JP3178997B2 - Frequency conversion circuit and wireless communication device provided with this frequency conversion circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency conversion circuit provided for converting a received radio frequency signal into an intermediate frequency signal or a base band signal in, for example, a radio communication device. The present invention relates to a frequency conversion device that performs frequency conversion by sampling with a pulse train.

[0002]

2. Description of the Related Art Conventionally, this kind of frequency conversion device is composed of a sampling circuit and a square wave generator for supplying a sampling signal as a local oscillation signal to the sampling circuit. The square wave generator generates a square wave signal having a lower frequency than the radio frequency input signal. The sampling circuit samples the input signal according to a square wave sampling signal generated from the square wave generator,
Thereby, the input signal is frequency-converted into an intermediate frequency signal and output.

[0003] The principle will be described below. The waveform of the band-limited input signal in the time domain is represented by r (t), and the spectrum of the input signal in the corresponding frequency domain is represented by R (f). This spectrum R (f) is obtained by performing a Fourier transform on r (t) and has a waveform as shown in FIG. Assuming that the period (pulse width: Ts / 2) of the square wave corresponding to the local oscillation signal l (t) is Ts as shown in FIG. 2, the spectrum L (f) of this square wave is as shown in FIG. Sin (πf) is added to the impulse train at the interval Ts (= 1 / Fs).
Ts / 2) / (πfTs / 2).

[0004] Sampling of an input signal r (t) with this square wave l (t) means that the spectrum R (f) of the input signal and the spectrum L (f) of the square wave are convolved in the frequency domain. Is equivalent to Therefore, when the input signal r (t) is sampled by the square wave l (t), an intermediate frequency signal is obtained as shown in FIG. The center frequency Fi of the intermediate frequency signal is the difference (Fc-Fs) between the center frequency Fc of the input signal and the reciprocal Fs of the period Ts of the square wave.

[0005]

However, in the frequency converter using the above-mentioned sampling method, depending on the value of the sampling frequency Fs, a plurality of input signals having different frequencies may be frequency-converted into the same frequency range. there were. That is, signals in a plurality of frequency ranges before conversion may be superimposed in the same frequency range after frequency conversion.
When this superposition occurs, it becomes impossible to reproduce any of the plurality of input signals in the demodulation circuit at the subsequent stage, and communication becomes impossible, which is very undesirable.

On the other hand, the frequency-converted intermediate frequency signal is
For example, after being converted into a digital signal by an A / D converter, the digital signal is input to a digital signal processing circuit (DSP).
Here, digital demodulation processing and decoding processing are performed. Considering this digital signal processing, it is desirable that the frequency of the intermediate frequency signal after frequency conversion is as low as possible.

However, when the input signal is sampled using the sampling signal composed of a square wave as described above, the signal level of the output signal after sampling in the low frequency range is greatly reduced depending on the pulse width of the square wave. As a result, an intermediate frequency signal having a sufficiently low signal level cannot be output.

As described above, in the conventional frequency conversion device using the sampling method, depending on the sampling frequency, signals in a plurality of frequency ranges before conversion after frequency conversion are superimposed and signal reproduction becomes impossible. There is a problem that, depending on the pulse width of the sampling signal, the amplitude is reduced in the low frequency range after the frequency conversion, so that an intermediate frequency signal with a sufficiently low signal level cannot be output. I was

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to prevent signals in a plurality of frequency ranges from being superimposed after frequency conversion and before conversion, whereby an accurate frequency conversion operation can be performed over the entire frequency band to be received. It is to provide a frequency conversion device.

It is an object of the present invention to provide a frequency conversion device capable of outputting a low-frequency intermediate frequency signal having a sufficiently low signal level while suppressing a decrease in signal level in a low frequency range.

An object of the present invention is to provide a radio communication apparatus having a frequency conversion device capable of performing frequency conversion on input signals of a plurality of radio channels so that signals after frequency conversion do not overlap each other.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a frequency converter capable of outputting an intermediate frequency signal having a sufficiently high signal level in a low frequency range without input signals being superimposed on a plurality of radio systems in different use frequency bands. An object of the present invention is to provide a wireless communication device provided with the device.

The present invention provides a sampling circuit for receiving an input signal having a predetermined center frequency and a predetermined bandwidth, sampling the input signal in accordance with a sampling signal having a predetermined sampling frequency, and outputting an intermediate frequency signal; And a sampling signal generating circuit for outputting to the sampling circuit a sampling signal having a frequency determined so that the frequency of the input signal does not fall within a frequency range of an integer multiple of three times or more. I do.

According to the present invention, a received signal arriving from one of a plurality of wireless devices in different frequency bands is received, and the received signal is converted into a first intermediate frequency signal having a lower frequency than the received signal frequency. A frequency conversion circuit, a sampling circuit that samples the first intermediate frequency signal according to a sampling signal of a predetermined sampling frequency, and outputs a second intermediate frequency signal; and a frequency that is an integer multiple of three times or more of the sampling frequency. A second frequency conversion circuit configured by a sampling signal generation circuit that outputs a sampling signal having a sampling frequency set so that the frequency of the first intermediate frequency signal does not enter to the sampling circuit; And a demodulating means for demodulating the intermediate frequency signal.

According to the present invention, it is possible to perform frequency conversion so that signals of a plurality of frequencies before sampling do not overlap each other in the same frequency range after sampling. Therefore, over the entire frequency band of one wireless system to be received, all channel signals can be accurately frequency-converted without overlapping.

According to the present invention, when a pulse signal having a pulse width is used as a sampling signal, the value of the pulse width is set to a value that satisfies a predetermined condition, thereby reducing the frequency of the signal after frequency conversion. Attenuation in the frequency range is suppressed, so that an intermediate frequency as low as possible can be obtained by frequency conversion by sampling.

