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UAA2073M

Image rejecting front-end for GSM applications

Philips Electronics 

Philips Semiconductors

Image rejecting front-end

for GSM applications

Product specification

UAA2073M

FUNCTIONAL DESCRIPTION

Receive section

The circuit contains a low-noise amplifier followed by two

high dynamic range mixers. These mixers are of the

Gilbert-cell type. The whole internal architecture is fully

differential.

The local oscillator, shifted in phase to 45° and 135°,

mixes the amplified RF to create I and Q channels. The

two I and Q channels are buffered, phase shifted by 45°

and 135° respectively, amplified and recombined internally

to realize the image rejection.

Pin SBS allows sideband selection:

• fLO < fRF (SBS = 1)

• fLO > fRF (SBS = 0).

Balanced signal interfaces are used for minimizing

crosstalk due to package parasitics. The RF differential

input impedance is 150 Ω (parallel real part), choosen to

minimize current consumption at best noise performance.

The IF output is differential and of the open-collector type,

tuned for 71 MHz. Typical application will load the output

with a differential 500 Ω load; i.e. a 500 Ω resistor load at

each IF output, plus a 1 kΩ to x Ω narrow band matching

network (x Ω being the input impedance of the IF filter).

The path to VCC for the DC current is achieved via tuning

inductors. The output voltage is limited to VCC + 3Vbe or

3 diode forward voltage drops.

Fast switching, on/off, of the receive section is controlled

by the hardware input RXON.

handbook, full pagewidth

VCC1

RFINA

RFINB

GND1

LNA

SYNTHON

MIXER

IF

amplifier

MIXER

IF

amplifier

LOIN

+45o

SBS

IF

COMBINER

+135o

RXON

IFA

IFB

MBG795

Fig.3 Block diagram, receive section.

1995 Dec 07

5

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