JP2001069044A - Hybrid circuit and communication equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease maximum power consumption of a termination resistor. SOLUTION: A signal to be sent to a telephone line and an output signal of 3rd amplifiers 3, 6 are summed to form a feedback loop to 2nd amplifiers 2, 5. Thus, even when a comparatively high resistance is selected for resistors R2, R5, the termination impedance is matched by increasing a gain of the feedback loop. Since the resistance is selected higher, the current consumption in the resistors can be reduced resulting in decreasing the maximum power consumption of the termination resistor. Thus, a small sized termination resistor can be employed to make a hybrid circuit 30 small in size.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for reducing power consumption by a terminating resistor in a hybrid circuit, and more particularly to a technique effective when applied to a modem.

[0002]

2. Description of the Related Art A hybrid circuit is arranged between a four-wire type modem and a two-wire type telephone line to perform 4-wire to 2-wire conversion. That is, the transmission signal transmitted through the transmission signal line of the modem is output to the telephone line without leaking to the reception signal line of the modem, and the reception signal transmitted through the telephone line is output. The signal is output to the reception signal line without leaking to the transmission signal line.

As an example of a document describing such a hybrid circuit, there is JP-A-6-303167.

[0004]

In the above prior art, the terminating impedance from the two-wire telephone line side is:
It is determined by the resistance connected to the output of the amplifier driving the transformer. Specifically, the transformer turns ratio is 1:
m (the telephone line side is 1) and the terminating impedance is Zt. If the winding resistance of the transformer is ignored, the value of the resistor connected between the amplifier driving the transformer and the transformer is m2. -Terminating by setting to Zt. Thus, the value of the resistor connected between the transformer and the drive amplifier is determined by the turns ratio of the transformer.

On the other hand, a DC voltage of several tens of volts for supplying power to a telephone is normally applied to the two-wire telephone line side, and this DC voltage changes every time a call is made. Also, since telephone lines are wired outdoors, lightning surges, AC100V,
There is a danger of applying an overvoltage by a commercial power supply such as AC200V. For this reason, a voltage transformed according to the turns ratio of the transformer is generated on the secondary side of the transformer. The terminating resistor also functions as a current limiting resistor that protects the transformer driving amplifier from these overvoltages. here,
In order to reduce these generated voltages by reducing the value of "m" at a transformer turns ratio of 1: m, the received signal level when entering from the two telephone lines to the four lines is also reduced. This causes a problem of S / N deterioration and lowers the resistance value m2 · Zt of the above-mentioned termination. The maximum power consumed by the resistor is when a lightning surge or an overvoltage is applied by a commercial power supply. When the resistor is designed to withstand this, even if the value of m is reduced, the impedance Zt to be terminated changes. Unless
No change, which hinders miniaturization of the hybrid circuit.

An object of the present invention is to provide a technique for reducing the maximum power consumption of a terminating resistor.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0008]

The following is a brief description of an outline of a typical invention among the inventions disclosed in the present application.

That is, a transformer having a first winding coupled to a telephone line, a second winding magnetically coupled to the first winding, and a voltage induced in the second winding of the transformer. A first amplifier for amplifying a signal, a resistor coupled to the second winding, and a second amplifier for driving the second winding via the resistor to enable signal transmission to the telephone line And a third amplifier for multiplying the output signal of the first amplifier by a predetermined transfer coefficient, a signal to be transmitted to the telephone line, and an output signal of the third amplifier. And a first adder for forming a feedback loop to the second amplifier by adding the first and second amplifiers. The second amplifier drives the second winding based on the output signal of the first adder. I do.

According to the above means, a feedback loop to the second amplifier is formed by adding the signal to be transmitted to the telephone line and the output signal of the third amplifier. This feedback loop forms an active type termination impedance circuit together with the above-mentioned resistor. Thus, even when the resistance is set to a relatively large value, the termination impedance can be matched by increasing the gain of the feedback loop. The fact that the value of the resistor can be increased means that the power consumption at the time of applying an overvoltage such as a lightning surge can be reduced, which lowers the maximum power consumption of the terminating resistor. Achieve the goal.