Further, according to the present invention, in a wireless communication apparatus provided with a frequency conversion apparatus, an optimum sampling frequency for frequency conversion is calculated for each wireless system to be communicated, and is changed to a sampling signal generation circuit. Can be set. For this reason, it is possible to perform frequency conversion with an optimum sampling frequency that does not cause the superimposition phenomenon for any of a plurality of wireless systems using different frequency bands.

Further, according to the present invention, in a wireless communication apparatus including a frequency converter employing a sampling method and using a pulse train having a pulse width as a sampling signal used in the frequency converter, an optimum sampling frequency is obtained. And a circuit for variably setting the sampling signal generation circuit and calculating the optimum pulse width and providing a circuit for variably setting the sampling signal generation circuit. Also, the frequency conversion can be performed using a sampling pulse set at an optimum sampling frequency that does not cause the superimposition phenomenon and at an optimum pulse width that can suppress signal level attenuation.

[0019]

FIG. 5 shows a digital portable telephone device provided with a frequency conversion device according to a first embodiment. According to this, a radio communication signal transmitted from a base station (not shown) via a radio communication channel receives a reception circuit (R) via an antenna 1 and an antenna duplexer (DUP) 2.
X) 3 is input. The receiving circuit 3 includes a plurality of stages of frequency converters, which will be described later. In these frequency converters, a wireless communication signal is transmitted by a frequency synthesizer (SY).
N) The signal is mixed with the reception local oscillation signal generated from 4 and converted to an intermediate frequency.

The received intermediate frequency signal IFS output from the receiving circuit 3 is converted into an analog-digital (A / D) converter 7.
Is converted into a digital signal DRS at the step S1 and then input to a digital demodulation circuit (DEM) 6. In the digital demodulation circuit 6, signal processing for digital demodulation is performed after frame synchronization and bit synchronization with respect to the received signal are achieved. The digital speech signal output from the digital demodulation circuit 6 is output to an error correction decoding circuit (CH-D
EC) 8, decodes the data in an error correcting manner, and then decodes it in a speech decoding circuit (SP-DEC) 9,
After the analog (D / A) converter 10 returns the signal to an analog call signal, it is supplied to a speaker 11 and
1 is output.

On the other hand, the transmission signal input to the microphone 12 is digitized by the A / D converter 13,
The acoustic echo component is canceled by the acoustic echo canceller (AEC) 14, and thereafter, the speech encoding circuit (SP)
-COD) 15. In the voice coding circuit 15, a digital transmission signal is coded by a coding method such as the VSELP method. The coded digital transmission signal obtained by this coding is subjected to error correction coding by an error correction coding circuit (CH-COD) 16 together with a digital control signal output from a control circuit 20A, and then to a digital modulation circuit (MOD). ) 17 is input.

In the digital modulation circuit 17, a modulation signal corresponding to the coded digital transmission signal is generated. This modulation signal is converted into an analog signal by the D / A converter 18, and then input to the transmission circuit (TX) 5. Is done. In the transmission circuit 5,
The modulated signal is mixed with the transmission local oscillation signal output from the frequency synthesizer 4 and converted into a radio frequency signal, and then the control signal TCS supplied from the control circuit 20A.
The transmission power is controlled according to the following. The radio frequency signal output from the transmitting circuit 5 is transmitted from the antenna 1 to a base station (not shown) via the antenna duplexer 2.

In the apparatus of this embodiment, the digital demodulation circuit 7, digital modulation circuit 17, error correction code circuit 8, error correction decode circuit 16, voice decode circuit 9, voice code circuit 15, and acoustic echo canceller 14 Are realized by digital signal processing by a digital signal processing circuit (DSP) 19.

The control circuit 20A includes, for example, a microcomputer as a main control section, and has a wireless channel connection control function, a communication control function, and the like as its control functions. The key input unit 21 is provided with a call key, an end key, a dial key, various function keys, and the like.
The LCD 24 is used to display the telephone number of the communication partner terminal, the operation state of the device, and the like. 22 is a power supply circuit (P
OW), and the power supply circuit 22 generates a required operating voltage Vcc based on the output voltage of the battery 23 and supplies it to each circuit.

The receiving circuit 3 is configured as follows. FIG. 6 is a circuit block diagram showing the configuration. In the figure, a received radio frequency signal is first amplified by a high frequency amplifier 31 and then input to a first mixer 32 where it is mixed with a local oscillation signal output from a frequency synthesizer 4 to form a first received intermediate frequency signal. Is converted. This first received intermediate frequency signal is supplied to a first intermediate frequency filter 33.
Then, after passing through the first intermediate frequency amplifier 34, it is input to the frequency conversion circuit 35 according to the present invention.

The frequency conversion circuit 35 includes a sampling circuit 36, an impulse train generator 37 as a sampling signal generator, and a low-pass filter 38.

The impulse train generator 37 generates an impulse train SP1 whose frequency is fixedly set in advance as a sampling signal, and supplies it to the sampling circuit 36. The sampling circuit 36 samples the first reception intermediate frequency signal in accordance with the impulse train SP1 supplied from the impulse train generator 37, and outputs the sampling output as a second reception intermediate frequency signal. Low-pass filter 38
Selectively passes the desired signal having the lowest frequency from the output signals of the sampling circuit 36. The received intermediate frequency signal output from the low-pass filter 38 is
The signal is input to the A / D converter 7 via the intermediate frequency amplifier 39.

The frequency Fs of the impulse train SP1 in the second frequency conversion circuit 35 is determined as follows based on the center frequency of the first reception intermediate frequency signal which is the input signal to the sampling circuit 36 and its bandwidth. Is set to That is, assuming now that the center frequency of the first reception intermediate frequency signal input to the sampling circuit 36 is Fc and its bandwidth is 2 · FB, the frequency Fs of the impulse train SP1 is

(Equation 5)

Next, the operation of the frequency conversion circuit configured as described above will be described.

