CX74036

Receive RF IC

2

Conexant – Proprietary

101105A

Data Subject to Change

October 17, 2000

Vvga

1st IF LO

VHF

Synth

÷P

19.44 M H z

Ext.1.8 M H z

÷ 4

Power

M anagem ent

Vcc

Standby

C ell LO

Im age R ejection Filter

PC S LO

IF Buffer

RX RFIC

CX74036

101105A-2_101200

Power Down

EN

DATA

CLK

LN A G ain

Band Select

VC O /R EF IN

I

IF O ut

Q

IQ /

IF

1st IF SAW

Im age R ejection Filter

450 KH z

Figure 2. CX74036 Functional Block Diagram

Technical Description

Low Noise Amplifiers: The CX74036 contains two

independent LNAs for the cellular and PCS bands. The gain of

both LNAs can be switched off to a loss mode via one command

line interface. Only one LNA is powered at any given time.

Control is done by an external band-select control signal. The

input and output matches are external to the chip. The LNAs’

parameters, Noise Figure (NF), and gain are chosen to provide

an excellent balance between system sensitivity and IIP3

requirements to achieve maximum dynamic range. Both LNA

outputs are ported off-chip to allow for image filtering before

being fed to the RF mixer inputs.

RF Mixers: The mixers are designed to operate with a low LO

input power level of –10 dBm. This eliminates the requirement of

buffer amplifiers for the external VCO. Cellular band mixer high

gain and low NF performance allow for the cellular LNA gain to

be lower, which saves current consumption. Both mixers are

designed to provide high suppression of one-half IF response.

The outputs of both mixers share a common interface path to

the external IF Surface Acoustic Wave (SAW) filter, which

reduces complexity and cost. The RF mixer load configuration is

shown in Figure 3. Inductors can be Surface Mount Multilayer

Chip (SMMC) components.

First IF Mixer: This mixer begins the common signal path for

both cellular and PCS band modes. Input and output impedance

are set to values that are close to the most commonly available

SAW and ceramic filters.

Vcc

Vcc

330 nH

330 nH

+

-

RF M ixers

Output

to IF SAW

Filter

101105A-3_101100

1200 pF

1200 pF

Figure 3. RF Mixer Load Configuration

Variable Gain Amplifier: The VGA itself provides 70 dB of

dynamic range to satisfy the high system dynamic range

requirement. With the inclusion of the LNA gain switch, the

system dynamic range is extended to more than 95 dB.

I/Q Demodulator: Using digital circuitry generates a stable

quadrature LO signal, on-chip direct connection to the VGA

output, on-chip LO source, and lowpass filtering for each

channel. This, in turn, provides a high performance I/Q

demodulator with very low amplitude and phase offsets. The

output signal quality is compatible with many baseband interface

requirements.