Here, the second amplifier includes a detecting means for detecting a voltage between both ends of the resistor, and an amplifying means for amplifying a difference between an output signal of the detecting means and a signal transmitted from the adder. And driving the second winding based on an output signal of the amplifying means.

A / D conversion means for converting a reception signal transmitted through the first amplifier into a digital signal, and a multiplication for multiplying the digital signal output from the A / D conversion means by a predetermined transmission coefficient. Means and means for adding a signal to be transmitted to the telephone line and an output signal of the multiplying means to form a feedback loop to the second amplifier to form a hybrid circuit. it can.

According to the above means, a feedback loop to the second amplifier is formed by adding the signal to be transmitted to the telephone line and the output signal of the multiplying means. This feedback loop forms an active type termination impedance circuit together with the above-mentioned resistor. Thus, even when the resistance is set to a relatively large value, the termination impedance can be matched by increasing the gain of the feedback loop. The fact that the value of the resistor can be increased can reduce the current consumption there, and this achieves the object of the present invention of reducing the maximum power consumption of the terminating resistor.

Further, for echo cancellation, a fourth amplifier for multiplying a signal to be transmitted by a predetermined transfer coefficient, and a fourth amplifier for adding the output signal of the fourth amplifier and the output signal of the first amplifier. And a second adder.
The output signal of the adder may be transmitted to a subsequent circuit as a reception signal.

[0015]

FIG. 8 shows a modem to which a hybrid circuit according to the present invention is applied.

The modem 300 is disposed between a higher-level device 400 such as a personal computer system and a telephone line, and includes a line connection switch (SW) 301, a hybrid circuit 302, and a digital signal processor (DS).
P) 303, an interface (IF) 304, an incoming call detection circuit 305, and a control circuit 306.

The line connection switch 301 forms a DC loop on the telephone line side when performing communication as a modem,
Generate a dial pulse. Then, the host device 400
In order to enable communication between the telephone line and another device (not shown) connected to the telephone line, the telephone line and the hybrid circuit 302 are connected.

The hybrid circuit 302 includes a DSP 303
The transmission digital signal 201 is output to the telephone line via the line connection switch 301 while leaking the transmission digital signal 201 to the reception system as much as possible. The signal is output to the DSP 303 in a state where it is not leaked to the transmission system as much as possible.

The DSP 303 includes the hybrid circuit 3
02, receives the received digital signal 202, demodulates it and outputs it to the interface 304, or conversely modulates the signal transmitted from the interface 304 and outputs it to the hybrid circuit 302 as a transmitted digital signal. .

The interface 304 is a host device 400
Interface with

The incoming call detection circuit 305 detects an incoming call by detecting a call bell signal from a telephone line.

The control circuit 306 controls the operation of the line connection switch 301, DSP 303, interface 304 and the like.

FIG. 1 shows an example of the configuration of the hybrid circuit 302.

Hybrid circuit 302 shown in FIG.
Is a differential circuit, although not particularly limited.

T1 and T2 are two line side terminals, which are coupled to a line connection switch 301 shown in FIG. The transformer 10 includes a first winding L1 and a second winding L2 for AC coupling the two-wire side and the four-wire side at a turn ratio of 1: m.
And Reference numeral 11 denotes a capacitor, which is connected in series to the primary winding L1 of the transformer 10, and supplies an AC voltage such as an audio signal generated between the line terminals T1 and T2 to the transformer 10. To block the flow of the direct current (DC) component. When a signal is applied to the first winding of the transformer 10, the signal induced in the second winding L <b> 2 is amplified by the amplifier 1. This amplifier 1
Has a differential input terminal and a differential output terminal, and its transmission gain is A1. An output signal from the non-inverting output terminal of the amplifier 1 is transmitted to the low-pass filter LPF2 via the adder ADD2 at the subsequent stage, and the low-frequency component passed through the low-pass filter LPF2 is arranged at the subsequent stage. A
The signal is transmitted to the non-inverting input terminal of the D converter 9. The output signal from the inverting output terminal of the amplifier 1 is output to an adder A
Transmitted to the low-pass filter LPF4 via the DD4,
Further, the low-frequency component passed through the low-pass filter LPF4 is transmitted to the inverting input terminal of the AD converter 9. After the analog signal input to the AD converter 9 is converted into a digital signal (received signal 202),
Is transmitted to the DSP 303 shown in FIG.

