JP2003018231A - Digital modulation transmitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transmitter which reduces power consumption to extend the time of operation with a battery by reducing the operation frequency of a quadrature modulator for IF signal generation or a DA converter and is made small-sized and lower-cost. SOLUTION: A low band local channel 2 or 3 is used for frequency conversion of a lower limit transmission channel 4 to a center transmission channel 5 in an entire RF band and a high band local channel 7 or 8 is used for frequency conversion of the center transmission channel 5 or an upper limit transmission channel 6 in the entire RF band, so that the IF frequency can be reduced. Thus the power consumption is reduced and the cost is reduced because the performance required, of the DA converter for IF signal generation or the quadrature modulator is relaxed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital modulation transmitter, and more particularly to a digital modulation transmitter capable of lowering an operating frequency.

[0002]

2. Description of the Related Art Conventionally, this type of digital modulation transmitter is
A DA converter and a low-pass filter are provided for each of the I-phase and the Q-phase to generate a baseband signal, the generated I-phase and Q-phase signals are quadrature-modulated by a quadrature modulator, and the mixer for frequency conversion converts the local signal from the frequency synthesizer. It is mixed with an oscillating signal, and a transmission signal is generated through a bandpass filter.

As an example of the conventional digital modulation transmitter as described above, the transmitter disclosed in Japanese Patent Laid-Open No. 10-285142 is known. In FIG. 8, I-phase and Q-phase subjected to digital signal processing are converted into analog signals by the DA converter 60, and the analog-digital filter (ADF) 61 band-limits the root Nyquist characteristic, and then the low-pass filter 62 detects harmonics. To be removed.
Then, these I-phase and Q-phase signals are quadrature modulator 63.
Is quadrature-modulated to generate an IF signal. Further, after the frequency is converted by the local oscillation signal in the mixer 64, an unnecessary frequency component is removed by the band pass filter 65, and is output as a transmission signal.

[0004]

However, in such a conventional transmitter, when the number of transmission channels is large and the bandwidth is wide, and the transmission frequency is high, the local frequency rejection performance of the bandpass filter 65 is restricted. By I
In order to increase the F frequency or to perform the frequency conversion in multiple stages, there are problems that a quadrature modulator that operates at a high frequency is used, the circuit scale becomes large, and the power consumption increases accordingly.

The present invention has been made in order to solve the above-mentioned conventional problems, and reduces the operating frequency of a quadrature modulator for generating an IF signal or lowers the operating frequency required by a DA converter for consumption. It is an object of the present invention to provide a transmitter that can reduce the power consumption, prolong the operating time of a battery, reduce the size, and reduce the cost.

[0006]

A digital modulation transmitter according to the present invention, a digital modulation baseband section for outputting a baseband signal, a DA converter for converting the baseband signal into an IF signal, and a local frequency signal are generated. And a frequency converter for converting the IF signal into a transmission frequency signal by the local frequency signal, when varying the frequency of the transmission signal,
For setting the frequency channels lower than the center of all channels, the local frequency signal supplied to the frequency converter is a low frequency signal, and for setting the frequency channels higher than the center of all channels, the local frequency signal supplied to the frequency converter. It has a configuration in which the frequency signal is a high frequency signal. With this configuration, the output frequency of the DA converter can be lowered, and the operating frequency required for the DA converter can be lowered, so that the current consumption can be reduced and the cost can be reduced.

The digital modulation transmitter according to the present invention generates a digital modulation baseband section for outputting a baseband signal, a quadrature modulator for converting the baseband signal into a quadrature-modulated IF signal, and a local frequency signal. A PLL synthesizer and a frequency converter that converts the IF signal into a transmission frequency signal by the local frequency signal are provided, and when the frequency of the transmission signal is varied, the frequency conversion is performed for setting a frequency channel lower than the center of all channels. The local frequency signal supplied to the frequency converter is a low frequency signal, and the local frequency signal supplied to the frequency converter is a high frequency signal for setting a frequency channel higher than the center of all channels. There is.
With this configuration, the IF frequency output from the quadrature modulator can be lowered, and the operating frequency required for the quadrature modulator can be lowered, so that low current consumption and cost reduction can be achieved.

