JPH08125701A - FSK modulator in wireless communication - Google Patents

Abstract

PURPOSE: To provide the respective functions of FSK modulation, channel changeover, frequency offsetting and waveform offsetting with the circuit of a small scale by using less synthesizers. CONSTITUTION: This modulator is provided with a mixer 3 for modulation to which the output of a non-modulated signal generation part 1 for generating a non-modulated first local frequency and the output of a direct digital synthesizer (DDS) 2 set beforehand so as to generate two frequencies for generating the corresponding one of frequency signals corresponding to inputted data signals are inputted. By passing the output of the mixer 3 for the modulation through a narrow band pass filter 4, one of single side band waves including desired waves is taken out and the frequency offsetting and the waveform offsetting are performed by the DDS 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to DDS in wireless communication.
It relates to an FSK modulator with a drive. FSK modulators used for transmitters that call mobile receivers from multiple wireless stations in wireless communication use an intermediate frequency F
A function for SK modulation, a channel switching function for selecting one channel from a plurality of channels, and a separate frequency changing means such as a frequency offset or a waveform offset for preventing the occurrence of a beat due to a radio signal of an adjacent radio station are required. Therefore, improvement is desired in terms of a large circuit scale and poor signal quality.

[0002]

2. Description of the Related Art FIG. 10 is an explanatory view of a conventional example, FIG. 11 is a block diagram of a synthesizer, and FIG. 12 is an explanatory view of frequency and waveform offset. This example is a configuration of a transmitter provided in a base station of a digital radio call (pager) that wirelessly calls a portable reception-only terminal.

In FIG. 10, reference numeral 80 is a control unit, and reference numeral 81 is frequency modulation (for example, +) with an intermediate frequency (for example, 70 MHz) by digital binary values (0 and 1) to be transmitted.
PLL (Ph that generates output of 5 KHz and -5 KHz)
ase Locked Loop type synthesizer (hereinafter, this type is called a synthesizer), 82 is a narrow band pass filter, and 83 is a variably set channel (for example,
A synthesizer for generating an unmodulated high frequency (for example, 210 MHz) corresponding to a band of one channel of 25 KHz, 84 is a first mixer, 85 is a second mixer, 86 is a frequency offset synthesizer, and 87 is a third. The mixer 88 is a waveform offset synthesizer.

The operation of FIG. 10 will be described. In the synthesizer 81, the control unit 8 is used for an intermediate frequency such as 70 MHz.
Corresponding to the binary value of data generated at 0, F of ± 5 KHz
Performs SK (frequency shift keying) modulation.

This synthesizer 81 has a PLL structure as shown in FIG. 11, and has a TCXO (crystal oscillator) 90.
The intermediate frequency (IF) generated from is supplied to the phase comparator 91 to be compared in phase with the output frequency, and the signal of the comparison result is supplied to the VCO (voltage controlled oscillator) 93 through the low pass filter 92 to be a phase difference. Corresponding frequencies are generated. A modulation signal representing binary data generated from the control unit 80 is input to the VCO 93, and the modulation signal causes the VCO 93 to be +5 with respect to the intermediate frequency (70 MHz).
The frequency is shifted by KHz or -5 KHz and is supplied to the phase comparator 91 via a loop. When this modulation is performed, since the frequency shift has a delay due to the loop control of the PLL, not only the output of the target frequency from the VCO 93, but also the spurious (intermodulation wave, harmonics) that occurs with the dynamic change of the frequency. Etc.) are included.

The narrowband bandpass filter 82 shown in FIG. 10 is provided to suppress spurious as described above, and its output is input to the first mixer 84, and the synthesizer 83 is provided.
Is mixed with the unmodulated local frequency (210 MHz) corresponding to the set channel from the above to generate a mixed output frequency (280 M ± 5 KHz). Normally, this output is transmitted as an RF signal after being subjected to processing such as power amplification.

On the other hand, in the case of wireless calling, a plurality of base stations send data to a same receiver at a constant data rate (for example, 51
2 bps) bit signal is transmitted. In this case, when signals of the same channel are sent from each base station, beats occur between signals of a plurality of base stations. For example, 512 bp
In the case of a signal speed of s, a beat of 256 bps occurs when "1" and "0" are alternately generated.

