JPS6223488B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a slope type automatic gain control circuit that variably controls different gain-frequency characteristics depending on the level range of an input signal.

Generally, in transmission communications, etc., a gradient automatic gain control circuit is installed on the transmission line in order to prevent and automatically compensate for unfavorable frequency characteristics caused by the transmission line when transmitting signals. Use by connecting to the receiving end. A conventional slope type automatic gain control circuit of this type, as shown in the configuration example of FIG. The input signal a is amplified by the frequency characteristic variable circuit 1,
Derive the output signal b. This output signal b is branched and applied to the peak value detection circuit 2 to derive a signal c proportional to the peak value of the signal b. This signal c is applied to the reference voltage of the power supply 4 in the error amplification circuit 3.
It is compared with E ₀ , and the difference between E ₀ and the voltage value of signal c is amplified and a control signal d is output. This control signal d
controls the variable frequency characteristic circuit 1 to reduce the gain of the variable frequency characteristic circuit 1 when the voltage value of the signal c is larger than the reference value _E0 , and the voltage value of the signal c is greater than the reference value _E0 . If it is small, it works to increase the gain of the variable frequency characteristic circuit 1. For example, on the control input side of the frequency characteristic variable circuit 1,
A variable element 1a constituted by a field effect transistor is connected, and a change in the value of the control signal d applied to the gate of this element 1a corresponds to the level of the input signal a applied to the variable frequency characteristic circuit 1. Relatedly, its gain-frequency characteristics are variably controlled. As can be seen from this, the selection of circuits and constants constituting the frequency characteristic variable circuit 1 including the variable element 1a is an important factor in obtaining the desired input/output characteristics.

By the way, in the conventional gradient type automatic gain control circuit as described above, the gain-frequency characteristic is changed from a high level a ₁ to a low level a ₄ with the input signal a as a parameter, as seen in the characteristic curve in Figure 2. If you want to change the gain-frequency characteristics with the same tendency with respect to changes in (for example, when using a cable of a fixed length as a transmission line to be compensated for),
The variable frequency characteristic circuit 1 can be designed relatively easily, but as seen in the characteristic curve in _{FIG .}
When you want to change the gain-frequency characteristics in different trends in the low level change range A ₃ to A ₅ (for example, when switching between two cables with different lengths as transmission paths to be compensated) ) or
When it is desired to have a large range of gain change, there is a drawback that it becomes difficult to design the variable frequency characteristic circuit 1.

SUMMARY OF THE INVENTION An object of the present invention is to provide a gradient automatic gain control circuit that can eliminate the above drawbacks and provide gain-frequency characteristics with different trends in response to different level ranges of an input signal. .

According to the present invention, a plurality of frequency characteristic variable circuits are connected in series and each has a gain frequency characteristic with a different tendency, and each of these gain frequency characteristics is variably controlled in accordance with the level range of an input signal. , a peak value detection circuit that detects a peak value from the output signal of the final stage of the plurality of frequency characteristic variable circuits, and a peak value detection circuit that receives each of the detected peak values and detects the peak value based on a reference signal level that sequentially differs in magnitude. The level of the input signal is -MdB (M is If the gain of the first stage of the plurality of variable frequency characteristic circuits is higher than the limit value), the gain of the first stage variable frequency characteristic circuit is controlled, and if it is less than -MdB, the gain of the variable frequency characteristic circuit of the next stage or later is controlled. A sloped automatic gain control circuit is obtained which controls the gain.

Next, a gradient type automatic gain control circuit according to the present invention will be described in detail by giving examples and referring to the drawings.

FIG. 4 is a block diagram showing the configuration of an embodiment according to the present invention.
are cascade-connected frequency characteristic variable circuits, each having gain-frequency characteristics that operate in response to different input signal level ranges, as shown in Figures 5 and 6. shall be.
13 is a peak value detection circuit, 14 and 15 are error amplifier circuits having gains of G ₁ and G ₂ , respectively, and 16 and 17 are error amplifier circuits 1 and 17, respectively.
This is a power supply for reference signals No. 4 and No. 15. Here,
The voltage value _E2 of the power supply 17 is set slightly larger than the voltage value _E1 of the power supply 16, and the output of the error amplifier circuit 14
G ₁ (E ₂ −E ₁ ) and the output G ₂ of the error amplifier circuit 15
(E ₂ −E ₁ ) is the frequency characteristic variable circuit 12 and 11
The values are chosen such that each can be varied over the maximum range of variation. In addition, 11a and 12a
are frequency characteristic variable circuits 11 and 12, respectively.
This is a variable element provided on the control input side of.

