RF2705 View Datasheet(PDF) - RF Micro Devices

Part Name

Description

Manufacturer

RF2705

QUADRATURE DEMODULATOR

RF Micro Devices 

RF2705

Pin Function Description

1

VCC2

Supply for LO buffers, frequency doubler and dividers.

Interface Schematic

VCC2

Modulator and

VGA

2

LO 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

VCC

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.

LO HB P

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 LO HB N

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 50Ω. 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.

3

LO HB N The complementary LO input for both LOHBP LO signals.

See pin 2.

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.

5-124

Rev A4 041026

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