JP4936128B2 - Loss compensation circuit - Google Patents

Description

  The present invention relates to a circuit that compensates for a loss in a transmission line such as a coaxial cable, and relates to a loss compensation circuit that can vary the compensation characteristic in accordance with the loss characteristic of the cable.

  It is known that a transmission line such as a coaxial cable has a conductor loss proportional to the square root of the frequency of a propagating signal. Therefore, by using a compensation circuit whose gain increases in proportion to the square root of the frequency, the conductor loss of the transmission line can be compensated and the frequency characteristic can be flattened.

  Patent Document 1 describes the invention of such a loss compensation circuit. Hereinafter, the invention described in Patent Document 1 will be described. FIG. 6 is a loss compensation circuit described in Patent Document 1, and has a configuration in which three loss compensation units 10 to 12 are connected in series. A signal transmitted from a coaxial cable or the like is input from the left end IN and output from the right end OUT. Note that IN and OUT are terminated at 50Ω, but are not shown in FIG.

  The loss compensators 10 to 12 have the same configuration. That is, the resistors R1 and R2 are connected in series, and the capacitor C1 is connected in parallel to this series circuit. A series circuit of a resistor R3 and an inductance L1 is connected to a connection point between the resistors R1 and R2, and the other end of the inductance L1 is connected to a common potential point. In order to avoid complication, the loss compensators 11 and 12 omit the description of R1 to R3, C1, and L1.

FIG. 7 shows the frequency characteristics of this loss compensation circuit. When the constants of the components of the loss compensators 10 to 12 are selected as follows, the frequency characteristics of the loss compensators 10 to 12 are as shown in (A) to (C). Since the loss compensation units 10 to 12 are connected in series, the frequency characteristic of the loss compensation circuit is (D) obtained by combining the frequency characteristics of (A) to (C), and the gain increases in proportion to the square root of the frequency. The characteristics to be obtained are obtained.
Loss compensator 10:
R1 = R2 = 1.77Ω, R3 = 705.58Ω, C1 = 800 pF,
L1 = 2μH
Loss compensator 11:
R1 = R2 = 4.42Ω, R3 = 280.91Ω, C1 = 40 pF,
L1 = 100 nH
Loss compensator 12:
R1 = R2 = 10.89Ω, R3 = 109.34Ω, C1 = 2pF,
L1 = 5nH

  FIG. 8 shows another loss compensation circuit described in Patent Document 1. In FIG. A series circuit of resistors R4 and R5 is connected between the input terminal IN and the output terminal OUT, and a capacitor C3 and a series circuit of the resistor R6 and the capacitor C2 are connected in parallel to the series circuit. A series circuit of a resistor R7 and an inductance L2 is connected between the connection point of the resistors R4 and R5 and the common potential point.

FIG. 9 shows the frequency characteristics of this loss compensation circuit. When the constants of the respective components are selected as follows, the frequency characteristics of the loss compensation circuit in FIG. Assuming that the cable attenuation characteristic is graph 21, the cable attenuation characteristic is compensated by the loss compensation circuit, and the combined characteristic is graph 22. That is, a substantially flat characteristic can be obtained up to a frequency of 5 GHz.
R4 = R5 = 16.6Ω, R6 = 80Ω, R7 = 67Ω,
C2 = 12 pF, C3 = 5.6 pF, L2 = 3.3 nH
US Pat. No. 6,734,759

  However, such a loss compensation circuit has the following problems. The amount of transmission line loss changes as the line material, size, or length changes. Even with transmission lines of the same model number, the material, size, and length may change due to variations in manufacturing. Therefore, the characteristics of the loss compensation circuit must also be changed in accordance with the characteristics of the transmission line actually used.

  However, the characteristics of the loss compensation circuit shown in FIG. 6 or FIG. 8 are determined by the values of the resistance, capacitor, and inductance used. Therefore, in order to change the characteristics of the loss compensation circuit, these values must be changed, and there is a problem that it is difficult to change them easily on site.

  In addition, there are limitations on the values of resistors, capacitors, and inductances that can be used, making it difficult to fine-tune the characteristics.

  Accordingly, an object of the present invention is to provide a loss compensation circuit that can easily change the characteristics and finely adjust the characteristics.

In order to solve such a problem, the invention according to claim 1 of the present invention,
In the loss compensation circuit that can vary the compensation characteristics according to the loss characteristics of the cable,
At least two high-pass filters to which an input signal is input, frequency characteristics are different, and gain can be varied;
An adder for adding the signal related to the input signal and the output of the high-pass filter;
A variable gain amplifier that receives the output signal of the adder and can change the gain;
Is provided. Frequency characteristics and gain can be changed independently and easily.

The invention according to claim 2
In the loss compensation circuit that can vary the compensation characteristics according to the loss characteristics of the cable,
At least two high-pass filters to which an input signal is input, frequency characteristics are different, and gain can be varied;
A first adder for adding the outputs of the high-pass filter;
A variable gain amplifier that receives the output of the first adder and can change the gain;
A second adder for adding the output of the variable gain amplifier and a signal related to the input signal;
Is provided. Frequency characteristics and gain can be changed independently.

The invention according to claim 3 is the invention according to claim 1 or 2 ,
A primary filter is used as the high-pass filter. The filter configuration can be simplified.

The invention according to claim 4
In the loss compensation circuit that can vary the compensation characteristics according to the loss characteristics of the cable,
At least two low-pass filters to which an input signal is input, frequency characteristics are different, and gain can be varied;
An adder for adding a signal related to the input signal and a signal having a reverse polarity of the low-pass filter output;
A variable gain amplifier that receives the output signal of the adder and can change the gain;
Is provided. Frequency characteristics and gain can be changed independently and easily.

The invention according to claim 5
In the loss compensation circuit that can vary the compensation characteristics according to the loss characteristics of the cable,
At least two low-pass filters to which an input signal is input, frequency characteristics are different, and gain can be varied;
A first adder for adding the outputs of the low-pass filter;
A variable gain amplifier that receives the output of the first adder and can change the gain;
A second adder that receives a signal related to the input signal and an output of the variable gain amplifier, and adds a signal related to the input signal and a signal having a reverse polarity of the low-pass filter output;
Is provided. Frequency characteristics and gain can be changed independently.

The invention according to claim 6 is the invention according to claim 4 or 5 ,
A primary filter is used as the low-pass filter. The filter configuration is simplified.

As is apparent from the above description, the present invention has the following effects.
According to the first, second, third, fourth, fifth and sixth inventions, the outputs of a plurality of high-pass filters or low-pass filters whose gains can be varied are added, and this added value or the added value of the opposite polarity is added to the input signal Added.

  The frequency characteristic and gain of the loss compensation circuit can be changed simply by changing the gain of the high-pass filter or low-pass filter. Therefore, by adjusting the gain and frequency characteristics of the loss compensation circuit to the loss characteristics of the cable, there is an effect that the frequency characteristics after compensation can be flattened.

  In addition, since the frequency characteristics and gain can be easily changed, even if there are variations in the cable characteristics, it is possible to match the actual loss amount of the cable and to compensate accurately.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a loss compensation circuit according to the present invention. In FIG. 1, a current output type buffer with 20 differential inputs and differential outputs is inputted with an input signal. Two output terminals of the buffer 20 are pulled up to the power source V + by resistors 26 and 27.

  Reference numerals 21 to 23 denote differential output and differential output current output type high-pass filters, to which an input signal input to the buffer 20 is input, and the output terminal is a connection point between the output terminal of the buffer 20 and the resistors 26 and 27. Are connected in phase. That is, the non-inverting output terminals and the inverting output terminals of the buffer 20 and the high-pass filters 21 to 23 are connected. Since the buffer 20 and the high-pass filters 21 to 23 are current outputs, the output current is added at this connection point, that is, 24 surrounded by a dotted line corresponds to the adder. This added current is converted into a voltage signal by the resistors 26 and 27.