A DA for converting a digital signal output from DSP 303 shown in FIG.
A converter 8 is provided. An output signal from the non-inverting output terminal of the DA converter 8 is output to a low-pass filter LPF
1 is input to the adder ADD1 and the amplifier 4. The output signal from the inverting output terminal of the DA converter 8 is supplied to an adder A via a low-pass filter LPF3 at the subsequent stage.
The signal is input to the DD 3 and the amplifier 7. The transmission gains of the amplifiers 4 and 7 are A4 and A7, respectively.

The output signal from the non-inverting output terminal of the amplifier 1 is transmitted to an adder ADD1 after being multiplied by a transmission gain A3 in a subsequent amplifier 3, where the output signal 103 of the low-pass filter LPF1 is output. Is added. The result of this addition is input to the subsequent amplifier 2, where it is multiplied by the transmission gain A2. The output terminal of the amplifier 2 is connected to the second winding L2 of the transformer 10 via a resistor R2.
Are connected to one terminal. The output signal of the amplifier 3 is input to the adder ADD1, and the low-pass filter LPF
A feedback loop to the amplifier 2 is formed by being added to the output signal of No. 1.

The output signal from the inverting output terminal of the amplifier 1 is transmitted to the transmission gain A6
Is transmitted to the adder ADD3, where it is added to the output signal 106 of the low-pass filter LPF3. The result of this addition is input to the subsequent amplifier 5, where it is multiplied by the transmission gain A5. The output terminal of the amplifier 5 is connected to the second winding L of the transformer 10 via a resistor R5.
2 to the other terminal. The output signal of the amplifier 6 is input to the adder ADD3 and the low-pass filter LP
By adding the signal to the output signal of F3, a feedback loop to the amplifier 5 is formed.

The second winding L2 of the transformer 10 is driven by the amplifiers 2 and 5. By this driving, a signal induced in the first winding L1 is transmitted to the telephone line via the capacitor 11.

Here, the amplifier 1 corresponds to a first amplifier in the present invention, the amplifiers 2 and 5 correspond to a second amplifier in the present invention, and the amplifiers 3 and 6 correspond to a third amplifier in the present invention. .

The operation of the circuit configured as described above will be described.

For convenience of explanation, the differential type shown in FIG.
A description will be given of a non-differential type as shown in FIG. The non-differential type circuit shown in FIG. 2 basically corresponds to the non-inverting side circuit in FIG. In the non-differential type circuit shown in FIG. 2, one terminal of the secondary winding is coupled to the low-potential power supply Vss, and the transmission gain of the amplifier 1 is A · 1 /
2, especially 1/2 of the case shown in FIG.

The voltage appearing on the secondary side of the transformer 10 is denoted by Vi.
When n is set, the output voltage Vo of the amplifier 2 is represented by Expression 1.

[0034]

## EQU1 ## Vo = Vin. (A1 / 2) .A3.A2

Now, assuming that a resistor connected between the output of the amplifier 2 and the secondary side of the transformer 10 is R2, this resistor R2
Is expressed by the following equation.

[0036]

## EQU2 ## Iin = (Vin-Vo) / R2

The realized impedance Zin can be obtained as follows.

[0038]

## EQU3 ## Zin = Vin / Iin

[0039]

## EQU4 ## Zin = 2 · R2 / [1- (A · 1/2) · A
3. A2]

As is apparent from this equation, the terminating impedance Zin is not only the resistance value of the resistor R2 but also the transmission gains A1, A2,
A3 can be set by arbitrarily selecting A3, so that the resistor R also serves as a protection resistor against an excessive voltage.
2 is set to a relatively large value, and [1
− (A · 1/2) · A3 · A2] can be set to be large.

FIG. 3 shows a configuration example of the amplifier 1 shown in FIGS.

