JP2000022465A - High speed agc circuit and its control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high speed AGC circuit by setting an initial setting value of a control voltage of a variable gain element to a center of a control voltage range so as to make a variable range narrow thereby reducing a convergence time of AGC and attaining the high speed operation of the AGC circuit. SOLUTION: A gain of a veriable gain element 1 is controlled in response to a terminal voltage of a capacitor connecting with the variable gain element 1, and the variable gain element 1 is used to make constant the different levels of a burst signal of a high speed in the high speed AGC circuit. The capacitor 5 is charged up to a prescribed voltage during idle throttle of the burst signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-speed AGC circuit and a control method thereof, and more particularly, to a high-speed AGC circuit using a variable gain element.
The present invention relates to a high-speed AGC circuit in which the signal levels of high-speed burst signals having different levels are fixed, and a control method thereof.

[0002]

2. Description of the Related Art In particular, a burst signal used for burst transmission such as data communication has an A signal for each burst signal.
It is necessary to apply GC, and by shortening the convergence time of AGC, data slew rate is increased. Therefore A
It is required to shorten the convergence time of GC.

In order to meet this demand, for example, as disclosed in Japanese Patent Application Laid-Open No. 4-108206, the control voltage of the variable gain element is controlled by charging and discharging of a capacitor, and the control voltage is forcibly applied when a burst signal has an idle time throttle. There has been proposed a technology in which a capacitor is discharged to a reset state, the capacitor is charged simultaneously with the input of a burst signal, the gain of the variable gain element is changed, and the gain is held at a desired level.

In the above-mentioned method, when a burst signal of a new time slot is input, the variable gain element starts operating from the maximum or minimum gain. For this reason, since the variable range of the variable gain element may be maximized, the convergence time of the AGC becomes longer, and there is a disadvantage that the preamble needs to be set longer. Furthermore, since the control voltage fluctuation of the variable gain element becomes large, there is a disadvantage that the output signal of the variable gain element is changed in a DC manner.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to improve the above-mentioned drawbacks of the prior art and, in particular, to set the initial value of the control voltage of the variable gain element at the center of the control voltage range. , So A
It is an object of the present invention to provide a novel high-speed AGC circuit that shortens the convergence time of GC and enables high-speed operation, and a control method thereof.

[0006]

SUMMARY OF THE INVENTION The present invention basically employs the following technical configuration to achieve the above object. That is, in the first aspect of the high-speed AGC circuit according to the present invention, the gain of the variable gain element is controlled in accordance with the terminal voltage of the capacitor connected to the variable gain element, and high-speed different In a high-speed AGC circuit in which the signal level of a burst signal of a constant level is made constant, the capacitor is charged to a predetermined voltage during an idle throttle of the burst signal. In a second aspect, a first level detection circuit is provided on the output side of the variable gain element, and when the first level detection circuit detects a level higher than a predetermined level, the capacitor is charged. When the first level detection circuit detects a level equal to or lower than a predetermined level, the capacitance is reduced. Charging the capacitor to increase the gain of the variable gain element, and when the terminal voltage of the capacitor has reached a predetermined voltage, charging and discharging of the capacitor is stopped, In a third aspect, a charging / discharging circuit is connected to the capacitor via a switch, and the charging / discharging circuit includes one discharging circuit and at least two charging circuits. In a fourth aspect, a switch control circuit for controlling the charge / discharge circuit is provided, and the switch control circuit is configured to be controlled by the first level detection circuit. In a fifth aspect, a second level detection circuit is provided on the input side of the variable gain element, and when the second level detection circuit detects that there is no input signal, the switch control circuit is turned off. To a predetermined voltage the capacitor via is characterized in that it has configured to charge again.

