JPH0738555B2 - Hybrid circuit - Google Patents

Description

The present invention relates to a balanced impedance circuit for suppressing near-end echo, which is used for 2-wire to 4-wire conversion between a metallic subscriber line and a transmitting / receiving circuit. The present invention relates to a hybrid circuit provided.

[Conventional technology]

A conventional hybrid circuit of this type has a configuration as shown in FIG. In FIG. 2, reference numeral 22 is a balanced impedance circuit, 14 is a subscriber line, and 15 is a subtractor. FIG. 3 shows an example of the configuration of the balanced impedance circuit 22. In FIG. 2, the input impedance on the near end side of the subscriber line whose far end is terminated by a resistor R is Zin, and the impedance of the balanced impedance circuit 22 is Za.

Since the bridge circuit is configured by the two resistors R and the impedances Za and Zin, the near-end echo E, which is the transmission signal component that wraps around from the transmission end A to the reception end B, is
It is expressed by the following equation (1).

As is clear from the equation (1), the balanced impedance Za that can completely suppress the near-end echo is Za = Zin (2). That is, the near-end echo can be completely suppressed by matching the balanced impedance Za with the impedance Zin of the subscriber line. However, usually, in order to simplify the circuit, the balanced impedance Za is often fixed to a constant value.

[Problems to be Solved by the Invention]

In the conventional hybrid circuit described above, the balanced impedance Za is fixed to a constant value, so the length of the subscriber line changes, the line type of the subscriber line is different, or a bridged tap is additionally connected to the line. When the input impedance Zin of the subscriber line is not constant, as in the case described above, the near-end echo cannot be sufficiently suppressed unless the optimum balanced impedance is obtained. Furthermore, if the transmitter / receiver circuit is an LSI, if the balanced impedance Za is fixed, the near-end echo cannot be sufficiently suppressed when the input impedance Zin is different, as described above, and the dynamic range of the LSI is narrowed. is there.

[Means for Solving the Problems] A hybrid circuit of the present invention is a hybrid circuit that performs 2-wire to 4-wire conversion between a subscriber line and a transmission / reception circuit, and a signal sneak from the transmission side to the reception side of the transmission / reception circuit. In the peak detection circuit for detecting the peak value of the near-end echo generated in, the control circuit for generating a control signal for selecting the balanced impedance in response to the output signal of the peak detection circuit, and in response to the control signal And a balanced impedance circuit that variably sets the balanced impedance.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention. In the figure, reference numeral 11 is a balanced impedance circuit, 12 is a control circuit, 13 is a peak detection circuit, 14 is a subscriber line, and 15 is a subtractor. A configuration example of the balanced impedance circuit 11 is shown in FIG.

First, a training period is provided before actual communication, and a solitary wave is input as a transmission signal. Assuming that the amplitude of the input solitary wave at the transmission end A is Vin and the amplitude of the solitary wave transmitted to the reception end C is V ₂ , the input impedance Zin of the subscriber line 14 and the voltage division at the resistance R result in Becomes The amplitude V ₂ of this solitary wave changes as shown in FIG. 5 depending on the line type of the subscriber line, the length, and the presence / absence of a bridged tap.

The peak detection circuit 13 detects the peak value of the amplitude V ₂ of the solitary wave at the receiving end C and inputs it to the control circuit 12. In the control circuit 12, a plurality of types of threshold values V _{0 to} V ₄ are set, and it is detected which threshold value the peak value of the amplitude V ₂ belongs to, and the balanced impedance circuit 11 is detected. Send a control signal to.

As shown in FIG. 4, the balanced impedance circuit 11 has built-in impedance components Ra _{1 to} Ra ₄ corresponding to the section of the peak value of the solitary wave in advance, and in accordance with the control signal of the control circuit 12, each time. By selecting the optimum balanced impedance, the solitary wave echo at the receiving end B can be suppressed. By holding the balanced impedance selected by the above-mentioned procedure when shifting to communication, the near-end echo during communication is suppressed.

In this embodiment, since the peak value of the near-end echo is detected and the balanced impedance corresponding to the peak value is selected to suppress the near-end echo, two peaks are generated in the solitary wave response as shown in FIG. Even when there is a bridged tap, the peak of the response waveform can be detected to suppress the near-end echo, and the near-end echo can be suppressed regardless of the presence or absence of the bridged tap.

〔The invention's effect〕

As described above, in the present invention, the training signal is input as the transmission signal during the training period, the level value of the training signal that wraps around to the receiving end is detected, and the balanced impedance is variably selected according to the detection result. The near-end echo can be suppressed regardless of the line type, the length, and the presence or absence of the bridged tap of the main line.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram of a conventional hybrid circuit, FIG. 3 is a circuit diagram showing a configuration example of a balanced impedance circuit in the conventional hybrid circuit, and FIG. FIG. 5 is a circuit diagram showing a configuration example of the balanced impedance circuit in the embodiment of the present invention, and FIG. 5 is a signal waveform diagram for explaining the operation of the embodiment of the present invention. 11,22 …… Balanced impedance circuit, 12 …… Control circuit, 1
3 ... Peak detection circuit, 14 ... Subscriber line, 15 ... Subtractor, R ... Resistance.

Claims (1)

[Claims] 1. Two lines between a subscriber line and a transmission / reception circuit.
In a hybrid circuit that performs 4-wire conversion, a peak detection circuit that detects a peak value of a near-end echo that occurs due to a signal wraparound from a transmission side to a reception side of the transmission / reception circuit, and a balance in response to an output signal of the peak detection circuit. A hybrid circuit comprising: a control circuit for generating a control signal for instructing selection of impedance; and a balanced impedance circuit for variably setting the balanced impedance in response to the control signal.