The digital modulation transmitter according to the present invention has a configuration in which, when the local frequency signal supplied to the frequency converter is a high frequency signal, the input signal is switched between the I phase and the Q phase. With this configuration, the modulated signal at the output of the RF signal maintains the original modulation phase relationship, and since phase conversion in the demodulator is not necessary, it can be realized with a simple system and cost reduction can be achieved.

In the digital modulation transmitter according to the present invention, when the local frequency signal supplied to the frequency converter is a high frequency signal, the phase of the carrier signal input to the multiplier of the digital modulation baseband section is switched. Have a configuration. With this configuration, even if the I-phase and Q-phase baseband signals are not switched, the original modulation phase relationship of the modulation signal at the output of the RF signal is maintained, and the phase conversion in the demodulator is not required, so a simple system is realized. Therefore, the cost can be reduced.

In the digital modulation transmitter according to the present invention, the local frequency signal supplied to the frequency converter is 1 / n.
The 1 / n frequency divider is provided, and the frequency division ratio is switched when the high frequency signal is supplied to the frequency converter and when the low frequency signal is supplied to the frequency converter. With this configuration, it is possible to realize a wide RF band even if the variable width of the variable local frequency oscillator such as the VCO is narrow.

The digital modulation transmitter according to the present invention comprises an m-multiplier for multiplying the local frequency signal supplied to the frequency converter by m, and when the high frequency signal is supplied and the low frequency signal is supplied, The configuration is such that the multiplication number of the local frequency signal supplied to the frequency converter is switched. With this configuration, it is possible to realize a wide RF band even if the variable width of the variable local frequency oscillator such as the VCO is narrow.

The digital modulation transmitter according to the present invention has a structure in which a transmission time of a transmission signal is provided with a guard time for switching between a high band local frequency and a low band local frequency. With this configuration, data discontinuity due to switching of the local frequency in the communication data does not occur, and it becomes possible to secure the communication quality of the data.

In the time-division multiplex communication, the digital modulation transmitter according to the present invention switches between the high band local frequency and the low band local frequency between the end of transmission of the own station slot and the start of transmission of the next own station slot. It has the following configuration. With this configuration, data discontinuity due to switching the local frequency in the communication data does not occur,
It is possible to secure the communication quality of data.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the relationship between the IF frequency, the local (local oscillation) frequency and the transmission frequency used in the present invention will be described with reference to FIG. FIG. 1 shows the operating principle of a signal according to the present invention. In the case where the lower limit transmission channel 4 (f _RFL ) to the central transmission channel 5 (f _RFM ) of the entire RF band is frequency-converted, the lower limit low local channel 2 is used. (F _LOL1 ) or the upper limit low band local channel 3 (f _LOH1 ) is used, and the central transmission channel 5 (f _RFM ) or the upper limit transmission channel 6 in the entire RF band is used.
(F _RFH) lower high frequency local channel 7 when frequency conversion of (f _LOL2) to limit high frequency local channel 8
(F _LOH2 ) is used. It should be noted that Δf9 is a required band due to the performance of the out-of-band attenuation characteristics of the local frequency provided after the frequency conversion mixer and the band pass filter (BPF) that removes unnecessary spurious.

As an example of setting the frequency band in the frequency usage pattern shown in FIG. 1, the relationship among the IF frequency, the local frequency and the transmission frequency is set as follows. 1. Transmission frequency f _{RFL to} f _RFM f _LO =
f _RF −f _IF (where f _LO is the local frequency (local oscillation frequency) f _RF is the RF frequency (transmission frequency) f _IF is the IF frequency (intermediate frequency)) 2. For transmission frequency f _{RFM to} f _RFH f _LO =
If f _RF + f _{IF is established} and f _RFM is set at the center of the band, the IF frequency f _IF should satisfy f _IF ≧ Δf + (BW _RF / 2) (where BW _RF is the entire RF band frequency).

