JPS6362439A - Carrier leakage prevention circuit - Google Patents

Abstract

PURPOSE:To suppress the carrier component leaked to an amplitude modulation wave by detecting, integrating a peak value of the amplitude modulation wave, synthesizing and feeding back it to an amplitude modulator. CONSTITUTION:A comparator means 7 compares an output of a D/A converter 1 with a setting level and gives a comparison output to a detection means 8. The detection means 8 uses a positive polarity detector or a negative polarity detector driven by the comparison output to detect a positive peak or a negative peak of the output of the amplitude modulator, integrate the peak and then synthesize it. Since it is a DC component corresponding to the leakage component of the carrier, the carrier component leaked to the amplitude modulation wave is suppressed by feeding back the DC component to the input of the amplitude modulator 2.

Description

[Detailed Description of the Invention] [Summary] In the carrier wave leakage prevention circuit, since the operation of the amplitude modulator is not ideal, the carrier wave component leaks into the amplitude modulated wave, and the error rate deteriorates on the receiving side.

Therefore, after detecting the positive peak value or the negative peak value of the amplitude modulated wave with a positive polarity detector or negative polarity detector and integrating it, the resulting composite signal is fed back to the amplitude modulator. This suppresses carrier wave component leakage.

[Industrial application field]

The present invention relates to an improvement in a carrier wave leakage prevention circuit, for example, a carrier wave leakage prevention circuit used in a multilevel quadrature amplitude modulator.

In recent years, in order to use frequencies more effectively in digital multiplex radio systems, for example, the 16-level quadrature amplitude modulation method (hereinafter abbreviated as 16QAM method) has been changed to 64QAH method,
Furthermore, there is a trend toward the 25SQAM method and multi-value technology.

However, as the number of values increases, the performance of the device is required to be improved, and leakage of the carrier wave component of the double-balanced modulator is also required to be improved.

[Conventional technology]

FIG. 3 shows a block diagram of a conventional example.

Hereinafter, using a 640 AM modulator as an example, the process of generating a modulated wave will be described with reference to FIG.

First, input digital data is passed through a serial/parallel converter (
(not shown) into 6-bit parallel data, Ich
It is divided into 3 bits each for use and Qch. Then, the 3-bit parallel data for Ich is applied to the digital/analog converter 1 and converted into an 8-level signal, then band-limited by the roll-off filter 2 and applied to the double-balanced modulator 3.

On the other hand, the carrier wave from the carrier wave generator 5 is distributed by the hybrid 4 into two carrier waves with a phase difference of 90 degrees, one of which is applied to the double balanced modulator 3 to obtain an amplitude modulated wave, and the synthesizer 9 Added to 6.

Since the Qch amplitude modulated wave is also applied to this synthesizer 6, the 64QAM modulated wave is synthesized and outputted via the band pass filter 7.

[Problem that the invention seeks to solve]

Here, if the double-balanced modulator operates ideally, the carrier wave will be suppressed and will not leak into the modulated wave, but - this modulator does not operate ideally.

- Affected by temperature fluctuations in other circuits.

Due to such reasons, the carrier wave component usually leaks slightly and has an offset.

That is, FIG. 4(a) of the diagrams explaining the operation of the double-balanced modulator shown in FIG. 4 is a diagram explaining the input signal level versus the modulated wave output level. Case (solid line)
For example, the output level of the modulated wave will be A on both the positive side and the negative side with respect to the level of the input signal, but if it is not ideal (dotted line), the output level of the modulated wave will be A on the positive side and A It on the negative side. becomes A', and the output level changes by the offset.

On the receiving side, when identifying the multi-level analog signal shifted in this way, the identification level does not change as shown in Figure 4(b), and the entire demodulated multi-level signal (dotted line) is shifted. This increases the possibility of misidentification.

Incidentally, FIG. 4(b) is an explanatory diagram of the multi-level signal and the discrimination level, and the solid line indicates no carrier wave leakage.

Therefore, there is a problem in that leakage of the carrier wave component of the amplitude modulator must be suppressed.

