JP4795059B2 - Variable gain high frequency amplifier - Google Patents

Description

  The present invention relates to a variable gain high frequency amplifier provided in a transmission line of a CATV system, for example.

  Conventionally, in a CATV system, a variable gain high frequency amplifier is provided as a bidirectional CATV amplifier on a transmission line to amplify a downstream signal and an upstream signal (see, for example, Patent Documents 1 to 3).

  FIG. 5 is a block diagram showing the basic configuration of a bidirectional bidirectional variable gain high-frequency amplifier used conventionally. In FIG. 5, reference numeral 1 denotes a downlink input / uplink output terminal provided on the CATV broadcast center side. A downlink signal from the CATV broadcast center input to the downlink input / uplink output terminal 1 is amplified by the downlink amplifier 10. .

  The downlink amplifying unit 10 generally includes a high-pass filter (HPF) 11 that selects a downlink signal that uses a frequency band of 70 to 770 MHz, an input-side gain adjuster 12, a downlink amplifier 13 that amplifies the downlink signal, and an output-side gain. It comprises an adjuster 14 and a high-pass filter 15 that allows the downstream signal to pass. The output signal of the high-pass filter 15 is sent to the downstream output / upstream input terminal 2.

A downstream signal is output from the downstream output / upstream input terminal 2 and sent to a television receiver or the like at the home of the CATV subscriber.
Further, the downstream output / upstream input terminal 2 receives an upstream signal from a terminal device at a CATV subscriber's home. This upstream signal generally uses a frequency band of 10 to 55 MHz. The uplink signal input from the terminal device to the downlink output / uplink input terminal 2 is amplified by the uplink amplification unit 20.

  The upstream amplification unit 20 includes a low-pass filter (LPF) 21 that passes an upstream signal, an input-side gain regulator 22, an upstream amplifier 23 that amplifies the upstream signal, an output-side gain regulator 24, and a low-pass filter 25 that passes the upstream signal. The output signal (upstream signal) of the low-pass filter 25 is output to the transmission line via the downstream input / upstream output terminal 1 and sent to the CATV broadcasting center.

In the variable gain high frequency amplifier configured as described above, the CATV downlink signal and the uplink signal are separated by the high-pass filters 11 and 15 and the low-pass filters 21 and 25. In addition, gain adjusters 12 and 14 are provided at the input and output sections of the downlink amplifying section 10, and gain adjusters 22 and 24 are provided at the input and output sections of the uplink amplifying section 20, so that the level width of the input signal is reduced. Flexible. Further, a downstream amplifier 13 for amplifying a signal is provided between the gain adjusters 12 and 14 of the downstream amplifying unit 10, and an upstream amplifier 23 for amplifying a signal is provided between the gain controllers 22 and 24 of the upstream amplifying unit 20. Is amplifying the signal. The downstream signal side gain adjusters 12 and 14 and the upstream signal side gain adjusters 22 and 24 input signals of appropriate levels to the downstream amplifier 13 and upstream amplifier 23, and set the levels of the output signals to appropriate values. And is responsible for improving signal transmission quality.
JP 2004-2000874 A JP 2004-343545 A JP 2005-136619 A

  However, in the conventional variable gain high frequency amplifier, the gain of the internal amplifier is not changed, and the signal input to the amplifier is attenuated by the gain adjuster. If the gain is attenuated, C / N degradation is likely to occur, and if a gain adjuster is provided between the amplifiers or on the output side, distortion interference is likely to occur, and the quality of the transmission signal is deteriorated in any case. It is also one of the causes.

  The C / N characteristic of the amplification device is expressed by the following equation.

C / N = input level−noise figure−1
For example, when the input level is 80 dBμ and the noise figure of the amplifier is 6 dB,
C / N = 80-6-1
= 73 (dB).

In addition, when two amplifying devices having a noise figure of 6 dB are arranged on the transmission line as the amplifying devices 26 and 27 as shown in FIG. 6, the input 80 dBμ signal is subjected to other C / N degradation. Even in the best state where there is no factor, the C / N value at the output of the amplifier 27 is
2 units combined C / N = 73dB-3dB
= 70 (dB)
It becomes.

  If multiple amplifiers are installed on the TV signal transmission path, the quality of the TV signal will deteriorate as many as the number of installed amplifiers. Therefore, it is necessary to improve the performance of each amplifier as much as possible. is there.

  On the CATV transmission path, there are downstream signal components from the CATV broadcasting center and upstream signal components from the terminal to the CATV broadcasting center. Differences between downstream signals and upstream signal frequencies, transmission line cables and transmission lines Due to the conditions of various devices inserted in the network, a difference occurs in transmission loss between the downstream signal and the upstream signal, and a level difference occurs between the downstream signal and the upstream signal, respectively.

