JP3039073B2 - Line terminal equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a line terminal device connected to a telephone line for automatically adjusting a transmission level of an analog signal.

[0002]

2. Description of the Related Art As shown in FIG. 2, a conventional line terminal apparatus 1 includes a signal transmitting section 2 for outputting a push button signal and a fine adjusting section 3 for finely adjusting the level of an input signal to a signal amplifying section 4 manually. And a signal amplifying unit 4 for amplifying the transmission signal with a fixed gain, and a network control unit 5 which is an interface circuit with the telephone line 6.

Next, a state when the line terminal device 1 is outputting a transmission signal will be described. In the line terminal device 1, a push button signal is output from the signal transmission unit 2, the transmission signal is finely adjusted in the transmission level by the fine adjustment unit 3, and is input to the signal amplification unit 4. Further, the transmission signal is
The signal is amplified by a fixed gain in the signal amplifier 4 and input to the network controller 5. Since the network control unit 5 closes the telephone line 6 when transmitting a signal, a transmission signal is output to the telephone line 6.

When the selection signal to be transmitted when connecting the line terminal device 1 to a communication partner is a push button signal, the transmission level must be adjusted within a range defined by the technical standards of the line terminal device. However, the signal level transmitted from the line terminal device 1 to the telephone line 6 varies. There are mainly two causes of the variation in the level of the transmission signal, one of which is due to the variation of the transmission level of the signal transmission unit 2, and the other is the impedance mismatch between the line terminal device 1 and the telephone line 6. It is caused by. The transmission signal level variation in the signal transmission unit 2 is caused by the integrated circuit used, and varies by about ± 1 dB even when a stable power supply voltage is used.

Next, a description will be given of a transmission level variation caused by impedance mismatch between the line terminal device 1 and the telephone line 6 with reference to FIG. FIG. 3 shows an equivalent circuit when the line terminal device 1 is transmitting a signal. The impedance of the telephone line 6 is Z1, the impedance of the line terminal device 1 is Z2, and the transmission signal in the line terminal device 1 is equivalent. Are represented as signal sources SG. The level of the signal transmitted to the telephone line 6 is determined by the division ratio of the impedance, and the transmission level at the connection point is lower than the level at the signal source by 20 log10Z1 / (Z1 + Z2). When the impedance Z1 of the telephone line 6 is 600Ω and the impedance Z2 of the line terminal device 1 is 600Ω, the level decrease is 6 dB. However, the impedance Z1 of the telephone line 6 differs for each line, and 3
It varies about 0%. Now, assuming that the impedance Z1 of the telephone line 6 is 600Ω-30% = 420Ω,
The level drop from the signal source SG to the connection point is 7.7 dB
Becomes In other words, even if the line terminal device 1 is designed to have a resistance of 600Ω, the transmission level has a variation of 1.7 dB due to the impedance variation of the telephone line 6.
To some extent.

In order to reduce the above-mentioned variation, a fine adjustment unit 3 is provided in the line terminal device 1 and is connected to a pseudo telephone line at the time of shipment and adjusted manually. In addition, variations caused by telephone lines were generally ignored or construction staff made adjustments on site.

[0007]

However, the above-mentioned conventional configuration has the following problems. 1) At the time of shipment, the transmission level of the line terminal device 1 must be adjusted.
2) Line terminal 1
When correcting the transmission level due to the variation in impedance of the telephone line to which the telephone line is connected, the person in charge of construction must go to the site and make adjustments.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and eliminates the need for manual adjustment of the transmission level of a line terminal device, and further enables automatic adjustment of the transmission level for each connected telephone line. The purpose is to provide.

[0009]

In order to achieve the above object, a line terminal device according to the present invention has a level measuring section for measuring an absolute transmission level of a signal transmitted to a telephone line, and an actual measured value of the level measuring section. A transmission level correction unit for detecting a difference between the transmission level and the set absolute value and outputting a correction signal, and a transmission level adjustment unit for receiving the correction signal and adjusting the transmission absolute level are provided.