In FIG. 3, AMP2 and AMP3 are operational amplifiers (referred to as "operational amplifiers").
4, R31 to R34 are resistors. Operational amplifier AMP2
And the resistors R21 to R24, the first amplifier circuit is formed, and the operational amplifier AMP3 and the resistors R31 to R3
4 are combined to form a second amplifier circuit. A difference voltage between the input voltages Vip and Vim from the second winding L2 is obtained, and is output from the output terminal as voltages Vop and Vom. This relationship is an addition / subtraction circuit that outputs a voltage according to the relationship shown in Expression 5. Here, for simplicity, R21 = R22 = R31 = R32, R23 = R2
4 = R33 = R34.

[0043]

Vom = − (Vip−Vim) · (R23 / R21)

[0044]

Vop = (Vip−Vom) · (R23 / R21)

Therefore, the differential output (= Vop-Vom)
As a result, an output represented by the following equation is obtained.

[0046]

Vop−Vom = 2 · (Vip−Vom) ·
(R23 / R21)

In this case, the amplifier 1 shown in FIGS.
Is as follows.

[0048]

A1 = 2 · R23 / R21

FIG. 4 shows the amplifiers 3 and 2 shown in FIG.
One configuration example in which the adder ADD1 is put together is shown.

In FIG. 4, AMP1 is an operational amplifier, R11 to R13 are resistors, and constitute an inverting type adder circuit. The relationship between the inputs Vi1 and Vi2 and the output Vo is as shown in the following equation.

[0051]

Vo = − (R13 / R11) · Vi1 + (R1
3 / R12) · Vi2)

In this case, assuming that Vi1 is the output voltage of the differential amplifier 1, the transfer gains A2 and A3 by the amplifiers 2 and 3 shown in FIGS. 1 and 2 are as follows.

[0053]

A2 · A3 = −R13 / R11

In the above case, the configurations of the amplifiers 1, 2, 3, and the adder ADD1 are not particularly limited to the circuit configuration examples shown in FIGS.

The above is the terminating impedance Z on the secondary side.
has been described, but T1 and T2 on the telephone line side
When the mutual inductance of the transformer is very large and the capacitance value of the capacitor 11 is negligibly large, the terminating impedance Zt on the secondary side and the terminating impedance Zt on the primary side are viewed from The relationship is as follows:

[0056]

## EQU11 ## Zt = Zin / m2

Also, the termination circuit shown in FIGS.
When performing 4-wire conversion, the following operation is performed.

The signal of the two telephone lines is converted into a voltage of 1: m by a transformer, appears on the second winding L2 of the transformer, amplified by the amplifier 1, and added by the adder ADD2. , A low-pass filter L as a positive-side reception signal
It is transmitted to PF2. The signal added by the adder ADD4 is a low-pass filter L as a negative-side reception signal.
It is transmitted to PF4. The low-pass filter LPF2,
The LPF 4 is provided to prevent aliasing due to components exceeding the sampling frequency when performing AD conversion. The output signal is input to the AD converter 9 and becomes a digital reception signal 202. Conversely, the digital transmission signal 201 is converted into an analog signal by the DA converter 8, and the low-pass filters LPF1, LPF3
As a result, a low-frequency component is extracted and becomes a positive-side transmission signal 103 and a negative-side transmission signal 106, respectively. These signals are passed through adders ADD1 and ADD3 to the amplifiers 2 and 5 respectively.
And transmitted to the second winding L2 of the transformer 10 via the resistor R2 and the resistor R5, and output to the telephone line side via the transformer 10. Amplifier 4 and Amplifier 7
Are the positive transmission signal 103 and the negative transmission signal 106
Is provided to prevent the signal from being transmitted to the amplifier 1 when transmitted to the secondary side of the transformer and returning to the received signal 202 on the digital side. That is, the output signals of the amplifiers 4 and 7 are added to the corresponding adders ADD, respectively.
2 and the adder ADD4, where the signal is added to the output signal of the amplifier 1 to remove an undesired return signal component (echo cancellation).