  In recent years, Internet connection using the CATV upstream signal band has been increasing, and the number of noise components from each terminal is concentrated in the CATV broadcasting center, and examples of causing communication failures are increasing.

  The following two methods are conceivable as methods that do not improve or deteriorate the C / N of the transmission line.

  (1) The maximum input level that does not require changing the gain of the amplifier is input.

  (2) Improve the noise figure of the amplifier.

  As an example, the variable gain type high frequency amplifying apparatus shown in FIG. 5 is simulated with the input level of 70 to 95 dBμ under the following conditions, and the result of obtaining C / N is shown in FIG.

Amplifier gain: 30 dB
Noise figure: 6 dB at maximum gain
Rated output level: 110 dBμ
Even if the input level of the amplifying device is large, it must be below the rated maximum output level in order to suppress the occurrence of distortion below the specified value, so if a level exceeding the input level at the maximum gain is input, The input level to the amplifier unit must be made constant by the input gain adjuster. Therefore, even if the input signal level is increased, the C / N value at the output terminal of the amplifying device is not less than the input signal level 80 dBμ (= rated maximum output level (110 dBμ) −amplification, as can be seen from the simulation result of FIG. The device gain (30 dB) does not change with increasing input signal level. That is, the method for increasing the input signal level has a limit in improving C / N. Other C / N improvement measures include improving the noise figure of the amplifier circuit constituting the amplifier and increasing the output signal level, both of which are technically difficult, costly, and significantly Improvement effect cannot be obtained.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a variable gain type high frequency amplifying apparatus capable of improving C / N with a simple circuit configuration.

According to a first aspect of the present invention, there is provided a variable gain high-frequency amplifier that bypasses a path of a plurality of amplifiers, a gain adjuster that adjusts an input signal level of the amplifier, and an amplifier of an arbitrary stage among the amplifiers of the plurality of stages. And a detour switch circuit for switching and connecting the input signal to the next stage amplifier, the detour switch circuit is constituted by a slide switch, and until the input signal to the plurality of stages of amplifiers reaches a predetermined level, Power is supplied to the corresponding amplifier via the bypass switch circuit to operate it, and the paths of the amplifiers of the plurality of stages are maintained, and the bypass switch circuit is switched when the input signal is at a predetermined level or more. bypassing path of the amplifier of the arbitrary stage while blocking the power supply of the corresponding amplifier of any stage, configured to connect the input signal to the next-stage amplifier RF In the width device, a low-pass filter that cuts off a signal having a frequency higher than the amplification band of the amplifier is provided at the input or output of the amplifier at any stage to prevent abnormal oscillation due to coupling between the input and output of the slide switch. characterized in that it was.

  According to the present invention, the bypass switch circuit provided in parallel with the amplifier is switched between the bypass signal and the bypass circuit according to the level of the input signal, thereby switching the input signal with a simple circuit configuration. / N can be improved. In addition, by configuring the detour switch circuit with a slide switch and switching the detour switch circuit to detour the input signal when the input signal is above a predetermined level, the power to the corresponding amplifier is cut off, thereby simplifying the circuit configuration. C / N can be improved, wasteful power consumption can be suppressed, and abnormal oscillation of the amplifier due to coupling between input and output can be reliably prevented.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of a variable gain high frequency amplifier according to an embodiment of the present invention. In FIG. 1, reference numeral 31 denotes a downlink input / uplink output terminal provided on the CATV broadcast center side, and a downlink signal from the CATV broadcast center input to the downlink input / uplink output terminal 31 is input to the downlink amplifier 40. Amplified.

  The downlink amplifying unit 40 generally includes a high-pass filter (HPF) 41 that selects a downlink signal using a frequency band of 70 to 770 MHz, a gain adjuster 42, and a plurality of stages that amplify the downlink signal, for example, first and second It consists of downstream amplifiers 43 a and 43 b, a gain adjuster 44, and a high-pass filter 45 that allows downstream signals to pass therethrough. For the gain adjusters 42 and 44, for example, variable resistance attenuators are used.

  The downstream signal output from the downstream output / upstream input terminal 32 is sent to a television receiver or the like at the CATV subscriber's home.

  The downstream output / upstream input terminal 32 receives an upstream signal from a terminal device at a CATV subscriber's home. This upstream signal generally uses a frequency band of 10 to 55 MHz. The upstream signal input from the terminal device to the downstream output / upstream input terminal 32 is input to the upstream amplification unit 50 and amplified.