In order to prevent the occurrence of such a bit,
The frequency offset and the waveform offset shown in FIG. 12 are used. 12A. Is an example of frequency offset,
Call signals from three base stations of base station 1, base station 2 and base station 3 are sent to the receiver on the same channel (for example, 28
In the case of transmission at 0 MHz), in order to prevent the occurrence of beats, frequencies for shifting (shifting) binary data are set to different values for each base station.

That is, in the case of the base station 1, 280 MHz
Set to ± 5 KHz, in the case of base station 2 280 MHz ±
Frequency shift by + 1KHz for 5KHz signal, 280MHz + 6KHz and 280MHz-4KHz
, And in the case of base station 3, frequency shifts by +2 KHz to 280 MHz +7 KHz and 280 MH
Set to z-3 KHz.

Next, referring to FIG. Shows an example of waveform offset, and is set as shown so that the phases of the signals generated at each base station are different from each other even if the frequency is the same. In this case, making the phases different from each other is the same as performing the frequency offset in time.

In order to apply the frequency offset or the waveform offset as shown in FIG. 12, the mixer 85 is provided in the configuration of FIG. 10, and the frequency offset synthesizer 8 is provided.
Desired frequency offset value set to 6 (+ 1KH
When a frequency signal such as z or +2 KHz is generated, the signal and the signal output from the mixer 84 (280 MHz ± 5
KHz) to produce a frequency offset output signal. In the case of the waveform offset, a desired set waveform is generated in the waveform offset synthesizer 88, and is similarly mixed in the mixer 85 to output the set waveform signal.

[0012]

As described above, in order to construct the FSK modulator for wireless communication having the conventional frequency offset and waveform offset functions, the FSK modulator, the channel switching, the frequency offset or the waveform offset are used. Separate frequency changing means are required, and it is necessary to perform multi-stage mixing using 3 to 4 synthesizers. Therefore, the circuit scale becomes large, the C / N (carrier-to-noise ratio) is poor, and the residual FM (Frequency Modulation)
However, there was a problem that spurious could not be suppressed sufficiently.

The present invention solves the above problems and provides an FSK modulator which can realize various functions such as FSK modulation, channel switching and frequency or offset with a small circuit using a small number of synthesizers. To aim.

[0014]

FIG. 1 is a block diagram showing the principle of the present invention. In FIG. 1, reference numeral 1 is an unmodulated signal generator for generating a first local frequency, and 2 is a direct digital synthesizer for generating a frequency signal of either of two frequencies corresponding to a binary value of an input data signal. (DD
(Denoted by S), 3 is a modulation mixer that mixes the output of the first local frequency from the unmodulated signal generation unit 1 and the output of the DDS 2 to generate a modulation output, and 4 is one of the outputs of the modulation mixer 3 A narrow band bandpass filter (BPF) that extracts only a desired sideband wave, 5 is a synthesizer that generates a second local frequency that is variably set corresponding to a designated channel, and 6 is a bandpass filter 4. It is a frequency conversion mixer that mixes the output and the output of the synthesizer 5 to generate a transmission signal. The DDS2 has a built-in ROM that stores sample values of sine waveforms (or triangular waves). If two division numbers corresponding to two desired frequencies are set in advance, the ROM can be divided by dividing the high-speed clock. Data is sequentially read and a frequency signal corresponding to the value of the data signal is generated.

The present invention is a DDS for generating a frequency signal corresponding to a data signal from an unmodulated first local frequency signal.
The output of the F is mixed (mixed), modulated, and passed through a narrowband bandpass filter.
It realizes three functions of SK modulation, frequency offset, and waveform offset.

[0016]

In FIG. 1, the first local frequency is supplied to the modulation mixer 3 from the unmodulated signal generator 1. DDS
When the data signal is input, 2 generates a preset frequency signal corresponding to the binary value of the data. The first local frequency signal of the unmodulated signal generator 1 is FSK modulated by the frequency signal corresponding to the data generated from the DDS 2 in the modulation mixer 3. This modulation output is input to the narrow band bandpass filter 4, and only one sideband including the desired wave is passed from the upper and lower sidebands included in the modulation output and the unmodulated first local frequency signal, Other frequency components are blocked. The output of the narrowband bandpass filter 4 is input to the frequency conversion mixer 6, and the synthesizer 5
It is converted into a frequency corresponding to the channel used for communication set in the above and output as an RF signal for transmission.

