Rockwell SoniCrafter BT8960 - Manual (Page 28)

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2.0 Functional Description
2.1 Transmit Section
Bt8960
Single-Chip 2B1Q Transceiver
N8960DSB
2.1.2 Variable Gain Digital-to-Analog Converter
A four-level Digital-to-Analog Converter (DAC) is integrated into the Bt8960 to
accurately convert the output of the symbol source to analog form. The normal-
ized values of these four analog levels are: +3, +1, –1 and –3. Each represents a
symbol or quat.
To provide precise adjustment of the transmitted power, the level of the DAC
may be adjusted. The Transmitter Gain Register [tx_gain; 0x29] sets the level.
During the manufacturing of the Bt8960, one source of variation in the trans-
mitter levels is process variations. The Transmitter Calibration Register
[tx_calibrate; 0x28] contains a read-only value which nulls this variation. The
value of this register is determined for each Bt8960 device during production test-
ing. Upon initialization, the Transmitter Gain Register should be loaded based on
the Transmitter Calibration Register.
If there are other sources of transmit power variation (e.g., a nonstandard
hybrid or attenuative lightening protection), the transmitter gain must be adjusted
to include these affects.
2.1.3 Pulse-Shaping Filter
The pulse-shaping filter filters the quats output from the variable-gain DAC. This
filter, when combined with other filtering in the signal path, produces a transmit-
ted signal on the line that meets the power spectral density, transmitted power,
and pulse-shaping requirements, as specified in the Electrical Specifications sec-
tion of this datasheet.
2.1.4 Line Driver
The line driver buffers the output of the pulse-shaping filter to drive diverse loads.
The output of the line driver is differential.