(First Embodiment) First, the configuration of a digital modulation transmitter according to the first embodiment of the present invention will be described with reference to FIG. In FIG. 2, the digital modulation transmitter according to the present embodiment has a serial-parallel converter 26 for converting an input signal from serial to parallel,
A mappin circuit 25 that symbol-codes the output of the serial-parallel converter 26, and the I phase and Q of the mappin circuit 25.
I-Q phase switch 24 for switching the phase output, digital filters 22, 23, multipliers 19, 20 for multiplying the carrier by the I-phase and Q-phase signals, and the base by adding the I-phase and Q-phase signals Adder 18 that outputs a band signal (quadrature modulation signal)
A DA converter 17 that converts a digital baseband signal (quadrature modulation signal) into an analog signal and outputs it as an IF signal; and an IFBPF 16 that blocks unnecessary waves of the IF frequency.
And a PLL synthesizer circuit 14 that outputs a local oscillation frequency (local frequency) under the control of the control circuit 15.
A mixer 13 as a frequency converter that mixes the IF frequency and the local oscillation frequency, a band pass filter (RFBPF) 12 that removes unnecessary waves, and a high frequency amplifier 11.

In the above construction, the constituent portion composed of the constituent elements from the serial-parallel converter 26 for inputting data to the adder 18 becomes the digital modulation baseband portion for outputting the baseband signal.

Next, the operation of the digital modulation transmitter according to the first embodiment of the present invention will be described with reference to FIG. First, the output data of the serial-parallel converter 26 is symbol-coded by the mapping circuit 25. When switching between the low band local channel and the high band local channel,
Since the relationship of the phase change between the I phase and the Q phase is opposite, the I phase-
By switching between the I phase and the Q phase with the Q phase switch 24,
The antenna 10 transmits a normal modulated signal. The digital filters 22 and 23 limit the band of the modulated signal such as Nyquist characteristic so that there is no intersymbol interference. In the multipliers 19 and 20, the carrier wave generated by the carrier wave generating circuit 21 is multiplied by the I-phase and Q-phase signals, respectively, and the adder 18 adds them to obtain a baseband signal.

The quadrature modulated signal from the adder 18 is converted into a digital IF signal by the DA converter 17 into an analog IF signal, and an IFB for cutting off unnecessary waves such as the oversampling frequency of the DA converter 17 and its spurs.
After passing through the PF 16, the mixer 13 transmits the transmission frequency (RF
Frequency). The local frequency used for frequency conversion is the PLL controlled by the control circuit 15.
Generated from the synthesizer circuit 14. The RFBPF 12 removes unnecessary waves such as a local frequency from the signal that has passed through the mixer 13, the high frequency amplifier 11 amplifies the signal to the required power, and the signal is transmitted from the antenna 10.

(Second Embodiment) Next, a digital modulation transmitter according to a second embodiment of the present invention will be described with reference to FIG. The digital modulation transmitter shown in FIG. 3 does not use the I-phase / Q-phase switch 24 shown in FIG. 2, but instead uses a carrier phase switch 27 that switches the phase of the carrier output from the carrier generation circuit 21. Figure 2 in terms of
Unlike the digital modulation transmitter according to the first embodiment of the present invention shown in FIG. 5, the other points are the same.

That is, when the low band local channel and the high band local channel are switched, the relationship of the phase changes of the I phase and the Q phase becomes opposite, so that the carrier wave input to the multipliers 19 and 20 by the carrier wave phase switcher 21. To switch the phase of
The normal modulated signal can be transmitted from the antenna 10 without switching the phases of the I-phase and Q-phase signals input to the digital filters 22 and 23.

(Third Embodiment) Next, a digital modulation transmitter according to a third embodiment of the present invention will be described with reference to FIG. The digital modulation transmitter shown in FIG. 4 has an output of the PLL synthesizer circuit 14 shown in FIG.
/ N frequency divider 28 is connected to the first point of the present invention shown in FIG.
Different from the digital modulation transmitter in the embodiment, the other points are the same.

