L64733 LSI Logic Corporation, L64733 Datasheet - Page 5

• Manufacturer Part Number: L64733
• Description: Tuner/receiver Chipset
• Manufacturer: LSI Logic Corporation

range from 925–2175 MHz, with a 0.5 MHz step size when using a
4-MHz crystal reference. The on-chip VCO tuning frequency is 543 MHz
to 1088 MHz. To tune channels from 925–1086 MHz, the L64734
disables the frequency doubler (X2 block) on the L64733. To tune
channels from 1086 MHz to 2175 MHz, the L64734 enables the
frequency doubler. The VCO requires an external resonant tank circuit,
which includes varactor diodes to vary the frequency of oscillation.
The VCO signal goes to the Prescaler block before it is passed to the
L64734 differentially through the PSOUTp and PSOUTn pins. The
L64734 MODp and MODn differential signals control the divider ratio for
the Prescaler block. The L64734 dynamically changes the divide ratio to
ensure that the tuning step size is not affected by the divider. The
L64734 contains programmable counters to further divide the signal in
frequency before the signal is fed back to the L64733 through the PLLINp
and PLLINn pins. The crystal reference oscillator frequency is divided by
eight, then fed to the phase detector. The phase detector generates a
current signal proportional to the difference in phase between PLLINp,
PLLINn, and the divided crystal frequency. A charge pump circuit (which
controls pins CP, FB) and an external transistor (to buffer the L64733
against the tuning voltage of 28 V) generate the current. The current is
filtered, fed through a discrete loop filter, and converted to a tuning
voltage that drives the external varactor diodes for the VCO tank circuit.
A complete frequency controlled loop is formed, and the VCO frequency
can be varied by changing the frequency divider ratios in the L64734
registers. See
Figure 7
on
page 22
for more details regarding the
external circuitry for the VCO, crystal oscillator, charge pump, tank
circuitry, and entire frequency-controlled loop.
The chipset provides maximum integration and flexibility for system
designers at a minimum cost. The number of external components
required to build a system is minimal because the synthesizer, variable
rate filters, and clock and carrier loops are all integrated into the two
devices.
L64733/L64734 Tuner and Satellite Receiver Chipset
5