KR20010081319A - Auto gain control apparatus - Google Patents

Abstract

PURPOSE: An automatic gain control device is provided to reduce a determination error at an ending terminal of receiver by compensating for an amplitude of a signal which is weak but rapid. CONSTITUTION: A slicer unit(101) receives a signal output from a phase compensation unit and determines a signal whose Euclidean distance is shortest on a constellation. A gain control unit(102) compares the signal determined in the slicer unit(101) with the signal output from the phase compensation unit, and outputs a gain control signal according to the comparison value. A multiplier(103) multiplies the gain control signal output from the gain control unit(102) by a signal output from a channel equalizing unit, and outputs a controlled gain signal.

Description

Automatic gain control device {AUTO GAIN CONTROL APPARATUS}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic gain control apparatus, and more particularly, to an automatic gain control apparatus for improving signal determination performance in a receiver for receiving a signal transmitted by modulating phase or level.

In general, a signal transmission channel using a cable is one of channels suitable for transmission of various contents such as digital broadcasting and the Internet in the future. As a modulation method for transmitting a digital signal using such a cable channel, spherical amplitude modulation is used. (QAM: Quadrature Amplitude Modulation) is widely used, and it is a modulation method that carries information not only on the signal phase but also on the signal level.

FIG. 1 is a block diagram showing the configuration of a conventional digital spherical amplitude modulation (QAM) receiver. As shown in FIG. 1, only a signal of a channel selected from a high frequency signal received through an antenna 11 is received and demodulated and an intermediate frequency (IF: A tuner unit 12 for converting and outputting a signal of an intermediate frequency band; An IF amplifier 13 for filtering the signal lowered into the intermediate frequency band and amplifying the signal magnitude; A symbol timing recovery unit (14) for lowering the signal of the intermediate frequency band to the base band and restoring the timing of symbols; A channel equalizer 15 for compensating for ghost and various channel distortions caused by impedance mismatch in a cable transmission channel; A phase correction unit 16 which detects and corrects a phase error due to a phase jitter of the tuner; The automatic gain control unit 17 calculates an error between the power of the received signal and the reference power and feeds it back to the tuner unit 12 and the IF amplifier unit 13.

2 is a block diagram showing a detailed configuration of the automatic gain control unit in FIG. 1, which includes a detector 17a for detecting the amplitude or power of a signal; A subtractor 17b for subtracting a reference amplitude / power from the amplitude / power output from the detector 17a; A loop filter 17c for controlling the distortion of the amplitude output through the subtractor 17b; The amplifier 17d is controlled according to the value output from the loop filter 17c and amplifies the input signal. Hereinafter, the operation of the QAM receiver configured as described above will be described.

First, the symbol timing recovery unit 14 plays an important role in determining the performance of the system in digital data communication technology. In particular, the symbol timing recovery unit 14 finds the temporal position of the transmitted data from the received signal.

Next, the automatic gain control unit 17 automatically controls the gain in order to prevent the performance of the receiver from being deteriorated by the amplitude of the received signal which is subjected to a large amount of distortion due to various causes, that is, the amplitude distortion of the received signal is possible. It reduces and maintains a received signal at a constant amplitude level.

In other words, after the input signal is amplified in proportion to the characteristic function of the amplifier 17d, the amplitude or power component is detected in the amplified and output signal through the detector 17a, and the subtractor 17b is used to determine the amplitude and power. The gain is adjusted to compare and compensate for the error.

At this time, since there is a large difference between the average power of the signal and the power of the signal changing in the symbol unit, the automatic gain control unit 17 adjusts the gain by averaging a large number of symbol powers in order to maintain a constant average power at the output terminal. .

Therefore, the loop filter 17c of the automatic gain control unit 17 designs the time constant large so as to be insensitive to the amplitude of the signal changing between symbols.

And, if the amplitude distortion is severe, multi-stage automatic gain control is applied in the RF and IF stages.

However, in the case of information modulation on the signal level such as spherical amplitude modulation (QAM) or VSB (Vestigial Sideband), the signal has the same average power (for example, when the average power of 64QAM and 256QAM are the same). As the number of levels increases, the interval between signals decreases, which causes a large number of decision errors in the last stage of the receiver even with a small amplitude change of the received signal.

Accordingly, the present invention has been made to solve the above-mentioned conventional problems, and is a gain jitter, that is, a small and fast signal, which was not compensated by the conventional automatic gain controller in a spherical amplitude modulation (QAM) method that is sensitive to the amplitude change of the signal. It is an object of the present invention to provide an automatic gain control device that accurately compensates the amplitude of the signal and reduces the determination error at the receiver end.

1 is a block diagram showing the configuration of a conventional digital spherical amplitude modulation (QAM) receiver.

FIG. 2 is a block diagram showing a detailed configuration of the automatic gain control unit in FIG.

3 is a configuration diagram of a QAM receiver configured by adding an automatic gain controller according to the present invention.

4 is a block diagram showing a detailed configuration of the decision-directed automatic gain controller in FIG.

5 is a block diagram showing a detailed configuration of a gain control unit in FIG.

*** Description of the symbols for the main parts of the drawings ***

100 decision-oriented automatic gain controller 101 slicer portion

102: gain control unit 103: multiplier

102a: power calculator 102b: reference power calculator

102c: power comparison unit 102d: counter unit

102e: limiter

In order to achieve the above object, the present invention provides a receiver for receiving a signal modulated to a phase or a level and receiving a signal (I / Q) which is determined and output at a receiver end to improve the signal determination performance of the receiver. A slicer unit for receiving a signal and determining and outputting a signal having the nearest Euclidean distance in the constellation diagram; A gain controller which compares the power determined by the slicer unit with the power of the signal output from the receiver terminal and outputs a gain control signal based on the compared value; And a multiplier configured to multiply the gain control signal output from the gain control unit to a channel equalizer output signal.

Hereinafter, an embodiment according to the present invention will be described in detail with reference to the accompanying drawings.

3 is a block diagram showing a configuration of a QAM receiver configured by adding an automatic gain control device capable of compensating for a determination error at a final stage of a QAM receiver according to the present invention. To adjust the output gain of the leading channel equalizer 15 by comparing the output of the phase correction unit 16 with the power of its decision signal to compensate for the determination error in the phase correction unit 16 at its final stage. It further comprises a decision-directed automatic gain controller 100.

Here, the decision-directed automatic gain controller 100 receives the signal I / Q output from the phase correction unit 16 as shown in FIG. 4 and has an Euclidean distance on the constellation. A slicer unit 101 for determining and outputting the nearest signal; A gain controller (102) for comparing the power of the signal determined by the slicer unit (101) with the signal output from the phase correction unit (16) and outputting a gain control signal based on the compared value; And a multiplier 103 for multiplying the gain control signal output from the gain control unit 102 with the signal output from the channel equalizer 15 and outputting the adjusted gain signal.

At this time, the gain control unit 102 is the power of the signal (I / Q) output from the phase correction unit 16 as shown in FIG. A power calculation unit 102a for calculating); The signal determined through the slicer unit 101 Power of) A reference power calculation unit 102b for calculating); A power comparison unit (102c) for outputting a counter control signal by comparing the power output from the power calculation unit (102a) and the reference power calculation unit (102b); A counter unit (102d) which up / downs a gain control value by a counter control signal output from the power comparison unit (102c); The limiter 102e is configured as a limiter 102e for limiting the upper limit and the lower limit of the gain control value output up / down by the counter part 102d to prevent excessive output of the gain control value. The operation of the directed automatic gain control device 100 will be described in more detail.

First, the gain control unit 102 calculates the power of the signal I / Q output from the phase correction unit 16 at the final stage of the QAM receiver by the power calculation unit 102a.

Next, the signal determined by the slicer unit 101 ) Is calculated through the reference power calculator 102b and then the magnitude of the power is compared.

Accordingly, when the output signal power of the phase correction unit 16 is smaller than the power of the signal determined by the slicer 101, the counter value is increased to increase the gain, and the power of the signal determined by the slicer 101 is increased. If the output signal power of the phase correction unit 16 is larger, the counter value is lowered to lower the gain.

Of course, when the power values of the two signals are the same, the counter value is held to maintain the proper gain.

Here, the counter 102d corresponds to a loop filter, which will be described in more detail as follows.

In general, in the white Gaussian noise channel, the probability that the power of the output of the slicer unit 101 is large and small is equal to each other. LSB) Discard M bits and use the remaining most significant (MSB) N bits as a gain.

In other words, at the beginning of the operation of the decision-oriented automatic gain controller 100, the counter section 102d sets the value corresponding to gain 1 as the counter initial value, and the loop bandwidth that the gain control loop can track is the counter section. The number of bits (M, N) of (102d) and the size when up / down are adjusted. Accordingly, when the counter is up / down with the same size, the value of M is larger and the value corresponding to gain 1 is larger. The change in gain becomes smaller, and the larger the value of N, the longer it takes to affect the output gain of the actual counter 102d, so that the bandwidth of the loop is reduced.

This method does not compare the average power of the signal with the signal power that varies greatly in time, but compares the power of the received signal with the power of the determined signal. can do.

In order for the decision-oriented automatic gain controller 100 to operate effectively to improve the performance of the receiver, first, the digital QAM receiver must have a small amount of decision-directed errors.

Therefore, the timing of operating the decision-directed automatic gain controller 100 can be determined by calculating the decision-directed error in the phase correction unit 16, that is, calculating the power of noise and comparing it to a threshold value, even in a channel with ghosts. Since the channel equalizer compensates for this at the front, it does not interfere with the operation of the decision-oriented automatic gain controller 100.

As described above, the automatic gain control device of the present invention precisely compensates the gain jitter, that is, the small and fast signal amplitude, which was not compensated by the conventional automatic gain controller in the QAM method sensitive to the amplitude change of the signal. It is possible to reduce the decision error at the receiver end, thereby improving the performance of the receiver.

Claims (2)

A receiver receiving a signal transmitted by modulating a phase or a level, and receiving a signal (I / Q) determined and output at the end of the receiver to improve the signal determination performance of the receiver, the Euclidean distance in the constellation A slicer unit for determining and outputting the nearest signal; A gain controller which compares the power determined by the slicer unit with the power of the signal output from the receiver terminal and outputs a gain control signal based on the compared value; And a multiplier for multiplying a gain control signal output from the gain control unit with a channel equalization signal and outputting a regulated gain signal. The method of claim 1, wherein the gain control unit is the power of the signal (I / Q) output from the receiver terminal ( A power calculation unit for calculating); The signal determined by the slicer unit Power of) A reference power calculation unit for calculating); A power comparator for comparing a power output from the power calculator and a reference power calculator to output a counter control signal; A counter unit which up / downs a gain control value according to a counter control signal output from the power comparison unit; And a limiter unit configured to limit an upper limit and a lower limit width of a gain control value which is output up and down by the counter unit to prevent excessive output of the gain control value and output the limiter.