As described above, the terminating impedance is changed to the resistance R
Not only 2, but amplifiers 1, 2, 3 (A1, A2, A3)
Feedback loop and amplifiers 1, 5, 6 (A1, A5,
Since it can be set by the gain of the feedback loop according to A6), the impedance can be matched even if the values of the resistors R2 and R5 are set large.

According to the above example, the following functions and effects can be obtained.

(1) The signal 103 to be transmitted to the telephone line,
106 and the output signals of the amplifiers 3 and 6 are added by the adders ADD1 and ADD2, respectively, so that a feedback loop to the amplifiers 2 and 5 is formed.
Even when R2 and R5 are set to relatively large values, the termination impedance can be matched by increasing the gain of the feedback loop. Since the values of the resistors R2 and R5 can be increased, power consumption when an overvoltage such as a lightning surge is applied can be reduced, thereby reducing the maximum power consumption of the terminating resistor. Since the maximum power consumption of the terminating resistor is reduced, a small resistor for the terminating resistor can be used, whereby the size of the hybrid circuit can be reduced.

(2) Amplifiers 4 and 7 for multiplying a signal to be transmitted by a predetermined transfer coefficient, and an adder A for adding the output signals of amplifiers 4 and 7 and the output signal of amplifier 1
DD2 and ADD4 are provided.
By transmitting the output signal of D4 to the subsequent circuit as a received signal, the echo component included in the received signal can be canceled.

FIG. 5 shows another configuration example of the hybrid circuit 300.

The difference between the hybrid circuit 300 shown in FIG. 5 and that shown in FIG. 1 is that the voltage controlled current sources 51 and 52 are replaced with the amplifiers 2 and 3 and the resistors R2 and R5 shown in FIG. This is the point provided. The voltage control current source 51 includes the amplifier 2 and the resistor R2.
2 comprises an amplifier 5 and a resistor R5. In FIG. 5, the terminating impedance Zin is realized by feedback as an output current corresponding to the input voltage. The amplifiers 12 and 13 are amplifiers for forming a voltage-controlled current source, and are not particularly limited, but may employ the configuration shown in FIG. AMP4 and AMP5 are operational amplifiers having transmission gains A and K, respectively. The resistor R2 performs a current-to-voltage conversion for detecting an output current and converting it to a voltage. The converted voltage is amplified by an operational amplifier AMP5, and its output signal is added to an adder ADD1.
The difference from the output signal Vc from (or ADD3) is obtained by the operational amplifier AMP4. Assuming that the transfer gain A of the operational amplifier AMP4 is very large, the following is obtained.

[0065]

[Formula 12] Io ≒ Vc / (K · R2)

For this reason, the amplifiers 12 and 15 operate as voltage-controlled current sources having a conductance G of 1 / (K · R2).

FIG. 6 shows the differential circuit shown in FIG.
For convenience of explanation, a non-differential circuit is shown.

As described above, the impedance Zin realized on the secondary side of the transformer is obtained as follows. 2
The voltage Vin generated on the next side passes through the amplifier 11 and the amplifier 3 and passes through the voltage control current source 22 as an output current Ii.
Since n is fed back, it is expressed by the following equation.

[0069]

## EQU13 ## Iin = Vin A1 / 2 A3 G2

Here, G2 is the transfer conductance of the amplifier 12 forming the voltage-controlled current source.
Is the configuration shown in FIG. 7, the transfer conductance G is expressed by the following equation.

[0071]

G2 = 1 / (K · R2)

For this reason, the terminating impedance Zin is
From Zin = Vin / Iin, it is expressed by the following equation.

[0073]

## EQU15 ## Zin = K · R2 / [(A · 1/2) · A3]

In setting the termination impedance Zin, not only the resistance R2 but also the transmission gain A of the feedback loop is set.
The terminal impedance can be set by arbitrarily setting the values of 1, A2, and K used for the current control current source. For this reason, as in the above-described example, the terminating impedance can be matched by setting the resistance R2, which also functions as a protection resistor against an excessive voltage, to a large value and increasing the values of the transmission gains A1, A2.