In this configuration, the mixer 3 enables the FSK
It is possible to perform modulation, provide the DDS 2 with a plurality of setting means, and apply arbitrary frequency offset and waveform offset.

[0018]

FIG. 2 is a block diagram of the first embodiment. The configuration of FIG. 2 is an example in which the present invention is applied to a wireless call (pager) transmitter.

In the figure, 10 is a control unit for outputting data and controlling each synthesizer, 11 is a crystal oscillation circuit (TCX) for generating a signal of a reference frequency (10 MHz).
(Indicated by O), 12 is a DDS that generates frequency signals of 50 KHz (mark) and 60 KHz (space) by data input, 13 is a non-modulated fixed frequency (70 MHz-55
A fixed synthesizer for generating a frequency of KHz),
A variable synthesizer 14 generates a corresponding frequency signal (a channel of 280 MHz band) by setting a channel of a transmission signal, and a first mixer 15 uses, for example, a DBM (Double Balanced Mixer). 16 is a narrow band pass filter that passes a frequency signal centered at 70 MHz, 17 is an IF amplifier (Amp) that amplifies the intermediate frequency (IF) of 70 MHz, and 18 is the frequency of the FSK modulation signal output from the IF amplifier 17. It is a second mixer which is changed by a second local frequency signal (210 MHz designating a channel) generated from the variable synthesizer 14.

Reference numerals 19 to 22 are circuits similar to those of the conventional transmitter. Reference numeral 19 is a sideband (280M) of the addition component of the two signal components (addition component and subtraction component) generated from the second mixer.
Band pass filter for passing the signal (Hz), 20 is RF (R
adio Frequency) Amplifier (Amp), 21 is a low pass filter (indicated by LPF), and 22 is an isolator that generates an output to the antenna.

The control unit 10 controls the DDS 12 to store a set value for generating a frequency to be generated corresponding to the binary value of the data before operating the DDS 12, and the DDS 12 transmits the data signal to be transmitted during the transmission operation. Supply to. Also,
The control unit 10 outputs a signal for controlling the operation of the fixed synthesizer 13 and also outputs a channel set value of the transmission signal and an operation control signal to the variable synthesizer 14.

FIG. 3 shows the basic structure of the DDS. DD
S12 is 2 ³² sample values (digital code) representing a sine wave (1 cycle) in the sine wave table 120.
Is written in the sine wave table 120, and a sine wave having a corresponding frequency can be generated by changing the cycle (interval) of reading the digital code representing the sampling value of the sine wave. In the two frequency division registers 121 and 122 shown in FIG. 3, the frequencies (corresponding to "1") and spaces (corresponding to "0") desired to be generated, in this example, the frequency division numbers corresponding to 50 KHz and 60 KHz When a clock signal preset from the control unit 10 and generated from the TCXO 11 is input, the frequency division operation of the frequency division number set for each is performed. Further, according to the transmission data (“1” or “0”) input from the control unit 10, one of the outputs of the frequency division number register 121 or the frequency division number register 122 is switched to be output to the sine wave table 120. , 124 are arranged. The digital code read from the sine wave table 120 is converted into an analog signal by the DA converter 125, and a sine wave of 50 KHz or 60 KHz is output.

Returning to the description of FIG. 2, the fixed synthesizer 1
3 is 70 MHz-55 KHz as a non-modulated fixed frequency
And is input to the first mixer (consisting of DBM) 15. The first mixer 15 is mixed (mixed) with a frequency signal that changes according to the data output from the DDS 12 (for example, a speed of 512 bps).

FIG. 4 shows the distribution of frequency components output from the first mixer 15. The main signal output from this mixing is (70 MH-55 KHz) ± 50 KH
z and (70MHz-55KHz) ± 60KHz in total 4
There are two frequency components, 70MHz + shown in Fig. 4d
Two of 5KHz and 70MHz-5KHz are desired waves corresponding to 50KHz and 60KHz of data, respectively.
Retrieved by narrow band BPF 16 (FIG. 2).