[0010]

According to the present invention, the level measuring section measures the absolute level of the signal transmitted to the telephone line, and the transmission level correcting section sets the measured value and the transmission level from the level measuring section.
Upon detecting the difference from the absolute value, a correction signal is output, and in response to the correction signal, the transmission level adjuster corrects the transmission absolute level of the signal. Therefore, the absolute signal level sent to the telephone line is automatically adjusted to the set absolute value .

[0011]

FIG. 1 shows an embodiment of a line terminal device 7 according to the present invention.
This will be described with reference to FIG. In FIG. 1, components having the same numbers as those in FIG. 2 indicate the same components as those in the conventional example. The level measuring section 8 in FIG. 1 measures the transmission level of the push button signal transmitted to the telephone line 6, and can be constituted by, for example, a peak hold circuit. Reference numeral 9 denotes a transmission level correction unit which compares an actual measurement value of the transmission level from the level measurement unit 8 with a set value of the transmission level, detects a difference, and outputs a difference from the set value as a correction signal. Reference numeral 10 denotes a transmission level adjustment unit which automatically adjusts the amplification degree of the transmission signal according to the correction signal from the transmission level correction unit 9.

The operation of the above configuration will be described.
When a transmission signal is transmitted from the signal transmission unit 2, the transmission signal is amplified by the transmission level adjustment unit 10 and transmitted to the telephone line 6 via the network control unit 5. At this time, the network control unit 5
The telephone line 6 is closed to output a signal to the telephone line 6. The transmission level of the signal transmitted to the telephone line 6 is actually measured by the level measurement unit 8, and the measured value is output to the transmission level correction unit 9. Next, the transmission level correction unit 9
Then, the preset transmission level setting value is compared with the actual measurement value input from the level measurement unit 8, and the difference is detected. The detected difference between the actually measured value and the set value is output to the transmission level adjusting unit 10 as a correction signal. The transmission level adjusting unit 10 receiving the correction signal corrects the amplification of the transmission signal and automatically adjusts the transmission level.

As described above, according to the line terminal device 7 of the present invention, the level measuring section 8 actually measures the level of the signal transmitted to the telephone line 6, and the transmission level correcting section 9 receives the signal from the level measuring section 8. Since the measured value is compared with a preset value, the difference is detected and output as a correction signal to the transmission level adjustment unit 10, and the transmission level adjustment unit 10 corrects the amplification of the transmission signal according to the correction signal. Thus, the adjustment of the transmission level can be automatically adjusted. Further, since the transmission level can be automatically adjusted while the line terminal device 7 is connected to the telephone line 6, it is possible to eliminate variations in the transmission level caused by impedance mismatch of the telephone line.

According to the present invention, the present invention is also applicable to automatic adjustment of the transmission level of a modem of a system using a data communication terminal.

[0015]

As described above, in the line terminal device of the present invention, the level measuring section measures the absolute level of the signal transmitted to the telephone line, and the transmission level correcting section inputs the signal from the level measuring section. The measured actual value is compared with a preset absolute value, and the difference is detected and output as a correction signal to the transmission level adjustment unit. The transmission level adjustment unit corrects the amplification of the transmission signal according to the correction signal. This eliminates the need to manually adjust the transmission level as in the past, and the transmission level can be automatically adjusted while the line terminal device is connected to the telephone line, so that the transmission absolute level caused by the impedance mismatch of the telephone line. Can be eliminated.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a line terminal device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a conventional line terminal device.

FIG. 3 is a diagram showing an equivalent circuit of a line terminal device and a telephone line;

[Explanation of symbols]

 8 Level measurement unit 9 Transmission level correction unit 10 Transmission level adjustment unit

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Masaaki Sakata 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-2-162927 (JP, A) JP-A-61- 256854 (JP, A) JP-A-61-78254 (JP, A) JP-A-60-235564 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04M 1/00 H04M 1 / 76 H04M 11/00 302

Claims (1)

(57) [Claims] A level measuring section for measuring an absolute transmission level of a signal transmitted to a telephone line; and detecting a difference between an actually measured value of the level measuring section and a set absolute value of the transmission level. A line terminal device comprising: a transmission level correction unit that outputs a correction signal; and a transmission level adjustment unit that receives the correction signal and adjusts the transmission absolute level.