MAS9081 Micro Analog Systems, MAS9081 Datasheet - Page 3

• Manufacturer Part Number: MAS9081
• Description: Stand-alone Dual Band Time Signal AM Receiver IC
• Manufacturer: Micro Analog Systems

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
The internal antenna tuning capacitor switch (RFI2)
and crystal filter output switches (QO1, QO2) are
controlled according table 1. See switch in block
diagram on page 1.
If frequency 1 is selected the RFI2 switch is open
and only crystal output QO1 is active. Antenna
frequency is determined by antenna inductor L
(see Typical Application on page 5), antenna
capacitor C
to antenna inputs RFI1, RFI2 and RFI3 (see
Antenna Tuning Considerations below). Frequency
1 is the higher frequency of two selected
frequencies.
ANTENNA TUNING CONSIDERATIONS
The ferrite bar antenna having inductance L
parasitic coil capacitance C
reception frequencies f
C
internal antenna capacitor switch have capacitances
(C
Frequency f
C
Frequency f
C
ANT1
TOT1
TOT2
RFI1
High
High
Low
Low
=C
=C
,
and C
COIL
COIL
C
OFF2
+C
+C
ANT1
1
2
(higher frequency):
(lower frequency):
PDN2
ANT2
High
High
)
ANT1
ANT1
Low
Low
and parasitic capacitances related
. The receiver input stage and
which
+C
+C
RFI1
ANT2
1
RFI2 Switch
and f
+C
+C
Closed
Closed
affect
OFF2
Open
Open
RFI1
2
COIL
by parallel capacitors
=C
=C
COIL
COIL
is tuned to two
the
+C
+C
ANT1
ANT1
resonance
Selected Crystal
+6.5pF+37pF=C
+C
ANT
Output
ANT2
QO1
QO2
QO2
and
ANT
-
+ 6.5pF,
If frequency 2 is selected then RFI2 switch is closed
to connect C
tune it to frequency 2. Then only crystal output QO2
is active. Frequency 2 is lower frequency of the two
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.
frequencies. C
switch is open. When the switch is closed this
capacitance is shorted by on resistance of the
switch and is effectively eliminated. Following
relationships can be written into two tuning
frequencies.
COIL
f
2
=
Power down
Frequency 1
Frequency 2, RFI2 capacitor connected in
parallel with antenna
Frequency 2, RFI2 capacitor connected in
parallel with antenna
+C
2
π
ANT1
L
+ 43.5pF,
ANT
1
ANT2
⋅
C
OFF2
TOT
in parallel with ferrite antenna and
2
Description
is switch capacitance when
f
1
=
2
π
L
ANT
1
⋅
1 August, 2005
C
TOT
DA9081.006
1
3 (12)