TDA8046 Datasheet, PDF (15/48 Pages) NXP Semiconductors – Multi-mode QAM demodulator

Philips Semiconductors
Multi-mode QAM demodulator
Product specification
TDA8046
7.1.5 CLOCK RECOVERY
The clock recovery function uses the unequalized I and Q
signals, i.e. the half Nyquist filter outputs (see Fig.4).
The clock recovery section generates a control value each
symbol period. As this algorithm is based on the energy
maximization, both main and mid symbols are required at
the input. Consequently, the input data rate is twice the
symbol rate. The schematic diagram of this detector is
illustrated in Fig.11.
The clock generator generates the required internal clocks
from the VCXO clock signal at 4 × r_s. The input stage
amplifier of this generator enables the designer to supply
a low amplitude oscillator signal to the TDA8046. The DAC
output current range (I_CLK) can be varied via the I²C-bus.
The sign of the output current can also be inverted to
adjust for the correct sign of the VCXO slope.
For characteristics see Chapter 13.
handbook, full pagewidth
external
I
DAC
CLOCK
RECOVERY
ICLK
DETECTOR
rs Iref3
Vref
Q
to
VCXO
4rs
2rs
2
rs
4
from
VCXO
MGG172
Fig.11 Schematic diagram of the clock recovery.
1996 Nov 19
15