  The upstream amplifying unit 50 includes a low-pass filter 51 that allows an upstream signal to pass through, an input-side gain adjuster 52, a plurality of stages that amplify the upstream signal, such as first and second upstream amplifiers 53a and 53b, an output-side gain adjuster 54, A low-pass filter 55 that passes an upstream signal and a bypass switch circuit 56 that bypasses the first upstream amplifier 53 a, and an output signal (upstream signal) of the low-pass filter 25 is transmitted via a downstream input / upstream output terminal 31. And sent to the CATV broadcasting center. For the gain adjusters 42 and 44, for example, variable resistance attenuators are used.

  In the variable gain high frequency amplifier configured as described above, when the signal input level to the upstream amplification unit 50 is 90 dBμ or less, for example, the bypass switch circuit 56 is set to the non-detour side, that is, the first upstream amplifier 53a When the input side gain adjuster 52 is adjusted and the signal input level of the first upstream amplifier 53a is held at a predetermined value while the amplification operation is being performed, and the signal input level exceeds 90 dBμ, for example, 95 dBμ Further, the detour switch circuit 56 is used as a detour side so that the upstream signal bypasses the first upstream amplifier 53a. As described above, when the signal input level exceeds a predetermined value, the bypass switch circuit 56 is set to the bypass side and the first upstream amplifier 53a is bypassed, so that the C / N can be improved.

FIG. 2 shows the same condition as that of the conventional variable gain high-frequency amplifier shown in FIG. 5 for the upstream amplification unit 50 in the variable gain high-frequency amplifier configured as described above.
Amplifier gain: 30 dB
(First upstream amplifier 53a: 15 dB, second upstream amplifier 53b: 15 dB)
Noise figure: 6 dB at maximum gain, 9 dB when bypassing the amplifier
Rated output level: 110 dBμ
And the simulation was performed with an input level of 70 to 105 dBμ and C / N was obtained.

  As can be seen from FIG. 2, between the input levels of 80 to 90 dBμ, even if the input level is increased as in the conventional variable gain type high frequency amplifier, the C / N is constant at 73 dB due to the deterioration of the noise figure of the amplifier itself. It is the value of.

  However, when the input level is 95 dBμ or more that can bypass the first upstream amplifier 53a, the C / N is 85 dB, which can be improved by 12 dB compared to 73 dB of the conventional device.

  Next, specific configuration examples of the first upstream amplifier 53a and the detour switch circuit 56 in the upstream amplification unit 50 will be described with reference to FIG. As shown in FIG. 3, a capacitor 63, a bypass switch circuit 56, and a capacitor 64 are provided in series between the input terminal 61 and the output terminal 62. The detour switch circuit 56 is, for example, a slide switch that switches between two circuits, and switches and connects the first circuit contacts a1 and b1 and the second circuit contacts a2 and b2 to the common contacts a and b by a movable contact c. It is like that. The first circuit contacts a1 and b1 are short-circuited by a short circuit 57.

  The first upstream amplifier 53a is connected between the second circuit contacts a2 and b2. The first upstream amplifier 53 a is composed mainly of an NPN transistor 71, for example, and the second circuit contact a 2 is connected to the base of the transistor 71 via a capacitor 72. The base of the transistor 71 is grounded via a resistor 73. The emitter of the transistor 71 is grounded via a resistor 74 and grounded via a capacitor 75 and a resistor 76 in series. The collector of the transistor 71 is connected to the second circuit contact b2 of the bypass switch circuit 56 and grounded through the high-frequency coil 77 and the capacitor 78 in series. Further, resistors 79 and 80 are connected in series between the collector and base of the transistor 71, and a capacitor 81 is connected in parallel to the resistor 79.

  Further, the signal line 65 connecting the output terminal (common contact b) of the detour switch circuit 56 and the capacitor 64 is connected to the operating power supply of the first upstream amplifier 53a from the power supply terminal 66 via the high frequency coil 67. Supplied. The connection point between the power supply terminal 66 and the high frequency coil 67 is grounded via a capacitor 68.

  In the above configuration, when the movable contact c of the bypass switch circuit 56 is switched to the second circuit contacts a2 and b2 side, i.e., the first upstream amplifier 53a side, the operating power is supplied from the power terminal 66 to the high frequency coil 67, The signal 71 is supplied to the collector of the transistor 71 via the signal line 65 and the detour switch circuit 56, and is supplied from the collector to the base via the resistors 79 and 80, so that the transistor 71 is in an operating state.

  As a result, the upstream signal sent from the downstream output / upstream input terminal 32 of FIG. 1 to the input terminal 61 of FIG. 2 via the low-pass filter 51 and the input side gain adjuster 52 is input to the first upstream amplifier 53a. Then, after being amplified by the transistor 71, it is output via the bypass switch circuit 56, the signal line 65, the capacitor 64, and the output terminal 62, and sent to the second upstream amplifier 53b in FIG. 1 for amplification. The signal amplified by the second upstream amplifier 53b is output to the transmission line via the output side gain adjuster 54 and the downstream input / upstream output terminal 31, and is sent to the CATV broadcasting center.

