AN107
Rev 1.0 | Page 2/10
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Notes:
1.
L2 is the VCO tank inductor. The VCO oscillates at the frequency which is 2x of the RF frequency. In order to
suppress the spurious emission and minimize phase noise, a high-Q inductor is used. For a 433.92 MHz
design it is suggested to use a 22 nH inductor with Q > 25 at 800 MHz. For a 315 MHz design it is suggested to
use a 33 nH inductor with Q > 25 at 600 MHz.
2.
L1 and C4 transform the impedance seen at the RFIN pin to the antenna impedance.
3.
C1 and C2 are the power supply decoupling capacitors. C1 is an optional decoupling capacitor depending on
the power supply purity level
.
4.
The crystal oscillator consists of an extent crystal X1 and two loading capacitors (C5 and C6). The Total load
capacitance seen between the crystal terminals should equal C
L
for the crystal to oscillate at the specified
frequency.
C
L
=
C5
*
C6
C5 + C6
+
Δ
C
2
The parasitic capacitance
Δ
C is constituted by pin input capacitance and PCB stray capacitance. The ESR of
the crystal should be within 60 Ω in order to ensure a reliable start
-up. The total tolerance is ±20 ppm typically,
which include initial tolerance, crystal loading, aging, and temperature dependence. The acceptable tolerance
depends on RF frequency and channel spacing/bandwidth.
5.
An external clock source can easily be used in place of a crystal oscillator. The incoming clock signal is
recommended to have a peak-to-peak swing in the range of 300 mV to 700 mV and AC-coupled to the XTAL
pin.
6.
P1 is
a SMA connector for a 50 Ω antenna
.
7.
The DOUT pin outputs the
demodulated data.
8.
The test points (TP1/2/3/4/5 connected to VDD, GND, SCL, SDA, and CSB respectively) must be reserved if
EEPROM programming is required. The CSB, SDA and SCL should be left un-connected if they are not used.
9.
By default, an active low reset signal is generated by the internal POR and output via the nRSTO pin. It can be
used to reset the external MCU if it is required. The CMT2210A can provide a configurable system clock output
from the CLKO pin to drive the external device. The nRSTO and CLKO should be left un-connected if they are
not used.
10. Pin descriptions of the CMT2210A, and the BOM for CMT2210A application are shown in Table 1 and Table 2.
