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TS635D датащи(PDF) 6 Page - STMicroelectronics |
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TS635D датащи(HTML) 6 Page - STMicroelectronics |
6 / 10 page TS635 6/10 THE TS635 AS LINE DRIVER ON ADSL LINE INTERFACE. SINGLE SUPPLY IMPLEMENTATION WITH PASSIVE OR ACTIVE IMPEDANCE MATCHING. THE LINE INTERFACE - ADSL Remote Terminal (RT): The Figure1 shows a typical analog line interface used for ADSL service. On this note, the accent will be made on the emission path. The TS635 is used as a dual line driver for the upstream 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 TS635 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 TS635. 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 this case the load impedance is 25 Ω for each driv- er. For the ADSL upstream path necessary to avoid any distortion. In this simple non-inverting amplifi- cation configuration, it will be easy to implement a Sallen-Key lowpass filter by using the TS635. For ADSL over POTS, a maximum frequency of 135kHz is reached. For ADSL over ISDN, the maximum frequency will be 276kHz. INCREASING THE LINE LEVEL BY USING AN ACTIVE IMPEDANCE MATCHING With passive matching, the output signal ampli- tude of the driver must be twice the amplitude on the load. To go beyond this limitation an active maching impedance can be used. With this tech- nique it is possible to keep good impedance matching with an amplitude on the load higher than the half of the ouput driver amplitude. This concept is shown in Figure 3 for a differential line. Figure 1 : Typical ADSL Line Interface Figure 2 : TS635 as a differential line driver with a +12V single supply impedance matching twisted-pair telephone line HYBRID CIRCUIT LP filter TS635 Line Driver reception (analog) emission (analog) high output current upstream downstream ST70135 ST70134 TS636 Receiver VGA ASCOT ADSL Chip-Set 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 Figure 3 : TS635 as a differential line driver with an active impedance matching R4 R2 Vi Vi Vo Vo RL 100 Ω 1:n Hybrid & Transformer GND Vcc+ 10 µ 100n 100n 100n 1k 1k Rs1 Rs2 10n 1 µ R3 R5 Vo° Vo° GND Vcc+ Vcc+ + _ + _ GND 1/2 R1 1/2 R1 Vcc/2 |
Аналогичный номер детали - TS635D |
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Аналогичное описание - TS635D |
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