JPH03210824A - Signal transmitter and high frequency amplifier for the transmitter - Google Patents

Abstract

PURPOSE:To reduce fluctuation of a lower frequency due to a temperature change in a signal level by controlling automatically a signal level of an upper limit frequency of a tilt characteristic of a high frequency amplifier at a proper step number interval and controlling a signal level of the lower limit frequency to a prescribed value automatically in response to the temperature change. CONSTITUTION:A high frequency signal fed from a pre-stage amplifier to an input terminal 10 via a coaxial cable 4 is fed to a post-stage amplifier via an equalizer 12, a high frequency amplifier stage 14, an equalizer 16, a gain adjustment circuit 18, a high frequency amplifier stage 20, a branch device 22, an output terminal 24 and the coaxial cable 4. The gain adjustment circuit 18 has a 1st gain adjustment means such as a PIN diode 30, generates an AGC signal in response to the signal level of a pilot signal to make a level near the upper limit frequency of the tilt characteristic to nearly a prescribed value at all times. The gain adjustment circuit 18 has a T-shaped variable attenuator 40 as a 2nd gain adjustment means to adjust the attenuation of the variable attenuator 40 in response to the temperature change and the signal level at the lower limit frequency is made almost constant. The amplifier constituted in this way is employed at a proper interval of stages.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a signal transmission device for transmitting high-frequency signals from a head end of a communal viewing facility, etc., for television broadcast signals in the 7011 Hz to 450 MHz band, for example. , relates to high frequency amplifiers used in such devices.

[Prior Art] Conventionally, a device for transmitting a high frequency signal from a head end as described above includes, for example, high frequency amplifiers 21, 22...2n (the middle part is omitted in the figure) as shown in Fig. 3. 230 (shown here) are connected in multi-stage cascade via a coaxial cable 4. These high frequency amplifiers 21.2□...2. , have a tilt characteristic in which the gain is large at high frequencies and small at low frequencies, and in order to maintain such tilt characteristics, the pilot at the upper limit frequency of the transmission frequency band is The signal is transmitted together with the high frequency signal, and each amplifier 23.2□...2. , then extract this pilot signal, generate a control signal by detecting and DC amplifying this pilot signal, and adjust the gain of the first variable attenuator using this control signal so that the signal level of the pilot signal is constant. . On the other hand, a high frequency signal at the lower limit frequency of the transmission frequency band or a control signal with a constant value so that it becomes the reference value! 1!2 is supplied to the variable attenuator.

[Problem to be solved by the invention] However, in such a signal transmission device, each amplifier uses a pilot signal to keep the signal level constant at the upper limit frequency, so the tilt characteristics of each amplifier near the upper limit are as follows. Even if there is a temperature change, Figure 4 (a), (b),
As shown in (c), it is almost constant. In addition, the rotation (a)
is the amplifier 24, (b) is the amplifier 2, 6, and (c) is the amplifier 24.
1 and 2 show the tilt characteristics of the amplifier 230, respectively. However, since the lower limit of the tilt characteristic is controlled by a control signal with a constant value, the signal level near the lower limit is affected by temperature changes, and as shown in Figs. 4(a), (b), and (c).
As shown in , it decreases as the temperature rises, and increases by 1 as the temperature decreases. In particular, this signal transmission device includes each amplifier 21.
Since 2□...2o are connected in multi-stage cascade, the signal level changes in the previous stage are accumulated in the amplifiers in the subsequent stages, causing large fluctuations. Figure 5 shows each amplifier 20, 22...
...Continuously shows how the fluctuation width of the signal level changes around the lower limit frequency of 2n.

As a method to prevent such changes in signal level near the lower limit frequency, in addition to the pilot signal of the upper limit frequency, the pilot signal of the lower limit frequency is also transmitted from the head end 6 to each amplifier 21, 22, 2n, etc. It is conceivable to transmit the signal and automatically adjust the signal levels of both the upper limit frequency and the lower limit frequency. However, this poses a problem in that the configuration of each amplifier becomes complicated and the cost also increases.

An object of the present invention is to provide a signal transmission device that solves the above-mentioned problems, and a high frequency amplifier suitable for use in such a signal transmission device.

[Means for Solving the Problems] In order to achieve the above object, the signal transmission device according to the first invention connects a plurality of amplifiers each having a tilt characteristic that amplifies a high frequency signal through a coaxial cable. These amplifiers are connected in multi-stage cascade through the amplifiers, and the signal level at the upper limit frequency of the tilt characteristic is automatically controlled to a constant value by automatically controlling the signal level at the upper limit frequency of the tilt characteristic to a constant value, and the signal level at the lower limit frequency is increased when the temperature rises. It is characterized in that it is made to decrease when the temperature is lowered. Further, in contrast to the above, the signal transmission device of the second invention automatically controls the signal level of the lower limit frequency, and changes the signal level of the upper limit frequency in accordance with temperature changes in the same manner as above.