At this time, the opposite side bands (70 MHz-105 KHz and 70 MHz-115 K) shown as b
Hz), a local signal (70 MHz-55 KHz) of a non-modulated wave of the fixed synthesizer 13 shown in c, and a band that spreads during dynamic characteristics (modulation) and leaks to a band corresponding to an adjacent channel. Signal waves such as high-order spurious components (50 KHz, 60 KHz intervals) shown in (1) and spurious near the carrier caused by the modulation shown in (d) are blocked by the narrow band BPF 16 as unnecessary waves. The narrow band BPF 16 uses a narrow band and a high attenuation amount, and generally uses a crystal filter having a plurality of cuts.

70 MHz ± after passing through the narrow band BPF 16
The IF (intermediate frequency) signal of 5 KHz is supplied to the IF amplifier 17
It is amplified by and input to the second mixer 18. The second local signal corresponding to the transmission channel is input from the variable synthesizer 14 as the other input of the second mixer 18. In this example, the second local signal is a signal from the control unit 10 that indicates the number of channels (n), and the variable synthesizer 14 provides a channel n of a plurality of channels prepared at a channel interval of 25 KHz in the 210 MHz band.
It is assumed that the frequency (210 MHz ± 25 × nKHz) corresponding to is generated.

In the second mixer 18, the IF amplifier 17
280MHz ± 5KHz-25, which is the sum of the IF output and the second local signal
A signal wave of × nKHz and a signal wave of the difference between the two are generated,
Only the signal in the frequency band of 280 MHz is passed through the band pass filter 19, and is transmitted from the antenna through the RF amplifier 20, the low pass filter 21 and the isolator 22.

Next, the modulation control according to the present invention will be described in each of the following cases (1) to (3). (1) When there is no frequency offset or waveform offset only with FSK modulation In this case, simply add DDS12 to the mark data.
The output of (FIG. 2) may be 50 KHz, and the output of the DDS 12 may be 60 KHz for space data. Figure 5
Shows how the DDS output is switched. In this way, even if the frequency is changed, the phase of the signal output from the DDS is switched so as to be continuous, so that it becomes as shown in FIG. 5, and only a refraction point is generated at the switching position and no discontinuous point is generated. .

When a DDS-IC (integrated circuit) as shown in FIG. 3 is used, two registers have 50 KHz,
Modulation can be applied only by writing data of 60 KHz (corresponding to the frequency division number) and then performing control to select a register according to input data. If the widening of the bandwidth during modulation (near spurious generated at intervals corresponding to the bit rate of the transmission data) cannot be sufficiently suppressed by the narrow band filter, it can be reduced by changing the frequency stepwise. .

In this case, the achievable number of steps is determined by the relationship between the time required to change the DDS output frequency and the bit rate. If multi-step frequency change is required, DDS is required every time.
It is effective to use a DDS-IC equipped with a large number of frequency registers and switch the frequency in a short time, instead of updating all the data.

(2) When there is a frequency offset If the frequency offset is +750 Hz, ± 5 KHz
The FSK shift amounts of the above may be set as follows.

In case of mark -5KHz + 750Hz
= -4.25 KHz In the case of space +5 KHz +750 Hz = +5.75
Therefore, the DDS output frequency when the local frequency offset is -55 KHz can be set as follows. The stepwise change in frequency is the same as in (1) above.

In case of mark: -4.25 KHz-(-
55KHz) = 50.75KHz In the case of space: + 5.75KHz-(-55KHz)
= 60.75 KHz (3) When there is a waveform offset FIG. 6 is a diagram showing an example of controlling the waveform offset. In this example, when the data rate is 512 Hz (512 bps), the waveform of the output signal is shifted in the range of +750 Hz to −750 Hz to apply the waveform offset. Such a waveform offset is generated by changing the output frequency of the DDS, but the waveform is also generated as the IF frequency output from the first mixer 15. Therefore, the vertical axis of FIG. 6 indicates the DDS output frequency (H
z) or 70M (mega) IF frequency (Hz),
The horizontal axis represents time, and the waveforms of space data and mark data are shown.