  Reference numeral 25 denotes a current output type variable gain amplifier having a differential input and a differential output capable of changing the gain. The signal is added by the adder 24 and converted into a voltage by the resistors 26 and 27. The output terminal of this variable gain amplifier is pulled up to the power source V + by 50Ω resistors 28 and 29. The output of the variable gain amplifier 25 becomes the output of the loss compensation circuit.

  The high-pass filters 21 to 23 include a differential input, differential output current output type variable gain amplifier Q1, resistors R10, R11 connected between the two input terminals of the variable gain amplifier Q1 and a common potential point. It consists of capacitors C11 and C12 inserted in the middle of the path of the input signal. For this reason, the high-pass filters 21 to 23 operate as primary high-pass filters that allow only high-frequency components of the input signal to pass. In addition, in order to avoid complexity, the high-pass filters 22 and 23 omit the description of Q1, R11, R12, C11, and C12.

  The high-pass filters 21 to 23 pass only the frequency components higher than the break frequency determined by the resistors R10 and R11 and the capacitors C10 and C11 in the input signal, and attenuate the frequency components lower than the break frequency with primary characteristics. Further, the amplitude of the output signal can be varied by adjusting the gain of the variable gain amplifier Q1.

  When the resistance values of the resistors R10 and R11 in the high pass fill 21 are 1 kΩ and the capacitance values of the capacitors C11 and C12 are 10 pF, the break frequency of the high pass filter 21 is 15.9 MHz. Similarly, when the resistance values of the resistors R10 and R11 in the high-pass filter 22 are 350Ω and the capacitance values of the capacitors C11 and C12 are 1 pF, the break frequency of the high-pass filter 22 is 454 MHz. Furthermore, when the resistance values of the resistors R10 and R11 in the high-pass filter 23 are 150Ω and the capacitance values of the capacitors C11 and C12 are 0.2 pF, the break frequency of the high-pass filter 23 is 5.3 GHz.

  As described above, the outputs of the buffer 20 and the high-pass filters 21 to 23 are added by the adder 24 and input to the variable gain amplifier 25. Since the high-pass filters 21 to 23 attenuate frequency components that are equal to or lower than the break frequency, the signal added by the adding unit 24 has a characteristic in which high-frequency components are raised. By setting this characteristic to a characteristic opposite to the attenuation characteristic of the cable, the loss of the cable can be compensated. Further, by adjusting the gain of the variable gain amplifier 25, only the output amplitude can be changed without changing the frequency characteristic.

  FIG. 2 shows an example of the configuration of a differential input / differential output current output type variable gain amplifier. In FIG. 2, reference numerals 30 and 31 denote transistors, and an input signal is input to the base thereof. Reference numeral 32 denotes a current source, one end of which is connected to the emitters of the transistors 30 and 31, and the other end is connected to a negative power source V−. An output signal is output from the collectors of the transistors 30 and 31. By changing the output current value of the current source 32, the gain of the amplifier can be changed. This configuration is an example, and an amplifier having another configuration can be used as the variable gain amplifier Q1.

  FIG. 3 shows the characteristics of this loss compensation circuit. In FIG. 3, 40 is the attenuation characteristic of the cable, 41 is the characteristic of the loss compensation circuit of FIG. 1, and 42 is the characteristic after compensation. However, the attenuation characteristics of the cable are expressed as absolute values. The gain of the buffer 20 and the variable gain amplifier 25 is 1, and the gain of the variable gain amplifier Q1 in the high pass filters 21 to 23 is 0.0467, 0.143, and 0.533, respectively. As can be seen from this figure, the compensated characteristic 42 is within ± 0.1 dB in the range of 0 to 6 GHz.

  The characteristics of the loss compensation circuit can be continuously changed by changing the gain of the variable gain amplifier Q1 in the high-pass filters 21 to 23. For example, when the gain of the high-pass filter 21 is increased, the characteristic increases in the low frequency range, and when the gain of the high-pass filter 23 is increased, the characteristic increases in the high frequency range. Further, when the gain of the variable gain amplifier 25 is changed, only the output amplitude can be changed without changing the frequency characteristic. The gain of the variable gain amplifier 25 can be varied within a range of 0.5 to 1.6, for example. Note that the values of the resistors and capacitors and the gain of the amplifier are not limited to this embodiment, and can be arbitrarily determined according to the compensation characteristics.

