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DA9079.003

19 May, 2005

FREQUENCY SELECTION

The frequency selection and power down control is

accomplished via two digital control pins PDN1 and

PDN2. The control logic is presented in table 1.

Table 1 Frequency selection and power down control

PDN1

PDN2

RFI2 Switch

RFI3 Switch

Selected Crystal

Output

Description

High

High

Open

Open

-

Power down

High

Low

Open

Open

QO1

Frequency 1

Low

High

Closed

Open

QO2

Frequency 2, RFI2 capacitor

connected in parallel with antenna

Low

Low

Closed

Closed

QO3

Frequency 3, RFI2 and RFI3

capacitors connected in parallel

with antenna

The internal antenna tuning capacitor switches

(RFI2, RFI3) and crystal filter output switches

(QO1, QO2, QO3) are controlled according table 1.

See switches in block diagram on page 1.

If frequency 1 is selected the RFI2 and RFI3

switches are open and only crystal output QO1 is

active. Antenna frequency is determined by

capacitances related to antenna inputs RFI1, RFI2

and RFI3 (see Antenna Tuning Considerations

below). Frequency 1 is the highest frequency of the

three selected frequencies.

If frequency 2 is selected then RFI2 switch is closed

tune it to frequency 2. Then only crystal output QO2

is active. Frequency 2 is the medium frequency of

the three selected frequencies.

If frequency 3 is selected both RFI2 and RFI3

tune it to frequency 3. Then only crystal QO3 is

active. Frequency 3 is the lowest frequency of the

three selected frequencies.

It is recommended to switch the device to power

down for 50ms before switching to another

frequency. This guarantees fast startup in switching

to another frequency. The 50ms power down period

is used to discharge AGC capacitor and to initialize

fast startup conditions.