L64733C LSI Logic Corporation, L64733C Datasheet - Page 5

• Manufacturer Part Number: L64733C
• Description: Tuner And Satellite Receiver Chipset Data Sheet 2/01
• Manufacturer: LSI Logic Corporation

has 3-state operation (see the “Synthesizer Control Interface” section on
page 20).
The VCO requires an external resonant tank circuit, which includes
varactor diodes to vary the frequency of oscillation.
The VCO signal is fed to the Prescaler block before being passed
deferentially through the PSOUTp and PSOUTn pins to the L64734. 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
frequency before it is fed back to the L64733C through the PLLINp and
PLLINn pins. The crystal reference oscillator frequency is divided by
eight and 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
generates current that controls pins CP and FB, and an external
transistor to buffer the L64733C against the tuning voltage (28 V). The
current is passed through a discrete loop filter and is converted to a
tuning voltage that drives the external varactor diodes for the VCO tank
circuit. A frequency controlled loop is formed. Changing the frequency
divider ratios in the L64734 registers varies the VCO frequency. See
Figure 7, on page 23, for more details regarding the external circuitry for
the VCO, crystal oscillator, charge pump, tank circuitry, and
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 integrated into the two
devices.
L64733C/L64734 Tuner and Satellite Receiver Chipset
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