  By adjusting the gain of the variable gain amplifier in the high-pass filters 21 to 23 and the gain of the variable gain amplifier 25 in accordance with the loss characteristic of the cable to be compensated, the compensated characteristic can be flattened. Further, even if the loss characteristic of the cable changes, the characteristic of the loss compensation circuit can be readjusted only by gain adjustment, so that it can be easily adjusted in the field.

  FIG. 4 shows another embodiment of the present invention. In this embodiment, a low pass filter is used instead of the high pass filter. In addition, the same code | symbol is attached | subjected to the same element as FIG. 1, and description is abbreviate | omitted.

  In FIG. 4, 50 to 52 are low-pass filters. The low-pass filters 50 to 52 are disposed in the variable gain amplifier Q1 to which the input signal is input, capacitors C13 and C14 connected between the input terminal of the variable gain amplifier and the common potential point, and the path of the input signal. It comprises resistors R13 and R14. Compared with the high-pass filters 21 to 23 in FIG. 1, the positions of the resistors and capacitors of the low-pass filters 50 to 52 are interchanged. Therefore, it has the characteristics of a first-order low-pass filter that passes only the low-frequency component of the input signal.

  The outputs of the low-pass filters 50 to 52 are connected in reverse phase to the connection point between the output terminal of the buffer 20 and the resistors 26 and 27. That is, the non-inverting output terminal of the buffer 20 and the inverting output terminals of the low-pass filters 50 to 52 are connected, and the inverting output terminal of the buffer 20 and the non-inverting output terminals of the low-pass filters 50 to 52 are connected. Since the outputs of the buffer 20 and the low-pass filters 50 to 52 are currents, 53 surrounded by a dotted line corresponds to the adding unit.

Therefore, if the output of the buffer 20 is Vb and the outputs of the low-pass filters 50 to 52 are V50 to V52, respectively, the input V of the variable gain amplifier 25 is
V = Vb- (V50 + V51 + V52)
become. As described above, since the outputs of the low-pass filters 50 to 52 have a characteristic in which the high frequency component is attenuated, V in the above equation has a frequency characteristic in which the high frequency component is raised. Similarly to the embodiment of FIG. 1, the frequency characteristic of the loss compensation circuit can be changed by adjusting the gain of the variable gain amplifier Q1 in the low-pass filters 50-52. Furthermore, by changing the gain of the variable gain amplifier 25, only the output amplitude can be changed without changing the frequency characteristic.

  1 and 4, the variable gain amplifier 25 can be omitted. In this case, since the gain of the loss compensation circuit must be performed by changing the gain of the variable gain amplifier Q1 in the high-pass filters 21 to 23 or the low-pass filters 50 to 52, only the gain cannot be changed independently. However, since the variable gain amplifier 25 is unnecessary, the configuration can be simplified.

  FIG. 5 shows another embodiment. In addition, the same code | symbol is attached | subjected to the same element as FIG. 1, and description is abbreviate | omitted. In this embodiment, the added value of the outputs of the high-pass filters 21 to 23 is input to a variable gain amplifier, and the output of the variable gain amplifier and the output of the buffer 20 are added.

  In FIG. 5, the outputs of the high-pass filters 21 to 23 are connected to each other, and the connection point is pulled up to the power source V + by resistors 60 and 61. This connection point, that is, 62 surrounded by a dotted line is an adder, and the output current of this adder 62 is converted into a voltage by resistors 60 and 61. This voltage is input to the variable gain amplifier 63, and its output is added to the output of the buffer 20 by the adder. The variable gain amplifier 62 and the output terminal of the buffer 20 are connected in phase, and this connection point, that is, 64 surrounded by a dotted line, corresponds to the adder. In this embodiment, it can be considered that the position of the variable gain amplifier 25 of FIG. 1 embodiment is changed, and the frequency characteristics can be changed by changing the gain of the high-pass filters 21 to 23, and the gain of the variable gain amplifier 63 can be changed. Can change the output amplitude.