Further, according to an aspect of the high-speed AGC circuit and the control method thereof according to the present invention, the gain of the variable gain element is controlled in accordance with the terminal voltage of a capacitor connected to the variable gain element. And controlling the high-speed AGC circuit so that the signal level of the high-speed burst signal having a different level is constant, charging the capacitor to a predetermined voltage in advance, and detecting a level detected at the output side of the variable gain element. When the circuit detects a level equal to or higher than a predetermined level, the charge of the capacitor is discharged to lower the gain of the variable gain element, and thereafter, a level detection circuit provided on the output side of the variable gain element determines a predetermined level. When the detected level is detected, the discharging of the capacitor is stopped, the capacitor is charged to a predetermined voltage in advance, and the capacitor is provided on the output side of the variable gain element. When the bell detection circuit detects a level equal to or lower than a predetermined level, the capacitor is charged to increase the gain of the variable gain element, and thereafter, a level detection circuit provided on the output side of the variable gain element determines a predetermined level. When the detected level is detected, the charging of the capacitor is controlled to be stopped.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A high-speed AGC circuit and a control method thereof according to the present invention are characterized in that an initial value of a gain of an AGC amplifier in an AGC circuit is set to a center level of a variable gain element. This is a high-speed AGC that controls the charge / discharge time constant of the A.B.C.

As shown in the block diagram of FIG. 1, a variable gain element 1, a level detection circuit 2, a switch control circuit 3
, A switch circuit 4, a capacitor 5, and an input level detection circuit 6. The capacitor 5 is charged by the switch circuit 4 during the idle throttle of the burst signal, and the gain of the variable gain element 1 is set to the center level Vt. The switch circuit 4 is switched to charge or discharge the capacitor according to the burst signal input level, and the switch circuit 4 is opened at a desired level.

[0010] Accordingly, the AGC control range is substantially halved, and high-speed response is possible.

[0011]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a high-speed AGC circuit according to the present invention. FIG. 1 is a block diagram showing a specific example of a high-speed AGC circuit according to the present invention. In FIG. 1, the gain of the variable gain element 1 according to the terminal voltage of a capacitor 5 connected to the variable gain element 1 is shown. In a high-speed AGC circuit using the variable gain element 1 to make the signal levels of high-speed burst signals of different levels constant, the capacitor 5 is supplied with a predetermined voltage between idle throttles of the burst signal. A high-speed AGC circuit configured to charge up to 200 A is shown.

Hereinafter, the present invention will be described in detail with reference to FIG. The AGC circuit according to the present invention includes a variable gain element 1, a level detection circuit (first level detection circuit) 2 for detecting a level on the output side of the variable gain element 1, and a switch control circuit 3.
A capacitor 5 for determining the gain of the variable gain element 1, a switch circuit 4 for switching and controlling the charging and discharging of the capacitor 5,
The variable gain element 1 includes an input level detection circuit (second level detection circuit) 6 for detecting the level on the input side of the variable gain element 1, and the gain of the variable gain element 1 is varied by the voltage Vc of the capacitor 5. The level detection circuit 2 includes a diode D and a comparator 2a, and detects an output level of the variable gain element 1. Similarly, the input level detection circuit 6 includes a diode and a comparator.
Detects the presence or absence of an input signal. The switch control circuit 3 controls the switch circuit 4 based on signals from the level detection circuit 2 and the input level detection circuit 6. The switch circuit 4
The charge / discharge of the capacitor 5 is controlled.

Next, the configuration of the level detection circuit 2 will be described. A detection diode D is provided between the output side of the variable gain element 1 and one input terminal of the comparator 2a. A predetermined voltage is applied to the other input terminal of the comparator 2a. Is composed. The level detection circuit 6 provided on the input side of the variable gain element 1 has the same configuration.

When the output level of the variable gain element 1 is higher than a predetermined level, the switch control circuit 3 uses the output of the level detection circuit 2 as a circuit for lowering the gain of the variable gain element 1. The signal is guided to the AND circuit 31 and the signal of the level detection circuit 6 is inputted to the AND circuit 31 via the diode 32. A resistor 33 is connected in parallel with the diode 32, and a capacitor 34 is provided between the cathode of the diode 32 and the ground.

The output signal of the AND circuit 31 is configured to be input to the latch circuit 35, and the switch 4a of the switch circuit 4 is controlled via the latch circuit 35 and the AND circuit 48. Make up. The AND circuit 48 is configured to AND the output signal of the AND circuit 31 and the output signal of the latch circuit 35.

The clock terminal of the latch circuit 35 has a delay element 36, an inverter 37, and an exclusive OR (XO).
R) an edge detection circuit 3 for detecting the rising edge and the falling edge of the burst signal B constituted by the circuit 38
9 is input. Therefore, when a burst signal is input and a signal of a predetermined level or more is detected by the level detection circuit 2, the output signal of the latch circuit 35 becomes "H" level at the rising edge of the burst signal, and the switch 4a is closed and the capacitor is closed. 5 is the resistance Rg
To reduce the gain of the variable gain element 1.