A high-frequency amplifier according to a third aspect of the invention includes: a first gain adjustment means for controlling the gain of an input signal including a pilot signal having a frequency approximately equal to the upper limit frequency of the tilt characteristic according to a first control signal; a first control signal generation means for extracting a pilot signal from the output of the first control signal and generating a first control signal based on the pilot signal; and a means connected in parallel with the first gain adjustment means for extracting a signal at a lower limit frequency. and controlling the gain of the extracted signal in response to the second control signal.
gain adjusting means for; and means for generating a second control signal;
A temperature sensor is connected to the second control means and adjusts the second control signal so that when the temperature rises, the gain of the second gain adjustment means increases and when the temperature decreases, the gain of the second gain adjustment means decreases. means. Further, in the high frequency amplifier of the fourth invention, contrary to the above, the signal level of the lower limit frequency is controlled by the first gain adjustment means and the first control signal generation means, and the signal level of the upper limit frequency is controlled by the second gain adjustment. It is controlled by means and a temperature sensing element.

[Operation] In the signal transmission device according to the first invention, the high frequency amplifiers arranged at appropriate intervals automatically control the signal level at the upper limit frequency of the tilt characteristic to a constant value, so the signal level at the upper limit frequency is always approximately constant. Furthermore, these high frequency amplifiers arranged at appropriate intervals are configured to increase the signal level of the lower limit frequency of the tilt characteristic when the temperature rises, and to decrease it when the temperature falls. Therefore, when the temperature rises in the amplifier between these amplifiers,
Although the signal level of the lower limit frequency has decreased, this can be compensated for.Also, when the temperature has decreased, the signal level of the lower limit frequency has increased, but this can be compensated for. Contrary to the above, the signal transmission device of the second invention automatically controls the signal level of the lower limit frequency, and controls the signal level of the upper limit frequency in accordance with temperature changes.

Further, in the high frequency amplifier according to the third invention, a pilot signal is extracted from the high frequency signal that has passed through the first gain adjustment means, thereby generating a first control signal, and using this first control signal. The gain of the first gain adjustment means is automatically adjusted. Therefore, the signal level of the upper limit frequency is
It is maintained at a nearly constant value even if the temperature changes. On the other hand, in the second gain adjustment means that adjusts the gain in response to a second control signal having a constant value, when there is a temperature change, the signal level of the lower limit frequency decreases when the temperature rises, and The temperature sensing means changes the second control signal in response to temperature changes, so that when the temperature rises, the signal level of the lower limit frequency increases, and when the temperature falls, the signal level of the lower limit frequency increases. Since the second control signal is changed so that the level decreases, the signal level of the lower limit frequency is maintained constant even if the temperature changes.

Contrary to the above, the high frequency amplifier of the fourth invention automatically controls the signal level of the lower limit frequency, and controls the signal level of the upper limit frequency in accordance with temperature changes.

[Embodiment] In this embodiment, in the signal transmission device having the configuration shown in FIG.
．． 28.212.2□6.22°, 2□4.2□6,
The configuration is as shown in FIG.

In FIG. 1, lO is an input terminal, which is connected to the previous stage amplifier 23.2? , 211.2+s, 219,223°2
A high frequency signal is supplied from 27 via the coaxial cable 4. This high frequency signal includes a pilot signal, and this pilot signal has a frequency near the upper limit frequency of the tilt characteristic. The high frequency signal supplied to the input terminal 10 is supplied to a high frequency amplification stage 14 via an equalizer 12, and further supplied to an equalizer 16. These equalizers 12.
Reference numeral 16 is for obtaining a tilt characteristic (in this embodiment, a characteristic in which the level of the upper limit frequency is large and the level of the lower limit frequency is small) in accordance with the attenuation characteristic of the coaxial cable 4.

The high frequency signal that has passed through the equalizer 16 is sent to an fr gain adjustment circuit with a tilt adjustment circuit (hereinafter referred to as gain adjustment circuit).
18 to the high frequency amplification stage 20, where it is amplified, and then supplied to the output terminal 24 via the 1-brancher 22, and then sent via the coaxial cable 4 to the subsequent stage amplifiers 25, 29, .
213.21? , 221 + 228° 229.

