adf7012 Analog Devices, Inc., adf7012 Datasheet - Page 21

• Manufacturer Part Number: adf7012
• Description: Multichannel Ism Band Fsk/gfsk/ook/gook/ask Transmitter
• Manufacturer: Analog Devices, Inc.

433 MHZ OPERATION
The recommendations here are guidelines only. The design
should be subject to internal testing prior to ETSI site testing.
Matching components need to be adjusted for board layout.
The ETSI standard EN 300-220 governs operation in the
433.050 MHz to 434.790 MHz band. For many systems, 10%
duty is sufficient for the transmitter to output 10 dBm.
Design Criteria
433.92 MHz center frequency
FSK modulation
10 mW output power
200 m range
Meets ETSI 300-220
The main requirement in the design of this remote is a long
battery life and sufficient range. It is possible to adjust the
output power of the ADF7012 to increase the range depending
on the antenna performance.
The center frequency is 433.92 MHz. It is possible to operate the
VCO at this frequency. Figure 36 shows the inductor value vs.
center frequency. The inductor chosen is 22 nH. Coilcraft
inductors such as 0603-CS-22NXJBU are recommended.
Crystal and PFD
The phase noise requirement is such to ensure the power at the
edge of the band is < −36 dBm. The PFD is chosen so as to
minimize spurious levels (beat note and reference), and to
ensure a quick crystal power-up time.
PFD = 4.9152 MHz − Power-Up Time 1.6 ms. Figure 10 shows a
typical power-up time for a 4 MHz crystal.
N-Divider
The N Divider is determined as being:
Deviation
The deviation is set to ± 50 kHz so as to accommodate a simple
receiver architecture.
The modulation steps available are in 4.9152 MHz/2
Bias Current
Because low current is desired, a 2.0 mA VCO bias can be used.
Additional bias current reduces any spurious, but increases
current consumption.
The PA bias can be set to 5.5 mA and achieve 10 dBm.
Nint = 88
Nfrac = (1152)/4096
VCO divide-by-2 is not enabled
Modulation steps = 300 Hz
Modulation number = 50 kHz/300Hz = 167
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Loop Filter Bandwidth
The loop filter is designed with ADIsimPLL Version 2.5. The
loop bandwidth design requires that the channel power be
< −36 dBm at ±870 kHz from the center. A loop bandwidth of
close to 160 kHz strikes a good balance between lock time for
data rates, including 32 kbps and spurious suppression. If it is
found that pulling of the VCO is more than desired in OOK
mode, the bandwidth could be increased.
Design of Harmonic Filter
The main requirement of the harmonic filter should ensure
that the third harmonic level is < −30 dBm. A fifth-order
Chebyshev filter is recommended to achieve this, and a
suggested starting point is given next. The Pi format is chosen
to minimize the more expensive inductors.
Component Values—Crystal: 4.9152 MHz
Loop Filter
Icp
LBW
C1
C2
C3
R1
R2
Matching
L1
L2
C14
C15
Harmonic Filter
L4
L5
CF1
CF2
CF3
2.0 mA
100 kHz
680 pF
12 nF
270 pF
910 V
3.3 kV
22 nH
10 pF
Short
Open
22 nH
22 nH
3.3 pF
8.2 pF
3.3 pF
ADF7012