In FIG. 4, the 1 / n frequency divider 28 increases the frequency division ratio n to increase the frequency division ratio when the low frequency local channel is input to the mixer 13, and also controls the high frequency local channel to the mixer. In the case of inputting to 13, the frequency division ratio n is reduced and the frequency division ratio is reduced to enable switching between the high band local channel and the low band local channel without increasing the variable width of the PLL synthesizer circuit 14. Become.

(Fourth Embodiment) Next, a digital modulation transmitter according to a fourth embodiment of the present invention will be described with reference to FIG. The digital modulation transmitter shown in FIG. 5 has the output m of the PLL synthesizer circuit 14 shown in FIG.
Unlike the digital modulation transmitter according to the first embodiment of the present invention shown in FIG. 2 in that a multiplier 28 is connected, the other points are the same.

In FIG. 5, the m multiplier 29 is a multiplier m when the low band local channel is input to the mixer 13.
Is reduced, and when the high-frequency local channel is input to the mixer 13, the multiplication factor m is increased to obtain P
It is possible to switch between the high band local channel and the low band local channel without increasing the variable width of the LL frequency synthesizer.

Next, with reference to FIG. 6, the structure of the transmission frame in consideration of the timing of switching the high band local channel and the low band local channel in the embodiment of the present invention will be described. If the high frequency local channel and the low frequency local channel are switched in the middle of the data when the data is continuously transmitted without time division multiplexing, the correct frequency cannot be transmitted until the frequency of the PLL synthesizer circuit 14 becomes stable. , The error rate increases due to the discontinuity of data on the receiver side.

In order to prevent this, as shown in FIG.
A guard time 41 for switching between the high band local channel and the low band local channel is provided in the transmission frame, and if the switching is completed within this time, no discontinuity of data occurs on the receiver side and good transmission is possible. Become. Further, by providing the guard time 41 before the preamble 42 and the unique word 43, the receiver side can resynchronize even if the timing between the frames is deviated, so that the discontinuity of the data 44 does not occur and good transmission can be achieved. It will be possible.

Next, with reference to FIG. 7, switching timing between the high band local channel and the low band local channel in the time division multiplexing system according to the embodiment of the present invention will be described. If you switch between the high band local channel and the low band local channel in the slot sending the data,
Until the frequency of the PLL synthesizer circuit 14 stabilizes, the correct frequency cannot be transmitted, and the error rate increases due to data discontinuity on the receiver side. In order to prevent this, after the end of the own station's slot, the interval up to the next own station's slot is defined as the high-range / low-range switching section 50, and if the switching is completed in this section, the discontinuity of data on the receiver side will occur. Occurs, and good transmission becomes possible.

In the embodiment of the present invention described above, the DA signal is used to generate the IF signal. However, instead of the DA converter, a quadrature modulator is used to generate an IF signal based on the baseband signal. Even when the IF signal is generated, the IF frequency can be lowered by the present invention, and therefore, the same effect as when the DA converter is used can be expected.

[0030]

The digital modulation transmitter according to the present invention comprises:
In particular, by using both the low band and the high band local channels for the required RF frequency band as configured above, as compared with the case of using only the low band or the high band local channel, Since the IF frequency can be lowered, the operating frequency of the DA converter that outputs the IF signal or the local frequency of the quadrature modulator can be lowered, which leads to lower current consumption and cost reduction. Moreover, the operation time can be lengthened.

Further, by switching the phase of the I and Q baseband signals or the carrier wave input to the multiplier, the original modulation phase relationship of the modulation signal at the output of the RF signal is maintained, and the phase conversion in the demodulator is unnecessary. Therefore, it can be realized with a simple system, and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing an operation principle of a digital modulation transmitter according to an embodiment of the present invention,

FIG. 2 is a diagram showing a configuration of a digital modulation transmitter according to the first embodiment of the present invention,

FIG. 3 is a diagram showing a configuration of a digital modulation transmitter according to a second embodiment of the present invention,

FIG. 4 is a diagram showing a configuration of a digital modulation transmitter according to a third embodiment of the invention,

FIG. 5 is a diagram showing a configuration of a digital modulation transmitter according to a fourth embodiment of the present invention,

FIG. 6 is a diagram showing a switching timing in continuous data transmission used in the digital modulation transmitter according to the embodiment of the present invention;

FIG. 7 is a diagram showing switching timing in time division multiplexing data transmission used in the digital modulation transmitter according to the embodiment of the present invention;

FIG. 8 is a diagram showing a configuration of a conventional digital modulation transmitter.

