SL1711
Quadrature Downconverter
Preliminary Information
Supersedes November 1996 version, DS4032 - 1.6
DS4032 - 4.0 October 1997
The SL1711 is a quadrature downconverter, intended
primarily for application in professional and consumer digital
satellite tuners.
The device contains all elements necessary, with the
exception of external local oscillator tank to form a complete
system operating at standard satellite receiver intermediate
frequencies. It is intended for use with external carrier
recovery.
The device includes a low noise RF input amplifier, a
reference VCO with prescaler output buffer and In-phase and
Quadrature mixers with baseband buffer amplifiers containing
AGC gain control.
The SL1711 is optimised to drive a dual ADC converter
such as the VP216.
The SL1711 utilises a power MP package, whereas the
SL1711B variant uses a standard MP16 plastic package and
features a revised operating temperature.
AGC
IOUT
VEEA
IFINB
IFIN
IVCCA
QOUT
VEEC
1
16
VCCB
VCODIS
VCO
B
VCO
A
VEEB
PSCAL
PSCALB
VCCC
SL1711
MH16
FEATURES
SL1711B
s
Single chip system for wideband quadrature
downconversion
s
Compatible with all standard high IF frequencies
s
Excellent gain and phase match up to 30MHz
baseband
s
High output referred linearity for low distortion and
multi channel application
s
Simple low component application
s
Fully balanced low radiation design with fully
integrated quadrature generation
s
High operating input sensitivity
s
On-board AGC facility
s
On chip oscillator for varactor tuning or SAW
resonator operation
s
ESD protection (Normal ESD handling procedures
should be observed)
APPLICATIONS
s
Satellite receiver systems
s
Data communications systems
s
Cable systems
AGC
IOUT
VEEA
IFINB
IFIN
IVCCA
QOUT
VEEC
1
16
VCCB
VCODIS
VCO
B
VCO
A
VEEB
PSCAL
PSCALB
VCCC
MP16
Fig. 1 Pin allocation
ORDERING INFORMATION
SL1711/KG/MH1P (Sticks)
SL1711/KG/MH1Q (Tape and Reel)
SL1711B/KG/MP1S (Sticks)
SL1711B/KG/MP1T (Tape and Reel)
SL1711
FUNCTIONAL DESCRIPTION
The SL1711 is a wideband quadrature downconverter,
optimised for application in both professional and consumer
digital satellite receiver systems and requiring a minimum
external component count. It contains all the elements
required for construction of a quadrature demodulator, with
the exception of tank circuit for the local oscillator.
A block diagram is shown in Fig. 2.
The SL1711 oscillator can be used with either a varator
tuned tank circuit or with a SAW resonator. Both
configurations are described in the Application Notes section
of this Data Sheet.
A typical digital satellite tuner application from tuner input
to data transport stream is shown in Fig. 13
In normal application the second satellite IF frequency of
typically 402.75 or 479.5 MHz is fed from the tuner SAW filter
to the RF preamplifier, which is optimised for impedance
match and signal handling. The amplifier output signal is then
split into two balanced channels to drive the In-phase and
Quadrature mixers. The typical RF input impedance is shown
in Fig. 3
In-phase and Quadrature LO signals for the mixers are
derived from the on board local oscillator, which uses an
external varactor tuned resonant network and is optimised for
low phase noise. The VCO also drives an on board divide by
32 prescaler whose outputs can be used for driving an external
PLL control loop for the VCO, where the PLL loop is contained
within the QPSK demodulator, for example the VP305. For
optimum performance in the varactor tuned application the
VCO should be fully symmetric. The VCO has a disable facility
by grounding pin 15, VCODIS; in normal applications this pin
is pulled to Vcc via a 4K7 resistor.
The mixer outputs are fed to balanced baseband AGC
amplifier stages, which provide for a minimum of 16 dB of AGC
control. The typical AGC characteristic is shown in Fig. 4.
These amplifiers then feed a low output impedance true
differential to single-ended converter output stage. In normal
application the output can be either directly AC coupled to the
ADC converter such as the VP216, which will generally have
a high input impedance, or to drive an anti alias filter. In this
later case the maximum load presented to the SL1711 must
not exceed a parallel combination of 1KΩ and 20pF. The
typical baseband output impedance is contained in Fig. 5.
It is recommended that the device is operated with an
output amplitude of 760mV under lock conditions.
Under transient conditions the output should not exceed
the clipping voltage.
Input and output interface circuitry is contained in Fig. 6.
The typical key performance figures at 480 MHz IF, 5V Vcc,
1 kΩ load and 25 deg C ambient are contained in table headed
'QUICK REFERENCE DATA'. With SAWR oscillator
application the gain and phase match performance will
typically exceed these numbers.
3
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