AS3977BQFU austriamicrosystems, AS3977BQFU Datasheet - Page 34

• Manufacturer Part Number: AS3977BQFU
• Description: Ultra-High Frequency FSK Transmitter IC
• Manufacturer: austriamicrosystems

Specifications of AS3977BQFU

• Modulation Type: FSK
• Supply Voltage Range: 2V To 3.6V
• Module Interface: Serial
• Supply Current: 17mA
• Ic Function: Multi-Channel Narrowband FSK Transmitter
• Termination Type: SMD
• No. Of Pins: 16
• Rohs Compliant: Yes
• Operating Temperature Range: -40°C To +85°C
• Filter Terminals: SMD
• Digital Ic Case Style: QFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AS3977
Data Sheet - A p p l i c a t i o n I n f o r m a t i o n
9.8 Output Frequency Setting
The output frequency f
Where:
P
f
M
N
AC
FRAC is the Fractional part
Predivider Division Ratio P and Pre Scaler Modulus M.
ratio P and the setting of the pre scaler modulus M. The setting of these values for the different frequency bands is given in
Table 24. P and M Values for Frequency Bands
The reference frequency should be in the range of 3 to 5, 75 MHz and can be calculated by:
The recommended setting of the divider is 4.
The next step is to calculate the Division ratio:
This division ration can be split into a part before the comma, called integer part and a part after the comma, also called fractional part DR
The N-counter value of the Fractional N Synthesizer can be calculated with the formula:
The A-Counter is the rest of this Division and can be calculated by:
In case, the Value of the A-counter is zero, the value of the A-counter has to be increased by M and the value of N has to be decreased by one
In case, the N-counter is in the range from 10 to 25 and the value of the A-counter is less than N-counter-7:
Note: In case, no solution can be found for the wanted center frequency, it may help to modify the reference frequency or INT<8>
www.austriamicrosystems.com/AS3977
REF
is the Predivider division ratio
is the N-counter division ratio
is the Reference frequency
is the Prescaler modulus
is the A-counter offset, AC determines together with FRAC the actual A-counter setting
Frequency Band
315 MHz
433 MHz
868 MHz
915 MHz
RF
is given by:
f
RF
P
1
1
2
2
DR
N = whole numbered part of
=
AC
=
P f
----------------- -
P f
⋅
=
⋅
REF
f
f
RF
REF
(
REF
INT < 7 : 4 > = AC - 1
DR
INT < 3 : 0 > = N - 10
⋅
(
=
INT
M N
The frequency band selection determines the value of the predivider division
=
N = N - 1
AC = M
------------------ -
divider
Revision 3.6
⋅
DR
–
f
XTAL
3
+
M
4
5
5
5
INT
) N
(
---------------------------- -
–
AC
DR
+
DR
+
×
INT
M
FRAC
M
FRAC
–
3
)
)
BSEL<1:0>
0 (00)
1 (01)
2 (10)
3 (11)
300 – 320 MHz
425 – 450 MHz
865 – 870 MHz
902 – 928 MHz
Table
Note
24.
(EQ 3)
(EQ 4)
(EQ 5)
(EQ 6)
(EQ 7)
(EQ 8)
34 - 47
(EQ 9)
FRAC