JP2005311420A - Hybrid circuit apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hybrid circuit apparatus usable up to a high frequency and for producing low noise. <P>SOLUTION: The hybrid circuit apparatus includes: a reception amplifier for outputting a differential signal between first and second reception terminals; two variable gain amplifiers respectively driving first and second transmission terminals; and four resistors for interconnecting the first and second transmission terminals and the first and second reception terminals. One of the resistors connected to the same transmission terminal has a lower resistance than that of the other resistor and the resistors with a high resistance and a low resistance connected to the different transmission terminals are connected to the same reception terminal. Further, the resistance of the resistors is selected so that the impedance viewed from the first reception terminal is equal to an impedance equivalent to the impedance of a transmission line. Noise generated in the variable gain amplifiers is respectively supplied to the two reception terminals, wherein the noise is cancelled with each other, resulting in attaining low noise. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hybrid circuit device, and more particularly to a low-noise hybrid circuit device that can be used up to a high frequency.

Conventionally, various hybrid circuits (2-wire 4-wire conversion circuits) have been proposed as circuits for separating transmission signals and reception signals of full-duplex lines. Patent Document 1 below discloses a hybrid circuit that digitally controls adjustable passive elements such as variable resistors and variable capacitors.
JP 2001-211105 A

  The conventional hybrid circuit described above can be realized in a low-speed transmission line, but there is no adjustable passive element having characteristics that can be used for a high-speed full-duplex digital data transmission line (LAN) of several Gbps or more. Therefore, it cannot be realized.

  Therefore, the present inventor sets the elements of the hybrid circuit (passive elements) to fixed values, and uses two variable gain amplifiers to drive the two transmission signal drive ends independently, thereby increasing the gains of the two variable gain amplifiers. A configuration has been invented that cancels the transmission signal at the receiving end of the hybrid circuit by relatively adjusting. By this method, a hybrid circuit capable of operating up to a high frequency was realized. This configuration has not been announced.

  However, in this method, the transmission signal at the receiving end can be canceled, but it has been found that the noise generated in each variable gain amplifier is output without being canceled at the receiving end.

  The present invention aims to solve the above-described problems. For this purpose, the hybrid circuit device of the present invention has a first receiving end to which a transmission line is connected and an impedance circuit equivalent to the transmission line. Receiving amplifier means for outputting a signal to and from the second receiving end, a first variable gain amplifier means for inputting the transmission signal and driving the first transmitting end, and a transmission signal being inputted, Second variable gain amplifier means for driving the transmission terminal, first resistance means for connecting the first reception terminal and the first transmission terminal, the first reception terminal and the second transmission. A second resistance means for connecting an end, a third resistance means for connecting the second reception end and the first transmission end, and a connection between the second reception end and the second transmission end. And a resistance value of the first resistance means is a resistance value of the third resistance means. Smaller than the value, and the resistance value of the fourth resistor means is mainly characterized in that less than the resistance value of the second resistor means.

Further, the resistance values of the first to fourth resistance means, the first and second variable gain amplifiers, so that the impedance viewed from the first receiving end is equal to the impedance equivalent to the transmission line. Another characteristic is that the output impedance of the means and the input impedance of the receiving amplifier means are selected.
Furthermore, the resistance value of the first resistance means and the resistance value of the fourth resistance means are equal, the resistance value of the second resistance means and the resistance value of the third resistance means are equal, and The ratio between the resistance values of the first and fourth resistance means and the resistance values of the second and third resistance means is selected to be as close to 1: 1 as possible within a range that can cover variations in the characteristics of the transmission line. There is also a feature.

  In the hybrid circuit device of the present invention, the noise generated in each variable gain amplifier is also supplied to the two receiving ends by the above-described configuration, so that the hybrid is substantially canceled at the receiving end and is a low noise hybrid. There is an effect that a circuit can be realized. In addition, a hybrid circuit can be configured only with elements that can be used up to a currently available high frequency without using an adjustable passive element, so that there is an effect that a hybrid circuit that can be used up to a high frequency can be realized. . Furthermore, a circuit configuration that does not use a transformer or a coil is possible, and there is an effect that an IC can be realized.