[Means for solving problems]

As shown in FIG. 1, the above problem is caused by the comparison means 7 that compares the level of the multi-level signal with a predetermined level, and the positive polarity detector or negative polarity detector driven by the output of the comparison means. This problem is solved by the carrier wave leakage prevention circuit of the present invention, which is provided with a detection means 8 that detects an amplitude modulated wave, integrates it, and then adds it, and feeds back the output of the detection means to the amplitude modulator 2.

[Effect]

In the present invention, the comparison means 7 compares the output of the digital/analog converter 1 with a set level, and the comparison output is sent to the detection means 8.
Add to.

Here, the positive or negative peak value of the output of the amplitude modulator is detected by a positive polarity detector or negative polarity detector driven by the comparison output, and then integrated.

When combined, a DC component corresponding to the leakage component of the carrier wave is obtained, so that this can be fed back to the input side of the amplitude modulator 2 to suppress the carrier wave component leaking into the amplitude modulated wave.

〔Example〕

FIG. 2 shows a block diagram of an embodiment of the invention.

Note that the same reference numerals indicate the same objects throughout the figures.

In the figure, comparator 71. Resistor R2 is a component of comparison means 7, which includes analog switches 81.82, diodes 83.84, integrators 85.86, combiners 82. Variable gain amplifier 88. R, is a component of the detection means 8.

Hereinafter, the present invention will be explained in detail with reference to FIG. 2, assuming that the same <640 AM modulated wave as in the conventional example is generated.

First, 8-level analog signals from digital/analog converter 1 to 0 to 7 are sent to comparator 71 and amplitude modulator 2.
Suppose that it is added to

The comparator 71 adjusts the resistor R2 and inputs the digital/
The output level from analog converter 1 is ・Level 3.5
When the level is 3.5 or less, the voltage is “H” from the output terminal ■ and the voltage is “L” from the output terminal ■. When the level is 3.5 or less, the voltage is “L” from the output terminal ■ and the voltage is “H” from the output terminal ■. Since it outputs voltage, the corresponding analog switch 81 or 8
2 is turned on.

On the other hand, the amplitude modulator 2 outputs an amplitude modulated wave corresponding to the level of the input multi-level signal, but this amplitude modulated wave is sent to the positive polarity detector 8 via the analog switch that is turned on.
3 or a negative polarity detector 84 detects the peak value on the positive side or the negative side, and integrates it in an integrator 85 or 86.

That is, the purpose of integration is to preserve the peak value of the amplitude modulated wave since it constantly changes randomly, and the integrated value is combined in the synthesizer 87 to obtain the average offset level,
That is, a value corresponding to the leakage amount of the carrier wave component is obtained.

Therefore, using this level as a control signal, the variable gain amplifier 8
8. By feeding back to the input side of the amplitude modulator 2 via the resistor R1 and applying a voltage offset in the opposite direction, it is possible to suppress the carrier wave component leaking into the modulation signal.

Note that the same applies to Qch (leakage of the carrier wave component is suppressed, thereby improving the deterioration of the error rate of the 64QAM modulated wave).

〔Effect of the invention〕

As described in detail above, the present invention has the effect of suppressing the carrier wave component leaking into the amplitude modulated wave.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the principle of the present invention, FIG. 2 is a block diagram of an embodiment of the present invention, FIG. 3 is a block diagram of a conventional example, and FIG. 4 is an explanatory diagram of the operation of a double-balanced modulator. In the figure, 1 is a digital/analog converter, 2 is an amplitude modulator, 7 is a comparison means, and 8 is a detection means. XL Izumi Igu 1/7 Block Same 3rd Garden

Claims (1)

[Claims] A binary digital signal is converted into a digital/analog converter (
After converting the multi-level signal into a multi-level signal in step 1), the multi-level signal is amplitude-modulated using a separate amplitude modulator using a carrier wave having a phase difference of π/2 to generate an amplitude modulated wave. The orthogonal amplitude modulation section which synthesizes the orthogonal amplitude modulated waves in the synthesizer (9) includes a comparison means (7) for comparing the level of the multi-level signal with a set level, and a comparator driven by the output of the comparison means. and a detection means (8) that detects the amplitude modulated wave with a positive polarity detector or a negative polarity detector, integrates it, and adds it, and the output of the detection means is fed back to the amplitude modulator. A carrier wave leakage prevention circuit featuring: