JPH06244660A - Agc circuit - Google Patents

Abstract

PURPOSE:To provide a automatic gain control(AGC) pull-in circuit suitable for receiving burst signals. CONSTITUTION:AGC is loaded so that the signal level of an output terminal 7 can be turned to a certain fixed level decided by an AGC reference level setting circuit 10 but in the pull-in process of AGC, pull-in is accelerated by fixing a loop filter band to wider one and inputted to a pull-in decision circuit 14 and when it is decided that the AGC is pulled in, the loop is stabilized by switching the band of a variable band loop filter 12 to narrower one corresponding to a loop filter band switching signal 15.

Description

Detailed Description of the Invention

[0001]

This invention relates to an automatic gain control (AG
The present invention relates to a C) circuit, and more particularly, to an AGC circuit that is capable of receiving a burst signal such as a packet signal whose reception timing is uncertain at a high speed by improving the pull-in operation of the AGC loop at a high speed.

[0002]

2. Description of the Related Art In order to receive a burst signal such as a packet signal, carrier recovery and clock recovery must be performed in a preamble section before a data section. However, in order to do so, the AG
C must be retracted. That is, in order to receive the burst signal, the AGC must be pulled in in a very short time at the beginning of the preamble section.

FIG. 7 shows an example of a conventional AGC circuit. In FIG. 7, 1 is an input terminal for inputting an IF (intermediate frequency) signal, and 2 is a gain controlled by an AGC bias signal 13. A variable gain circuit, 3 is a mixer for converting an IF signal into a baseband frequency, 4 is a local signal generator input to the mixer 3, and 5 is an LPF (low pass filter) for removing unnecessary waves of the baseband signal. , 6 is a baseband amplifier, 7 is an output terminal for outputting a baseband signal, 8 is a signal level detector for detecting the signal level of the baseband signal and outputting a DC signal, 9 is a signal level detection yellow 8 And an AGC reference level, the subtracter 10 outputs an output terminal 7
Is an AGC reference level setting circuit for determining the signal level of the signal, 11 is an amplifier, and 19 is a loop filter.

However, in the conventional AGC circuit as described above, in order to stabilize the AGC operation, it is necessary to narrow the band of the loop filter 19 of the AGC and slow the response speed of the loop. There is a problem that it takes a long time to pull in the AGC and the burst signal cannot be received.

[0005]

As described above, the conventional A
In the GC circuit, in order to stabilize the AGC operation, the AGC
It is necessary to narrow the band of the loop filter to slow down the response speed of the loop. Therefore, it takes time to pull in the AGC and there is a problem that the burst signal cannot be received.

The present invention has been made in view of the above conventional problems, and an object thereof is to provide an AGC circuit suitable for receiving a burst signal.

[0007]

To achieve the above object, the present invention forms an automatic gain control bias signal based on the output of a loop filter provided in an automatic gain control loop, and the automatic gain control bias signal. In the automatic gain control circuit for variably controlling the gain of the gain variable circuit to which the input signal is added, the loop filter is composed of a band variable filter, and the automatic gain control loop based on the automatic gain control bias signal is used. Determining pull-in, providing an automatic gain control pull-in determination circuit that switches the band of the band variable filter in accordance with the determination result, widening the band of the band variable filter in the pull-in process of the automatic gain control loop, After the pull-in is completed, the band of the band variable filter is set narrow.

[0008]

According to the present invention, the AGC pull-in determination circuit determines whether the AGC is pulled in by the AGC bias signal of the AGC loop, and the band of the variable band loop filter is widened in the AGC pull-in process to increase the loop pull-in speed. When the pulling-in of the AGC is completed, it is narrowed to stabilize the loop.

Therefore, it is possible to perform AG at high speed with respect to the burst signal.
C can be applied, and the burst signal can be reliably received.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. The same components as those used in the description of the above-mentioned conventional example will be described with the same reference numerals.

FIG. 1 is a block diagram showing the overall configuration of an embodiment apparatus to which the present invention is applied.

First, the configuration will be described. 1 is an input terminal to which an IF (intermediate frequency) signal is input, 2 is a gain variable circuit whose gain is controlled by an AGC bypass signal 13, and 3 is an IF signal in a baseband band. Mixer for frequency conversion, 4 is a local signal generator for input to the mixer 3, 5
Is an LPF for removing unnecessary waves in the baseband signal
(Low-pass filter), 6 is a baseband amplifier, 7 is an output terminal for outputting a baseband signal, 8 is a signal level detector that detects the signal level of the baseband signal and outputs a DC signal, and 9 is a signal A subtractor 10 for outputting the difference between the output of the level detection yellow 8 and the AGC reference level is an A for determining the signal level of the output terminal 7.
The GC reference level setting circuit 11 is an amplifier, and the above configuration is the same as that of the conventional example shown in FIG.

In this embodiment, in addition to the above configuration, the band variable loop filter 12 whose band can be changed by the loop filter band switching signal 15 and the AGC bypass signal 1 for controlling the gain of the gain variable circuit 2 are provided.
3, an AGC pull-in determination circuit 14 that determines whether or not the AGC is pulled in and outputs a loop filter band switching signal 15 is provided, and the AGC pull-in determination circuit 14 sends a loop filter band switching signal to the band variable loop filter 12. 15 is output.

The configuration of this embodiment has been described above, and its operation will be described below.

First, when the IF signal is not input to the input terminal 1, the variable gain circuit 2 has the maximum gain by the AGC bypass signal 13, and the loop band of the variable band loop filter 12 has a wide band.

Next, when the burst signal is input from the input terminal 1, it passes through the variable gain circuit 2 and is frequency-converted to the baseband band by the mixer 3, and the unnecessary wave is removed by the LPF 5, and then the amplifier 6 is operated. Is amplified. Then, the signal level detector 8 detects the signal level of the baseband signal and outputs the signal and the AGC reference level setting circuit 10
The difference from the level of is calculated by the subtractor 9, amplified by the amplifier 11, and then fed back to the variable gain circuit 2 as the AGC bypass signal 13 through the variable band loop filter 12.

By the loop as described above, A is set so that the signal level of the output terminal 7 becomes a certain signal level determined by the AGC reference level setting circuit 10.
It costs GC.

By the way, in the pull-in process of the AGC, the loop filter band is fixed to a wider one to increase the pull-in speed. However, if the loop filter band is wide, the loop is not stable and the receiving performance deteriorates.

Therefore, in this embodiment, when the AGC bypass signal 13 is input to the pull-in determination circuit 14 and it is determined that the AGC is pulled in, the loop filter band switching signal 1 is output.
5, the band of the band variable loop filter 12 is switched to a narrower band to stabilize the loop.

As described above, in this embodiment, the loop filter band of the AGC is widened when there is no signal,
When the signal comes in and the AGC loop completes the pull-in, the band is switched to the narrower band to stabilize the loop.
This ensures that the burst signal can be received.

FIG. 2 is a time chart showing a change state of each signal when a burst signal is input to the input terminal 1. (a) is an envelope of the IF signal waveform of the input terminal 1.
(B) is the envelope of the baseband waveform of the output terminal 7,
(C) shows the waveform of the AGC bias signal. In the figure, the section T1 is a section in which the AGC is not applied yet and the gain variable circuit 2 has the maximum gain because the burst signal is input immediately. The section of T2 is AGC
Of the baseband signal of the output terminal 7 is approaching a certain level. T1, T
In section 2, the band of the variable band loop filter 12 is wide. And the section of T3 is AG
This is a section in which the pulling of C is completed and the loop filter band is switched to a narrower one.

FIG. 3 is a diagram showing characteristics of the variable gain circuit 2. As shown in the figure, when the AGC bias signal 13 is large, the gain of the variable gain circuit 2 becomes small,
When the bias signal 13 is small, the gain of the variable gain circuit 2 is large. FIG. 4 is a detailed diagram of the band variable loop filter 12. In the figure, 121
Is a switch that is switched by the loop filter switching signal 15 output from the AGC pull-in determination circuit 14, 1
22 is a wide band loop filter having a wide band so that the AGC loop does not oscillate, and 123 is a narrow band loop filter for stabilizing the AGC loop.

In this configuration, the switch 121 is connected to the wide band loop filter 122 side by the loop filter switching signal 15 while the AGC is not pulled in,
When the AGC completes the pull-in, the switch 121 is connected to the wide band loop filter 123 side.

FIG. 5 is a detailed diagram of the AGC pull-in determination circuit 14. In the figure, 141 is an A / D converter for converting the AGC bias signal 13 into digital data, 142 is a first memory for storing the output of the A / D converter 141, and 143 is a first memory 142.
Second memory for storing the output of the first memory 142, 144 is a subtractor for outputting the difference between the data of the first memory 142 and the second memory 143, and 145 is a first memory for comparing the output of the subtractor 144. A comparator, 146 is a second comparator for comparing the AGC bias signal 13, and 147 is a first comparator 1.
It is an AND circuit that takes the logical product of 45 and the second comparator 146.

In this configuration, the AGC bias signal 1
3 is converted into digital data by the A / D converter 141, and the first memory 142 takes in this digital data at regular intervals. Further, the second memory 143 stores the data immediately before the data currently stored in the first memory 142. Then, the subtracter 144 takes the difference between the data in the first memory 142 and the data in the second memory 143, and the first comparator 145 detects the difference. When the difference is less than a certain value, the loop filter is narrowbanded. Output the signal. This makes it possible to determine whether the change in the AGC bias signal 13 has decreased, that is, whether the AGC has pulled in. However, since the change amount of the AGC bias signal 13 is small when the burst signal is not input to the input terminal 1 and immediately after the burst signal is input, in order to prevent the loop filter from having a narrow band here, The second comparator 146 determines the level of the AGC bias signal 13, and the AND circuit 147 validates the output of the first comparator 145 only when the level is high.

Next, FIG. 6 shows (T1 + T2) shown in FIG.
Another embodiment of the AGC circuit when the time is known in advance is shown. In the figure, the same components as those shown in FIG. 1 are designated by the same reference numerals and duplicate explanations are omitted, but 16 is a distributor for dividing the IF signal into two, and 17 is the presence or absence of the IF signal. Is a detection circuit for detecting a signal and generating a gate signal. Reference numeral 18 is a shift register for delaying the gate signal. In this configuration, the output of the variable gain circuit 2 is distributed by the distributor 16, the presence or absence of the IF signal is detected by the detection circuit 17, and the gate signal is output. Then, the shift register 18 is delayed by a certain time so that the switching timing of the loop filter switching signal 15 is at the end of the T2 section shown in FIG. As a result, FIG.
The effect similar to that shown in is obtained.

[0027]

As described above, according to the present invention, A
When the AGC pull-in determination circuit determines whether or not the AGC is pulled in by the AGC bias signal of the GC loop, widens the band of the band variable loop filter in the AGC pull-in process to increase the loop pull-in speed, and when the AGC pull-in is completed. It is made narrower to stabilize the loop.

Therefore, it is possible to perform AG at high speed with respect to the burst signal.
C can be applied, and the burst signal can be reliably received.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a time chart showing a change state of each signal when a burst signal is input to the input terminal shown in FIG.

FIG. 3 is a diagram showing characteristics of the variable gain circuit shown in FIG.

FIG. 4 is a detailed view of the band variable loop filter shown in FIG.

5 is a detailed diagram of the AGC pull-in determination circuit shown in FIG.

FIG. 6 is a diagram showing another embodiment of the AGC circuit when the time (T1 + T2) shown in FIG. 2 is known in advance.

FIG. 7 is a diagram showing a conventional AGC circuit.

[Explanation of symbols]

 1 Input Terminal 2 Gain Variable Circuit 3 Mixer 4 Local Signal Generator 5 LPF (Low Pass Filter) 6 Amplifier 7 Output Terminal 8 Signal Level Detector 9 Subtractor 10 AGC Reference Level Setting Circuit 11 Amplifier 12 Band Variable Loop Filter 12 13 AGC Bypass Signal 14 AGC pull-in determination circuit 14 15 Loop filter band switching signal

Claims (1)

[Claims] 1. An automatic gain control bias signal is formed on the basis of an output of a loop filter provided in an automatic gain control loop, and a gain of a gain variable circuit to which an input signal is added corresponding to the automatic gain control bias signal is varied. In the automatic gain control circuit for controlling, the loop filter is composed of a band variable filter, and the pulling of the automatic gain control loop is determined based on the automatic gain control bias signal, and the band variable is determined according to the determination result. An automatic gain control pull-in determination circuit that switches the band of the filter is provided, and the band of the variable band filter is widened in the pulling process of the automatic gain control loop, and the band of the variable band filter is set narrow after the pulling is completed. Characteristic automatic gain control circuit.