aliasing signal S1 is removed by the high-pass filter 43. Further, for example, the channel signal to be received is the channel signal S1.
, The low-pass filter 42 removes the aliasing signal S0. Note that the bandwidth Ba of the first intermediate frequency signal 31 of the digital signal output from the A / D converter 3 and the analog signal supplied to the A / D converter 3 from the radio unit 2 (second bandpass filter) No.
1 The bandwidth of the intermediate frequency signal is equal, but for the sake of convenience, the bandwidth of the first intermediate frequency signal of the analog signal in the following description is described as Ba 'in order to distinguish between the two. FIG.
(B) shows a case where the aliasing signal S1 is removed by the high-pass filter 43 and only the channel signal S0 is left.
1 shows an intermediate frequency signal 32. The first intermediate frequency signal 32 is a signal that is multiplied by the second local oscillation frequency signal. FIG. 4C shows the channel signal S0 output from the multiplier 45 as a result of multiplying the channel signal S0 in the first intermediate frequency signal 32 by the second local oscillation frequency signal.
2 shows the second intermediate frequency signal 33 including the channel signal S3 and the channel signal S3. The channel signal S2 is a signal obtained by multiplying the second local oscillation frequency signal by the channel signal S0, and is Fs / 4 which is the center frequency of the band-pass filter 46.
Has been shifted to overlap the value of FIG. 4 (d)
A second intermediate frequency signal 34 in which other signals have been removed from the second intermediate frequency signal 33 by a narrow band-pass filter 46 to become only the channel signal S2 is shown. As described above, in the conventional digital receiver 100, when performing quadrature detection, it is necessary to remove an aliasing signal with respect to a received channel signal. Therefore, the anti-aliasing including the high-pass filter and the low-pass filter is required. A filter had to be provided.

[0007]

However, the above-mentioned anti-aliasing filter removes a plurality of interfering waves in the first intermediate frequency signal 31 and also outputs a signal (S) / noise (N) of a target channel signal. ) To ensure the ratio,
The filter must have very steep characteristics. This anti-aliasing filter is used by the digital signal processing unit 4
Since the filter is realized by executing software inside the filter, the amount of processing of the digital signal at the point where the characteristic is changed becomes enormous due to the filter having a steep characteristic. The digital signal processing unit 4 generates the second local oscillation frequency signal, processes the first intermediate frequency signal 32 and the second
Since it is necessary to execute many processes such as a multiplication process with the local oscillation frequency signal and a demodulation process of the channel signal S2, if the amount of processing for the anti-aliasing filter becomes enormous, the processing for other processes is performed. An adverse effect such as a delay may occur. SUMMARY OF THE INVENTION The present invention has been made to solve the above-described conventional problems, and has as its object to provide a receiver capable of narrowing down channel signals without using an anti-aliasing filter.

[0008]