As described above, since the resistance R2 can be set to a large value, it can be suppressed to a small value and the same operation and effect as in the above-described example can be obtained.

Although the invention made by the present inventor has been specifically described above, the present invention is not limited to this, and it goes without saying that various modifications can be made without departing from the gist of the invention.

For example, in the above example, the amplifiers 1, 2, 3, 5, 6 (A1, A2, A3,
Although the feedback loop of A5 and A6) is realized in the analog part before AD conversion, a configuration in which a feedback loop is realized on the digital side after AD conversion and feedback is performed through the DA converter 9 is also possible. At this time, the echo canceling amplifiers 4 and 7 (A4 and A7) may be processed on the digital side. FIG. 9 shows the configuration in this case. 9, reference numeral 501 denotes a second winding L of the transformer 10.
2 is an amplifier that takes in the generated voltage, multiplies it by a transmission gain A501, and differentially outputs it to LPF2 and LPF4, 502 and 503 are amplifiers that drive the transformer 10, and 513 is an AD converter. 9 is a multiplier for multiplying the digital output signal 516 of No. 9 by D3 times.
D5 is an adder that adds the output signal of the multiplier 516 and the transmission digital signal 511 and outputs a digital input signal 515 to the DA converter 8. The multiplier 5
13. Since the adder ADD5 is provided, the amplifier 501 → LPF2 (and LPF4) → AD converter 9 →
A feedback loop is formed in the route of the multiplier 513 → adder ADD5 → DA converter 8. D4 is a multiplier for multiplying the transmission digital signal 511 by a factor of D4.
ADD6 is an adder that adds the output signal of the multiplier 514 and the digital output signal 516 of the AD converter 9 and outputs a received digital signal 512.
4, and the adder ADD6 realizes echo cancellation processing on the digital side. Even when the feedback loop is realized on the digital side in this manner, the termination impedance can be matched by increasing the gain of the feedback loop. Therefore, by increasing the values of the resistors R2 and R5, the value of the impedance can be improved. The current consumption can be reduced, thereby reducing the maximum power consumption of the terminating resistor. Thus, as in the example above,
A small resistor can be used as the terminating resistor, so that the size of the hybrid circuit can be reduced.

It is needless to say that only the echo cancellation processing may be performed on the digital side by the multiplier 514 and the adder ADD6 as shown in FIG.

The echo cancellation may be performed by the DSP 303.

In the above description, the case where the invention made by the present inventor is mainly applied to a modem, which is a field of application, has been described. However, the present invention is not limited to this, and is not limited to this. For example, the present invention can be applied to various communication devices.

The present invention can be applied on the condition that at least a transformer is included.

[0082]

The effects obtained by typical ones of the inventions disclosed in the present application will be briefly described as follows.

That is, by adding the signal to be transmitted to the telephone line and the output signal of the third amplifier, a feedback loop to the second amplifier is formed, whereby even when the resistance is set to a relatively large value. The termination impedance can be matched by increasing the gain of the feedback loop. Since the value of the resistor can be increased, the power consumption at the time of applying an overvoltage such as a lightning surge can be reduced, thereby reducing the maximum power consumption of the terminating resistor. Since the maximum power consumption of the terminating resistor is reduced, a small resistor for the terminating resistor can be used, whereby the size of the hybrid circuit can be reduced.

Further, a feedback loop to the second amplifier is formed by adding the signal to be transmitted to the telephone line and the output signal of the multiplying means, so that even when the resistance is set to a relatively large value, Since the termination impedance can be matched by increasing the gain of the feedback loop, a small resistor for the termination can be applied as in the case described above, thereby reducing the size of the hybrid circuit. Can be planned.

Further, a fifth amplifier for multiplying a signal to be transmitted by a predetermined transfer coefficient, and a second adder for adding an output signal of the fifth amplifier and an output signal of the first amplifier are provided. By transmitting the output signal of the second adder to the subsequent circuit as a reception signal, echo cancellation can be performed.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a configuration example of a hybrid circuit according to the present invention.

FIG. 2 is a circuit diagram of another configuration example of the hybrid circuit.

