JPS6143841A - Adaptive type two-wire four-wire converting circuit - Google Patents

Abstract

PURPOSE:To minimize a detour signal reaching a 4-wire transmission line from a 4-wire reception lien by providing the 1st coder/decoder (CODEC) applying A/D conversion, the 2nd CODEC having the same filter characteristic, a 2/4-wire converting characteristic simulating circuit simulating a detour signal eliminating characteristic and a selection circuit switching a balance connection network. CONSTITUTION:A 2/4-wire converting characteristic simulating circuit 31 receives a signal from a reception line 41 of a PCM highway, generates simulatingly a detour eliminating signal component caused by an impedance circuit 171 of a balance network 14 of a 2/4-wire converting circuit 30 at first, this signal component is added to a signal of a PCM highway transmission line 42 to calculate a signal detoured to a transmission line 42 from the reception line 41. A selection circuit 32 compares all detour of the 2/4-wire converting circuit 30 switching sequentially the balance network 14 obtained by the 2/4-wire conversion characteristic simulating circuit 31 in this way with the signal characteristic to select the optimum impedance thereby switching the balance network 14.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a two-wire four-wire conversion circuit, and particularly to an adaptive two-wire four-wire conversion circuit used in subscriber circuits such as telephones.

[Prior art]

In conventional 2-wire 4-wire conversion circuits, in order to prevent the received signal on the 4-wire side from going around to the transmitted signal on the 4-wire side, a balanced wiring network ( (hereinafter referred to as a "balance network") to a hybrid transformer, or to configure a balance network equivalent to a hybrid transformer in terms of electronic circuitry.

In this case, the impedance on the two-wire side varies depending on the type and length of the connected line, so multiple balance networks are placed side by side and the optimal one is selected manually or by software control using pre-investigated data. A selective method may also be used. Also, a method may be adopted in which an echo canceller that automatically minimizes leakage is installed for each 2-wire and 4-wire conversion circuit.

However, the former method requires manual intervention, and even when software control is performed, data corresponding to each subscriber is required. The latter method is also extremely advantageous in improving transmission characteristics, but it requires an echo canceller for each connected transmission line, and is not suitable for subscriber circuits that require low cost and space. It was disadvantageous and not realistic.

[Purpose of the invention]

The purpose of the present invention is to provide four
An object of the present invention is to provide an adaptive 2-wire/4-wire conversion circuit in which wrap-around signals from a line-side reception line to a 4-line-side transmission line are minimized.

[Structure of the invention]

The present invention provides a first codec/decoder (hereinafter referred to as "CODEC J") that converts analog signals and digital signals.
DEC). ), a second codec that operates at the same timing as the first codec and has the same filter characteristics, and a balanced wiring network (2) that simulates the wrap-around signal removal characteristics of all the included impedance circuits by digital calculation. Line 4-wire conversion characteristic simulation circuit and this 2-wire 4
and a selection circuit that compares all output signals of the line conversion characteristic simulating circuit and switches the balanced connection network so that the 2-line and 4-line conversion circuit has optimal wrap-around signal characteristics.

〔Example〕

Examples of the present invention will be described with reference to the meat side.

FIG. 1 is a block diagram showing one embodiment of an adaptive two-wire/four-wire conversion circuit according to the present invention.

This embodiment adds this 2-wire 4-wire conversion circuit 60 to the conventional 2-wire 4-wire conversion circuit 60.
Reproducing the same wrap-around signal characteristics as the line conversion circuit 60 2
The 2-wire 4-wire conversion characteristic simulating circuit 61 and the 2-wire 4-wire conversion circuit 6 are configured so that the 2-wire 4-wire conversion circuit 60 has the optimum wrap-around signal characteristic based on the output of the 2-wire 4-wire conversion characteristic simulating circuit 61.
Selection circuit 62 for switching the no-naki lance network within 0
and the 4-wire side transmission line 15 and the 4-line side reception line 16 of the 2-wire 4-wire conversion circuit 60 are respectively connected, and P CM /-
a first encoder/decoder 40 connected to the iway 41 and 42 and converting the analog 4i code and the digital signal;
A digital input line is connected to the receiving line of the PCM 1 way, and the signal of its own analog output is fed back to its own analog input, so that it operates at the same timing as the first encoder/decoder 40 and has the same filter characteristics. A second encoder/decoder 50 having the following functions is provided.