Now, it is assumed that the first reception intermediate frequency signal whose waveform in the time domain is r (t) and whose spectrum in the frequency domain is R (f) is input to the sampling circuit 36. At this time, from the impulse train generator 37, the period is set to Ts as shown in FIG. 7, and the spectrum L (f) in the frequency domain is changed to the frequency interval F as shown in FIG.
A plurality of impulse trains SP1 existing at s (= 1 / Ts)
Is occurring.

With such an impulse train SP1, the first
When the received intermediate frequency signal is sampled, this sampling is performed by the frequency spectrum R of the first received intermediate frequency signal.
(f) and the frequency spectrum L (f) of the impulse train SP1
As shown in FIG. 9, the sampling circuit 36 outputs the center frequency Fc of the first received intermediate frequency signal before sampling and the reciprocal of the period Ts of the impulse train SP1, that is, an integer multiple N · of the frequency Fs. A plurality of spectra appear at intervals corresponding to the difference from Fs (Fc-N.Fs). The one having the lowest center frequency among the plurality of spectra is selected by the low-pass filter 38 and supplied to the A / D converter 7 as a second reception intermediate frequency signal.

Incidentally, in the circuit of this embodiment, the frequency Fs of the impulse train SP1 is set to an arbitrary value within the range represented by the expression (1) as described above. Equation (1) satisfies the condition that an integer multiple of three or more times the sampling frequency Fs does not fall within the desired signal band. Therefore, it is possible to perform frequency conversion on the input signal without superimposing the desired signal.

This will be described with reference to a specific example. Now, the center frequency Fc of the first reception intermediate frequency signal, which is an input signal, is 2000 MHz, and its bandwidth is 2.FB = 20 MHz.
Assume z. That is, the input signal is a band signal from 1990 MHz to 2010 MHz. On the other hand, the frequency Fs of the impulse train SP1 that satisfies the condition of the present embodiment is
Is expressed as follows from Equation (1).

[0034]

(Equation 6)

According to this condition, for example, Fs = 49.7 MHz is selected as the sampling frequency, and the oscillation frequency of the impulse train generator 37 is set to this frequency Fs.
Then, the frequency component of the input signal at 2010 MHz becomes 2010- (49.7 × 40) = 22 MHz, and 2
The frequency component of 000 MHz is 2000- (49.7 × 4
0) = 12 MHz, respectively, and further converted to 1
The 990 MHz frequency component is 1990- (49.7 × 4
0) = 2 MHz. That is, 199
All signals in the band from 0 MHz to 2010 MHz are frequency-converted from 2 MHz to 22 MHz, and do not overlap each other.

Incidentally, the sampling frequency Fs is
Any value that does not satisfy the condition shown in equation (1), for example, 4
Assume that the frequency is set to 9.875 MHz. Then, in this case, the frequency component of the input signal at 2010 MHz is 20 MHz.
10− (49.875 × 40) = 15 MHz and 2
The frequency component of 000 MHz is 2000- (49.875).
× 40) = 5 MHz. However, the frequency component of the 1990 MHz is also (49.875 ×
40) -1990 = 5 MHz, so that the signal frequency overlaps with the signal frequency of 2000 MHz. That is, from 1990 MHz to 2000
The input signals of all the radio channels within the range of MHz will be superimposed, thereby increasing the frequency from 1990 MHz to 20 MHz.
All input signals belonging to the 00 MHz frequency band cannot be reproduced.

As described above, in the present embodiment, the first receiving intermediate frequency signal is sampled by the impulse train SP1 generated by the impulse train generator 37 in the sampling circuit 36. An arbitrary value is selected as a sampling frequency Fs from a frequency range satisfying the condition represented by the following expression, and an impulse train generator 37 configured to generate an impulse train SP1 of the selected sampling frequency Fs is provided. That is, the sampling frequency is set so that the band of the input signal does not fall within an integer multiple of three or more times the sampling frequency Fs.

Therefore, according to the present embodiment, frequency conversion can be performed so that signals of a plurality of frequencies before sampling do not overlap each other in the same frequency range after sampling. Therefore, over the entire frequency band of one radio system to be received, signals of all channels can be accurately frequency-converted without overlapping.

In the above-described embodiment, the filter 38 is provided in the second frequency conversion circuit 35 after the sampling circuit 36, but this filter is not always necessary.

Next, a second embodiment will be described. This second
In the embodiment, in a digital portable telephone device equipped with a sampling type frequency conversion circuit, a means for calculating an optimum sampling frequency for frequency conversion and variably setting it in a sampling signal generator is provided. Frequency conversion can be performed with an optimum sampling frequency that does not cause a superimposition phenomenon for any of a plurality of wireless systems in a used frequency band.

FIG. 10 is a circuit block diagram showing a configuration of a main part of a digital portable telephone device provided with the frequency conversion circuit according to the present embodiment. 6, the same parts as those in FIG. 6 are denoted by the same reference numerals, and detailed description is omitted.

The frequency conversion circuit 45 of this embodiment comprises a sampling circuit 36, an impulse train generator 47 constituted by a frequency synthesizer, and a low-pass filter 48 constituted by an active filter capable of variably setting a cutoff frequency from the outside. And Impulse train generator 4
Reference numeral 7 denotes a frequency synthesizer capable of variably setting the oscillation frequency from the outside as described above, and generates an impulse train SP2 having a frequency corresponding to the oscillation frequency control signal SYS supplied from the control circuit 20B. Low-pass filter 4
8 variably sets the cutoff frequency Fcut according to the cutoff frequency control signal CFS supplied from the control circuit 20B.

