JPS63260208A - Digital agc system - Google Patents

Abstract

PURPOSE:To obtain a sound signal with less sense of distortion even in a high speed signal transmission system by extracting an AGC signal, multiplying it with an input signal so as to obtain an output signal subjected to automatic gain control thereby decreasing the attack time. CONSTITUTION:The AGC signal smoothed by a smoothing filter of an AGC loop is inputted through a limiter 11 to a function device 12 which controls exponentially the signal in the digital AGC system. Through the constitution above, a reference value from a reference value generator 6 is impressed to an adder 5 and a control force alpha is impressed to a multiplier 7. Then the smoothed AGC signal X is fed to the function device 12 through the limiter 11. In this case, in constituting the function device 12 by a most basic exponential function y=10<x>, the output signal Y of the function device 12 changes from 0.01 to 1.00 when the smoothed AGC signal X varies from -2 to 0. Thus, the Y signal is changed very minutely against the change in the X signal and the AGC operation is quickened against the change to reduce the attack time.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial application field This invention relates to a digital AGC system, and in particular to an SS8
(C11, AM) This is an IWl application to the AGC method in the field of high-speed signal processing suitable for receiving modulated waves.

(b) Conventional technology Digital AGC (Automatic Ga1n)
The Control) method is used for high frequency signals such as modulated wave signals of SSB 1 inorganic 1 M receivers and wideband transmission systems, and the fact that digital processing is more stable than the analog AGC method, and the circuit configuration is The digital AGC method has come to be widely adopted because it has advantages such as a small structure.

Figure 3 shows the @path configuration of the conventional digital AGC system.
This @Rokirinari forms a first-order feedback loop,
The input signal is supplied to input terminal 1 and controlled by multiplier 2,
It was designed to be outputted to the output terminal 3 as an output signal subjected to AGC.

If this input signal suddenly changes for some reason, the gain is automatically controlled to a predetermined output level, and a smoothed output signal can be obtained. The sampling output level of the sampling period T is detected. Each detected sampling period is converted into an absolute value and supplied to the adder 5 as the absolute value. A predetermined reference value is added to the other end of the adder 5 by a reference value generator 6. The adder 5 takes the difference between the absolute value of the detected sampling output and the reference value, and supplies it to the multiplier 7 as a difference signal value.

On the other hand, the multiplier 7 is supplied with a control signal from the control signal generator 8 and multiplied by the difference signal. This I! III signal is A
It operates as a control force α that determines the time constant of the GC circuit. The output of this multiplier 7 is sent to an adder 9, which has an A delay V! equal to the sampling period T! A smoothing filter is formed together with a delay circuit 910 having a delay time, and the output of the multiplier 7 is smoothed.

This smoothed output is supplied to the multiplier 2 via the limiter circuit 11 as an AGC signal. The input signal is multiplier 2
The AGC signal is multiplied by the AGC signal, and the output signal is automatically gain controlled and sent to the output terminal 3.

Figure 3 shows a digital AGC system that forms a first-order feedback loop, but the AGC operation is made steeper and A
In some cases, a second-order or third-order (higher-order) feedback loop is used to achieve the C9tJ effect, but a higher-order feedback loop tends to oscillate and result in an unstable circuit configuration, so in general, a first-order feedback loop is used. A circuit configuration is used that forms a feedback loop and performs stable AGC operation.

(c) Problems to be solved by the invention However, in the conventional devices described above, the attack time, that is, when the input signal suddenly increases for some reason, the output signal is controlled to a predetermined constant level. The disadvantage is that it takes a long time to complete the process.

In addition, it is possible to faithfully maintain the transmission of digital data, and
In order to perform the GC operation well, it is necessary to increase the time constant of the AGC roof. The time constant of the AGC loop is determined by the sampling period T and the control force αl, but if the lower period is constant, increasing the control force a,
The fluctuation becomes larger and the time constant becomes smaller. Conversely, when the control force α is reduced, the time constant becomes larger. That is, in order to increase the time constant, it is necessary to reduce the control force α, but if the control force α is reduced, the accuracy of the digital data will decrease, and if the control force α is further reduced, the output of the multiplier 7 will decrease. There was a drawback that the value became zero and the AGC operation stopped.

If the attack time is long, 1 For example, nothing! II! S of
When a conventional digital AGC type circuit is used in the S8 modulated wave signal path, the attack time is relatively long, and the detected audio signal has the drawback of becoming a signal with a large sense of distortion.

This invention was made in view of the above points, and its purpose is to provide a digital AGC method that can shorten the attack time and obtain audio signals with less distortion even in high-speed signal transmission systems. It's about doing.

(d) Means for Solving the Problem The digital AGC method according to the present invention includes a detection means for detecting the level of an input signal at a sampling period, and a smoothing means for adding a reference value, multiplying it by a control signal, and smoothing it with a smoothing filter. , means for shortening the attack time via an I multiplier, and the AGC signal is extracted and multiplied by the input signal to obtain an automatically gain-controlled output signal. It is a digital AGC method.

(E) The input signal supplied to the input circuit of the operational digital AGC method is misplaced at the absolute value in the sampling period T, and the difference from the reference value is taken to output the change ii of the input signal. This sampled amount of change is multiplied by the control force α, resulting in a gain of 1I
IIIiII, and is smoothed through a smoothing filter formed by a delay circuit matching the sampling period T and an adder.

The smoothed change/quantity is calculated using a function unit (exponential unit).
It is possible to perform broadband high-speed transmission, speed up the AGC operation, and shorten the active time.

(f) Embodiment An embodiment of the digital AGC system according to the present invention will be explained based on FIG.

