JPS6251521B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention provides a plurality of channel-dedicated amplification sections for a plurality of channels of television signals, FM broadcast signals, and other signals (in this specification, all of these signals are included simply as a television signal). call)
This article relates to the AGC method of multi-channel amplifiers, which individually AGC-amplify and output each signal at a constant and stable level.

In this type of multi-channel amplifier, one equipped with an AGC control circuit such as a detection section and a comparison section as an amplifier dedicated to each channel has conventionally been used. However, with such a structure, when adjusting the comparison section that has the function of setting the AGC operating range, the number of channels is, for example, 7 in the case of a commonly used 7-channel amplifier.
There is a problem in that the above-mentioned adjustment work is extremely time-consuming because the comparison section includes a time constant element and requires a long time until the level becomes stable.

SUMMARY OF THE INVENTION The present invention aims to eliminate the above-mentioned problems and to provide an AGC system for a multi-channel amplifier that allows adjustment work to be completed with extremely little effort.

The drawings showing the embodiments of the present application will be described below. In FIG. 1, numeral 1 indicates an input terminal, which is exemplified as an input point and is connected to, for example, a dedicated antenna for a specific channel. 2 indicates the input filter, which filters the TV signal or FM of a specific channel.
It allows broadcast signals to pass through and blocks signals from other channels from passing through. 3 indicates an amplifier, for example, a wideband amplifier is used. Note that the input filter 2 and this amplifier 3 constitute a channel-dedicated amplification section 4. Reference numeral 5 denotes a mixing section, which is configured to combine the signals respectively input to a large number of input terminals 6 into one and output it from an output terminal 7. 8 indicates an output terminal. Next, in the AGC means indicated by the reference numeral 10, 12 is a first signal switching section, 13 is a second signal switching section, and 14 is a switching control section, which will be described later by signals from the switching control section 14. The switching operation is as follows. 15
16 is a well-known detector, and 16 is a well-known comparator, which compares the signal from the detector 15 with a reference value and outputs an attenuation amount control signal having a magnitude corresponding to the difference. Reference numeral 17 denotes a storage section, which is a circuit that temporarily stores the attenuation amount control signal sent out from the second signal switching section 13. Note that 11 is a signal superimposing section,
This is used to connect the amplifier 3 and the AGC means 10 through one path.

Next, the operation of the multichannel amplifier will be explained in detail based on FIG. 2, which shows the blocks in FIG. 1 in more detail. As is clear from Fig. 2, the same operation is performed in each circuit (block) in which a plurality of circuits are provided in parallel, so an example of this is shown in bold lines in Fig. 2. The operation of a block or circuit will be explained as a representative example. Further, in the figure, solid line arrows indicate transmission of a high frequency signal (television signal), dashed line arrows indicate transmission of an attenuation control signal, and two-dot chain arrows indicate transmission of a switching signal. In the figure, a high frequency signal entering input terminal 1 is passed through input filter 2 and attenuator 21.
The signal is sent to amplifier 3 through. Note that the attenuator 21
is provided, as is well known, in order to set the level of the input signal within the range followed by the AGC. In the amplifier 3, the above signal is transmitted to the amplification element 2.
2, 24, and 26, and attenuated by variable attenuators 23, 25. The output signal of the amplifier 3 then reaches the input 6 of the mixing section 5 and is delivered via the output filter 27 to the input terminal 8.
Note that the output filter 27 is used for the same purpose as the input filter 2.