  The high-pass filters 21 to 23 in FIG. 5 embodiment can be replaced with low-pass filters 50 to 52. As described in the embodiment of FIG. 4, the outputs of the low-pass filters 50 to 52 must be added in reverse phase with the output of the buffer 20. Therefore, the addition signal of the outputs of the low-pass filters 50 to 52 is input to the variable gain amplifier 63 in reverse phase, or the connection of the addition unit 64 is changed, and the output of the variable gain amplifier 63 is added to the output of the buffer 20 in reverse phase. do it. Further, the output may be inverted in the variable gain amplifier 63.

  In these embodiments, the current output type amplifier is used as the variable gain amplifier 24 and the variable gain amplifiers in the high pass filters 21 to 23 and the low pass filters 50 to 52. However, a voltage output type amplifier can also be used. . In this case, the adder can be configured with an adder using an amplifier or a resistor network. In these embodiments, differential input and differential output amplifiers are used, but single input / output amplifiers can also be used.

  Further, although the primary filter is used as the high-pass filter and the low-pass filter, filters having other characteristics can be used. In short, any filter may be used as long as it has a characteristic of blocking high frequency components or low frequency components and can change the gain. Further, the number of filters is not limited to three, and may be any number as long as it is two or more.

It is a block diagram which shows one Example of this invention. It is a block diagram of a variable gain amplifier. It is a characteristic view for demonstrating the effect of this invention. It is a block diagram which shows the other Example of this invention. It is a block diagram which shows the other Example of this invention. It is a block diagram of the conventional loss compensation circuit. It is a characteristic view of the conventional loss compensation circuit. It is a block diagram of the conventional loss compensation circuit. It is a characteristic view of the conventional loss compensation circuit.

Explanation of symbols

20 Buffers 21-23 High-pass filters 24, 53, 62, 64 Adders 25, 63, Q1 variable gain amplifiers 26-29, R11-R14 resistors 30, 31 Transistors 32 Current sources 40-42 Frequency characteristic graphs 50-52 Low-pass filters C11 to C14 capacitors

Claims (6)

In the loss compensation circuit that can vary the compensation characteristics according to the loss characteristics of the cable,
At least two high-pass filters to which an input signal is input, frequency characteristics are different, and gain can be varied;
An adder for adding the signal related to the input signal and the output of the high-pass filter;
A variable gain amplifier that receives the output signal of the adder and can change the gain;
A loss compensation circuit comprising: In the loss compensation circuit that can vary the compensation characteristics according to the loss characteristics of the cable,
At least two high-pass filters to which an input signal is input, frequency characteristics are different, and gain can be varied;
A first adder for adding the outputs of the high-pass filter;
A variable gain amplifier that receives the output of the first adder and can change the gain;
A second adder for adding the output of the variable gain amplifier and a signal related to the input signal;
A loss compensation circuit comprising: The loss compensation circuit according to claim 1, wherein the high-pass filter is a first-order filter. In the loss compensation circuit that can vary the compensation characteristics according to the loss characteristics of the cable,
At least two low-pass filters to which an input signal is input, frequency characteristics are different, and gain can be varied;
An adder for adding a signal related to the input signal and a signal having a reverse polarity of the low-pass filter output;
A variable gain amplifier that receives the output signal of the adder and can change the gain;
A loss compensation circuit comprising: In the loss compensation circuit that can vary the compensation characteristics according to the loss characteristics of the cable,
At least two low-pass filters to which an input signal is input, frequency characteristics are different, and gain can be varied;
A first adder for adding the outputs of the low-pass filter;
A variable gain amplifier that receives the output of the first adder and can change the gain;
A second adder that receives a signal related to the input signal and an output of the variable gain amplifier, and adds a signal related to the input signal and a signal having a reverse polarity of the low-pass filter output;
A loss compensation circuit comprising: 6. The loss compensation circuit according to claim 4, wherein the low-pass filter is a primary filter.

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