In order to achieve the above-mentioned object, a receiver according to the present invention of the first aspect comprises an analog first analog signal which is multiplied by a first local oscillation frequency. A radio section for outputting an intermediate frequency signal,
An A / D converter for outputting a digital first intermediate frequency signal obtained by analog-to-digital conversion of the analog first intermediate frequency signal by using a sampling method; and a second local oscillator different from the digital first intermediate frequency signal for each channel signal A digital signal processing unit that generates a digital second intermediate frequency signal by multiplying the digital second intermediate frequency signal by a frequency, narrows down the digital second intermediate frequency signal to a channel signal to be received by a band-pass filter, and demodulates the channel signal. Wherein the sampling frequency of the A / D conversion unit is a frequency equal to or higher than a value obtained by subtracting the value of the frequency bandwidth of the channel signal from a triple value of the frequency bandwidth of the digital first intermediate frequency signal. The lowest frequency value of the frequency bandwidth of the digital first intermediate frequency signal is the frequency bandwidth of the digital first intermediate frequency signal. Characterized in that the value is 1/2 or more of the value of the value obtained by subtracting the value of the frequency bandwidth of the channel signal. A receiver according to a second aspect of the present invention includes a radio section for outputting an analog first intermediate frequency signal of an analog signal by multiplying a received radio signal by a first local oscillation frequency, and the analog first intermediate frequency signal. Digital-to-analog-to-digital conversion using sampling method
An A / D converter that outputs an intermediate frequency signal; multiplies the digital first intermediate frequency signal by a second local oscillation frequency that differs for each channel signal to generate a digital second intermediate frequency signal; A digital signal processing unit for narrowing down a frequency signal to a channel signal to be received by a band-pass filter and demodulating the channel signal, wherein a sampling frequency of the A / D conversion unit is:
A frequency equal to or higher than a value obtained by subtracting the value of the frequency bandwidth of the channel signal from the triple value of the frequency bandwidth of the digital first intermediate frequency signal, and the highest frequency value in the digital first intermediate frequency signal and the A The frequency interval between the value of the sampling frequency of the / D conversion unit and the value of the frequency bandwidth of the digital first intermediate frequency signal is 1 / the value of the value obtained by subtracting the value of the frequency bandwidth of the channel signal. It is characterized in that the value is 2 or more. According to a third aspect of the present invention, in the receiver according to the first or second aspect, the bandwidth of the wide-band analog first intermediate frequency signal output from the wireless unit is a band-pass provided in the wireless unit. It is characterized by being set by a filter.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on illustrated embodiments. FIG. 1 is a block diagram showing a configuration of a digital receiver according to one embodiment of the present invention. FIG.
In the figure, portions having the same functions as those of the conventional digital receiver shown in FIG. 3 are denoted by the same reference numerals, and redundant description will be omitted. As shown in FIG. 1, the digital receiver 200 of the present embodiment is configured to multiply a receiving antenna 1 and a radio signal connected to the receiving antenna 1 and received by a first local oscillation frequency signal to obtain a first intermediate frequency. A radio unit 60 that outputs a signal (analog); and an A / D that outputs a first intermediate frequency signal composed of a digital signal by converting the first intermediate frequency signal (analog) from analog (A) to digital (D). The converter 70 multiplies the first intermediate frequency signal (digital) by the second local oscillation frequency signal to generate a second intermediate frequency signal (digital), and further demodulates the second intermediate frequency signal to output a demodulated signal. A digital signal processing unit (DSP) 50,
Consists of The general flow of the received signal of the present embodiment flowing from the wireless unit 60 to the digital signal processing unit 50 via the A / D conversion unit 70 is the same as that of the conventional digital receiver 100 shown in FIG. From inside the signal processing unit 50, a low-pass filter 42, a high-pass filter 43, and a switching unit 41 for switching a pass band.
Is structurally different in that is deleted. Further, in the present embodiment, in order to eliminate the low-pass filter 42, the high-pass filter 43, and the switching unit 41, the radio unit 60, the A / D conversion unit 70, and the digital signal processing unit (DSP) The processing contents in each of the 50 are different. The internal configuration of the radio unit 60 includes a first band-pass filter 21, a first local oscillator 22, a multiplier 23,
Is the same as that of the conventional digital receiver 100 shown in FIG. 3, but the pass frequency band (bandwidth Ba ') of the second band-pass filter 61 for removing extra frequency components other than the first intermediate frequency signal is 3 is different from the pass band of the conventional second band pass filter 24 shown in FIG. As a configuration inside the digital signal processing unit (DSP) 50,
As described above, except that the low-pass filter 42, the high-pass filter 43, and the switching unit 41 are deleted, the digital signal processing unit 4 has the same configuration as the conventional digital signal processing unit 4 shown in FIG. I have. Here, the bandwidth of the first intermediate frequency signal of the analog signal output from the radio unit 60 shown in FIG. 3 is Ba ', and the frequency bandwidth of the first intermediate frequency signal after being converted into a digital signal is Ba. The center frequency of the channel signal to be received is Fa, the bandwidth of the channel signal to be received is Bc, the sampling frequency of the A / D converter 70 is Fs, and the center frequency of the highest frequency channel signal in the bandwidth Ba is Fa_max (the highest frequency value), and the center frequency of the lowest frequency channel signal in the bandwidth Ba is Fa_min (the lowest frequency value).