On the other hand, the above-mentioned high frequency signal is transmitted to the branching circuit 28 of the three amplifiers.
from there to the signal superimposing section 11. This signal passes through a capacitor 29 that allows high frequencies to pass and blocks direct current, and then reaches an input terminal 30 in the first signal switching section 12. On the other hand, in parallel with the above,
In the switching control section 14, the unstable multivibrator 31 produces an output as shown in FIG.
2b, 32c, . . . output signals having waveforms as shown in FIG. 3, respectively. This signal is transmitted through a chiyoke coil 33 that passes direct current and blocks high frequencies (TV signals), as shown by the double-dashed arrow.
The signal is sent to the switching diode 34 via the switching diode 34. Note that the switching diode 34 is a well-known device that passes a high frequency when forward biased, and by biasing these diodes in order according to the output waveform of the ring counter shown in FIG. It operates in order to pass high frequency signals. Therefore, the input terminal 30
When the diode 34 shown by the thick line in the figure is biased in the forward direction, the high-frequency signal that enters the diode 34 passes through the diode 34 as shown by the solid arrow and is sent out from the output end 35. The signal is then detected in the detection section 15, and the detected signal is sent to the comparison section 16 as indicated by the dashed arrow.
The detection section 15 is for producing a DC voltage of a magnitude corresponding to the signal level of the channel selected by the first signal switching section, and for example, a well-known diode detection section is used. The comparison section 16 is configured using a well-known operational amplifier 36, and compares the output signal from the detection section 15 with a reference voltage (also referred to as a reference value) set by a variable resistor 37 for setting the reference voltage. A signal having a value corresponding to the difference between the two is sent out as an attenuation amount control signal. The sent out attenuation amount control signal then reaches the input end 38a of the second signal switching section 13. Second signal switching section 13
As shown in the figure, it is composed of a plurality of switching transistors 39. The bases of these transistors are respectively connected to the switching control section 14 as shown in the figure, and by applying a signal as shown by the output waveform of the ring counter in FIG. 3 to the base of each transistor 39,
These transistors are made conductive in turn, and the signals received at the input terminal 38a are selectively sent out to a plurality of output terminals 38b, respectively. The first signal switching section 12 and the second signal switching section 13 are configured to operate in synchronization with each other, and among the many input terminals 30 in the first signal switching section 12, for example, When a high frequency signal enters the third input terminal, an attenuation amount control signal corresponding to the level of the high frequency signal is sent to the third output among the many output terminals 38b in the second signal switching section. It is made to appear at the edge. The signal appearing at the output terminal 38b then reaches the storage element 40 in the storage section 17. The storage element 40 is composed of a resistor 41 and a capacitor 42, and is configured to temporarily store the attenuation amount control signal from the output terminal 38b. Next, the attenuation amount control signal that has passed through the storage element 40 passes through the variable attenuator 43 in the amplifier 3, which passes direct current and blocks high frequencies, in the signal superimposing section 11, as shown by the broken line arrow. 23 and 25. Then, those variable attenuators exhibit an attenuation amount according to the value of the attenuation amount control signal. Therefore, the high frequency signal being transmitted as described above is attenuated by these attenuators 23 and 25 in accordance with the signal level. As a result, the high frequency signal appearing at the output terminal 8 is always maintained at a constant level.

In the above-mentioned operating state, the level of the signal entering the input terminal 1 is, for example, 50 to 70 dBμ, and the level of the signal output from the output terminal 8 is, for example, 92 dBμ.

Further, in the above operating state, when the signal of a specific channel, for example, the channel amplified by the third amplifier from the top as shown in the figure, is not selected by the signal switching units 12 and 13, that is, those signal switching units When a signal of another channel is selected in steps 12 and 13, an attenuation amount control signal is not generated in the detection section 15 and the comparison section 16 based on the signal of the specific channel, but at this time, the attenuation amount control signal is not generated in the corresponding storage element 40. The stored value continues to be output from the storage element 40, and the amount of attenuation of the attenuators 23, 25 continues to be controlled in accordance with the output value. Note that the stored value of the storage element 40 is the stored value of the attenuation amount control signal when the above-mentioned specific channel was selected in the signal switching sections 12 and 13. Therefore, the switching units 12 and 1 are switched at a cycle shorter than the general fluctuation cycle of the high frequency signal that enters the input terminal 1.
3, the storage element 40 can always output an attenuation control signal with a value sufficient to compensate for the level of the signal entering the input terminal 1, and therefore the output terminal 8 It is possible to continue sending out signals at a constant and stable level. Note that the speed of signal switching in the first and second signal switching sections 12 and 13 is generally set so that fluctuations in the television signal entering the input terminal 1 can be sufficiently compensated for by the above-described operation. It is recommended to choose the following speed depending on the period of fluctuation. In other words, if we represent the sequential switching time (the time indicated by the symbol t in Figure 3), the time t is the horizontal synchronization signal of the television (63.5 μsec).
It is preferable to set the time to at least twice the time (130 μsec) and 2 to 4 minutes (when compensating for fluctuations in the television signal due to cable temperature changes) or less.

Furthermore, the storage time of the attenuation amount control signal in the storage element 40 is such that the signal of a specific channel is stored in the switching unit 12,
The time should be selected such that the value of the attenuation amount control signal can be stored and output continuously over the time period from when the signal of the specific channel is selected in step 13 until the signal of that specific channel is selected again. is preferred. As an example, it is preferable that the time constant of the capacitor 42 and the resistor 41 be about 4 seconds.

Note that if the transmission of the high frequency signal from the amplifier 3 to the AGC means 10 and the transmission of the attenuation amount control signal from the AGC means 10 to the amplifier 3 are performed through separate routes, the signal superimposition section 11 may be omitted.

In this specification, the portion indicated by the symbol A is also referred to as the television signal input terminal of the AGC means 10, and the portion indicated by the symbol B is also referred to as the attenuation amount control signal output terminal. Further, the variable resistor 37 in the storage section 16
The range of AGC operation as described above is, for example, 50 dBμ based on the level of the input signal at input terminal 1.
70dBμ (operation reference point is 60dBμ).

