TDA8046 Datasheet, PDF (8/48 Pages) NXP Semiconductors – Multi-mode QAM demodulator

Philips Semiconductors
Multi-mode QAM demodulator
Product specification
TDA8046
7 FUNCTIONAL DESCRIPTION
Figure 3 shows the application of the TDA8046
multi-mode QAM demodulator. The frequency of the IF
signal (IF_QAM) is down converted to a frequency that
equals the symbol rate (r_s) by a mixer which is driven from
a local oscillator with a frequency of f_CAR = f_IF + r_s.
After low pass filtering this baseband signal is applied to an
external 8 or 9-bit ADC.
For 256-QAM, a 9-bit ADC is preferred, for the other
modes an 8-bit ADC is sufficient.
The multi-mode QAM demodulator has digital detectors for
AGC, carrier recovery and clock recovery. The on-chip
DACs translate the detector values to analog control
currents which are then integrated by a loop filter.
To perform this loop filtering, an operational amplifier is
integrated after each DAC.
The carrier recovery consists of a two-loop system.
The outer loop is shown in Fig.3, and controls both phase
and frequency at a low speed. The inner loop controls the
carrier phase at a high speed (wide loop bandwidth).
The AGC also consists of two loops; the outer loop is the
coarse AGC and one inner loop is the fine AGC.
The recovered symbols are converted into bits according
to a demapping scheme and represented at the output in
an 8-bit parallel output format. The QAM demodulator can
be initialized and monitored by the I²C-bus interface.
handbook, full pagewidth
RF
signal
TUNER
SAW ^IFQAM
LPF
fCAR = fIF + rs
8 or 9 bits
ADC
fclk
clock recovery
carrier recovery
AGC
TDA8046
DO7 to DO0
CLKOUT
CLKSDV
I²C-BUS
MGG167
Fig.3 Application with multi-mode QAM demodulator.
1996 Nov 19
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