First, in the present embodiment, the A / D converter 70
Sampling frequency Fs is a frequency equal to or higher than a value obtained by subtracting the value of the bandwidth Bc of the channel signal from the triple value of the bandwidth Ba of the digital first intermediate frequency signal 81 (Fs ≧ 3Ba−
Set to Bc). Sampling frequency Fs is 3Ba-
The reason for setting Bc or more is to prevent the folded frequency signal generated by shifting the channel signal from overlapping with the received frequency signal. next,
In the present embodiment, the received channel signal has a frequency of Fs /
4 and in the frequency band between frequency Fs / 2,
The minimum frequency value Fa_min is equal to or more than 値 of the value obtained by subtracting the value of the bandwidth Bc of the channel signal from the value of the frequency bandwidth Ba of the digital first intermediate frequency signal 81 (Fa_mi).
n> (Ba−Bc) / 2) so that the wireless unit 6
The bandwidth Ba 'of the analog first intermediate frequency signal output from 0 is set. Further, when the received channel signal is in a frequency band lower than the frequency Fs / 4, the highest digital first intermediate frequency signal 81 output from the A / D converter 70 to the digital signal processor 50 is used. The interval between the frequency Fa_max and the frequency Fs / 2 is (Ba−B
c) The bandwidth Ba 'of the first intermediate frequency signal of the analog signal output from the radio unit 60 is set to be equal to or more than / 2. At the time of the above setting, the bandwidth Ba '(= Ba) of the first intermediate frequency signal is set to １ ／ or less of the sampling frequency Fs of the A / D converter 70 (≦ Fs / 4).
The first analog signal output from the radio unit 60
The reason why the bandwidth Ba 'of the intermediate frequency signal is set as described above will be further described.

FIGS. 2A to 2C are diagrams showing signals of respective sections in the digital signal processing section 50 of FIG. FIG.
FIG. 2A is a diagram showing a wide band first intermediate frequency signal input to the digital signal processing unit 50, and FIG. 2B is a diagram showing a second intermediate frequency signal obtained by multiplying the first intermediate frequency signal by a second local oscillation frequency signal.
FIG. 2C is a diagram showing an intermediate frequency signal, and FIG. 2C is a diagram showing a channel signal narrowed down by a narrow band third band-pass filter. The horizontal axis in FIGS. 2A to 2C indicates frequency, and Fs / 2, Fs with respect to the sampling frequency Fs.
A scale is described for the value of s / 4. As shown in FIG. 2A, in the first intermediate frequency signal 81 output from the A / D converter 70, the frequency band is narrowed down by the second band-pass filter 61 in the radio unit 60. As a result, the bandwidth Ba includes only the received channel signal S0. As described above, in the present embodiment, the aliasing signal S
Since 1 does not exist before input to the digital signal processing unit 50, the anti-aliasing filter is not required. FIG. 2B shows a channel signal S2 output from the multiplier 45 as a result of multiplying the channel signal S0 in the first intermediate frequency signal 81 by the second local oscillation frequency signal.
And the second intermediate frequency signal 82 including the channel signal S3. The channel signal S2 is a signal obtained by multiplying the second local oscillation frequency signal by the channel signal S0, and is Fs / 4 which is the center frequency of the band-pass filter 46.
Has been shifted to overlap the value of FIG. 2 (c)
A second intermediate frequency signal 83 in which other signals have been removed from the second intermediate frequency signal 82 by the narrow band pass filter 46 to become only the channel signal S2 is shown. When setting the bandwidth Ba of the first intermediate frequency signal of the analog signal output from the radio unit 60, for example, when the received channel signal is in the frequency band between the frequency Fs / 4 and the frequency Fs / 2 Is the lowest frequency Fa_min of the pass frequency band Ba of the second band-pass filter 61, as shown in FIG.
(Ba)-(Bc) / 2 or more as shown in (a). With this setting, it is possible to prevent the folded frequency signal generated by shifting the channel signal from overlapping with the received frequency signal. Also,
When the channel signal to be received is in a frequency band lower than the frequency Fs / 4, the pass frequency band Ba of the second band-pass filter 61 is changed from the frequency value 0 to the frequency value Fs / 4.
Is set so that the folded frequency signal generated by shifting the channel signal does not overlap with the received frequency signal. A / D as in this embodiment
Sampling frequency Fs of conversion section 70 and radio section 60
By setting the bandwidth Ba of the first intermediate frequency signal output from the first intermediate frequency signal input from the A / D converter 70 to the digital signal processing unit 50, the aliasing signal does not exist. The anti-aliasing filter, which was conventionally required, is not required. Therefore,
A receiver capable of narrowing down channel signals without using an anti-aliasing filter can be provided.

