TDA8046 Datasheet, PDF (19/48 Pages) NXP Semiconductors – Multi-mode QAM demodulator

Philips Semiconductors
Multi-mode QAM demodulator
Product specification
TDA8046
7.1.7 OFFSET CONTROL
To compensate offsets in the I and Q branch, due to
spurious signals at the symbol frequency at the ADC input,
an offset compensation loop is included. This loop forces
the constellation to be symmetrically distributed over its
four quadrants. This function can be switched off by
I²C-bus bit OFFS.
7.1.8 LOOP AMPLIFIERS
Analog switches are integrated to discharge the loop filter
capacitors or for test purposes on application boards (a
reference voltage equal to the half of the positive supply
voltage V_DDA is available at the output of the amplifier
when the switches are closed). The I²C-bus bit ANAS
controls the three switches simultaneously. A schematic
diagram of the loop amplifier and analog switch is
illustrated in Fig.15.
For characteristics see Chapter 15.
handbook, halfpage
external
7.1.9 OUTPUT FORMATTER
The output formatter transforms the detected symbols into
bits in accordance with the selected mapping. The
TDA8046 has four possible mapping formats which can be
selected via the I²C-bus interface. The demapping
procedure and the corresponding bits are defined in
Fig.16. After demapping the bits are allocated to the
output. This output allocation corresponds to one of the
selected demapping schemes.
By using the I²C-bus, it is possible to obtain the following
output formats:
• 8 bits parallel
• semi-serial
• I and Q 8 bits multiplexed.
The implemented demapping formats and output bit
allocation are illustrated in Figs 17 to 30.
7.1.10 BOUNDARY SCAN
The TDA8046H offers the possibility of boundary scan
test. The IEEE Standard Test Access Port and Boundary
Scan Architecture allows board manufacturers to test
board interconnections by using the boundary scan
functions.
Complete information on boundary scan test is available in
“Application note AN96048”.
I²C-BUS
DAC
Vref
MGG174
Fig.15 Loop amplifier and analog switch.
1996 Nov 19
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