SL1935D ETC, SL1935D Datasheet - Page 3

• Manufacturer Part Number: SL1935D
• Description: Single Chip Synthesized Zero IF Tuner
• Manufacturer: ETC

Functional Description
General
The SL1935 is a complete wideband direct conversion
tuner incorporating an on board frequency synthesiser
and LNA/AGC, optimised for application in digital satellite
receiver systems. The device offers a highly integrated
solution to a satellite tuner function, incorporating an I
bus interface controller, a low phase noise PLL frequency
synthesiser and all tuner analogue functionality. The
analogue blocks include the reference oscillator,
consisting of two independent oscillators, a phase splitter,
RF preamplifier with AGC facility, channel mixers and
baseband amplifiers incorporating two selectable
baseband paths, allowing for two externally definable
bandwidths. In this application two varactor tuned tanks,
a reference crystal and baseband filtering components
are required to complete the tuner system.
A buffered crystal frequency output is available to clock
the QPSK demodulator and powers up in the active
state.
the local oscillator, the baseband path selection, the
buffered reference frequency output and an external
switching port.
Figure 2 shows the device block diagram and pin
allocations are shown in Figure 1.
The I
2
C bus interface controls the frequency synthesiser,
Table 1. Quick Reference Data
Note:
Operating range
Input dynamic range
VSWR with input match
Input NF
IPIP3 @ -20dBm operating sensitivity
IPIP2@ -20dBm operating sensitivity
IPP1dB@ -20dBm operating sensitivity
Baseband output limit voltage
Gain match up to 22MHz
Phase match up to 22MHz
Gain flatness up to 30MHz
Local oscillator phase noise
In band LO reradiation from RF input
LO second harmonic interference level at input level of
-20dBm per carrier
LNA second harmonic interference level at input level
of -25dBm per carrier
PLL maximum comparison frequency
PLL phase noise at phase detector
@ -70dBm operating sensitivity
@ -60dBm operating sensitivity
SSB at 10kHz offset
`
`
6dB interstage filter loss assumed in external base band paths.
dBm assumes 75Ω characteristic impedance.
Characteristic
2
C
Quadrature Downconverter Section
In normal application the tuner IF frequency of typically
950 to 2150MHz is fed direct to the SL1935 RF input
through an appropriate impedance match (Fig.16) and
LNB switching. The input stage is optimised for both NF
and signal handling.
The signal handling of the front end is designed to offer
immunity to input composite overload without the
requirement of a tracking filter. RF input impedance is
shown in Fig.3.
The RF input amplifier feeds an AGC stage and provides
system gain control. The system AGC gain range will
guarantee an operating dynamic range of -70 to -20dBm.
The AGC is controlled by the AGC sender and is optimised
for S/N and S/I performance across the full dynamic
range. Details of the AGC characteristics, variations in
IIP3, IIP2, P1dB and NF are illustrated in Figs.4, 5, 6, 7,
and 8 respectively.
The required I and Q local oscillator frequencies for
quadrature downconversion are generated by the on-
board reference oscillators designated ‘VCOS’ and
‘VCOV’. VCOS operates nominally from 1900 to 3000MHz
and is then divided by two to provide 950 to 1500MHz.
VCOV operates nominally from 1400 to 2200MHz. Only
the oscillator selected via bit VS in the I
transmission is powered.
950 to 2150
-75 to -15
Value
<-70
-152
+20
2.0
0.2
0.7
-80
-55
-35
+5
10
10
15
-5
1
4
dBc/Hz
dBc/Hz
Units
MHz
dBm
dBm
dBm
dBm
dBm
MHz
deg
dBc
dBc
dB
dB
dB
dB
dB
V
SL1935
2
C data
3