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
PDN2
RFI2 Switch RFI3 Switch
PDN1
High
High
Low
Low
High
Low
High
Low
Open
Open
Closed
Closed
Open
Open
Open
Closed
Selected Crystal
Output
-
QO1
QO2
QO3
Description
Power down
Frequency 1
Frequency 2, RFI2 capacitor
connected in parallel with antenna
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
antenna inductor L
ANT
(see Typical Application on
page 5), antenna capacitor C
ANT1
and parasitic
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
to connect C
ANT2
in parallel with ferrite antenna and
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
switches are closed to connect both C
ANT2
and
C
ANT3
capacitors in parallel with ferrite antenna and
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.
3 (9)
MAS [ MICRO ANALOG SYSTEMS ]
