JP2000115264A - Digital modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a digital modulator that employs no IQ modulator and to simplify the circuit configuration of the digital modulator. SOLUTION: The digital modulator 100 generates an RF transmission signal based on a signal 102 that represents an amplitude of the transmission signal and a signal 104 that represents its phase. The digital modulator 100 consists of a limiter 106 that provides an output of a signal with a constant amplitude whose frequency is equal to that of an RF transmission signal, a frequency divider 104, a VCO 1086 that is coupled with a frequency divider 1082 via a filter 1084 and outputs an RF transmission frequency, an operational amplifier 1104 that generates a differential signal between an envelope signal extracted from the RF transmission signal and an envelope input signal 102, and an amplifier stage 120 that generates the RF transmission signal based on the RF transmission frequency and the differential signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication device, and more particularly, to a digital modulation device used for a digital transmitter.

[0002]

2. Description of the Related Art In general, a digital transmitter uses a digital modulator to convert a baseband signal represented by binary information into an analog RF transmission signal. Digital modulators include polar and cartesian loops.
Some methods use a tesian loop or the like, but any method uses an IQ modulator (quadrature modulator). In an IQ modulator, it is necessary to accurately maintain a 90-degree phase difference and a gain between the in-phase component (I) and the quadrature component (Q). Otherwise, carrier leakage and image frequency will occur. For this reason,
Various attempts have been made to compensate for the phase difference and the gain, but there is a disadvantage that the circuit scale is large and complicated. An object of the present invention is to provide a digital modulator that does not use an IQ modulator. Still another object of the present invention is to simplify the circuit configuration.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a digital modulation system for generating an RF transmission signal based on an envelope input signal (102) representing the amplitude of the transmission signal and phase data (104) representing the phase of the transmission signal. Solved by the device (100). The digital modulator (100) has a frequency equal to the frequency of the RF transmission signal, outputs a constant amplitude signal having a constant amplitude, a limiter (106), and an RF transmission frequency based on the phase data (104) and the constant amplitude signal. (F
o) and a difference signal generating means (11) for generating a difference signal between the envelope signal extracted from the RF transmission signal and the envelope input signal (102).
0), and an amplification stage (120) for generating an RF transmission signal based on the RF transmission frequency (fo) and the difference signal. The transmission frequency setting unit (108) receives the phase data (104) and the frequency divider (108) for receiving the constant amplitude signal.
2) and a voltage-controlled oscillator (1086) that receives the signal from the frequency divider (1082) filtered by the filter (1084) and outputs a signal having an RF transmission frequency.

[0004]

FIG. 1 shows a digital modulator (1) according to the present invention.
00). FIG. The antenna (130) is coupled to a first terminal of the attenuator (122) via a directional coupler. A second terminal of the attenuator (122) is coupled to an input of the limiter (106). Limiter (1
The output of 06) is coupled to a first input terminal of a fractional frequency divider (1082) having first and second input terminals, the second input terminal receiving a digital signal of phase data (104). The output of the fractional divider (1082) is coupled to an input of a phase detector (PD) that is coupled to a local oscillator (1081). The output of the phase detector PD (1083) is input to the Nyquist filter (1084). The output of the Nyquist filter (1084) is a voltage controlled oscillator VC
O (1086) is coupled to the input.

On the other hand, an envelope input signal (102) is an analog signal corresponding to an amplitude component of a signal to be transmitted, and is coupled to a first input of an operational amplifier (1104). A first input of mixer (1102) is coupled to an input of limiter (106), a second input is coupled to an output of limiter (106), and an output of mixer (1102) is an operational amplifier (110).
4) is coupled to the second input.

Next, a first input of a modulation amplifier (1202) having first and second inputs is connected to a voltage controlled oscillator (1086).
And the second input is an operational amplifier (1104)
To the output of An input of the power amplifier (1204) is coupled to an output of the modulation amplifier (1202), and an output of the power amplifier (1204) is coupled to an antenna (130).

