JPH10336261A - Modulator - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To reduce the factor of error rate degradation due to carrier leakage. A carrier signal generator for generating a carrier signal of a desired frequency, a phase shifter for generating a quadrature component by changing the phase of the carrier signal, and a DC offset voltage to be added to the I modulated signal. And a DC offset variable adjuster 14 that adjusts
DC offset variable device 16 for adjusting C offset voltage
An adder 18 for adding a DC offset voltage to the I modulated signal, an adder 20 for adding a DC offset voltage to the Q modulated signal, and a phase shifter for quadrature modulation of the I modulated signal to which the DC offset voltage has been added. A mixer 22 for performing the quadrature modulation of the Q-modulated signal to which the DC offset voltage is added in accordance with the carrier signal from the phase shifter 28;
And a synthesizer 30 for synthesizing the signals modulated by the signals 2 and 24, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modulator having a quadrature modulation function for performing quadrature modulation on a signal to be modulated.

[0002]

2. Description of the Related Art As a system for performing quadrature modulation, there is a digital quadrature modulation system in which I and Q modulated signals are subjected to quadrature modulation with a carrier signal of a desired frequency and synthesized by a synthesizer to obtain an output signal. is there.

Conventionally, when performing quadrature modulation, I,
When modulation is applied to each modulated signal of each Q by each mixer of I and Q, it is input to the mixer due to the impedance imbalance of the mixer used for each of I and Q and the property of the mixer having an offset component. The carrier signal has occurred in the output signal as carrier leakage.

As a result, a carrier leakage component remains at the center of the output signal synthesized by the synthesizer. When this output signal is supplied to the receiver, the carrier leakage component is detected as a DC component when the output signal is detected by the demodulator on the receiver side.

FIG. 3 shows a vector diagram of a signal demodulated by a demodulator on the receiver side. FIG. 3A shows a normal case, and FIG. 3B shows a case where a carrier leakage component occurs.

As shown in FIG. 3 (b), when a carrier leakage component is generated, the vector moves from the center by the amount of the carrier leakage component, resulting in an error in the demodulated signal. become.

When a signal subjected to digital quadrature modulation is demodulated by a demodulator, if the vector of the demodulated signal is shifted, a threshold for identifying the signal is shifted. Therefore, the error rate generally used for evaluating digital transmission is degraded.

[0008]

As described above, in the conventional modulator, since the impedance imbalance of the mixer used for the modulation of each of the I and Q modulated signals and the property that the mixer has an offset component, the mixer has a disadvantage. However, the carrier signal input to the IGBT is generated as a carrier leak in the output signal, thereby deteriorating the error rate used for evaluating digital transmission. SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a modulation device capable of reducing a factor of error rate deterioration due to carrier leakage.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a modulator having a quadrature modulation function, a carrier signal generator for generating a carrier signal of a desired frequency, and a phase of the carrier signal output by the carrier signal generator. And a phase shifter that generates a quadrature component by changing the DC offset voltage to be added to the I modulated signal to be modulated.
A DC offset variable device, a second DC offset variable device for adjusting a DC offset voltage to be added to the Q modulated signal to be modulated, and the first DC offset variable device for modulating the I modulated signal. Rectified DC
A first adder for adding an offset voltage, a second adder for adding a DC offset voltage adjusted by the second DC offset variable device to a Q modulated signal to be modulated, and the first addition A first mixer that performs quadrature modulation of the I-modulated signal to which the DC offset voltage has been added by the adder according to the carrier signal from the phase shifter, and a Q that has the DC offset voltage added by the second adder. A second mixer that performs quadrature modulation of the modulated signal according to a carrier signal from the phase shifter; and a combiner that combines signals modulated by the first mixer and the second mixer. It is characterized by having done.

[0010] According to such a configuration, the carrier leakage that occurs when the first mixer and the second mixer perform the modulation uses the property that the signal from the modulator becomes a DC component when demodulated by the demodulator. Then, a DC offset voltage for canceling a carrier leak component is added to the I-modulated signal and the Q-modulated signal input to each mixer, respectively.
And by the second DC offset variable device, and is corrected by adding.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of a modulation device according to the present embodiment. The modulation device according to the present embodiment is a digital quadrature modulation device having a carrier leakage correction function.

As shown in FIG. 1, the modulation device comprises an I-modulated signal input terminal 10, a Q-modulated signal input terminal 12, a DC offset variable device 14, a DC offset variable device 16, a DC
Offset adder 18, DC offset adder 20, mixer 22, mixer 24, carrier signal generator 26,
It comprises a phase shifter 28, a synthesizer 30, and an output signal terminal 32.

The I-modulated signal input terminal 10 to which the I-modulated signal is input and the DC offset variable unit 14 are connected to the input terminal of a DC offset adder 18. The output terminal of the DC offset adder 18 is connected to the mixer 22.

The Q modulated signal input terminal 12 to which the Q modulated signal is input and the DC offset varying device 16
It is connected to the input terminal of the offset adder 20. The output terminal of the DC offset adder 20 is connected to the mixer 24.

The carrier signal generator 26 is connected to a phase shifter 28. The phase shifter 28 is connected to each of the mixer 22 and the mixer 24. The synthesizer 30 is connected to the output terminals of the mixers 22 and 24. An output signal terminal 32 is connected to the synthesizer 30.