The detection signal of the level detection circuit 6 is configured to control the switch 4c via the diode 32 and the inverter 46. In this case, the output of the inverter 46 becomes "L" level, and the switch 4c The gain of the variable gain element 1 which is opened decreases, and the output terminal "O"
When the level of "UT" reaches a predetermined signal level, the output of the level detection circuit 2 is inverted. That is, the switch 4a of the switch circuit 4 which has been closed via the AND circuit 31, the latch circuit 35, and the AND circuit 48 is opened, and the discharge of the capacitor 5 is stopped.

On the other hand, when the output level of the variable gain element 1 is lower than a predetermined level, the switch control circuit 3 outputs the output of the level detection circuit 2 via the inverter 40 as a circuit for increasing the gain of the variable gain element 1. AND circuit 4
1 and the signal of the level detection circuit 6 is inputted to the AND circuit 41 via the diode 32.

The output signal of the AND circuit 41 is configured to be input to the latch circuit 45. The switch circuit 4 is connected to the latch circuit 45 via the AND circuit 47.
Is controlled to control the switch 4b. In addition,
The AND circuit 47 is configured to AND the output signal of the AND circuit 41 and the output signal of the latch circuit 45.

Similarly to the latch circuit 35, the output of the edge detection circuit 39 for detecting the rising edge and the falling edge of the burst signal is input to the clock terminal of the latch circuit 45. Therefore, when a burst signal is input and a signal below a predetermined level is detected by the level detection circuit 2, the output signal of the latch circuit 45 becomes "H" level at the rising edge of the burst signal, and the switch 4b is closed and the capacitor is closed. 5 is charged from the power supply Vcc via the resistor Rv, and increases the gain of the variable gain element 1.
Also in this case, the output of the inverter 46 becomes "L" level, the switch 4c opens, the gain of the variable gain element 1 which is opened increases, and the level of the output terminal "OUT" becomes a predetermined signal level. The output of the detection circuit 2 is inverted. That is, the AND circuit 41, the latch circuit 45, the AND circuit
The switch 4b of the switch circuit 4 which has been closed via the circuit 47 is opened, and the charging of the capacitor 5 is stopped.

When the level detection circuit 6 detects that the burst signal has disappeared, the edge detection circuit 39 detects the falling edge of the burst signal, and the falling edge signal is input to the clock terminals of the latch circuits 35 and 45. When the falling edge signal is output, the switches 4a and 4b are opened. An inverter 46 is connected to the cathode of the diode 32,
The inverter 46 closes the switch 4c, charges the capacitor 5 again to a predetermined voltage, and initializes the gain of the variable gain element 1 to a predetermined gain.

Therefore, when the burst signal disappears, the switches 4a and 4b are opened and at the same time the switch 4c is closed to return to the reset state. Next, the overall operation of the present invention will be described with reference to FIG. First, the switch circuit 4 is switched to the Vt side during the idle throttle of the burst signal, and the capacitor 5 is charged to the center voltage Vt in the variable range of the control voltage Vc of the variable gain element 1 to be reset. Here, the gain of the variable gain element 1 increases when the control voltage Vc is high, and the control voltage Vc
It is assumed that the smaller the value, the smaller the value.

When a burst signal is input, the level detection circuit 2 determines whether the level is higher or lower than a desired level of AGC control. When the level detection circuit 2 determines that the level is higher than the desired level, the switch control circuit 3 switches the switch circuit 4 to the Rg side, and the charge of the capacitor 5 starts discharging. When the charge of the capacitor 5 is discharged, the control voltage Vc of the variable gain element 1 decreases, and the variable gain element 1
Output level becomes smaller.

When the level detection circuit 2 detects that the output level of the variable gain element 1 has reached a desired level, the switch control circuit 3 sets the switch circuit 4 to open.
Control to switch to the side. Switch circuit 4 is open
When switching to the n side, discharging of the capacitor 5 is stopped,
The gain of the variable gain element 1 is kept constant. Next, when the input level detection circuit 6 detects the end of the burst signal, the switch control circuit 3 switches the switch circuit 4 to the Vt side again, that is, puts the switch circuit 4 into a reset state.