FIG. 2 shows a block diagram for generating an envelope input signal (102) and phase data (104). In FIG. 2, the operations such as mapping and Nyquist filter are represented by D
It is performed using the SP, but is not limited to this. The use of the DSP simplifies the circuit configuration as compared with the case where individual discrete elements are used. Hereinafter, a case where the modulation method is π / 4 QPSK will be described as an example. The serial data shown on the left side in the figure is converted into a 2-bit signal (symbol) and mapped to a corresponding position on a signal constellation. Next, polar coordinate conversion is performed based on the mapped position (coordinate). Polarization is performed by calculating the magnitude (Mag) and phase (θ) of the amplitude based on the in-phase and quadrature components of the signal. The signal representing the magnitude of the amplitude is Nyquist
The signal is converted into an analog signal via a filter and becomes amplitude data (102). (Θ) representing the phase is differentiated and converted into frequency data to become phase data (104).

The operation will now be described.

The envelope input signal (102) and the phase data (104) are provided with signals representing, for example, the amplitude and phase of a π / 4 QPSK signal. The phase signal is a digital signal having a symbol rate of, for example, 4800 baud, and is input to the transmission frequency setting unit (108). On the other hand, the RF transmission signal is input to the limiter (106) via the attenuator (122). The constant amplitude signal output from the limiter (106) is a signal having an RF transmission frequency substantially equal to the frequency of the RF transmission signal and having a constant amplitude. The transmission frequency setting unit (108) operates to lock up to the RF transmission frequency (fo) using the constant amplitude signal and the phase data (104). That is, after the frequency obtained from the local oscillator (1081) is multiplied by a constant and an extra frequency component is removed by the Nyquist filter (1084), the signal having the RF transmission frequency (fo) is modulated from the voltage controlled oscillator (1086). Amplifier (1
202).

On the other hand, the mixer (1102) extracts an envelope signal, that is, an amplitude signal component based on the RF transmission signal obtained from the first terminal and the constant amplitude signal obtained from the second terminal, and converts the envelope signal. The second of the operational amplifier (1104)
Give to input. A first input of the operational amplifier (1104) is supplied with an envelope input signal, that is, an analog signal corresponding to an amplitude component of a signal to be transmitted. Operational amplifier (11
04) supplies a difference signal corresponding to the difference between the signals supplied to the first and second inputs to the second input of the modulation amplifier (1202). The modulation amplifier (1202) is a voltage controlled oscillator (108
6) and an RF transmission signal based on the signal from the operational amplifier (1104), and a power amplifier PA
After being amplified in (1204), it is transmitted from the antenna (130).

In this embodiment, a fractional frequency divider (Fractional-N) is used as the frequency divider (1082). However, the present invention is not limited to this. However, using fractional frequency dividers
Up time can be shortened. The lock-up time (τ) is generally calculated from the frequency (fr) of the local oscillator (1081) and the sampling number according to the following equation.

Τ = (1 / fr) * (number of samplings) For example, the frequency (fr) of the local oscillator is 10 kHz, and the frequency divider (108) is selected according to the phase data (104).
When the output of 2) changes like 1000, 1001, 1002, the frequency obtained from the voltage controlled oscillator (1086) is 10 kHz * 1000 = 10 MHz, 10.0
It changes like 1 MHz, 10.02 MHz. In this case, the lock-up time (τ) is about 1 / 10k * 100 = 10 when the sampling number is, for example, 100.
msec. The lock-up time can be shortened by increasing the frequency (fr) of the local oscillator. However, the output of the frequency divider can generally take only integer values such as 1000, 1001, and 1002. Is limited to the above value (10 msec). In this embodiment, since a fractional frequency divider is used instead of a normal frequency divider, the output is not limited to an integer value. In the above case, the local oscillation frequency (fr) is 1 MHz, and the output from the fractional frequency divider is 1
When the frequency is changed to 0.00, 10.01, 10.02, the frequency of the signal obtained from the voltage controlled oscillator becomes 10.00 MHz, 10.01 MHz,
It becomes 10.02 MHz. The lock-up time (τ) in this case is as follows:
Approximately 1/1 MHz * 100 = 100 μsec,
The lock-up can be performed in 1/100 time compared to the above numerical value (10 msec).

