RS8973 Mindspeed Technologies, RS8973 Datasheet - Page 84

• Manufacturer Part Number: RS8973
• Description: Single-chip Sdsl/hdsl Transceiver
• Manufacturer: Mindspeed Technologies

4.0 Interconnection Information
4.1 Transmission Line Interface
4.1.2 Impedance-Matching Resistors
4.1.3 Line Transformer
4-4
output impedance of the line interface more closely matches the impedance of the
transmission line and load. This maximizes the power transferred to the receiver
on the other end of the line. The load is assumed to be 135 .
be aliased back into the passband as noise. These filters can be made of all
passive components. The cutoff frequency (fc) should be as low as possible to
achieve maximum attenuation of aliasing frequencies without filtering out the
desired signal. Because the highest frequency in the desired signal is equal to
one-half of the symbol rate, there should be no more than 1 dB of attenuation at
this frequency.
antialiasing filters. Note that the other components in the hybrid affect the
frequency response of the antialiasing filters.
Table 4-2. Antialias Filter Component Values
creating a high-pass filter. The winding ratio of the transformer must be 2:1 (line
side:circuit side) to generate the appropriate voltage level on the line. The primary
inductance (L) of the transformer (line side) is a very critical parameter. If L is
too high, the cutoff frequency of the filter will be too low and the RS8973 Echo
Canceller and Equalizer will not be able to cancel out the low frequency
components of the echo and inter-symbol interference. If L is too low, part of the
information in the signal will be filtered out, thereby decreasing the SNR ratio. In
addition, the line transformer must meet other requirements to maximize system
performance. See
transformer, depending upon the application in which it is to be used. These
requirements have been submitted to several transformer vendors to expedite the
development process. A list of these transformer vendors along with their
associated transformer part numbers is listed in
may need to be modified to match the needs of a specific system. For example, if
remote line powering is being used, the transformer must operate under a fairly
high DC current condition. The exact current specification will depend on several
factors including the voltage provided over the line, and the power consumption at
the remote end. The application-specific requirements should be reviewed to
ensure the transformer is not under- or over-specified. An over-specified
transformer may unnecessarily increase cost, while an under-specified
transformer may not perform adequately under all system conditions.
Impedance-matching resistors are placed in the transmit path so that the
Anti-aliasing filters are built on-chip to filter out high frequencies that would
The line transformer provides DC isolation from the transmission line by
Table 4-4
Antialias Filter Components
lists additional requirements that may be needed to specify the line
Preliminary Information
Table 4-2
R9, R10
R7, R8
Table 4-3
C5
C6
Conexant
lists the component values recommended for the
for line transformer requirements.
Single-Chip SDSL/HDSL Transceiver
Table
4-5. These requirements
Value
56 pF
1 k
56pF
1 k
N8973DSD
RS8973