In Diagram N1, parts showing the same circuits as in Diagram Atsushi 3 are indicated by the same symbols. 12 is a divisor. This divisor 12 employs an exponential numerical value or a numerical value having a corresponding function such as transformation of an exponential numerical value.

FIG. 1 shows the conventional digital AGC system shown in FIG. 3 with a multiplier 12 added thereto. That is, an input terminal 1, a multiplier 2, an output terminal 3, a level detector 4 that detects at a sampling period T, an adder 5, a reference value generator 6, a multiplier 7,
Consisting of a control signal generator 8, an adder 9, a delay circuit 10 under the sampling period, and a limiter 11, the adder 5 receives the reference value from the reference value generator 6, and the multiplier 7 receives the control force α.
The circuit component to which is applied is a conventional digital AG
This is the same as method C (Fig. 3).

The AGC signal smoothed by the smoothing filter of the AGC loop is supplied to the multiplier 12 through the transmitter 11. Now, for example, the trowel is also a basic exponential number V・10m, and the number multiplier is 12.
When the smoothed AGC signal changes from -2 to 0, the output signal y of the multiplier 12 changes from 0.01 to 1.00.

The y signal can change very finely with respect to the change in the X signal, and can be regarded as a large amount of nitridation compared to the amount of change. That is, the AGC operation can be made faster in response to changes, and the attack time can be reduced.

Sampling period T = 20uS, AGC range 40dB with 16 hits, input signal frequency: +2
．． For a burst wave signal of 3 Hz, if the exponent number of the divisor 12 is set as y = 10'''-2.11/I.', the attack time will be 0.4 ms. (Value of experimental data) Under the same conditions, in the conventional digital AGC circuit configuration, the attack time is 40ss.

That is, it can be seen that by adding the multiplier 12 of the present invention, the attack time becomes 1/100 faster.

In this way, in order to increase the speed of AGC operation, up until now the number of bits has been set by changing the sampling period T and the control force α.
By choosing the best option, you can further speed up the process.

Figure 2 shows another embodiment of this invention. Figure 2 shows the circuit of the digital AGC system of the present invention and the analog AGC circuit Fe1I column direct reading to further improve the AGC effect.

In the figure, reference numeral 14 has the same configuration as the digital AGC type circuit of the present invention (FIG. 1).

The AGC output terminal 13 (OUT2) is an AGC signal that has been gain controlled and smoothed by a smoothing filter as described above. This AGC signal is converted into an analog signal by the D/A converter 15 and supplied to the analog AGC circuit 17.

The analog AGC circuit 17 is a circuit that uses, for example, a two-power FET element and has a multiplication W1 function.The analog input signal 16 is applied to one input terminal, and is multiplied by the AGC signal converted into the analog signal. Perform AGC circuit.

The output signal of the analog AGC circuit 17 subjected to analog AGC is supplied to the A/D converter 18, converted to a digital signal, and supplied to the input terminal 1 of the digital AGC system circuit 14.

An output signal controlled by an analog AGC circuit 17 and a digital AGC multiplier 2 is taken out to an output terminal 3 of a digital AGC circuit 14.

In this manner, in the digital AGC method 14, in order to perform stable digital processing, gain control of the analog signal can be performed in the analog AGC circuit 17 at the previous stage.

Roughly speaking, the characteristics of the divisor 12 of the present invention can be arbitrarily selected so that the operation of the analog AGC circuit 17 elements is optimized. Numerical number y = 1QIM of the above experimental values
-fi, 11/I·1'' are open values chosen to optimally operate the analog AGC circuit.

To perform stable digital processing of signal data, it is generally necessary to convert the analog signal into a digital signal using an A/D converter, but if the input level of the analog signal to the A/D converter becomes extremely high,
Overfollow may occur at the input end of the A/D converter, making accurate digital conversion impossible.

Also in the digital AGC method of the present invention, when converting the analog AGC signal into a digital signal using the A/D converter 18,
It is an important element to automatically apply gain control to one analog signal in the GC circuit 17.

(G) Effects of the Invention The digital AGC system according to the present invention can adjust the control force α, enable high-speed AGC operation without increasing the number of bits, and shorten the attack time of AGC operation.

Since the attack time is shortened, SSB change y4'a
When receiving a modulated wave or an All modulated wave, it is possible to obtain a good audio signal without any sense of distortion, so it is highly effective when used in a receiver using a digital IF system.

Moreover, the basic circuit configuration has excellent features such as being able to perform stable AGC operation by forming a -order feedback loop, and being simple and inexpensive, making it easy to implement. are doing.

[Brief explanation of the drawing]

Figure M1 is a block diagram showing an embodiment of the digital AGC system according to the present invention, Figure 2 is a block diagram showing another embodiment of the invention, and Figure 3 is a block diagram of a conventional digital AGC system. . 1... Digital signal input terminal, 2... Multiplier, 3...
... Output terminal (OUTl), 4... Level detector, 5... Adder, 6... Reference value generator, 7... Multiplier, 8... Control signal generator, 9... ... Adder, 10
...Delay circuit, 11.-.Limiter-112...Archival counter, +3.A G C output terminal (OUT2), 14.
...Digital AGC system circuit, 15...D/A cosciverter, 16...analog signal input terminal, 17...analog AGC circuit, 18...A/D cosciverter. Patent Application Directory Figure 1 Figure 2 Figure 3 C

Claims (1)

[Claims] In a digital AGC system used in high-speed signal transmission systems, there is a detection means for detecting the level of an input signal at a sampling period, and a smoothing means for adding a reference value, multiplying by a control signal, and smoothing the result with a smoothing filter. and a means for shortening the attack time via a function unit, and extracts the AGC signal and multiplies it with the input signal to obtain an automatically gain-controlled output signal. AGC method.