In this embodiment, the Nyquist filter (10
84), but is not limited to this.
It is also possible to use other types of filters, such as filters. But with the Nyquist filter,
The transition between symbols can be performed smoothly. π / 4
In QPSK, the phase of the signal to be transmitted is ± 45 degrees and ± 1.
It changes at 35 degrees. Symbol of phase data (104)
Assuming a rate of 4800 baud, the frequency is 45
* 4800/360 = 600Hz, 135 * 4800 /
It changes at 360 = 1800 Hz. Therefore, the loop
In the case of using a filter, it is necessary to smoothly transition the frequency by interpolating between symbols. In contrast, when a Nyquist filter is used, interpolation between symbols is not required. The frequency response characteristic of the loop filter requires a high cutoff characteristic so as not to cause an error in the transition between the interpolated symbols, but the Nyquist filter does not need such a high cutoff frequency and is smooth. This is because it has an excellent frequency response characteristic.

As described above, in the present embodiment, since signal processing is performed without using an IQ modulator, digital modulation can be favorably performed without complicating the circuit configuration. Further, since the configuration as in the present embodiment is employed, the saturation amplifier that transmits only the phase component is replaced with the amplifier (12).
02) before it can be used. This allows
For example, broadband noise generated by a high-gain multi-stage linear amplifier can be suppressed.

FIG. 3 is a block diagram showing another embodiment (300) of the digital modulator according to the present invention. Those having the same reference numerals as in FIG. 1 perform the same operation. FIG.
In the embodiment shown in FIG. 5, a first input of the mixer (124) is coupled to a second terminal of the attenuator (122), a second input is coupled to the local oscillator (126), and an output of the mixer (124) is connected to the limiter (106). ) Input and mixer (110)
2) is coupled to the first input. Local oscillator (12
6) functions as an offset synthesizer. That is, by making the internal processing frequency of the digital modulator (300) different from the RF transmission frequency (fo) (fi), the RF into the digital modulator (300) is changed.
This is to suppress the wraparound of the transmission frequency (fo).
As a result, interference between the transmission frequency and the internal processing frequency can be prevented. The number of elements constituting the circuit is increased by the amount of the local oscillator (126) and the mixer (124), but the effect on the portion where the RF transmission frequency (fo) has a large wraparound can be reduced.

FIG. 4 is a block diagram showing another embodiment (400) of the digital modulator according to the present invention. Figure 1
Those having the same reference numbers as in FIG. 3 perform the same function. In the embodiment shown in FIG. 4, in addition to the embodiment shown in FIG. 3, a first input coupled to the local oscillator (126) and a second input coupled to the output of the voltage controlled oscillator (1086);
A mixer (128) having an output coupled to a first input of a modulation amplifier (1202) is provided. In the embodiment shown in FIG. 4, processing is performed in the digital modulator using the internal processing frequency (fi) as in FIG. In the embodiment shown in FIG. 4, a new mixer (128) is required, but the frequency output from the voltage controlled oscillator (1086) is also the internal processing frequency (fi), and the RF transmission frequency (fo) from the antenna (130). Can be further suppressed. Therefore, interference between the transmission frequency and the internal processing frequency can be further prevented.

Although the present invention has been described with reference to a π / 4 QPSK modulation system, the present invention is not limited to this. For example, a single carrier (one in which a symbol can be represented by one vector) modulation system including 16 QAM is generally used. It is possible to

[Brief description of the drawings]

FIG. 1 is a block diagram showing a digital modulator according to the present invention.

FIG. 2 shows a block diagram for generating amplitude and phase input data using a DSP.

FIG. 3 is a block diagram showing another embodiment of the digital modulator according to the present invention.

FIG. 4 is a block diagram showing another embodiment of the digital modulator according to the present invention.