The 2-wire 4-wire conversion circuit 60 is connected to the 2-wire 4-wire conversion circuit coupling section 16
and impedance circuit 17. ,172,...

17n (impedance is Zllll r Zl
The output 15 and input 16 on the 4-wire side are connected to the analog input terminal 51 and analog output terminal 49 of the first codec 40, respectively. has been done. If the impedance connected to the 2-wire side 12 of the 244-wire conversion circuit 60 is zL, and the 2-wire side terminal impedance is Zo, then from the 4-wire side receiving line 16 to the 4-wire side transmitting line 15
The wrap-around signal characteristics of the signal leading to 11 μ - (i=1.2,...,n)...(1)
ZL (ZO+ZL) (Z6+241) *. In equation (1), the first term is the balance network 1
The second term is a term that represents the amount that goes around from the receiving side 16 to the sending side 15 when there is no balance network 14, and the second term is a term that represents the amount that is removed by adding the balance network 14.

The first codec 40 converts the analog signal received from the 4-line side 15 of the 2-wire 4-wire conversion circuit 60 into a digital signal, sends it to the transmission line 42 of the PCM highway, and receives it from the reception line 41 of the PCM highway. The 4-wire side 16 of the 2-wire 4-wire conversion circuit 60 converts the digital signal into an analog signal.
send to

′! In the J2 codec 50, the digital output 45 is connected to the PCM highway reception line 41 (2, the digital output 48 is connected to the 2-wire 4-wire conversion characteristic simulation circuit 61,
The analog outputs 46 are respectively connected to analog human power 47. The analog output 46 and analog input 47 may be connected using an analog loose pack function if the codec has it.

The purpose of digitizing the signal using a codec is, firstly, to enable digital signal processing (secondly, to enable stable calculations with less element variation, aging, etc. in the 2-wire 4-wire conversion characteristic simulation circuit 61). Second, the second codec 50, the two-line four-line conversion characteristic simulation circuit 61, and the balance network selection circuit 6 are connected via the PCM highway.
By connecting codec 50.2 to multiple 2-wire/4-wire conversion circuits, This is to facilitate common use of the simulation circuit 611 and selection circuit 62. Furthermore, the codec 40.50 used here is for a PCM device that is normally commercially available, and may or may not include a PCM filter. Furthermore, since the filter characteristics of a codec are normally flat in the audio band in terms of amplitude characteristics, but have phase characteristics, it is necessary to cancel this phase characteristic. For this reason, the second codec 50 (
2. It is necessary that the first codec 40 has the same filter characteristics and operates at the same timing (2. Therefore, the signal of the PCM highway receiving line 41 (
2. The phase characteristics of the codec of the included partner station are made to be the same as the phase characteristics of the first codec 40, and the 2-wire 4
This enables simulation in the line conversion characteristic simulation circuit 61.

The 2-wire 4-wire conversion characteristic simulating circuit 61 receives the signal from the PCM highway reception line 41 and first determines that the impedance of the balance network 14 of the 2-wire 4-wire conversion circuit 60 is Zu (i=1.2.=, The wraparound removal signal component 2 generated by the impedance circuit 17+ of
Za+/(Zo+Zm+) is generated by simulating this signal component 2Zi+/(Zo+Z+1) as the signal (wrapping signal) 2 of the transmission line 42 of the PCM highway.
m + (Zo+Zh) (Z.+2.1), (i-1,2,
..., n)...(2) to calculate the signal 2ZL/(ZO+ZL) that goes around from the reception line 41 to the transmission line 42 in the case where the balance network 14 is not provided. That is, an operation is performed to cancel the wraparound removal characteristic.