The control circuit 20B includes a sampling frequency setting control circuit 201 in addition to ordinary control functions such as wireless channel connection control and communication control. When the wireless system of the communication connection destination is switched, the sampling frequency setting control circuit 201 uses the formula (1) based on the center frequency Fc of the frequency band used by the switched wireless system and its bandwidth FB. To calculate the optimum sampling frequency Fs. An oscillation frequency control signal (division number designation signal) SYS for designating the calculated optimum sampling frequency Fs is supplied to the impulse train generator 47 of the frequency conversion circuit 45. At the same time, the optimum cutoff frequency Fcut is determined based on the optimum sampling frequency Fs, and the control signal CFS is supplied to the low-pass filter 48.

With such a configuration, for example, from the first digital radio system operated by a certain carrier,
When an instruction to switch the connection destination is input to the second digital wireless system of a different use frequency band operated by another carrier, the control circuit 20B follows the procedure shown in FIG. And optimal sampling frequency Fs2 and cutoff frequency Fcut2
Is calculated.

That is, first, the center frequency Fc2 and the bandwidth FB2 of the second digital radio system after the change in step 7a are read from the memory in the control circuit 20B.
Further, in step 7b, N1 is determined to an arbitrary value. Next, in step 7c, the left side of equation (1), that is,

(Equation 7)

Is calculated. In step 7e, an appropriate value is selected from the range represented by these calculated values, and this is set as the sampling frequency Fs2. Next, step 7f
Sets the frequency division number corresponding to the sampling frequency Fs2 in the impulse train generator 47.

The control circuit 20B calculates the frequency after the frequency conversion in accordance with the sampling frequency Fs2 in step 7g, and determines the cutoff frequency Fcut2 of the low-pass filter 48 in accordance with the calculated frequency in step 7h. I do. The designated control signal CFS of the cutoff frequency Fcut2 determined in step 7i is output to the low-pass filter 48.

As a result, the impulse train generator 47 thereafter generates an impulse train SP2 of the designated sampling frequency Fs2. Therefore, when the communication is started in this state, the sampling circuit 36 samples the first reception intermediate frequency signal using the impulse train SP2 of the frequency Fs2. At this time, the frequency Fs2 of the impulse train SP2 is a signal changed in the control circuit 20B so that a plurality of signals of different frequencies before frequency conversion are not converted to the same frequency after frequency conversion.
Therefore, even when wireless communication is performed with the second digital wireless system, frequency conversion can be accurately performed over the entire used frequency band without causing a superposition phenomenon of a plurality of channel signals.

Also, since the cutoff frequency Fcut of the low-pass filter 48 is reset to an optimum value, the spectrum having the lowest frequency is accurately extracted from a plurality of spectra appearing at the output of the sampling circuit 36. As a result, the received intermediate frequency signal having the lowest possible frequency can be supplied to the subsequent digital signal processing circuit.

Next, a third embodiment will be described. This third
In the embodiment of the present invention, when a pulse signal having a pulse width is used as a sampling signal, the value of the pulse width is set to a value that satisfies a predetermined condition, so that the attenuation of the frequency-converted signal in a low frequency range is reduced. In this way, an intermediate frequency as low as possible is obtained by frequency conversion by sampling. FIG. 12 is a circuit block diagram illustrating the configuration of the frequency conversion circuit according to the present embodiment. 6, the same parts as those in FIG. 6 are denoted by the same reference numerals, and detailed description is omitted.

The frequency conversion circuit 55 of the present embodiment has a pulse train generator 57 as a sampling signal generator. The pulse train generator 57 is set so that the frequency Fs satisfies the condition shown in the equation (1) similarly to the impulse train generator 37 described in the first embodiment (FIG. 6), The reciprocal Fp of Tp is

(Equation 8)

The pulse train SP3 is set so as to satisfy the condition shown in FIG.

The operation of the circuit according to the third embodiment will be described below.

When a pulse train having a pulse width Tp as shown in FIG. 13 is used as a sampling signal, the amplitude becomes sin (π) as shown in FIG. 14 due to the pulse width Tp.
fTp) / (πfTp), the frequency-converted signal may greatly attenuate in its low frequency range as shown in FIG. To prevent this, the pulse width is set to the impulse train S described in the first embodiment.
Although it is sufficient to make the pulse width P1 sufficiently small, it is actually impossible to generate a pulse train having no pulse width at all. However, the pulse width Tp of the sampling pulse is
By setting the value to satisfy the condition shown in the expression (7), it is possible to suppress the attenuation of the amplitude of the signal after the frequency conversion, particularly in the low frequency range.

This will be described with a specific example. Now, it is assumed that the center frequency Fc of the input signal to the sampling circuit 36 is 2000 MHz and its bandwidth FB is 20 MHz. That is, the input signal changes from 1990 MHz to 2010
MHz band signal. Also, the sampling frequency F
s is set to 49.7 MHz described in the first embodiment.
Then, the frequency component of the input signal at 2010 MHz becomes 2010- (49.7 × 40) = 22 MHz, and 2
The frequency component of 000 MHz is 2000- (49.7 × 4
0) = 12 MHz, respectively, and further converted to 1
The 990 MHz frequency component is 1990- (49.7 × 4
0) = 2 MHz. This is as described in the first embodiment.

Here, for example, the pulse width Tp of the sampling pulse train is set to 1 nsec, that is, Fp = 1 GHz.
Suppose you set Then, when the pulse width of the pulse train is Tp, its frequency spectrum is Fs (= 1).
/ Ts) to the impulse train of sin (πfTp) / (πfT
p), the frequency spectrum is F
s = 49.7 MHz impulse train with sin (πf · 1 ×
10−9) / (πf · 1 × 10−9).
Therefore, when the maximum level is 1, 1990 MH
The relative value of the level of the 2 MHz signal obtained by frequency-converting the z signal is

(Equation 9)

Is as follows. Similarly 12MHz and 22MH
The relative value of the signal level of z is −7.47 × 1
0-7, 5.04 × 10-3. As described above, depending on the pulse width Tp of the sampling pulse, the output level of the signal after frequency conversion is greatly reduced.