Next, FIG. 4 shows a different embodiment of the present application, in which the signals of a large number of channels that enter one input terminal 45 are divided into channels by an input filter 46, and the signals of each of these divided channels are A multichannel amplifier is shown as a block in which each channel is amplified by an amplifier 3e. Note that although the AGC means is not shown in the drawing, the AGC operation of each amplifier 3e is performed using the AGC means with the same configuration as above.Furthermore, it is functionally the same or equivalent to the one in the previous figure. Portions that are considered to be structural components are given the same reference numerals as those in the previous figure with an alphanumeric letter "e" added thereto, and redundant explanations are omitted.

As described above, in the present invention, when amplifying the signals of a plurality of channels, these signals are inputted to the dedicated channel amplifying section 3 provided individually, so that each channel is amplified. The signals of each channel can be individually amplified, and each of the signals of each channel can be sent to the mixing section at an appropriate level, and the signals output from the mixing section can be amplified at a uniform level for each channel. It has the effect of being of good quality.

Moreover, in the above case, AGC is applied to each channel amplifier individually, so even if there is a level fluctuation in the input signal to each amplifier, the level fluctuation is corrected individually for each channel. This has the effect of making it possible to maintain stable levels of the output signals for each channel.

Furthermore, even if the present invention is configured to correct level fluctuations for each channel individually in a plurality of amplifiers as described above, the first and second signal switching sections 12 and 13 are provided to correct each channel. Since the signals of each channel are sequentially and alternately passed through the detection section 15 and the comparison section 16, there is an advantage that only one comparison section 16 having the function of setting the AGC operating range is sufficient. This means that when adjusting this type of amplifier before shipping it from the factory, preparations for shipping can be completed with just one adjustment of the comparison section, and the time and effort required for adjustment can be drastically reduced compared to conventional methods (e.g. 1) effect per the number of channels.

[Brief explanation of the drawing]

The drawings show an embodiment of the present application, and FIG. 1 is a block circuit diagram of a multichannel amplifier, FIG. 2 is a circuit diagram showing the circuit shown in FIG. 1 in more detail, and FIG. 3 is a waveform diagram. FIG. 4 is a block circuit diagram (partial diagram) showing a different embodiment. 1... Input terminal, 4... Channel-dedicated amplifier section, 5... Mixing section, 12... First signal switching section,
13...Second signal switching unit, 14...Switching control unit, 15...Detecting unit, 16...Comparing unit.

Claims (1)

[Claims] 1. A plurality of input points into which television signals of a plurality of channels are individually input, a number of input ends corresponding to the number of input points, and one output end, and a a mixing section that mixes incoming signals and outputs the mixture to the output end, and a channel that includes variable attenuation sections, respectively, between the plurality of input points and the plurality of input ends of the mixing section. Dedicated amplification sections are individually provided for each of the above input points, and AGC means having a number of TV signal input terminals corresponding to the number of input points and the same number of attenuation amount control signal output terminals is provided, and each of the above TV signal The connection of the input end and the attenuation control signal output end to the above-mentioned channel-dedicated amplifier section is based on the level of each television signal that enters the television signal input end from the channel-dedicated amplifier section. An attenuation control signal is sent from the attenuation control signal to the variable attenuation section of the amplifier section dedicated to each channel, and the amplifier sections dedicated to each channel are individually AGC controlled and connected so that a TV signal of a constant level can be output from each amplifier section. In the multi-channel amplifier, the AGC means has a first signal input terminal having a number of input terminals corresponding to the number of input points and one output terminal connected to the input terminals sequentially and alternately. a second signal switching section having a switching section, a number of output terminals corresponding to the number of input points, and one input terminal connected to the output terminals in sequence and alternation; a switching control section configured to switch the signal switching section and the second signal switching section synchronously; each input terminal of the first signal switching section is one of the plurality of television signal input terminals; It is individually connected to the corresponding input terminal, and the second
Each output terminal of the signal switching section is individually connected to a corresponding output terminal of the plurality of attenuation amount control signal output terminals, and the output terminal of the first signal switching section and the second signal switching section Between the input terminal and the input terminal of the first signal switching section, there is a detection section that detects the television signal output from the output terminal of the first signal switching section, and a detection section that compares the signal output from the detection section with a reference value and calculates the difference between them. A comparison section outputting an attenuation amount control signal according to the above is interposed in cascade, and the television signal from the amplification section dedicated to each channel is sequentially selected by the first signal switching section. , detects the television signal of the selected channel and further compares it with a reference value to generate an attenuation control signal, and generates an attenuation control signal,
The signal is transmitted through the second signal switching section to the variable attenuation section in the channel-dedicated amplifier of the channel selected by the first signal switching section to control the amount of attenuation. AGC method of multi-channel amplifier.