  The hybrid circuit device of the present invention has been developed on the assumption that it is used for an ultrahigh-speed digital data transmission device (LAN) of several Gbps or more using a balanced cable or a coaxial cable represented by a twisted pair cable. Example 1 will be described below.

The first embodiment is an example of a hybrid circuit of the present invention when a twisted pair cable that is currently widely used as a LAN cable is used.
FIG. 2 is a block diagram showing the configuration of the entire transmission apparatus using the hybrid circuit of the present invention. The transmission apparatus to which the present invention is applied is connected to the counterpart transmission apparatus 49 having the same configuration through the twisted pair cable 17. An example using a coaxial cable will be described later.

  The transmission apparatus includes four full duplex transmission / reception circuits 30, a data distribution circuit 33, and a data synthesis circuit. The data distribution circuit 33 divides the transmission data into 8 bits, for example, and converts each of the 3 bits of data corresponding to the quinary pulse of 4 channels capable of error detection / correction into a total of 12 bits. 3 bits are distributed to each of the four full duplex transmission / reception circuits 30. In addition, the data synthesis circuit 34 restores the original 8-bit data to 3 bits each corresponding to the quinary pulses of 4 channels and 12 bits in total.

  FIG. 3 is a block diagram showing a configuration of the full duplex transmission / reception circuit 30. The transmission data is converted into a multi-value analog signal suitable for transmission by the transmission circuit 40, amplified to a size suitable for transmission by the amplifier 41, and output to the cable 17 by the hybrid circuit 42 of the present invention.

  A part of the transmission signal generates an unnecessary signal called “echo” due to reflection at a connection point or the like existing in the cable 17. This unnecessary signal needs to be removed appropriately for accurate data transmission. The reception signal from the cable 17 is separated from the transmission signal by the hybrid circuit 42 of the present invention and input to the amplifier 43. The cancel signal generation circuit 47 generates a cancel signal for erasing unnecessary signals based on the transmission data.

  The reception signal output from the amplifier 43 and the cancel signal output from the cancel signal generation circuit 47 are combined by the combiner 44, and unnecessary signals are removed. In the receiving circuit 45, the output signal of the synthesizer 44 is sampled by a plurality of sample and hold circuits, an analog product-sum operation is performed by a matrix circuit in order to correct distortion, and converted to a digital signal by an analog-digital converter. . The digital signals are collectively processed by a logic circuit such as parallel-to-serial conversion to obtain received data and an evaluation signal.

  With respect to the timing of the above series of operations, the clock signal is extracted by the clock recovery circuit 46, and various timing signals are generated. The adjustment control circuit 48 includes a CPU and adjusts each circuit including the hybrid circuit so that data can be correctly transmitted and received based on the evaluation signal.

  FIG. 1 is a block diagram showing an example of a hybrid circuit of the present invention when a twisted pair cable is used. The twisted pair cable 17 currently widely used as a LAN cable has a characteristic impedance of about 100Ω ± 10%. In the hybrid circuit of the present invention, each wire of the twisted pair cable is terminated by two hybrid circuits each having an input impedance of 50Ω.

  In the circuit of FIG. 1, the upper and lower circuits connected to the respective lines of the cable 17 have the same configuration. Therefore, only the upper circuit will be described. A + output signal (−output signal) of a differential output of the transmission signal is input to the upper (lower) circuit. The input signal is input to the two variable gain amplifiers A10 and B11. The relative gains of the variable gain amplifiers A10 and B11 are adjusted by the adjustment control circuit 48 shown in FIG. Note that one of the variable gain amplifiers A10 and B11 may have a fixed gain and only the other may be adjusted.

  The output (second transmission end) of the variable gain amplifier A10 is connected to each input terminal (first and second) of the differential input amplifier A16 via two resistors (0.9R) 12 and a resistor (1.1R) 13, respectively. Connected to the receiving end). The output (first transmission end) of the variable gain amplifier B11 is connected to the respective input terminals of the differential input amplifier A16 via two resistors (1.1R) 15 and a resistor (0.9R) 14, respectively. ing. One line of the twisted pair cable is connected to one input terminal (first receiving end) of the differential input amplifier A16. The differential input amplifier A16 outputs a differential output signal corresponding to the voltage difference between the two differential input terminals (first and second reception ends) as a reception signal.