FIG. 6 shows an example of 8-step triangular wave approximation for simplification of description. However, in practice, the number of steps is increased and the frequency value in the middle is adjusted to obtain a sine wave. It is desirable to approximate it. The change points of the waveforms of the space data and the mark data are omitted in FIG. 6, but
As in (1) and (2) above, it is possible to reduce the spread of the band by changing the frequency stepwise.

The phase of the waveform offset is A. As shown in Figure 3, in the case of three base stations, 2π /
Since it is necessary to shift three by three, it can be realized by providing three waveform offset tables in advance and selecting one of them to perform superposition with the frequency data corresponding to the mark data and space data.

FIG. 7 shows the configuration of the second embodiment. The second embodiment is characterized in that a quadrature modulator 23 is used in place of the first mixer 15 composed of the DBM in the first embodiment shown in FIG. 2 and a −90 ° shifter 24 is provided in association therewith. And each of the other symbols 10 to 14 and 16 to 2 in FIG.
Each part represented by 2 is the same as that in FIG.

In this embodiment, the first local signal (unmodulated) of 70 MHz-55 KHz from the fixed synthesizer 13 is divided into two, and a -90 ° shifter 24 adds a phase difference of 90 ° to the quadrature modulator 23. To do. I (Inphase), Q (Quadratu) of the quadrature modulator 23 by the sine wave from the DDS 12
re) When the input is driven (one is driven or both are driven by the same signal), the output of DDS12 is 50K.
In accordance with Hz and 60 KHz, signals of respective frequencies similar to those shown in FIG. 4 are generated and only the desired wave is extracted by the narrow band BPF 16 in the same manner as in the above-mentioned embodiment 1 (FIG. 2), and other frequency components Is attenuated. After that, the transmission signal is output by the same operation as in the first embodiment.

In the above-mentioned embodiment, the RF frequency is a relatively high frequency (280 MHz band) and the configuration is such that channel switching is required. However, the RF frequency is within the range (several 10 MHz or less) that can be supported by the crystal filter. An embodiment of a system that does not require channel switching will be described with reference to FIGS. 8 and 9.

FIG. 8 is a block diagram of the third embodiment. In this example, since the RF frequency is 50 MHz and channel switching is not necessary (fixed), the variable synthesizer 14 and the second mixer 18 which are indispensable structures in the first and second embodiments are unnecessary and a simple structure is obtained. It has become.

In FIG. 8, 30 is a control unit, 31 is a crystal oscillator (TCXO), 32 is DDS, 33 is a fixed synthesizer, 34 is a mixer, 35 is a narrow band BPF (band pass filter), 36 is an amplifier, and 37 is LPF (low-pass filter), 38 is an isolator, and 39 is an antenna. Note that 33 is not necessarily a synthesizer, and may be another oscillator circuit that generates a fixed frequency, such as TCX.
The output of O31 or its multiplied output can be used.

In this embodiment, the DDS 32 receives the 10 MHz clock generated by the crystal oscillator 31, and the control unit 3
50KHz or 60KHz corresponding to the data from 0
Frequency signal is generated and the fixed synthesizer 33 outputs 5
A frequency of 5 MHz-55 KHz is generated. Mixer 34
Is 50MHz-55KHz and 50MHz generated as the output by mixing the frequency signal from DDS32.
± 5KHz and 50MHz-105KHz, 50MHz
From −115 KHz, only the frequency of 50 MHz ± 5 KHz is passed through the narrow band BPF 35, and the amplifier 3
6, is transmitted from the antenna 39 via the LPF 37 and the isolator 38.

Also in the case of the third embodiment, the FSK modulation is performed in the mixer 34, and the frequency offset and the waveform offset can be applied by the DDS 32. FIG. 9 is a configuration diagram of the fourth embodiment. This embodiment is applied to the case of a system that does not require spurious (unnecessary radiation) suppression by weak radio waves or wires.

In FIG. 9, parts 40 to 42, 44 and 45 are the same as parts 30 to 32, 34 and 36 in FIG. Reference numeral 43 is a variable synthesizer for changing channels.

