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TS612 Scheda tecnica(PDF) 7 Page - STMicroelectronics |
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TS612 Scheda tecnica(HTML) 7 Page - STMicroelectronics |
7 / 10 page TS612 7/10 ADSL CONCEPT Asymmetric Digital Subscriber Line (ADSL), is a new modem technology, which converts the exist- ing twisted-pair telephone lines into access paths for multimedia and high speed data communica- tions. ADSL transmits more than 8 Mbps to a subscriber, and can reach 1Mbps from the subscriber to the central office. ADSL can literally transform the ac- tual public information network by bringing mov- ies, television, video catalogs, remote CD-ROMs, LANs, and the Internet into homes. An ADSL modem is connected to a twisted-pair telephone line, creating three information chan- nels: a high speed downstream channel (up to 1.1MHz) depending on the implementation of the ADSL architecture, a medium speed upstream channel (up to 130kHz) and a POTS (Plain Old Telephone Service), split off from the modem by filters. THE LINE INTERFACE - ADSL Remote Terminal (RT): The Figure1 shows a typical analog line interface used for ADSL. The upstream and downstream signals are separated from the telephone line by using an hybrid circuit and a line transformer. On this note, the accent will be made on the emission path. The TS612 is used as a dual line driver for the up- stream signal. For the remote terminal it is required to create an ADSL modem easy to plug in a PC. In such an ap- plication, the driver should be implemented with a +12 volts single power supply. This +12V supply is available on PCI connector of purchase. The figure 2 shows a single +12V supply circuit that uses the TS612 as a remote terminal trans- mitter in differential mode. The driver is biased with a mid supply (nominaly +6V), in order to maintain the DC component of the signal at +6V. This allows the maximum dy- namic range between 0 and +12 V. Several op- tions are possible to provide this bias supply (such as a virtual ground using an operational amplifier), such as a two-resistance divider which is the cheapest solution. A high resistance value is re- quired to limit the current consumption. On the other hand, the current must be high enough to bias the inverting input of the TS612. If we consid- er this bias current (5 µA) as the 1% of the current through the resistance divider (500 µA) to keep a stable mid supply, two 47k Ω resistances can be used. The input provides two high pass filters with a break frequency of about 1.6kHz which is neces- sary to remove the DC component of the input sig- nal. To avoid DC current flowing in the primary of the transformer, an output capacitor is used. The 1 µF capacitance provides a path for low fre- quencies, the 10nF capacitance provides a path for high end of the spectrum. In differential mode the TS612 is able to deliver a typical amplitude signal of 18V peak to peak. The dynamic line impedance is 100 Ω. The typical value of the amplitude signal required on the line is up to 12.4V peak to peak. By using a 1:2 trans- former ratio the reflected impedance back to the primary will be a quarter (25 Ω) and therefore the amplitude of the signal required with this imped- ance will be the half (6.2 V peak to peak). Assum- ing the 25 Ω series resistance (12.5Ω for both out- puts) necessary for impedance matching, the out- put signal amplitude required is 12.4 V peak to peak. This value is acceptable for the TS612. In this case the load impedance is 25 Ω for each driv- er. Figure 1 : Typical ADSL Line Interface impedance matching twisted-pair telephone line HYBRID CIRCUIT digital treatment LP filter TS612ID Line Driver reception (analog) emission (analog) digital to analog analog to digital high output current reception circuits upstream downstream Figure 2 : TS612 as a differential line driver with a +12V single supply 1/2 R1 R3 R2 Vi Vi Vo Vo GND +12V 25 Ω 100Ω 1:2 Hybrid & Transformer GND +12V 47k 47k 10µ 100n 100n 100n 1k 1k 12.5 12.5 10n 1µ +12V + _ + _ GND 1/2 R1 Vcc/2 |
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Descrizione simile - TS612 |
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