The ratio of the resistance values of the resistors 12 and 13 and the ratio of the resistance values of the resistors 14 and 15 are selected to be 0.9 to 1.1, respectively. Further, the respective resistance values are selected so that the input impedance viewed from the connection point of the twisted pair cable 17 is also 50Ω.
For example, when the output impedance of the variable gain amplifiers A10 and B11 is 50Ω and the impedance between the input terminals of the differential input amplifier A16 is 100Ω, by setting the resistors 12 and 14 to 91Ω and the resistors 13 and 15 to 110Ω, The impedance viewed from the cable connection end (first reception end) is approximately 50Ω.

  The impedance equivalent to the transmission line is half the characteristic impedance in the case of a balanced cable, and is equal to the characteristic impedance in the case of a coaxial cable. The impedance Z18 is a circuit having the same impedance (impedance equivalent to the transmission line) as half the standard characteristic impedance of the twisted pair cable 17, and may be a parallel circuit of a resistor and a capacitor, for example. Capacitors are caused by the floating capacity of cables, connectors, and wiring.

  When the impedance of the twisted pair cable 17 is equal to twice this Z18, that is, when the impedance equivalent to the transmission line is equal to Z18, the transmission signal at the receiving end can be obtained by equalizing the gains of the two variable gain amplifiers A10 and B11. Are in phase and level and canceled. However, since the characteristic impedance of the cable varies, the transmission signal level at the receiving end does not become the same level. For example, when the characteristic impedance of the cable 17 is small, the transmission signal level at the first receiving end on the cable side is also lowered. Therefore, by making the gain of the variable gain amplifier B11 larger than that of the amplifier A10, the first on the cable side. The transmission signal level at the receiving end can be raised and balanced.

  Note that noise components generated in the amplifiers A10 and B11 by the amount of imbalance between the resistors 12 and 14 and the resistors 13 and 15 are output without being canceled at the receiving end. , 15 is significantly reduced as compared with the case without 15.

  Further, if the imbalance between the resistors 12 and 14 and the resistors 13 and 15 is reduced, the noise component is reduced accordingly, but the impedance adjustment range is narrowed accordingly. Therefore, the ratio between the resistors 12 and 14 and the resistors 13 and 15 is as close to 1: 1 as possible within a range that can secure an adjustment range that covers variations in characteristics of LAN cables that are currently widely used. Adjustment of ± 20% is possible when the ratio is 0.9 to 1.1. Since this embodiment does not use a transformer or a choke coil, it can be integrated into an IC.

  FIG. 4 is a circuit diagram illustrating a circuit example of the first embodiment. Since the upper and lower circuits are the same, only the upper circuit will be described. The (+) transmission signal is input to the two variable gain amplifiers A10 and B11 via resistors 50, 51 and 52 for signal distribution and impedance matching, and capacitors 53 and 54 for DC cut. Further, the outputs of the amplifiers A10 and B11 are inputted to two fixed gain monolithic amplifiers ICs 57 and 58 via DC cut capacitors 55 and 56, respectively.

  As the variable gain amplifiers A10 and B11, for example, AD8370 manufactured by ANALOG DEVICES (registered trademark) can be used. This IC can digitally control the gain from the outside. NEC (registered trademark) μPC2712TB can also be used. Since the gain of this IC can be adjusted by changing the power supply voltage, a power supply circuit capable of controlling the voltage is necessary to perform the adjustment.

  As the monolithic amplifier ICs 57 and 58, for example, ERA-4 manufactured by Mini-Circuits (registered trademark) can be used. Since this IC has an output impedance of 50Ω and supplies power from the output end, in this embodiment, power is supplied to the respective ICs 57 and 58 via a transformer 61 and resistors 12 and 15 described later. .