However, if the pulse width Tp of the sampling pulse is set to a value satisfying the condition of the expression (7),
It is possible to suppress a decrease in the level of the signal after frequency conversion. That is, at this time, the conditional expression (7) is as follows: 2000 / N2 [MHz] <Fp <1990 / (N2 -1) [MHz] (9) Here, for example, Fp is set to Fp = 4020 / N3 (10). For example, if Np = 5 and Fp = 804 MHz, that is, Tp = 1.244 nsec, 199
The relative value of the level when the frequency of the 0 MHz signal is converted is

(Equation 10)

Is as follows. Similarly 12MHz and 22MH
The signal levels of z are also 0.128 and 0.127, respectively, and it is possible to suppress a decrease in the signal level after frequency conversion as compared with the case where Tp=1.times.10@-9 as described above.

As described above, in the present embodiment, in the frequency conversion circuit using a pulse train having a pulse width as the sampling signal, the frequency Fs is set to a value satisfying the condition of the above-mentioned equation (1), A pulse train generator 57 for generating a pulse train in which the width Tp is set to a value satisfying the condition shown in Expression (7) is provided.

Therefore, according to the present embodiment, it is possible not only to prevent superposition from occurring in the spectrum after frequency conversion, but also to use the signal after frequency conversion in spite of using the pulse train having the pulse width Tp. Thus, the signal level attenuation in the low frequency range can be suppressed, and the received intermediate frequency signal in the low frequency range with a sufficiently large signal level can be output.

Next, a fourth embodiment will be described. In the present embodiment, in a digital portable telephone device having a sampling type frequency conversion circuit and using a pulse train having a pulse width as a sampling signal used in the frequency conversion circuit, an optimum sampling frequency is calculated to generate a sampling signal. A circuit for variably setting the pulse generator and a circuit for calculating the optimum pulse width and variably setting the sampling signal generator are provided. The frequency conversion can be performed using a sampling pulse set at an optimum sampling frequency that does not cause the occurrence of the signal level and at an optimum pulse width that can suppress the signal level attenuation.

FIG. 16 is a circuit block diagram showing a configuration of a main part of a digital portable telephone device provided with the frequency conversion circuit according to the present embodiment. In this figure, the same parts as those in the embodiment of FIG. 10 are denoted by the same reference numerals, and the detailed description is omitted.

The frequency conversion circuit 65 of this embodiment comprises a sampling circuit 36, a pulse train generator 67 composed of a frequency synthesizer and a pulse width modulation circuit, and an active filter having a cutoff frequency variably set from the outside. And a band-pass filter 48. The pulse train generator 67 includes a frequency synthesizer capable of variably setting the oscillation frequency from the outside, and a pulse width modulation circuit variably setting the pulse width of the pulse train output from the frequency synthesizer. The oscillation frequency supplied from the control circuit 20C A pulse train SP4 having a frequency Fs according to the control signal SYS and a pulse width Tp according to the pulse width control signal PWS is generated.

The control circuit 20C includes a sampling frequency setting control circuit 201 and a pulse width setting control circuit 202 in addition to ordinary control functions such as wireless channel connection control and communication control. The pulse width setting control circuit 202, when the wireless system of the communication connection destination is changed, based on the center frequency Fc of the frequency band used by the changed wireless system and the bandwidth FB thereof, Calculate the optimum pulse width Tp of the sampling pulse according to the equation (7). The pulse width control signal PWS for designating the calculated optimum pulse width Tp is supplied to the pulse width modulation circuit of the pulse train generator 67. The function of the sampling frequency setting control means 201 is the same as that described in the second embodiment (FIG. 6).

With such a configuration, for example, from the first digital radio system operated by a certain carrier,
When an instruction to switch the connection destination is input to the second digital wireless system of a different operating frequency band operated by another carrier, the control circuit 20C firstly determines the optimum sampling frequency Fs2 and cutoff frequency according to the procedure shown in FIG. The off-frequency Fcut2 is calculated, and the calculated sampling frequency Fs2 and cutoff frequency Fcut2 are set in the frequency synthesizer of the pulse train generator 67 and the low-pass filter 48, respectively.

Next, the control circuit 20C executes control for calculating and setting the pulse width Tp2 according to the procedure shown in FIG. That is, first, N2 is arbitrarily set in step 13a, and then, in steps 13b and 13c, respectively.

[Equation 11]

Is calculated. In step 13d, an appropriate value Fp2 is selected from the range represented by these calculated values, and in step 13e, the pulse width Tp2 is calculated from this Fp.
(= 1 / Fp2), and a pulse width control signal PWS for setting the pulse width Tp2 is supplied to the pulse width modulation circuit of the pulse train generator 67. Therefore, the pulse train generator 67 thereafter generates the pulse train SP4 having the sampling frequency Fs2 specified by the control circuit 20C and the pulse width Tp2. Therefore, when communication is started in this state, the sampling circuit 36 samples the first reception intermediate frequency signal by the pulse train SP4 having the frequency Fs2 and the pulse width Tp2.

At this time, the frequency F of the impulse train SP4
s2 is changed so that the control circuit 20C does not convert a plurality of signals of different frequencies before frequency conversion to the same frequency after frequency conversion. Therefore, even when communication is performed with the second digital wireless system, frequency conversion can be accurately performed over the entire use frequency band without causing a superposition phenomenon of a plurality of channel signals.

Also, since the cutoff frequency Fcut2 of the low-pass filter 48 has been reset to the optimum value, the spectrum having the lowest frequency among a plurality of spectra appearing in the output of the sampling circuit 36 can be accurately determined. Thus, the received intermediate frequency signal having the lowest possible frequency can be supplied to the subsequent digital signal processing circuit.