[Explanation of symbols]

1 IF frequency 2 lower limit local channel 3 upper limit low band local channel 4 lower limit transmission channel 5 Central transmission channel 6 upper limit transmission channel 7 Lower limit high range local channel 8 upper limit high band local channel 9 RFBPF attenuation cannot be guaranteed 10 antennas 11 high frequency amplifier 12 Band pass filter (RFBPF) 13, 64 mixer 14 PLL synthesizer circuit 15 Control circuit 16 IFBPF 17,60 DA converter 18 adder 19, 20 Multiplier 21 Carrier wave generation circuit 22, 23 Digital filter 24 I-Q phase switch 25 Mapping circuit 26 Serial-parallel converter 27 Carrier phase switch 28 1 / n frequency divider 29 m multiplier 41 Guard time 42 preamble 43 unique words 44 data 50 low-high range switching section 61 Analog / Digital Filter 62 Low-pass filter (LPF) 63 Quadrature modulator 65 Band Pass Filter (BPF)

Claims (8)

[Claims] 1. A digital modulation baseband unit for outputting a baseband signal, a DA converter for converting the baseband signal into an IF signal, a PLL synthesizer for generating a local frequency signal, and the IF signal for the local frequency signal. When the frequency of the transmission signal is varied, the local frequency signal supplied to the frequency converter is set to a low frequency signal when setting the frequency channel lower than the center of all channels. The digital modulation transmitter is characterized in that the local frequency signal supplied to the frequency converter is a high frequency signal for setting a frequency channel higher than the center of all channels. 2. A digital modulation baseband unit for outputting a baseband signal, a quadrature modulator for converting the baseband signal into a quadrature-modulated IF signal, a PLL synthesizer for generating a local frequency signal, and the IF signal. And a frequency converter for converting the local frequency signal to a transmission frequency signal, and in the case of varying the frequency of the transmission signal, a local frequency signal supplied to the frequency converter for setting a frequency channel lower than the center of all channels. Is a low frequency signal, and a local frequency signal supplied to the frequency converter is a high frequency signal for setting a frequency channel higher than the center of all channels. 3. When the local frequency signal supplied to the frequency converter is a high frequency signal, the I phase and the Q phase of the input signal are switched.
Digitally modulated transmitter as described. 4. When the local frequency signal supplied to the frequency converter is a high frequency signal, the phase of the carrier signal input to the multiplier of the digital modulation baseband unit is switched. Or the digital modulation transmitter according to 2. 5. A 1 / n frequency divider for 1 / n the local frequency signal supplied to the frequency converter, wherein a high frequency signal is supplied to the frequency converter and a low frequency signal is supplied to the frequency converter. 5. The digital modulation transmitter according to claim 1, wherein the frequency division ratio is switched. 6. An m-multiplier for multiplying a local frequency signal to be supplied to the frequency converter by m, wherein the local frequency signal is supplied to the frequency converter when a high frequency signal is supplied and when a low frequency signal is supplied. 5. The digital modulation transmitter according to claim 1, wherein the frequency signal multiplication factor is switched. 7. The digital modulation transmitter according to claim 1, wherein a guard time for switching between a high band local frequency and a low band local frequency is provided in a transmission frame of a transmission signal. 8. In time division multiplex communication, the high band local frequency and the low band local frequency are switched between after the end of transmission of the own station slot and before the start of transmission of the next own station slot. 7. The digital modulation transmitter according to any one of 1 to 6.