  The values of the resistors 12, 14 and 13, 15 are, for example, 91Ω and 110Ω, which are the values described above, respectively. The resistor Rz68 and the capacitor 67 constituting the impedance Z18 are selected to be equal to half the standard characteristic impedance of the twisted pair cable. Capacitors 59, 60, 62, 63 and 66 are DC cut capacitors, and are equivalent to those in which both ends of the capacitor are short-circuited in terms of AC. Also, Vcc itself supplied to Rz68 is not necessary, but Rz68 needs to be DC cut, and there is a solid printed wiring pattern of Vcc for board production, and it is grounded in terms of high frequency. Connected.

  The transformer 65 has a structure as will be described later, and blocks common mode noise. FIG. 5 is a plan view and a connection diagram showing the structure of the transformer used in the embodiment of the present invention. FIG. 5A shows a configuration of a transformer 65 for a twisted pair cable. In this transformer, two thin coaxial cables 71 and 72 are wound around a toroidal core 70 made of a magnetic material in the same direction, and the core wire and the outer conductor of each coaxial cable are respectively wound. By inserting a transformer with such a structure between the input / output end of the hybrid circuit and the cable, impedance matching can be obtained for the differential signal transmitted through each line of the cable, but in-phase due to electromagnetic induction or the like. It has the effect of blocking common mode noise. Moreover, the characteristic impedance between lines can be precisely set by using a coaxial cable having a known characteristic impedance and an accurate coaxial cable.

  As an input amplifier, a differential input amplifier 16 may be used as shown in FIG. 1, but in the embodiment circuit of FIG. 4, a transformer 61 and a single end are used instead of the differential input amplifier A16 of FIG. Amplifier A64. FIG. 5B shows the configuration of the transformer 61. This transformer is also obtained by winding a thin coaxial cable 91 around a toroidal core 90 in the same manner as the transformer 65 described above. The transformer 61 can also perform impedance matching for differential signals (received signals), but has an effect of blocking common mode noise (transmitted signals, noise generated in the amplifier). Note that the ERA-4 described above can be used as the amplifier A64. With the above configuration, a hybrid circuit for a twisted pair cable that can be used up to a high frequency and has low noise can be realized.

  Example 2 is an example of the hybrid circuit of the present invention when a coaxial cable is used. FIG. 6 is a block diagram showing an example of a hybrid circuit of the present invention when a coaxial cable is used. The characteristic impedance of the coaxial cable 80 is, for example, 50Ω. For example, one of the hybrid circuits for the twisted pair cable shown in FIG. 1 can be used as the hybrid circuit for the coaxial cable. The elements, functions, and operations are also the same as those in the above circuit. Since the coaxial cable is less attenuated than the twisted pair cable, transmission over a longer distance is possible.

FIG. 7 is a block diagram showing a modification of the circuit of FIG. In this circuit, similarly to the circuit shown in FIG. 4, a transformer 61 and a single-ended amplifier 64 are used instead of the differential input amplifier 16.
FIG. 8 is a circuit diagram illustrating a circuit example of the second embodiment. This circuit example is the same as one of the circuits of the first embodiment shown in FIG. 4 except that the differential input amplifier 16 is used as the input amplifier. In this embodiment, power is supplied to the respective ICs 57 and 58 via the resistor 68 and the resistors 12 and 15. This configuration can be made into an IC.

  FIG. 9 is a circuit diagram illustrating a modification of the circuit example of the second embodiment. In this circuit example, a transformer 61 is inserted between the coaxial cable 80 and the input / output end of the hybrid circuit. The transformer 61 has the configuration shown in FIG. Again, it has the effect of blocking common mode noise while taking impedance matching. This embodiment can also be made as an IC except for the transformer.