[0012]

As described above, according to the present invention, the sampling frequency of the A / D conversion unit and the bandwidth of the first intermediate frequency signal output from the radio unit are set, and the signals input to the digital signal processing unit are set. Since the aliasing signal can be eliminated, it is possible to provide a receiver capable of narrowing down the channel signal without using an anti-aliasing filter which requires a large amount of software processing.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a digital receiver according to an embodiment of the present invention.

FIGS. 2A to 2C are diagrams showing signals of respective units in the digital signal processing unit of FIG.

FIG. 3 is a block diagram showing a configuration of a conventional digital receiver.

FIGS. 4A to 4D are diagrams illustrating signals of respective units in the digital signal processing unit of FIG. 3;

[Explanation of symbols]

1 ··· Antenna, 2 and 60 ··· Wireless section, 3 and 70 ·
..A / D converters, 4, 50... Digital signal processors, 21... First band-pass filters, 22.
Local oscillator, 23 ... multiplier, 24, 61 ... second
Band-pass filter, 31 ... second intermediate frequency signal (with aliasing signal), 32, 81 ... first intermediate frequency signal (without aliasing signal), 33, 82 ...
1st intermediate frequency signal (before band narrowing), 34, 83
..First intermediate frequency signal (after band narrowing), 41...
Switching section, 42 ... Low-pass filter, 43 ...
High-pass filter, 44... Second local oscillator, 45.
..Multiplier, 46... Third band-pass filter, 47.
..Demodulation units

Claims (3)

[Claims] 1. A radio unit for outputting an analog first intermediate frequency signal of an analog signal by multiplying a received radio signal by a first local oscillation frequency, and sampling the analog first intermediate frequency signal using a sampling method. A for outputting a digital first intermediate frequency signal obtained by analog / digital conversion
/ D conversion unit, multiplies the digital first intermediate frequency signal by a second local oscillation frequency different for each channel signal to generate a digital second intermediate frequency signal, and converts the digital second intermediate frequency signal by a band-pass filter. A digital signal processing unit for narrowing down to a channel signal to be received and demodulating the channel signal, wherein a sampling frequency of the A / D conversion unit is a frequency bandwidth of the digital first intermediate frequency signal. A frequency equal to or higher than a value obtained by subtracting the value of the frequency bandwidth of the channel signal from the tripled value, and the lowest frequency value of the frequency bandwidth of the digital first intermediate frequency signal is the frequency bandwidth of the digital first intermediate frequency signal A value obtained by subtracting the value of the frequency bandwidth of the channel signal from the value of the channel signal. 2. A radio section for multiplying a received radio signal by a first local oscillation frequency to output an analog first intermediate frequency signal of an analog signal, and sampling the analog first intermediate frequency signal using a sampling method. A for outputting a digital first intermediate frequency signal obtained by analog / digital conversion
/ D conversion unit, multiplies the digital first intermediate frequency signal by a second local oscillation frequency different for each channel signal to generate a digital second intermediate frequency signal, and converts the digital second intermediate frequency signal by a band-pass filter. A digital signal processing unit for narrowing down to a channel signal to be received and demodulating the channel signal, wherein a sampling frequency of the A / D conversion unit is a frequency bandwidth of the digital first intermediate frequency signal. A frequency equal to or higher than a value obtained by subtracting the value of the frequency bandwidth of the channel signal from the tripled value, and the highest frequency value in the digital first intermediate frequency signal and a half of the sampling frequency of the A / D converter. The frequency interval between the two values is 1/1/3 of the value obtained by subtracting the value of the frequency bandwidth of the channel signal from the value of the frequency bandwidth of the digital first intermediate frequency signal. Receiver, which is a value greater than or equal. 3. The receiver according to claim 1, wherein a bandwidth of the wide-band analog first intermediate frequency signal output from the radio unit is set by a band-pass filter provided in the radio unit. Receiver.