The pulse width Tp2 is also determined by the control circuit 20C.
Has been changed to a value such that the signal level after frequency conversion does not greatly attenuate in the low frequency range. Therefore, even when a radio signal arriving from the second digital radio system is received, no significant attenuation of the signal level occurs in the low frequency band of the frequency-converted signal, and the signal level is sufficiently low. Can be output. In the above-described embodiment, the filter 48 is provided in the second frequency conversion circuit 65 after the sampling circuit 36, but the filter 48 is not always required.

Next, a fifth embodiment will be described.

By using the sampling frequency Fs that satisfies the condition shown in the first embodiment (FIG. 6), it is possible to convert the frequency of an input signal to near the baseband without superimposing a desired signal on another signal. However, according to the fifth embodiment, when the band signal of the input signal is composed of a plurality of narrow band signals, the signal of any one desired channel is always the same intermediate signal. Converted to frequency. This embodiment is applied to, for example, frequency conversion of a system composed of a so-called “channel” that is 77 narrowband signals in a band of 23.1 MHz, such as a PHS.

When demodulation is performed in such a system, it is desirable that the intermediate frequency after frequency conversion be the same in order to easily configure a circuit at the subsequent stage by the frequency converter.

Here, by setting the sampling frequency Fs as described below, it is possible to always convert the received signal to the same intermediate frequency. That is, the value of N1 in the equation (1) is selected to be an integer satisfying the following condition.

[0076]

(Equation 12)

By using N1 which satisfies such a condition, the intermediate frequency FIF is always set to 2FB by changing the sampling frequency Fs according to the channel to be demodulated.
It becomes possible. However, [] in the above formula is a Gaussian symbol, and represents the largest integer not exceeding the number of characters in []. The sampling frequency Fs is determined using the following equation, where Fn is the center frequency of the desired channel.

[0078]

(Equation 13)

This will be specifically described.

Now, the center frequency Fc of the input signal is 200
Assume 0 MHz, bandwidth 2 FB = 20 MHz. That is, the input signal is a band signal from 1990 MHz to 2010 MHz. In addition, 4 kHz at 500 kHz
It is assumed that there is 0 channel. That is, the first channel is 1990.25 MHz..., And finally the 40th channel is 2009.075 MHz. In this case, the above equation (1) is used so that the frequency can always be converted to the same intermediate frequency.
The following N1 may be selected from 5) and (16).

[0081]

[Equation 14]

For example, if N1 = 51 and the intermediate frequency is FIF = 20 MHz, [(Fc + FB) / 2
Since FB] -N1 is an odd number, when the desired signal is 199.25 MHz which is the first channel, the sampling frequency Fs = (1990.25-20) / {100-
(51 + 1)｝ / 2 = 82.09375 MHz. In addition, the second channel of 1990.75 MHz
In the case of, the sampling frequency Fs = (1990.75-
20) / {100− (51 + 1)} / 2 = 82.114
The frequency may be set to 6 MHz. Channel 40, 200
In the case of 9.75 MHz, the sampling frequency Fs = (2
009.75-20) / {100- (51 + 1)} / 2
= 82.9063 MHz.

It is assumed that N1 = 50 and the intermediate frequency is FIF
= 20 MHz, [(Fc + FB) / 2FB]-
Since N1 is an even number, if the desired signal is 199.25 MHz which is the first channel, the sampling frequency F
s = (1990.25 + 20) / {100-50} / 2
= 80.41 MHz. In the case of the second channel of 199.75 MHz, the sampling frequency Fs = (199.75 + 20) / {100-50}.
/ 2 = 80.43 MHz. In the case of 2009.75 MHz which is the 40th channel, the sampling frequency Fs = (2009.75 + 20) / ｛100−5
0) It is sufficient to set｝ /2=81.19 MHz.

The above frequencies are all values satisfying the expression (1) shown in the first embodiment.

In the equation (1), when N1 = 51, the range of the sampling frequency Fs is

(Equation 15)

That is, 82.04 [MHz] <Fs <82.92 [MHz].

In the equation (1), when N1 = 50, the range of the sampling frequency Fs is

(Equation 16)

That is, 80.40 [MHz] <Fs <81.22 [MHz].

The case of PHS is as follows. PHS
, The center frequency Fc = 1906.55 MHz and the bandwidth 2FB = 23.1 MHz. That is, the input signal is a band signal of 1895.0 MHz to 1918.1 MHz. Furthermore, there are 77 channels at an interval of 300 kHz. That is, the first channel is 1895.15M
Hz, the second channel is 1895.45..., And finally the 77th channel is 1917.95 MHz. In this case, the following N1 may be selected from the above equation so that the frequency can always be converted to the same intermediate frequency.

[0090]

[Equation 17]

For example, if N1 = 42 and the intermediate frequency FIF = 23.1 MHz, [(Fc + FB) / 2
Since FB] -N1 is an odd number, if the desired signal is 1895.15 MHz which is the first channel, the sampling frequency Fs = (1895.15-23) / ｛83- (4
2 + 1)｝ / 2 = 93.6025 MHz.
In the case of 1895.45 MHz as the second channel, the sampling frequency Fs = (1895.45-23)
/{83-(42+1)}/2=93.6175 MHz
And it is sufficient. Channel 1917.95M
Hz, the sampling frequency Fs = (1917.9)
5−23.1) / {83− (42 + 1)} / 2 = 94.
The frequency may be 4725 MHz.

It is assumed that N1 = 41 and the intermediate frequency is FIF =
Assuming 23.1 MHz, [(Fc + FB) / 2FB]
Since -N1 is an even number, the sampling frequency Fs =
(189.15 + 23.1) / {83-41} / 2 =
The frequency may be 91.34524 MHz. In the case of 1895.45 MHz as the second channel, the sampling frequency Fs = (1895.45 + 23.1) /） 83−
41｝ /2=91.35952 MHz. In the case of 1917.95 MHz, which is the 77th channel, the sampling frequency Fs = (1917.23 + 23.1) /
{83−41)} / 2 = 92.43095 MHz.

