JPH01317010A - Automatic gain control circuit - Google Patents

Abstract

PURPOSE:To improve the deterioration in the reception side code error rate by detecting a level difference between base band signals inputted to an orthogonal amplitude modulation means by a level difference detection means and controlling the gain of either amplification means automatically so that the level difference is made zero. CONSTITUTION:Inputted base band signals of Ich and Qch are fed via low pass filters 21, 31, attenuators 22, 32 and amplifiers 23, 33 to an orthogonal amplitude modulator 51, where the carrier is subject to multi-value QAM modulation and the result is sent. In this case, parts of the base band signals of Ich and Qch inputted to the orthogonal amplitude modulator 51 are detected respectively by detectors 42, 45 via buffer amplifiers 41, 44 with a high input impedance, integrated by integration devices 43, 46, compared by a comparator 47, a differential signal is extracted, fed to an attenuator 22 via a choke ch and the attenuation is automatically controlled so as to make the difference signal zero. Thus, the deterioration of the code error rate of the reception side caused by the level difference of the base band signals of Ich and Qch is improved.

Description

Detailed Description of the Invention [Summary] For example, regarding an automatic gain control circuit used in a multi-level quadrature amplitude modulation section of a digital multiplex radio device, the control circuit for Ich and Qch baseband signals input to the multi-level quadrature amplitude modulation means This is caused by level differences.

In order to improve the deterioration of the bit error rate on the receiving side, when a quadrature amplitude modulation wave is generated by the quadrature amplitude modulation means using the Ich and Qch baseband signals added via the amplification means, the orthogonal Ic input to the amplitude modulation means
Level difference detection means for detecting the level difference between h and Qch baseband signals is provided, and the output of the level difference detection means controls the gain of one of the amplification means to automatically reduce the level difference to 0. Configure it as follows.

[Industrial application field]

The present invention relates to an automatic gain control circuit used, for example, in a multilevel quadrature amplitude modulation section of a digital multiplex radio device.

In recent years, with the increasing trend of transmitting digital signals over wireless lines, in order to increase the efficiency of using two frequencies, the 16-level quadrature amplitude modulation method (hereinafter abbreviated as 16QAM), 54QAM method, and furthermore 256QAM method have been developed. Methods and multivalued systems are progressing. However, as multivalued technology progresses,
The level difference between the Ich and Qch baseband signals input to the quadrature amplitude modulator degrades the bit error rate on the receiving side.

Therefore, it is necessary to improve the deterioration of the receiving side bit error rate caused by this level difference.

[Conventional technology]

FIG. 3 is a block diagram of a conventional example, and FIG. 4 is an explanatory diagram of the operation of FIG. 3. The operation shown in FIG. 3 will be explained below with reference to FIG.

First, the m-series data is converted to a 26-value analog (No. 3 (hereinafter referred to as baseband signal)) by an Ich digital/analog converter, and then passed through a low-pass filter 12, a variable attenuator 13, and a buffer amplifier 14. is applied to the quadrature amplitude modulator 19 through.

Further, another m-series digital signal applied to the Qch digital/analog converter 15 is passed through the low-pass filter 16. Since the signal is applied to the quadrature amplitude modulator 19 via the variable attenuator 17° and the buffer amplifier 18, a 22'' QAM wave with a signal point arrangement as shown in FIG. 4 is obtained.

Here, the Planning Center issued it on March 1, 1985. n(li
The approximate formula for the bit error rate P of the QAM wave (n=2'') is given by the minimum signal point distance d7.

becomes.

Here, A is the maximum amplitude of the received signal, and erfc is the number of error interpolations.

As shown in the above equation, as the value of n increases and multileveling progresses, the minimum signal point distance d7 decreases, and the code error rate also deteriorates accordingly.