FIG. 3 is a circuit diagram illustrating a configuration example of a main part in the hybrid circuit.

FIG. 4 is a circuit diagram showing a configuration example of a main part in the hybrid circuit.

FIG. 5 is a circuit diagram illustrating another configuration example of the hybrid circuit.

FIG. 6 is a circuit diagram illustrating another configuration example of the hybrid circuit.

FIG. 7 is a circuit diagram showing a configuration example of a main part in the hybrid circuit shown in FIGS. 5 and 6;

FIG. 8 is a block diagram illustrating a configuration example of a modem including the hybrid circuit.

FIG. 9 is a circuit diagram illustrating another configuration example of the hybrid circuit.

FIG. 10 is a circuit diagram illustrating another example of the configuration of the hybrid circuit shown in FIG. 9;

[Explanation of symbols]

 1 to 7, 12 Amplifier 8 DA converter 9 AD converter 10 Transformer 11 Capacitor 91 Adder 92 Multiplier 300 Modem 301 Line connection switch 302 Hybrid circuit 303 DSP 304 Interface 305 Incoming detection circuit 306 Control circuit ADD1 to ADD4 Adder LPF1 LPF3 Low-pass filter R1, R2 Resistance 501 Differential amplifier 502, 503 Transformer drive amplifier 511 Transmit digital signal 512 Receive digital signal 513, 514 Multiplier 515 Digital input signal to DA converter 516 Digital output signal of AD converter D3, D4 Multiplier ADD5, ADD6 Adder

Claims (5)

[Claims] A transformer having a first winding coupled to a telephone line, a second winding magnetically coupled to the first winding, and a transformer induced in a second winding of the transformer. A first amplifier for amplifying a signal; a resistor coupled to the second winding; and a second amplifier for driving the second winding via the resistor to enable transmission of a signal to the telephone line. And a third amplifier for multiplying an output signal of the first amplifier by a predetermined transfer coefficient, and adding a signal to be transmitted to the telephone line and an output signal of the third amplifier. And a first adder for forming a feedback loop to the second amplifier. The second amplifier drives the second winding based on an output signal of the first adder. A hybrid circuit characterized by the above. 2. A transformer having a first winding coupled to a telephone line, a second winding magnetically coupled to the first winding, and a transformer induced in the second winding of the transformer. A first amplifier for amplifying a signal; a resistor coupled to the second winding; and a second amplifier for driving the second winding via the resistor to enable transmission of a signal to the telephone line. And a third amplifier for multiplying an output signal of the first amplifier by a predetermined transfer coefficient, and adding a signal to be transmitted to the telephone line and an output signal of the third amplifier. And a first adder for forming a feedback loop to the second amplifier, wherein the second amplifier has a detecting means for detecting a voltage across the resistor, Increase the difference between the output signal and the signal transmitted from the adder. Having amplifying means for width,
A hybrid circuit for driving the second winding based on an output signal of the amplifying means. A transformer having a first winding coupled to the telephone line; a second winding magnetically coupled to the first winding; and a transformer induced in the second winding of the transformer. A first amplifier for amplifying a signal; a resistor coupled to the second winding; and a second amplifier for driving the second winding via the resistor to enable transmission of a signal to the telephone line. And A / D conversion means for converting a received signal transmitted via the first amplifier into a digital signal; and a predetermined transfer coefficient for the digital signal output from the A / D conversion means. Multiplication means, and addition means for forming a feedback loop to the second amplifier by adding a signal to be transmitted to the telephone line and an output signal of the multiplication means. Features hybrid times Road. 4. A fourth amplifier for multiplying a signal to be transmitted by a predetermined transfer coefficient, and a second adder for adding an output signal of the fourth amplifier and an output signal of the first amplifier. And transmitting the output signal of the second adder to a subsequent circuit as a reception signal from the telephone line.
The hybrid circuit according to any one of the preceding claims. 5. A hybrid system according to claim 1, further comprising: a receiving system that receives a signal transmitted via a telephone line via said hybrid circuit and processes the signal; and And a receiving system for transmitting a transmission signal to the telephone line.