8-311
RF2498
Rev A4 070308
ISET Pins
ISET1 sets the internal reference voltage for the bias control circuits to all functional blocks. An external resistor of 5.1k
Ω
to ground is required. We do not recommend adjusting this resistor value. This resistor is pulled out to allow for a higher
precision off chip value and not as a significant tuning adjustment.
ISET2 sets the DC current through the LNAs in all bands when IPSET is high. Higher resistance to ground results in
lower current through the LNA. Increasing the LNA current will improve the IIP3 of the LNA and slightly increase gain in
all modes. NF typically will get worse as you increase current. Increasing the LNA current in one mode, i.e. Cellular, will
also increase the LNA current for the high IPSET state for PCS and the GPS LNAs as well.
ISET3 sets the DC current through the mixer and mixer preamplifier for all bands. Higher resistance to ground results in
lower current. Lower current will improve mixer NF but will degrade IIP3. Mixer and the mixer preamp gain is not signifi-
cantly changed with current.
Pin
Function
Type Description
Interface Schematic
28
GPS MIX IN
AI
GPS mixer RF single-end input.
29
VCC1
P
DC supply for internal reference, logic control, cellular mixer
preamp, and GPS mixer preamp (PCS mixer preamp has its’
own DC supply, PCS_RFA_VCC). External bypass capacitor
between 1nF and 47nF required.
30
ISET1
AO
Resistor for internal voltage reference setting. Recommended
value 5.1k
Ω.
31
ISET2
AO
Resistor to ground sets the LNA current in boost mode (all
three LNAs). Higher resistance results in lower current.
32
ISET3
AO
Resistor to ground sets preamp and mixer currents in all
bands. Higher resistance results in lower currents.
Pkg
Base
GND
P
Ground connection. The backside of the package should be
soldered to a top side ground pad which is connected to the
ground plane with multiple vias.
Legend:
DI=Digital Input from Baseband Chip
AI=Analog Input
AO=Analog Output
P=VCC or GND
GPS MIX IN
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