Now, if there is a level difference between the Ich and Qch baseband signals, d shown in FIG. 4 becomes small and the bit error rate deteriorates. Therefore, in order to reduce this, Ic
The variable attenuator 13. adds random data to h and Qch so that both levels match, that is, the bit error rate is maximized. Alternatively, the attenuation amount of 17 was manually adjusted and fixed.

[Problem to be solved by the invention]

However, the digital/analog converter 11 on the Ich side,
Low-pass filter 12. Temperature characteristics of variable attenuator 13 and buffer amplifier 14, and digital/analog converter 15 on the Qch side. The temperature characteristics of the low-pass filter 16° variable attenuator 17 and buffer amplifier 18 do not completely match.

Therefore, when the ambient temperature changes, a level difference occurs between the Ich and Qch baseband signals input to the quadrature amplitude modulator 19, which causes a problem in that the bit error rate on the receiving side deteriorates.

The present invention is caused by the level difference between the Ich and Qch baseband signals input to the multilevel orthogonal amplitude modulation means.

The purpose is to improve the deterioration of the receiving side code error rate.

[Means to solve problems]

FIG. 1 shows a block diagram of the principle of the present invention.

In the figure, 4 is the Ich and Q input to the quadrature amplitude modulation means.
This is level difference detection means for detecting a level difference between baseband signals of channels.

The output of this level difference detection means controls the gain of either one of the amplification means 2 or 3 connected to the input side of the quadrature amplitude modulation means 5 to automatically reduce the level difference to 0. Configure.

[Effect]

In the present invention, the Ich and Q
A level difference detecting means 4 detects a level difference between baseband signals of channels, and automatically controls the gain of one of the amplifying means so that this level difference becomes O. This improves the deterioration of the receiving side code error rate.

〔Example〕

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

Here, the low-pass filter 21. The variable attenuator 22° amplifier 23 is a component of the amplification means 2, and the low-pass filter 31. Attenuator 32. Amplifier 33 is a component of amplification means 3, buffer amplifiers 41, 44 . A detector 42, a 45° integrator 43, 46, and a comparator 47 are components of the level difference detection means 4. The operation shown in FIG. 2 will be described below assuming that the level of the Ich baseband signal is changed.

First, input Ich and Qch baseband signals are passed through low-pass filters 21, 31 . '$i attenuator 22,3
2. applied to quadrature amplitude modulator 51 via amplifier 23.33.

Here, the carrier wave is multi-level QAM modulated and sent out.

At this time, Ich and Q input to the quadrature amplitude modulator 51
A part of the baseband signal of the channel is sent to the detectors 42 and 45 via high input impedance buffer amplifiers 41 and 44.
After being detected by integrators 43 and 46 and then compared by comparator 47, a difference signal is extracted.

This difference signal is applied to the attenuator 22 via the choke channel, and the amount of attenuation is automatically controlled so that the difference signal becomes zero. Therefore, this occurs due to the level difference between the Ich and Qch baseband signals. Deterioration of the receiving side code error rate is improved.

〔Effect of the invention〕

As explained in detail above, according to the present invention, the level difference between the Ich and Qch baseband signals input to the multilevel quadrature amplitude modulator is automatically zeroed out, thereby improving the deterioration of the receiving side bit error rate. There is an effect called.

[Brief explanation of the drawing]

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 FIG. 3. In the figure, 2.3 is an amplification means, 4 is a level difference detection means, and 5 is a quadrature amplitude modulation means. Iko Izumi's 0 Sofu's grass 3 days long 4 days

Claims (1)

[Claims] Ich and Q added via amplification means (2, 3)
Quadrature amplitude modulation means (5
) is provided with a level difference detection means (4) for detecting a level difference between Ich and Qch baseband signals input to the orthogonal amplitude modulation means (5) when generating a quadrature amplitude modulated wave; The output of one of the amplifying means (
2. An automatic gain control circuit characterized in that the circuit is configured to automatically reduce the level difference to 0 by controlling the gain of 2) or 3).