The gain adjustment circuit 18 has a PIN diode 30 as a first gain adjustment means, the cathode of which is connected to the equalizer 16 via a DC blocking capacitor 26,
The anode is connected to the high frequency amplification stage 20 via a DC blocking capacitor 28. The cathode of the PIN diode 30 is grounded via a resistor 32, and the anode of the PIN diode 30 is connected to the AG via a high frequency blocking coil 34.
A C signal signal generating section 36 is connected.

A pilot signal is extracted from the high frequency signal branched from the AGC signal signal generator 361 splitter 22, and an AGC signal which is a first control signal is generated according to the signal level. This AGC signal or high frequency blocking coil 34, PIN
Diode 30. The signal flows through the resistor 32 and changes the high frequency resistance value of the PIN diode 30. Therefore, when the signal level of the pilot signal that has passed through the gain adjustment circuit 18 increases due to the influence of temperature changes, the AGC voltage decreases, and the high frequency resistance value of the PIN diode 30 is increased to attenuate the high frequency signal. Increase the amount. Furthermore, when the signal level of the pilot signal is low, the AGC voltage increases, the high frequency resistance value of the PIN diode 30 decreases, and the amount of attenuation of the high frequency signal is decreased. As a result, the level near the upper limit frequency of the tilt characteristic always remains at a substantially constant value.

Note that 38 is a bypass capacitor.

The gain adjustment circuit 18 further includes, for example, a T-type variable attenuator 40 as a second gain adjustment means. This variable attenuator 40 has resistors 42.44 connected in series between its input and output sides, and these resistors 42.4
4 and the reference potential point, the anode of a PIN diode 46 is connected to the cathode or the reference potential point. The input side of the variable attenuator 40 mainly extracts signals near the lower limit frequency and is connected to the equalizer 16 via the actuator 48, and the output side of the variable attenuator 40 mainly passes signals around the lower limit frequency. It is connected to the high frequency amplification stage 20 via a reactor 50 and a DC blocking capacitor 52. A resistor 54 is connected in parallel to this PIN diode 46.
or connected. This is to limit the current flowing through the PIN diode 46. Further, the anode of the PIN diode 46 is connected to an arm of a variable resistor 58 via a current limiting resistor 56. One end of this variable resistor 58 is connected to a 10B power supply, and the other end is connected to a reference potential point. Therefore, the variable resistor 58
The current value flowing through the PIN diode 46 is adjusted to a specific value by adjusting the position of the arm of the variable resistor 58, and the high frequency resistance value of the PIN diode 46 is set to a specific value. The attenuation amount of the variable attenuator 40 is set to a specific attenuation amount. Therefore, unless the signal level of the input high-frequency signal of the lower limit frequency changes,
The high frequency signal of the lower limit frequency is attenuated by a specific amount and supplied to the high frequency amplification stage 20.

However, the signal level of the high frequency signal of the lower limit frequency supplied to the variable attenuator 40 varies due to temperature changes. This variation cannot be compensated for because the amount of attenuation of the variable attenuator 40 is fixed.

Therefore, a temperature sensing element, for example a thermistor 60, is connected in parallel to the resistor 54. That is, at high temperatures, the resistance value of the thermistor 60 decreases, and the current flowing through the PIN diode 46 decreases. Therefore PIN diode 46
The high frequency resistance value of becomes large and the amount of attenuation becomes small. Also, at low temperatures, the resistance value of the thermistor 60 increases,
The current flowing through the PIN diode 46 increases, so the high frequency resistance value of the PIN diode 46 decreases, and the amount of attenuation increases. Since the amount of attenuation of the variable attenuator 40 is adjusted in accordance with temperature changes in this way, the signal level at the lower limit frequency is also approximately constant.

As mentioned above, the amplifier constructed in this manner is the amplifier 24.26.212.216.22o shown in FIG.

224.2□, as shown in Figure 2, the amplifier 24.28.2□, 2, 6.22°, 224.228
Signal level fluctuations due to temperature changes at the lower limit frequency are absorbed. Therefore, looking at the signal transmission equipment as a whole,
Although more than 30 stages of amplifiers are actually connected in cascade, the signal level only fluctuates at the lower limit frequency, which is the same as in a 4-stage cascade connection.

In the above embodiment, the signal level of the upper limit frequency is automatically controlled by the pilot signal, and the signal level of the lower limit frequency is automatically controlled by the temperature sensing element 60, or conversely, the signal level of the upper limit frequency is automatically controlled by the temperature sensing element 60. The signal level at the lower limit frequency may be automatically controlled by a pilot signal.

