STB5610 Datasheet, PDF (4/11 Pages) STMicroelectronics – GPS RF FRONT-END IC

STB5610
BLOCK DIAGRAM (GPS L1)
SAW Filter
LC Filter
LC Filter
Passive
Antenna
Two gain
LNA
RF Amp.
Gain
Select.
1.57 GHz
16.368 MHz
Quartz
PLL
Mixer
1ST Lim. amp. 2ND Lim. amp.
1.55 GHz
~ ^VCO
20 MHz
20 MHz
D Latch Output buffer ^{Data @ 4 MHz}
CMOS levels
D
Q
CK
4 MHz
CLK @ 16MHz
CMOS levels
16 MHz
Loop Freq.
Filter select
ExternalTank
CE
ASout
CE2
FUNCTIONAL DESCRIPTION
LNA section
The RF input signal is amplified by two gain levels
LNA. Using gain control pin the LNA gain is set to
19 dB to support passive antenna or 10 dB to sup-
port active antenna. The LNA output signal is fil-
tered by 1575.42 MHz SAW filter.
VCO and PLL
Using external tank the VCO is able to provide
very low phase noise signal. Through the freq. se-
lector pin the VCO signal is set at 1554.96 MHz
and at 1571.328 MHz. The on-chip reference os-
cillator uses a low cost 16.368 MHz crystal.
RF Amplifier plus mixer section
The 1575.42 MHz input signal, amplified by RF
amp., is mixed with the VCO signal to generate a
differential 20.46MHz IF signal
IF section
Two LC filters at mixer output and at first limiting
output are used to suppress undesirable signals
and mixer products. The second stage limiting
amplifier is connected to a D-Type latch clocked
by 16.368MHz crystal oscillator signal. The effect
of sampling the 20.46MHz signal at 16.368MHz is
to create sub-sampling alias at 4.092MHz. This is
fed to the output level converter.
Output section
The output buffers perform level translation from
the internal ECL levels to CMOS output levels re-
ferred to ground. The Data signal changes during
the clock signal negative edge.
Antenna sensor circuitry
Integrated sensor circuitry is able to evaluate the
antenna current consumption; the Asout pin out-
put provides this info externally. Using external
sensing resistor of 10 Ohm if the antenna current
consumption is inside the range 10mA…40mA
(active antennas typical current consumption) the
Asout output logic level is High, if the antenna cur-
rent consumption is outside the above reported
range (passive antenna or problem on antenna
connection) the Asout output logic level is low.
Chip enable
Using the CE pin it is possible to switch off all the
chip ( neither data nor clock available).
Using CE2 pin it is possible to disable the analog
portion of the chip (no data available) maintaining
the digital portion active (Clock available) optimiz-
ing the chip current consumption.
Power supplies
The STB5610, has been designed to support
from 2.7 V to 3.6 V supply voltage.
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