  Further, when the movable contact c of the bypass switch circuit 56 is switched to the first circuit contacts a1 and b1, the first upstream amplifier 53a is separated from the second circuit contacts a2 and b2, and the supply of power is cut off. In addition, the first circuit contacts a1 and b1 are short-circuited by the short circuit 57. As a result, the upstream signal sent from the downstream output / upstream input terminal 32 to the input terminal 61 via the low-pass filter 51 and the input-side gain adjuster 52 bypasses the first upstream amplifier 53a and passes through the second upstream amplifier 53a. It is sent to the amplifier 53b.

  By configuring the first up amplifier 53a and the detour switch circuit 56 as described above, the detour switch circuit 56 is switched to the signal detour side, that is, the short circuit circuit 57 side, so that the power of the first up amplifier 53a can be simultaneously switched on. It is possible to cut off the power consumption, reducing unnecessary power consumption and preventing abnormal oscillation of the amplifier.

  FIG. 4 shows a π-type low-pass filter comprising a high-frequency coil 82 and capacitors 83 and 84 on the input side (base side) of the transistor 71 with respect to the first upstream amplifier 53a and the bypass switch circuit 56 shown in FIG. An example in which LPF) 85 is inserted is shown. As the low-pass filter 85, for example, a filter that passes a frequency of 55 MHz or less is used.

  By providing the low-pass filter 85 for the first upstream amplifier 53a as described above, an amplifier based on coupling between input and output that may occur when an inexpensive slide switch with poor high-frequency signal separation performance is used. Abnormal oscillation can be prevented. The same effect can be obtained even if the low-pass filter 85 is inserted into the output side (collector side) of the transistor 71.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying constituent elements without departing from the scope of the invention in the implementation stage.

It is a block diagram which shows the structure of the variable gain type | mold high frequency amplifier which concerns on one Embodiment of this invention. It is a figure which shows the result of having calculated | required C / N of the gain variable type | mold high frequency amplifier in the same embodiment by simulation. It is a figure which shows the structural example of the upstream amplifier in the same embodiment. It is a figure which shows the other structural example of the upstream amplifier in the same embodiment. It is a block diagram which shows the structure of the conventional variable gain type high frequency amplifier. It is a figure which shows the example at the time of arrange | positioning two amplification apparatuses on a transmission line. It is a figure which shows the result of having calculated | required C / N in the conventional gain variable type | mold high frequency amplifier with simulation.

Explanation of symbols

  31 ... Downlink input / uplink output terminal, 32 ... Downlink output / uplink input terminal, 40 ... Downlink amplification unit, 41, 45 ... High-pass filter (HPF), 42, 44 ... Gain regulator, 43a ... Second downlink amplifier, DESCRIPTION OF SYMBOLS 50 ... Up amplification part, 51, 55 ... Low pass filter (LPF), 52 ... Input side gain regulator, 53a ... 1st upstream amplifier, 53b ... 2nd upstream amplifier, 54 ... Output side gain regulator, 55 ... Low-pass filter (LPF), 56 ... detour switch circuit, 57 ... short circuit, 61 ... input terminal, 62 ... output terminal, 63, 64 ... capacitor, 65 ... signal line, 66 ... power supply terminal, 67, 77, 82 ... high frequency Coil, 68, 72 ... capacitor, 71 ... transistor, 73, 74, 76 ... resistor, 75, 78, 81, 83, 84 ... capacitor, 79, 80, ... resistor, 85 ... low pass filter Data

Claims (1)

A plurality of amplifiers, a gain adjuster for adjusting the input signal level of the amplifier, and a path of an amplifier of an arbitrary stage among the amplifiers of the plurality of stages are bypassed, and an input signal is switched and connected to the amplifier of the next stage. A detour switch circuit, the detour switch circuit is configured by a slide switch, and power is supplied to the corresponding amplifier via the detour switch circuit until an input signal to the plurality of stages of amplifiers reaches a predetermined level. Supplying and operating, maintaining the paths of the amplifiers of the plurality of stages, switching the bypass switch circuit in a state where the input signal is equal to or higher than a predetermined level, shutting off the power supply of the corresponding amplifier of the arbitrary stage, and bypassing the path of any stage of the amplifier, the high-frequency amplifying device configured to connect the input signal to the next-stage amplifier, the input of the amplifier of said arbitrary stages , Or a low-pass filter that blocks signals of frequencies higher amplification band of the amplifier provided in the output section, the variable gain type high frequency amplifying device, characterized in that to prevent abnormal oscillation due to input-output coupling of the slide switch.

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