As described above, according to this embodiment, it is possible to always convert an arbitrary signal among a plurality of narrow band signals within a certain band to a certain same intermediate frequency.
The circuit subsequent to the frequency converter can be greatly simplified.

Next, a sixth embodiment will be described. This embodiment is an embodiment in which the first embodiment is applied to a wireless communication device.

As shown in FIG. 18, a received signal input from an antenna is amplified by a low noise amplifier 101 to a desired level. The signal is input to the band-pass filter 102 and band-limited. Bandpass filter 102
The output signal band-limited by the sampling circuit 103 is sampled by the sampling circuit 103 described in the first embodiment. The sampling pulse is provided by a pulse train generator 104, and the frequency of the sampling pulse is the first
This frequency satisfies the condition described in the embodiment.

The signal sampled by the sampling circuit 103 is then input to the A / D converter 106.

By the above operation, the input signal is A / D converted and becomes a digital signal. This signal is then channel-selected by the digital signal processing circuit 109,
Demodulated. A digital signal obtained by A / D conversion may include a plurality of channels. At this time, a plurality of channels are selected and demodulated by the digital signal processing circuit. This makes it easy to demodulate a plurality of channels simultaneously.

Next, a seventh embodiment will be described. The seventh embodiment is an embodiment in which the fifth embodiment is applied to a wireless communication device. As shown in FIG. 19, a received signal input from an antenna is amplified by a low noise amplifier 101 to a desired level. The signal is input to the band-pass filter 102 and band-limited. The output signal band-limited by the band-pass filter 102 is sampled by the sampling circuit 103 described in the first embodiment. The sampling pulse is provided by the pulse train generator 104, and the frequency of the sampling pulse is a frequency that satisfies the condition described in the fifth embodiment.

The signal sampled by the sampling circuit 103 is as described in the fifth embodiment.
The frequency is always converted to a certain intermediate frequency. The sampled intermediate frequency signal is input to the band pass filter 110. The purpose of the filter 110 is to prevent a signal obtained by sampling by the second sampling circuit 111 at the next stage from being superimposed on the intermediate frequency signal. At this time, the characteristics are defined by the fixed sampling frequency of the second pulse train generation circuit 112. Regarding the sampling at the second stage, the second pulse train generator 112 that generates the sampling frequency may oscillate a fixed fixed frequency.

The output signal of the sampling circuit 111 is A /
The signal is converted into a digital signal by the D converter 114 and input to the demodulator 115.

Further, the sampling circuit 111 and the pulse train generator 112 at the second stage shown in FIG. 19 can be replaced with a more general frequency conversion circuit 116 and oscillator 117 as shown in FIG. In this case, the output frequency of the oscillator 117 is relatively low and may be fixed, so that there is no need to use a complicated circuit.

The output frequency of the first-stage pulse train generator 104 shown in FIG. 19 needs to be varied in order to keep the intermediate frequency constant regardless of the desired channel. A specific method of realizing this is shown in FIG. Here, 1
The frequency synthesizer 118 is used for the pulse train generator of the stage. The frequency synthesizer 118 uses a normal PLL and has a crystal oscillator 118-1 for generating a reference signal.
And a reference frequency divider 118-2 for dividing the output of the oscillator.
And a VCO (voltage controlled oscillator) that generates an oscillation output signal
118-6, a variable frequency divider 118-3 for dividing the frequency of the VCO, a phase comparator 118-4 for comparing the phases of the reference signal and the comparison signal, and a loop for smoothing the output voltage of the phase comparator And a filter 118-5. The oscillation frequency of the frequency synthesizer 118 is determined by setting the number of divisions of the reference frequency divider 118-2 and the variable frequency divider 118-3 by the oscillation frequency control signal from the control unit 119.

[0103]

According to the present invention described above, a frequency capable of outputting an intermediate frequency signal having a sufficiently large signal level in a low frequency range without causing a superposition phenomenon for a plurality of radio systems having different operating frequencies. A wireless communication device including a conversion circuit can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing a frequency spectrum of an input signal before frequency conversion.

FIG. 2 is a diagram illustrating a time-domain waveform of a square wave used as a sampling signal.

FIG. 3 is a diagram showing a frequency spectrum of the square wave shown in FIG. 2;

FIG. 4 is a diagram showing a frequency spectrum of an intermediate frequency signal obtained by sampling the input signal shown in FIG. 1 with the square wave shown in FIG. 2;

FIG. 5 is a circuit block diagram showing an example of a configuration of a digital mobile phone device provided with a frequency conversion circuit according to the first embodiment of the present invention.

FIG. 6 is a circuit block diagram illustrating a configuration of a receiving circuit illustrated in FIG. 5;

FIG. 7 is a diagram showing a waveform in a time domain of an impulse train used as a sampling signal.

FIG. 8 is a diagram showing a frequency spectrum of an impulse train used as a sampling signal.

FIG. 9 is a diagram showing a frequency spectrum of an intermediate frequency signal after frequency conversion.

FIG. 10 is a circuit block diagram showing a configuration of a main part of a digital portable telephone device provided with a frequency conversion circuit according to a second embodiment of the present invention.

11 is a flowchart showing a sampling frequency setting control procedure and control contents by the control circuit shown in FIG. 10;

FIG. 12 is a circuit block diagram showing a configuration of a frequency conversion circuit according to a third embodiment of the present invention.

FIG. 13 is a diagram showing an example of a time-domain waveform of a pulse train used as a sampling signal.

FIG. 14 is a diagram showing amplitude frequency characteristics of the pulse train shown in FIG. 13;

FIG. 15 is a diagram showing a frequency spectrum of an intermediate frequency signal sampled by the pulse train shown in FIG. 13;

FIG. 16 is a circuit block diagram showing a configuration of a main part of a digital portable telephone device provided with a frequency conversion circuit according to a fourth embodiment of the present invention.