The operation of the modulator (digital quadrature modulator) according to the present embodiment will be described below. Generally, it is technically difficult to completely eliminate carrier leakage generated in the mixers 22 and 24 for modulating the I and Q modulated signals. Therefore, in the modulation device according to the present embodiment, since the carrier leakage component becomes a DC component when demodulated in the demodulator, the carrier leakage component is added to each of the I and Q modulated signals input to the mixers 22 and 24. The canceling DC offset voltage is added so that carrier leakage in the output signal can be canceled. By making the value of the DC offset voltage to be added variable, it is possible to correct the carrier leakage by adding the DC offset voltage according to the actual carrier leakage situation.

First, a signal having no DC component, for example, an AC signal or a digital signal whose energy is sufficiently diffused, is applied to the I-modulated signal input terminal 10 and the Q-modulated signal input terminal 12, respectively. The modulated signal and the Q modulated signal are input.

The I modulated signal is supplied to a DC offset adder 1
Input to the mixer 22 through 8. The Q modulated signal is supplied to the mixer 2 through the DC offset adder 20.
4 is input.

On the other hand, a carrier signal of a desired frequency is generated by a carrier signal generator 26 and input to a phase shifter 28 which generates a quadrature signal. The phase shifter 28 generates carrier signals having phases different from each other by 90 degrees from the carrier signal from the carrier signal generator 26, and outputs the carrier signals to the mixers 22 and 24 as carrier signals.

The mixer 22 performs quadrature modulation on the I modulated signal according to the carrier signal from the phase shifter 28. Further, mixer 24 performs quadrature modulation on the Q modulated signal according to a carrier signal having a phase that differs from the carrier signal from phase shifter 28 to mixer 22 by 90 degrees.

In the quadrature modulation in the mixers 22 and 24, carrier leakage occurs for the reasons described above. The mixer 2 of each of these I modulated signal and Q modulated signal
FIG. 2 shows an output signal including a carrier leak from the mixer 2 and the mixer 24 measured by a waveform measuring instrument or the like. That is, a carrier leakage component is observed at the center of the output signal.

In this embodiment, the DC offset variable unit 14 is adjusted for the output signal from the mixer 22 and the DC offset variable is adjusted for the output signal from the mixer 24 for the carrier leakage component as shown in FIG. By adjusting the vessel 16, the carrier leakage component can be reduced.

That is, the DC offset adder 18 adjusts the DC offset variable unit 14 so as to cancel the carrier leakage component while observing the output signal of the mixer 22 so that the carrier offset component is added to the I modulated signal. A predetermined DC offset voltage required for canceling is added and output to the mixer 22.

The DC offset adder 20 adjusts the DC offset variable unit 16 so as to cancel out the carrier leakage component while observing the output signal of the mixer 24, so that the DC offset adder 20 adds the carrier leakage component to the Q modulated signal. A predetermined DC offset voltage required for canceling is added and output to the mixer 24.

The adjustment of the DC offset variable device 14 and the DC offset variable device 16 is performed by the mixer 22,
In addition to performing while observing the output signals of the mixers 24, the output may also be performed while observing the output signals of the synthesizer 30 in which the output signals of the mixers 22 and 24 are synthesized.

Thus, the DC offset variable device 14 and D
By adjusting the C offset variable device 16 and changing the DC offset component added to each of the I modulated signal and the Q modulated signal as necessary, the mixer 22 and the mixer 2 are changed.
4 can correct the carrier leakage component.
Therefore, it is possible to reduce the deterioration of the error rate when the signal synthesized by the synthesizer 30 and output from the output signal terminal 32 is demodulated by the demodulator on the receiving side. In this case, the vector diagram of the signal demodulated by the demodulator on the receiver side can be maintained in a normal state as shown in FIG.

[0027]

As described in detail above, according to the present invention, I
A carrier leak generated when a mixer corresponding to each of the modulated signal and the Q modulated signal modulates the signal is used to cancel a carrier leak component in the I modulated signal and the Q modulated signal input to each mixer. Since the DC offset voltage is adjusted by the DC offset variable device and corrected by adding, the factor of the error rate deterioration due to carrier leakage can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a modulation device according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a waveform of an output signal including carrier leakage measured by a waveform measuring device or the like.

FIG. 3 is a vector diagram of a signal demodulated by a receiver-side demodulator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... I modulated signal input terminal 12 ... Q modulated signal input terminal 14, 16 ... DC offset variable device 18, 20 ... Adder 22, 24 ... Mixer 26 ... Carrier signal generator 28 ... Phaser 30 ... Synthesizer 32 ... Output signal terminal

Claims (1)

[Claims] 1. A modulation device having a quadrature modulation function, a carrier signal generator for generating a carrier signal of a desired frequency, and a quadrature component being generated by changing a phase of a carrier signal output by the carrier signal generator. A phase shifter; a first DC offset variable adjuster for adjusting a DC offset voltage to be added to an I modulated signal to be modulated; and a DC offset voltage to be added to a Q modulated signal to be modulated A first DC adder for adding a DC offset voltage adjusted by the first DC offset adjuster to the I modulated signal to be modulated; and a Q modulated signal to be modulated. A second adder for adding the DC offset voltage adjusted by the second DC offset variable device to the second DC offset variable device; A first mixer that performs quadrature modulation of an I modulated signal to which a set voltage has been added in accordance with a carrier signal from the phase shifter; and a Q modulated signal to which a DC offset voltage has been added by the second adder. A second mixer that performs quadrature modulation according to a carrier signal from the phase shifter; and a combiner that combines signals modulated by the first mixer and the second mixer, respectively. A modulation device characterized by the following.