While the embodiments have been disclosed, the following modifications are also conceivable for the present invention. In the embodiment, for example, the example in which the four resistors 12 to 15 are used in the configuration of FIG. 1 is disclosed. However, even in the configuration in which the resistor 13 and the resistor 15 are removed (no electrical connection), the transmission signal component in the received signal is It is possible to cancel. Therefore, in an application where the dynamic range (S / N ratio) does not have to be very large, the configuration in which the resistor 13 and the resistor 15 are removed can be implemented.
In the configuration of FIG. 1, when the variable gain amplifier is configured by a differential circuit, the variable gain amplifiers A10 and D21 and the variable gain amplifiers B11 and C20 can be configured by an integrated circuit.
In the configuration of FIG. 4, when the variable gain amplifier is configured by a differential circuit, the variable gain amplifiers A10 and D21, the variable gain amplifiers B11 and C20, and further the variable gain amplifiers A64 and B26 are configured by an integrated circuit. It is also possible to do.

It is a block diagram which shows the hybrid circuit example of this invention in the case of using a twisted pair cable. It is a block diagram which shows the structure of the whole transmission apparatus. 2 is a block diagram showing a configuration of a full duplex transmission / reception circuit 30. FIG. FIG. 3 is a circuit diagram illustrating a circuit example of the first embodiment. It is the top view and connection diagram which show the structure of the transformer used in the Example of this invention. It is a block diagram which shows the example of a hybrid circuit of this invention in the case of using a coaxial cable. FIG. 7 is a block diagram illustrating a modified example of the circuit of FIG. 6. 6 is a circuit diagram showing a circuit example of Example 2. FIG. FIG. 10 is a circuit diagram illustrating a modification of the circuit example of the second embodiment.

Explanation of symbols

10, 11 Variable gain amplifier 12-15 Resistor 16 Differential input amplifier 17 Twisted pair cable 18 Impedance circuit

Claims (7)

Receiving amplifier means for outputting a signal between a first receiving end to which the transmission line is connected and a second receiving end to which an impedance circuit equivalent to the transmission line is connected;
First variable gain amplifier means for receiving the transmission signal and driving the first transmission end;
Second variable gain amplifier means for receiving the transmission signal and driving the second transmission end;
First resistance means for connecting the first receiving end and the first transmitting end;
Second resistance means for connecting the first receiving end and the second transmitting end;
Third resistance means for connecting the second receiving end and the first transmitting end;
A fourth resistance means for connecting the second receiving end and the second transmitting end;
The resistance value of the first resistance means is smaller than the resistance value of the third resistance means, and the resistance value of the fourth resistance means is smaller than the resistance value of the second resistance means. A hybrid circuit device.   The resistance values of the first to fourth resistance means, the first and second variable gain amplifier means, such that the impedance viewed from the first receiving end is equal to the impedance equivalent to the transmission line. 2. The hybrid circuit device according to claim 1, wherein an output impedance and an input impedance of the reception amplifier means are selected.   The resistance value of the first resistance means and the resistance value of the fourth resistance means are equal, the resistance value of the second resistance means and the resistance value of the third resistance means are equal, and the first resistance means The ratio between the resistance values of the first and fourth resistance means and the resistance values of the second and third resistance means is selected to be as close as possible to a one-to-one ratio within a range that can cover variations in the characteristics of the transmission line. The hybrid circuit device according to claim 1.   A hybrid circuit device, wherein a twisted pair cable is used as a transmission line, and two transmission lines of the twisted pair cable are respectively terminated by two sets of hybrid circuits according to claim 1.   The reception amplifier means includes a common mode choke means using a coaxial cable having an input end connected to the first and second reception ends, and an output corresponding to the first reception end of the common mode choke means. The hybrid circuit device according to claim 1, further comprising a single-ended amplifier unit connected to the terminal.   The hybrid circuit device according to claim 1, further comprising a common mode choke transformer using a coaxial cable between a transmission / reception terminal of the hybrid circuit and a transmission path. Receiving amplifier means for outputting a signal between a first receiving end to which the transmission line is connected and a second receiving end to which an impedance circuit equivalent to the transmission line is connected;
First variable gain amplifier means for receiving the transmission signal and driving the first transmission end;
Second variable gain amplifier means for receiving the transmission signal and driving the second transmission end;
First resistance means for connecting the first receiving end and the first transmitting end;
A hybrid circuit device comprising: the second receiving end and second resistance means for connecting the second transmitting end.

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