In this structure, a frequency of 50 KHz or 60 KHz is generated from the DDS 42 by data input from the control unit 40, and the variable synthesizer 43 controls the control unit 4 from the variable synthesizer 43.
A frequency of several tens of MHz (for example, a 50 MHz band) corresponding to a channel designated from 0 is generated. DDS4
2 and the output of the variable synthesizer 43 are mixed by the mixer 44, and the output is amplified by the amplifier 45 without passing through the narrow band BPF and sent to the antenna or the wired transmission path. A light low-pass filter (LPF), a broadband BPF, an isolator or the like may be added to the output of the amplifier 45 depending on the situation.

A mixer used as a modulator of the FSK in the configuration of each of the first, third and fourth embodiments described above (the first mixer 15 in FIG. 2, the mixer 34 in FIG. 8 and the mixer 44 in FIG. 9). Can use a mixer having a known configuration, and specifically, a DBM (double balanced mixer)
Or a mixer such as a transistor. Further, the quadrature modulator 23 according to the second embodiment having a function corresponding to the mixer is
It is used with one signal instead of two signals of I and Q.

[0046]

According to the present invention, generally, only two synthesizers (excluding the first and second synthesizers and DDS) can realize the FSK modulation function and all the functions of the frequency offset and the waveform offset. The circuit scale can be reduced. Further, since it is not necessary to perform multi-step mixing as in the conventional case, it is possible to secure C / N, reduce residual FM (frequency modulation), and suppress spurious.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of the present invention.

FIG. 2 is a configuration diagram of a first embodiment.

FIG. 3 is a diagram showing a basic configuration of a DDS.

FIG. 4 is a diagram showing a distribution of frequency components output from the first mixer.

FIG. 5 is a diagram showing how DDS output is switched.

FIG. 6 is a diagram showing an example of control of a waveform offset.

FIG. 7 is a configuration diagram of a second embodiment.

FIG. 8 is a configuration diagram of a third embodiment.

FIG. 9 is a configuration diagram of a fourth embodiment.

FIG. 10 is an explanatory diagram of a conventional example.

FIG. 11 is a block diagram of a synthesizer.

FIG. 12 is an explanatory diagram of frequency and waveform offset.

[Explanation of symbols]

1 Unmodulated signal generator 2 Direct digital synthesizer (DD
S) 3 Mixer for modulation 4 Narrow band pass filter 5 Synthesizer 6 Mixer for frequency conversion

Claims (6)

[Claims] 1. In an FSK modulator for wireless communication, an unmodulated signal generator that generates an unmodulated first local frequency, and a frequency that is set in advance to generate two frequencies, depending on an input data signal. A direct digital synthesizer (DDS) for generating one of the corresponding frequency signals, the output of the non-modulated signal generator and the D
FSK modulation in wireless communication, comprising a modulation mixer that mixes DS outputs to generate an FSK modulation output, and a narrowband bandpass filter that extracts one single sideband from the output of the modulation mixer vessel. 2. In an FSK modulator for wireless communication, a non-modulated signal generating section for generating a non-modulated first local frequency and a pre-set two frequencies are set in accordance with an input data signal. The direct digital synthesizer for generating one of the corresponding frequency signals, the output of the non-modulation generating section, and the output obtained by adding the phase difference are input, and the output of the direct digital synthesizer is received at the IQ input. An FSK modulator in wireless communication, comprising: a quadrature modulator driven by a quadrature modulator; and a narrow bandpass filter for extracting one single sideband from an output of the quadrature modulator. 3. A variable synthesizer for generating a second local frequency corresponding to a designated channel, the output of the narrowband bandpass filter and the output of the variable synthesizer according to claim 1, An FSK modulator in wireless communication, comprising: a frequency conversion mixer for converting a frequency for transmission. 4. The direct digital synthesizer according to any one of claims 1 to 3, wherein a frequency offset given in advance to a station for transmitting an FSK modulation output is set in the direct digital synthesizer, and a frequency offset is generated when a frequency corresponding to the input data is generated. An FSK modulator in wireless communication characterized by applying an offset. 5. The direct digital synthesizer according to any one of claims 1 to 4, wherein a waveform offset given in advance to a station for transmitting an FSK modulation output is set, and the waveform is generated when a frequency corresponding to the input data is generated. F in wireless communication characterized by applying an offset
SK modulator. 6. The radio according to claim 1, wherein the direct digital synthesizer is provided with a large number of frequency registers, and the frequency of an output signal is changed in small steps by switching the frequency registers. FSK modulator in communication.