Conversely, if the level detection circuit 2 determines that the level is lower than the desired level, the switch control circuit 3 switches the switch circuit 4 to the Rv side, and starts charging the capacitor 5. When the capacitor 5 is charged, the control voltage Vc of the variable gain element 1 rises, the output level of the variable gain element 1 increases, and the level detection circuit 2 detects that the output level of the variable gain element 1 has reached a desired level. Then
The switch control circuit 3 controls the switch circuit 4 to switch to the open side. When the switch circuit 4 is switched to the open side, charging of the capacitor 5 is stopped and the gain of the variable gain element 1 is kept constant.

When the input level detection circuit 6 detects the end of the burst signal, the switch control circuit 3 switches the switch circuit 4 to the Vt side, that is, enters the reset state.

[0027]

Since the high-speed AGC circuit and the control method according to the present invention are configured as described above, the AGC convergence time can be reduced to about half the conventional time. Moreover,
Since the configuration is simple, it has excellent features such as easy implementation.

[Brief description of the drawings]

FIG. 1 is a block diagram of a high-speed AGC circuit according to the present invention.

FIG. 2 is a specific circuit diagram of a high-speed AGC circuit according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Variable gain element 2 Level detection circuit 2a Comparator D diode 3 Switch control circuit 4 Switch circuit 4a, 4b, 4c Switch 5, 34 Capacitor 6 Input level detection circuit 32 Diode 33 Resistance 31, 41 AND circuit 35, 45 Latch circuit 36 Delay Element 37, 40, 46 Inverter 38 Exclusive OR (XOR) circuit B Burst signal

Claims (6)

[Claims] 1. The gain of the variable gain element is controlled according to a terminal voltage of a capacitor connected to the variable gain element,
A high-speed AG that uses this variable gain element to make the signal level of high-speed burst signals of different levels constant.
2. A high-speed AGC circuit according to claim 1, wherein said capacitor is charged to a predetermined voltage during an idle throttle of said burst signal. 2. A first level detection circuit is provided on an output side of the variable gain element, and when the first level detection circuit detects a level higher than a predetermined level, the capacitor is charged. Discharging the charge to lower the gain of the variable gain element, and when the first level detection circuit detects a level lower than a predetermined level, charges the capacitor to reduce the gain of the variable gain element. 2. The high-speed AGC circuit according to claim 1, wherein when the terminal voltage of the capacitor reaches a predetermined voltage, charging and discharging of the capacitor are stopped. 3. A charge / discharge circuit connected to the capacitor via a switch, wherein the charge / discharge circuit comprises one discharge circuit and at least two charge circuits. 2. The high-speed AGC circuit according to 2. 4. A high-speed switch according to claim 3, further comprising a switch control circuit for controlling said charge / discharge circuit, wherein said switch control circuit is controlled by said first level detection circuit. AGC circuit. 5. A second level detection circuit is provided on an input side of the variable gain element. When the second level detection circuit detects that there is no input signal, the second level detection circuit transmits the second level detection circuit via the switch control circuit. 5. The high-speed AGC circuit according to claim 4, wherein the capacitor is recharged to a predetermined voltage. 6. The gain of the variable gain element is controlled according to a terminal voltage of a capacitor connected to the variable gain element,
A high-speed AG that uses this variable gain element to make the signal level of high-speed burst signals of different levels constant.
In the control method of the C circuit, the capacitor is charged to a predetermined voltage in advance, and when the level detection circuit provided on the output side of the variable gain element detects a level higher than a predetermined level, the charge of the capacitor is discharged. Then, the gain of the variable gain element is reduced, and thereafter, when a level detection circuit provided on the output side of the variable gain element detects a predetermined level, the discharging of the capacitor is stopped, and the capacitor is turned off. The battery is charged to a predetermined voltage in advance, and when a level detection circuit provided on the output side of the variable gain element detects a level lower than a predetermined level, the capacitor is charged to increase the gain of the variable gain element, Thereafter, when a level detection circuit provided on the output side of the variable gain element detects a predetermined level, control is performed so as to stop charging the capacitor. Control method for high-speed AGC circuit according to claim and.