[Explanation of symbols]

 100, 300, 400 Digital modulator 102 Envelope input signal 104 Phase data 106 Limiter 108 Transmission frequency setter 1081 Local oscillator 1082 Divider 1083 Phase detector 1084 Filter 1086 Voltage controlled oscillator 110 Difference signal generator 1102 Mixer 1104 Operational amplifier 120 Amplification stage 1202 Modulation amplifier 1204 Power amplifier 122 Attenuator 124, 128 Mixer 126 Local oscillator 130 Antenna

Claims (9)

[Claims] An envelope input signal (102) representing an amplitude of a transmission signal and phase data (1) representing a phase of the transmission signal.
04) A digital modulator (100) for generating an RF transmission signal based on the digital modulation device (100), wherein the digital modulation device (100) has a frequency substantially equal to the frequency of the RF transmission signal and is substantially constant. A limiter (106) for outputting a constant amplitude signal having an appropriate amplitude; a transmission frequency setting means (108) for generating an RF transmission frequency (fo) based on the phase data (104) and the constant amplitude signal; Difference signal generating means (110) for generating a difference signal representing a difference between the envelope signal extracted from the signal and the envelope input signal (102); an RF transmission signal based on the RF transmission frequency (fo) and the difference signal The transmission frequency setting means (108) includes: an amplifier for receiving the phase data (104) and the constant amplitude signal; Vessel (1082); the filter (10
84: a voltage-controlled oscillator (1086) for receiving the signal from the frequency divider (1082) filtered by (84) and outputting a signal having an RF transmission frequency. ). 2. The digital modulator according to claim 1, wherein said frequency divider is a fractional frequency divider. 3. The digital modulation device according to claim 1, wherein said filter (1084) is a loop filter or a Nyquist filter. 4. An envelope input signal (102) representing an amplitude of a transmission signal and phase data (1) representing a phase of the transmission signal.
04) A digital modulator (300) for generating an RF transmission signal based on the internal processing frequency (fi) having a predetermined frequency difference from the frequency of the RF transmission signal. A limiter (106) for outputting a constant amplitude signal having a substantially constant amplitude; transmission frequency setting means for generating an RF transmission frequency (fo) based on the phase data (104) and the constant amplitude signal (108); difference signal generating means (110) for generating a difference signal representing a difference between the envelope signal extracted from the RF transmission signal and the envelope input signal (102); the RF transmission frequency (fo) and the difference Amplifying means (120) for generating an RF transmission signal based on a signal; the transmission frequency setting device (108) comprises: Divider for receiving the amplitude signal (1
082); a voltage-controlled oscillator (108) that receives the signal from the frequency divider (1082) filtered by the filter (1084) and outputs a signal having an RF transmission frequency.
6); a digital modulation device (300), characterized by comprising; 5. The digital modulator according to claim 4, wherein said frequency divider is a fractional frequency divider. 6. The digital modulation device according to claim 4, wherein the filter (1084) is a loop filter or a Nyquist filter. 7. An envelope input signal (102) representing an amplitude of a transmission signal and phase data (1) representing a phase of the transmission signal.
A digital modulator (400) for generating an RF transmission signal on the basis of the internal processing frequency (fi) having a predetermined frequency difference from the frequency of the RF transmission signal. A limiter (106) for outputting a constant amplitude signal having a substantially constant amplitude; transmission frequency setting means for generating an RF transmission frequency (fo) based on the phase data (104) and the constant amplitude signal (108); difference signal generating means (110) for generating a difference signal representing a difference between the envelope signal extracted from the RF transmission signal and the envelope input signal (102); the RF transmission frequency (fo) and the difference Amplifying means (120) for generating an RF transmission signal based on the signal; the transmission frequency setting means (108) comprises: A frequency divider (1082) for receiving a constant amplitude signal; a voltage controlled oscillator for receiving a signal from the frequency divider (1082) filtered by a filter (1084) and outputting a signal having an internal processing frequency (fi) (1086); a mixer (12) for converting a frequency of the signal having the internal processing frequency (fi) into an RF transmission frequency.
8). A digital modulation device (400), comprising: 8. A digital modulator according to claim 7, wherein said frequency divider is a fractional frequency divider. 9. The digital modulation device according to claim 7, wherein said filter (1084) is a loop filter or a Nyquist filter.