FIG. 17 is a flowchart showing a sampling frequency setting control procedure and control contents by the control circuit shown in FIG. 16;

FIG. 18 is a block diagram of a wireless communication device using the frequency conversion circuit of the first embodiment.

FIG. 19 is a block diagram of a wireless communication apparatus using the frequency conversion circuit according to the fifth embodiment.

20 is a block diagram of a wireless communication device using a general frequency conversion circuit and a frequency conversion circuit using an oscillator instead of the sampling circuit and the pulse train generator shown in FIG. 19;

21 is a block diagram of a wireless communication apparatus using a frequency conversion circuit in which the output frequency of the pulse train generator shown in FIG. 19 is variable.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Antenna, 2 ... Antenna duplexer (DUP), 3 ... Receiving circuit (RX) 4 ... Frequency synthesizer (SYN), 5 ... Transmitting circuit (T
X) 6 ... Digital demodulation circuit (DEM), 7, 13 ... A / D
Converter 8: Error correction decoding circuit (CHDEC), 9: Voice decoding circuit (SPDEC) 10, 18: D / A converter, 11: Speaker, 12: Microphone 14: Acoustic echo canceller (AEC), 15: Voice code Circuit (SPCOD) 16 Error correction code circuit (CHCOD), 17 Digital modulation circuit (MOD) 19 Digital signal processing circuit (DSP), 20A, 2
0B, 20C: Control circuit (CONT), 21: Key input unit 22: Liquid crystal display (LCD), 23: Battery, 24 ...
Power circuit (POW) 31 high frequency amplifier, 32 first mixer, 33 first intermediate frequency filter 34 first intermediate frequency amplifier, 35, 45, 55, 65
Frequency conversion circuit 36: sampling circuit, 37, 47: impulse train generator 57, 67: pulse train generator, 38, 48: low-pass filter 39: second intermediate frequency amplifier, 101: low noise amplifier 102: band-pass filter , 103: sampling circuit, 105: filter, 106: A / D converter, 109
... Digital signal processing circuit, 114 ... A / D converter 115 ... Demodulator, 118 ... Frequency synthesizer 201 ... Sampling frequency setting control means 202 ... Pulse width setting control means, SP1, SP2, SP
3, SP4: sampling signal SYS: sampling frequency control signal CFS: cut-off frequency control signal PWS: pulse width control signal

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Shoji Odaka 1 Kosuka Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture Toshiba Research and Development Center Co., Ltd. (56) References JP-A-5-327356 (JP, A) JP-A-63-294131 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H03D 7/00 H04B 1/26

Claims (8)

(57) [Claims] An input signal having a predetermined center frequency and a predetermined bandwidth is received, and the input signal is sampled according to a sampling signal having a predetermined sampling frequency.
A sampling circuit that outputs an intermediate frequency signal; and a sampling circuit that outputs a sampling signal having a frequency determined so that the frequency of the input signal does not fall within an integer multiple of three times or more of the sampling frequency to the sampling circuit. A frequency conversion device comprising: a signal generation circuit; 2. The sampling signal generating circuit according to claim 1, wherein: F _C : The center frequency of the input signal. F _B : The bandwidth of the input signal. A sampling signal generating means for generating, as the sampling frequency signal, a pulse train signal preset at an arbitrary frequency within a range indicated by Item 2. The frequency conversion device according to item 1. Wherein said sampling signal generating means, the inverse F _P of the pulse width of the pulse train signal is Equation 2] 3. The frequency converter according to claim 2, wherein a pulse train signal preset at an arbitrary frequency within a range represented by N2 = 2, 3, 4,... 4. One of a plurality of wireless devices of different frequency bands
A first frequency conversion circuit for receiving a received signal arriving from the first intermediate frequency signal and converting the received signal into a first intermediate frequency signal having a lower frequency than the received signal frequency; A sampling circuit that samples in accordance with a frequency sampling signal and outputs a second intermediate frequency signal, and a frequency that is an integer multiple of three times or more of the sampling frequency is set so that the frequency of the first intermediate frequency signal does not enter. A second frequency conversion circuit configured by a sampling signal generation circuit that outputs a sampling signal having the adjusted sampling frequency to the sampling circuit; and a demodulation unit that demodulates the second intermediate frequency signal. Communication device. 5. The sampling signal generating circuit according to claim 1, wherein: F _C : The center frequency of the input signal. F _B : The bandwidth of the input signal. A sampling signal generating means for generating, as the sampling frequency signal, a pulse train signal preset at an arbitrary frequency within a range indicated by Item 5. The wireless communication device according to item 4. Wherein said sampling signal generating means, the inverse F _P of the pulse width of the pulse train signal is Equation 4] 6. The wireless communication apparatus according to claim 5, wherein a pulse train signal set in advance to an arbitrary frequency within a range indicated by. 7. A filter for band-limiting a received signal in a different frequency band, a sampling circuit for sampling a band-limited received signal from the filter according to a sampling signal of a predetermined sampling frequency, and outputting an intermediate frequency signal;
A sampling signal generating circuit for outputting to the sampling circuit a sampling signal having a sampling frequency set so that a frequency that is an integer multiple of three or more times the sampling frequency is not included in the frequency of the intermediate frequency signal. And a means for demodulating the intermediate frequency signal. 8. One of a plurality of received signals in different frequency bands.
And a first frequency conversion circuit for converting the frequency of the received signal according to a predetermined frequency signal and outputting a first intermediate frequency signal; and sampling the first intermediate frequency signal with a sampling frequency signal. A sampling circuit that outputs an intermediate frequency signal of 2 and a sampling signal having a sampling frequency set so that an integer multiple of three times or more of the frequency of the sampling frequency signal is not included in the frequency of the reception signal. A wireless communication apparatus comprising: a second frequency conversion circuit configured by a sampling signal generation circuit that outputs a signal to a circuit; and demodulation means configured to demodulate the second intermediate frequency signal.