In the circuit configured in this way, first, an input signal with a relatively high level is applied to the variable frequency characteristic circuit 11 as e, and the peak value of the output signal g of the variable frequency characteristic circuit 12 is set to a constant value to be controlled. Considering the case where the output signal g appears larger than , the output signal g is detected by the peak value detection circuit 13, and the peak value detection circuit 13 outputs a signal h proportional to the peak value. Since this signal h is initially larger than either of the reference values E ₁ and E ₂ , the error outputs i and j of the error amplifier circuits 14 and 15 both have large values. Therefore, the gains of the frequency characteristic variable circuits 11 and 12 are both controlled to decrease, and the output signal g decreases. Then, the value of the signal h decreases to a certain value that is almost close to the value of the reference value _E2 , and the variable frequency characteristic circuit 11 is controlled by the output j of the error amplifier circuit 15, which decreases accordingly, and as a result, the output The signal g is stabilized to a constant value. In this state, the reference voltage
Since the value of E ₁ is set smaller than E ₂ , the error amplifier circuit 14 derives a control output approximately equal to G ₁ (E ₂ −E ₁ ) as the signal i. Signal i at this time
is sufficiently large, therefore, the frequency characteristic variable circuit 1
The gain of No. 2 is controlled to be approximately zero.

Next, the operation when the input signal e gradually decreases will be described. As the input signal e decreases, the output j of the error amplifier circuit 15 decreases in order to maintain the peak level of the output signal g at a constant value, thereby increasing the gain of the variable frequency characteristic circuit 11. However, since the gain limit of the variable frequency characteristic circuit 11 is set to M, the input e
As the input and output level difference (g-
When e) exceeds MdB, gain control of the variable frequency characteristic circuit 11 becomes impossible. Then, the level of the output signal g decreases below a certain value, and the level of the output signal h of the peak detection circuit 13 also decreases. As a result, the level of the output signal h becomes lower than the reference value _E2 , and approaches the value of _{E1 in order to reduce the level difference with E1 .} Thus, the value of the output i of the error amplifier circuit 14 falls within the variable control range of the variable frequency characteristic circuit 12, and the gain of the variable frequency circuit 12 is controlled to return the level of the output signal g to a constant value. That is, according to this embodiment, when the level of the input signal e is -MdB or more with respect to the reference voltage _E2 , the gain of the frequency characteristic variable circuit 11 is controlled, and -
MdB or less, the gain of the frequency characteristic variable circuit 12 is controlled, and this means that the slope type automatic gain control circuit has a gain-frequency characteristic that varies in tendency depending on the input signal level range. This means that it is possible to control and separate the

Although the above embodiment shows an example in which two frequency characteristic variable circuits are used in cascade, the present invention is not limited to this. It goes without saying that the variable frequency characteristic circuits can be connected in series and each can be controlled in accordance with the level range of the input signal.

As is clear from the above description, according to the present invention, it is possible to control a plurality of variable frequency characteristic circuits having gain-frequency characteristics with different trends depending on the range of input signal levels. Of course, it is suitable for use in compensating the characteristics of transmission lines with different cable lengths in communication systems, etc.
This has great effects in that it reduces the distortion of the received signal and also enables signal transmission over longer distances and with higher quality as the gain variable range is expanded.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a conventional gradient automatic gain control circuit, FIG. 2 is a characteristic diagram showing an example of gain-frequency characteristics easily obtained in the conventional example of FIG. 1, and FIG. , FIG. 1 is a characteristic diagram showing an example of desirable gain-frequency characteristics that cannot be easily obtained in the conventional example, FIG. 4 is a block diagram showing an embodiment of the slope type automatic gain control circuit according to the present invention, 5 and 6 are characteristic diagrams showing examples of gain-frequency characteristics with different trends obtained in the embodiment of FIG. 4, respectively. In the figure, 1, 11, 12 are frequency characteristic variable circuits, 1a, 11a, 12a are variable elements, 2, 13 are peak value detection circuits, 3, 1
4 and 15 are error amplification circuits, and 4, 16 and 17 are reference signal power supplies.

Claims (1)

[Claims] 1. A plurality of frequency characteristic variable circuits which are connected in cascade and each have a gain frequency characteristic with a different tendency, and each of which has a gain frequency characteristic that is variably controlled in accordance with the level range of an input signal; a peak value detection circuit that detects a peak value from the output signal of the final stage of the frequency characteristic variable circuit; In response to the outputs of the error amplification circuit and the plurality of error amplification circuits, the level of the input signal is -MdB (M is the frequency characteristic of the plurality of frequency characteristics) with respect to the maximum value of the plurality of reference signal levels. If the limit value of the gain of the first stage of the variable circuit is exceeded, the gain of the first stage variable frequency characteristic circuit is controlled, and if it is below -MdB, the gain of the frequency characteristic variable circuit of the next stage and subsequent stages is controlled separately. A slope type automatic gain control circuit.