Next (2, impedance is Z, 4 (j=1.2.・
..., n) when the impedance circuits 17j are sequentially connected, the wraparound removal signal component 22m1/ (Zo+ZnJ)
2+ "'r n), and the signal 2zb
2-wire 4-wire conversion circuit 60 when the balance network 14 is sequentially switched by subtracting from / (ZO+ZL)
Compute the wraparound signal characteristics of.

In this way, the selection circuit 62 uses the balance network 1 obtained by the 2-wire 4-wire conversion characteristic simulation circuit 61 (2).
The optimum impedance is determined by comparing the wrap-around signal characteristics of all 2-wire 4-wire conversion circuits 60 in which 4 are sequentially switched, (2 Takashi - Shokoi), - Arrival 1 Δmotoi, (Hisaka - Tsuyoshi n) Select a circuit and switch the balance network 14.

Such a 2-wire 4-wire conversion characteristic simulation circuit 61 and selection circuit 3
2, further codec 1.12 40.50 2 lines 4
By adding the line conversion circuit 60 (2), it is possible to automatically select and switch the optimal balance network 14 depending on the value of the impedance 20 connected to the 2-line side line 12, and this operation can be performed while making a call. This can be done without affecting the road at all.

Since it is possible to connect a plurality of bare circuits based on the combination of the 2-wire 4-wire conversion circuit and the first codec to the PCM highway (2. 2-wire 4-wire conversion characteristic simulation circuit 612 selection of the 2nd codec 50. By using the circuit 62 as a common circuit, it is easy to optimally switch the balance network of a plurality of 2-wire and 4-wire conversion circuits.

〔Effect of the invention〕

The present invention provides an adaptive two-wire four-way
This has the effect of realizing a line conversion circuit and minimizing the wrap-around signal from the 4-line side receiving line to the 4-line side transmitting line.

In addition, since calculations using digital signal processing are used,
Stable calculations with less element variation, aging, etc.
The optimal balance network can be automatically selected (two selection circuits), and the second codec, the simulation circuit, and the balance network selection circuit are connected via the PCM highway, so these circuits can be connected to multiple two A four-wire conversion circuit (it has the advantage of being easy to use in common for two wires).

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of an adaptive 2-wire/4-wire conversion circuit according to the present invention. 14: Switchable balanced wiring network, 15: 4-wire side transmission line of 2-wire 4-wire conversion circuit, 16: 2-wire 4
4th side reception line of the line conversion circuit, 60: 2-wire 4-wire conversion circuit, 61: Simulation circuit for 2-wire 4-wire phase change characteristics, 62; Selection circuit for balanced connection #ij<balanced network), 40: 1st codec/decoder (codec), 41: PC
Reception line of M highway, 42: Transmission line of PCM highway, 45: Digital input of second coder/decoder, 46: Analog output of second coder/decoder, 47; Analog input, 48: Digital output of second coder-decoder, 50: Second coder-decoder.

Claims (1)

[Claims] In a 2-wire 4-wire conversion circuit having a switchable balanced connection network, a 4-wire transmission line and a 4-wire reception line of the 2-wire 4-wire conversion circuit are respectively connected to a PCM highway. A first encoder/decoder is connected to the converter and converts an analog signal to a digital signal, and a digital input line is connected to the receiving line of the PCM highway, and the signal of its own analog output is connected to its own analog input. A second encoder/decoder operates at the same timing as the first encoder/decoder and has the same filter characteristics; A digital operation is performed to simulate and generate a wrap-around cancellation signal component generated by the appropriately connected balanced wiring network of the 2-wire 4-wire conversion circuit, and to add this simulation result to the signal from the transmission line of the PCM highway. All the impedances included in the balanced wiring network are calculated by performing a digital calculation to subtract the wrap-around removal signal component when all the impedance circuits included in the balanced wiring network are switched and connected from this calculation result. A 2-wire 4-wire conversion characteristic simulation circuit that outputs a wrap-around signal of the 2-wire 4-wire conversion circuit by the circuit is compared with all output signals of the simulation circuit, and the 2-wire 4-wire conversion circuit has an optimal wrap-around signal. an adaptive two-wire four-wire conversion circuit comprising: a selection circuit that switches the balanced connection network so as to have signal characteristics;