5-124
RF2705
Rev A4 041026
Pin
Function
Description
Interface Schematic
1VCC2
Supply for LO buffers, frequency doubler and dividers.
2LO HB P
High band local oscillator input (1800MHz).
In “low band FLO/2” modes the signal (LOHBP-LOHBN) undergoes a
frequency division of 2 to provide the low band LO signal for the modu-
lator.
In “high band FLOx1” modes the signal (LOHBP-LOHBN) is used as
the high band LO signal for the modulator.
In “high band bypass” a modulated DCS1800/PCS1900 signal
(LOHBP-LOHBN) is switched into the RF signal path. The modulator
is disabled and the signal is routed to the RFOutHb outputs through a
differential PA driver amplifier.
The LOHBP input is AC-coupled internally.
The noise performance, carrier suppression at low output powers and
sideband suppression all vary with 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 phase noise in
the LO circuitry and poorer sideband suppression.
The input impedance should be externally matched to 50
Ω. The port
can be driven either differentially or single ended. The port impedance
does not vary significantly between active and power down modes.
The RF2705 is intended for use with the RF6002. This 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 EDGE900 mode is derived by frequency division by 2 of
the RF6002’s DCS1800 VCO. This helps protect the system against PA
pulling.
3LO HB N
The complementary LO input for both LOHBP LO signals.
In any of the modes the LOHB 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
ground signal can significantly degrade the LO leakage performance.
See pin 2.
Modulator and
VGA
VCC2
LO HB P
LO HB N
V
CC
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