Further, in the above embodiment, the gain adjustment circuit 18.4
Although a variable attenuator using a PIN diode is shown as 0, a resistor and a transistor or FET can be used instead.
It is also possible to use a variable attenuator configured by the above, or it is also possible to use a variable gain amplifier whose gain changes depending on the control signal. Further, in the above embodiment, the T-type variable attenuator 40 is used, but a π-type variable attenuator may also be used.

[Effects of the Invention] As described above, according to the signal transmission devices according to the first and second inventions, the high frequency amplifiers arranged at appropriate intervals can control the signal level of the upper limit frequency of the tilt characteristic in the first invention. The second invention is configured to automatically control the signal level of the lower limit frequency, and the first invention is configured to automatically control the signal level of the lower limit frequency.
In the invention, the signal level of the upper limit frequency is automatically controlled to a constant value according to temperature changes, so this signal transmission device actually consists of cascade-connected amplifiers with more stages than the appropriate number of stages mentioned above. Nevertheless, in the first invention, the fluctuations due to temperature changes in the signal level of the lower limit frequency, and in the second invention, the signal level of the upper limit frequency, can be reduced to the same level as when only the above-mentioned appropriate number of stages of amplifiers are connected in multi-stage cascade. Can be reduced.

Furthermore, according to the high frequency amplifiers according to the third and fourth inventions, the third invention controls the signal level of the upper limit frequency, and the fourth invention controls the signal level of the upper limit frequency, without using a pilot signal. Since the temperature sensing element is used, only one pilot signal is required for controlling the signal level of the upper limit frequency in the third invention and the lower limit frequency in the fourth invention, which simplifies the configuration of the high frequency amplifier. I can do it,
Costs can be reduced. Therefore, the cost of a signal transmission device using such a high frequency amplifier can also be reduced.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of a high-frequency amplifier according to the present invention, FIG. 2 is a diagram showing a fluctuation state of the lower limit frequency level of a signal transmission device using the same embodiment, and FIG. 3 is a conventional signal transmission device. The block diagram of FIG. 4 (a), (b), and (c) is the third
FIG. 5 is a diagram showing the tilt characteristics of the high frequency amplifier used in the signal transmission device shown in FIG. 3, and FIG. 18...first variable gain adjustment circuit, 36...A
GC signal generation section (first control signal generation means), 40...
... Second variable gain adjustment circuit, 58 ... Variable resistor (second control signal generation means), 60 ... Thermistor (temperature sensing means)

Claims (4)

[Claims] (1) A plurality of amplifiers each having tilt characteristics that amplify high-frequency signals are connected in multi-stage cascade via a coaxial cable, and among these amplifiers, amplifiers at an appropriate number of stages are connected,
Signal transmission characterized in that the signal level at the upper limit frequency of the tilt characteristic is automatically controlled to a constant value, and the signal level at the lower limit frequency of the tilt characteristic is increased when the temperature rises and decreased when the temperature falls. Device. (2) A plurality of amplifiers each having tilt characteristics that amplify high-frequency signals are connected in multi-stage cascade via a coaxial cable, and among these amplifiers, amplifiers at an appropriate number of stages are connected,
Signal transmission characterized in that the signal level at the lower limit frequency of the tilt characteristic is automatically controlled to a constant value, and the signal level at the upper limit frequency of the tilt characteristic is increased when the temperature rises and decreased when the temperature decreases. Device. (3) a first gain adjustment means for controlling the gain of an input signal including a pilot signal having a frequency approximately equal to the upper limit frequency of the tilt characteristic in accordance with a first control signal; a first control signal generation means for extracting the signal and generating the first control signal based on the first control signal; and a first gain adjustment means connected in parallel with the first gain adjustment means to apply the gain of the signal having the tilt characteristic to the second control signal. a second gain adjustment means for controlling the second gain adjustment means, a means for generating a second control signal; 1. A high-frequency amplifier for a signal transmission device, comprising: temperature sensing means for adjusting a second control signal to a state where the gain of the second gain adjusting means is reduced. (4) a first gain adjustment means for controlling the gain of an input signal including a pilot signal having a frequency approximately equal to the lower limit frequency of the tilt characteristic according to a first control signal; and a means for extracting the upper limit frequency of the tilt characteristic; a second gain adjusting means for controlling the gain of the obtained signal in accordance with a second control signal; a second gain adjusting means for generating a second control signal; A high-frequency amplifier for a signal transmission device, comprising temperature sensing means for adjusting a second control signal to a state where the gain of the gain adjustment means increases and the gain of the second gain adjustment means decreases when the temperature decreases.