Philips Semiconductors

Objective specification

SA9503

Dual-band, CDMA/AMPS LNA

and downconverter mixers

1999 Jul 29

4

FUNCTIONAL DESCRIPTION

Mode selection

The SA9503 has several modes of operation for which the selection

logic is defined in Tables 2 and 3. Different mode selections require

different portions of the circuit to be active. Modes from unlisted

combinations of logic pins are not permitted. The LNA and

downconverter together can be programmed to operate in the PCS

or cellular bands using the PCS/CEL logic input pin, and in CDMA or

FM modes using the CDMA/FM logic input pin.

The LNA can be set to four different gain values and one special

high linearity setting. Thus, the LNA can be programmed into five

different modes with associated gain, noise figure, and input IP3,

using the S0, S1, and S2 control lines. The whole circuit (LNAs and

mixers) is powered down when control lines S0 = 1, S1 = 0, and

S2 = 0. It is also possible to independently switch off the LNAs and

keep the mixers on, as shown in Table 3.

LNA

External components can be used to match the LNA inputs, and if

required, the outputs, for the Cellular and PCS bands. The input and

output return loss of better than 10 dB can be achieved in all modes.

For Cellular band FM, only the CEL_1 mode is required for the LNA.

For CDMA, LNA modes CEL_1 and PCS_1 are used for normal

operation, as they have the highest gains and lowest noise figures.

For higher levels of multi-tone interference, other modes with lower

gains are to be used. The high linearity CEL_L and PCS_L modes

are used when there is a very strong adjacent channel interference,

while at the same time the mobile is transmitting close to its full

power. The high linearity is required in order to reduce the cross

modulation of the LNA from the mobile’s transmitter, in the presence

of strong adjacent channel interferer. The maximum transmitter

power leakage which can be tolerated at the LNA input is

approximately –30dBm to meet the single tone desensitization

requirements. The cross modulation power can be derived from:

Cellular band: (2

PCS band:

(2

The LNA requires less than one hundred microseconds to settle

when it changes from one mode to another. This is expected to have

insignificant impact on the CDMA frame error rate.

Downconverter

The SA9503 has three mixers, one for Cellular FM, one for Cellular

CDMA, and one for PCS CDMA. Each one is individually optimized

for their specific requirements. The Cellular CDMA and FM mixers

have a common single-ended RF input.

The PCS mixer’s RF input port is differential, and requires an

external balun when used with a single-ended source. Both the PCS

and the Cellular mixer RF inputs should be AC coupled.

Local oscillator drive for the mixers is provided through pins

CEL LO_IN and/or PCS LO_IN. The local oscillator inputs are

single-ended, AC-coupled. The CEL LO_IN signal is internally

buffered to drive the following:

– (Tx) LO output buffer,

– cellular FM mixer,

– cellular CDMA mixer,

– PCS LO frequency doubler.

In the PCS mode, mixer LO drive can be either direct (PCS LO_IN)

or through the frequency doubler after CEL LO_IN. The mixer local

oscillator signal is made available externally via the (Tx) LO output

buffer for potential use elsewhere in the radio. For example, this

signal typically can be used with the transmitter circuitry. The

(Tx) LO output buffer can be powered down independently, using

the (Tx) LO_ENABLE logic input. The (Tx) LO output buffer has

open collector differential outputs which are internally biased to

The PCS and Cellular CDMA mixers have open collector differential

IF outputs. The two IF outputs can either supply two separate IF

filters, or they can be connected together externally for use with one

common receive IF filter. The differential IF outputs must be biased

at the supply voltage through external inductors that may also be

part of the matching circuit to the SAW filter. The cellular band FM

mixer also has a differential open collector IF output.

Table 1.

Typical Cellular Mode LNA Gain Change Points for 2-tone CDMA Interference Test

GAIN, dB

MAXIMUM ANTENNA IN-BAND POWER, dBm

MINIMUM ANTENNA IN-BAND POWER, dBm

16.5

–95

< –104

9

–90.5

–98.5

3

–86.7

–93.5

–3

> –79

–89.7