5-125
RF2705
Rev A4 041026
Pin
Function
Description
Interface Schematic
4LO LB P
Low band local oscillator input (900MHz).
In “wideband FLOx2” and “high band FLOx2” modes the signal
(LOLBP-LOLBN) is doubled in frequency to provide the LO signal for
the modulator.
In “Low band FLOx1” modes the signal (LOLBP-LOLBN) is used as
the LO signal for the modulator.
In “Low band Bypass” a modulated GSM900 signal (LOLBP-LOLBN)
is switched into the RF signal path. The modulator is disabled and the
signal is routed to the RFOutLb outputs through a differential PA driver
amplifier.
This LOLBP input is AC-coupled internally.
The noise performance, carrier suppression at low output powers and
sideband suppression performance are functions of LO power. The
optimum LO power is between -3dBm and +3dBm. The device will
work with LO powers as low as -20dBm however this is at the expense
of higher noise performance at high output powers and poorer side-
band suppression.
The input impedance should be externally matched to 50
Ω. The port
impedance does not vary significantly between active and powered
modes.
The RF2705 is intended for use with the RF6002 which performs the
GSM GMSK modulation within a Frac-N synthesizer loop. The 8PSK
EDGE and W-CDMA signal modulations are performed in the RF2705
and uses the RF6002’s synthesizers to generate the LO signals. The
LO signal for DCS1800 mode is derived by frequency doubling
RF6002’s GSM900 VCO. This helps protect the system against PA pull-
ing.
5LO LB N
The complementary LO input for both LOLBP LO signals.
In any of the modes the LOLB input may be driven either single ended
or differentially. If the LO is driven single ended then the PCB board
designer can ground this pin.
It is recommended that if this pin is grounded that it is kept isolated
from the GND1 pin and the die flag ground. All connections to any other
ground should be made through a ground plane. Poor routing of this
GndLO signal can significantly degrade the LO leakage performance.
See pin 4.
6MODE C
Chip enable control pin. See the Logic Truth table.
CMOS Logic inputs: Logic 0=0V to 0.4V; Logic 1=1.4V to VCC.
7MODE D
Mode control pin. See the Logic Truth table.
CMOS Logic inputs: Logic 0=0V to 0.4V; Logic 1=1.4V to VCC.
See pin 6.
LO LB P
LO LB N
V
CC
V
CC2
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