RS8973 Mindspeed Technologies, RS8973 Datasheet - Page 27

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

RS8973
Single-Chip SDSL/HDSL Transceiver
2.1.2 Variable Gain Digital-to-Analog Converter
N8973DSD
to be + 3 and – 3, as shown in
Table 2-3. Two-Level Bit-to-Symbol Conversions
(LFSR). The feedback points are programmable for central office and remote
terminal applications using the htur_lfsr bit of the Transmitter Modes Register.
The LFSR polynomials for local (HTU-C/LTU) and remote (HTU-R/NTU) unit
operations are:
four-level mode is specified. In two-level scrambled-1s mode, the LFSR is
clocked once per symbol; in four-level mode, the LFSR is clocked twice per
symbol.
transmitter using the transmitter_off control bit.
templates. When in the isolated pulse mode, the output consists of a single pulse
surrounded by 0s.
NOTE:
A four-level DAC is integrated into the RS8973 to convert the output of the
symbol source to analog form. The normalized values of these four analog levels
are + 3, + 1, – 1 and – 3. Each represents a symbol, or quat.
be adjusted. The Transmitter Gain Register [tx_gain; 0x29] sets the level.
changes in transmitter levels. The Transmitter Calibration Register [tx_calibrate;
0x28] contains a read-only value which nulls this variation. The value in this
register is determined for each RS8973 device during production testing. Upon
initialization, the Transmitter Gain Register should be loaded based on the
Transmitter Calibration Register.
hybrid or attenuative lightening protection), the transmitter gain must be adjusted
to include these effects. The range of adjustment of the transmitter gain is from
– 1.60 dB to 1.40 dB.
In two-level mode, the magnitude bit is forced to a 0. This forces the symbols
The scrambler is essentially a 23-bit-long Linear Feedback Shift Register
The scrambler operates differently depending on whether a two-level or
The Transmitter Modes Register can also be used to zero the output of the
The RS8973 can generate isolated pulses to support the testing of pulse
To provide precise adjustment of transmitted power, the level of the DAC can
During the manufacturing of the RS8973, process variations can cause
If there are other sources of transmit power variation (e.g., a nonstandard
Zero is not a valid 2B1Q level and occurs only in this special mode or
when the transmitter is off. The repetition rate of the pulses is controlled by
the meter timer. Any of the four 2B1Q levels can be chosen through the
Transmitter Modes Register’s isolated_pulse[1,0] control bits.
First Input Bit
(Sign)
0
1
Preliminary Information
Conexant
remote
local
Table
Second Input Bit
(Magnitude)
Don’t Care
Don’t Care
2-3.
x
x
–
–
23
23
x
x
5 –
–
18
1
1
2.0 Functional Description
Output Symbol
2.1 Transmit Section
– 3
+ 3
2-3