ML7436N LSI Hardware Design Manual
FEXL7436NDG-01
20
7.3.1.
Addition of higher harmonics trap filter
Figure 7.13
shows the addition of the trap filter to suppress higher harmonics of transmission signal. The trap filter
impedance is small value at the resonance frequency of the inductor and the capacitor. It is possible to propagate the
signal to GND at the resonance frequency. The transmission line (Thick line) between antenna and RF_PA_OUT2(#38)
has 50Ω characteristic impedance.
Figure 7.13
Higher harmonics trap filter configuration
The inductor and capacitor values configuring the trap filter is calculated as the following formula.
ω
RF
⋅ 𝑁 =
1
√𝐿
trap
⋅ 𝐶
trap
ω
RF
is the transmission frequency. N is the multiple number of higher harmonics. It is required to decide the maximum
value of the higher harmonics and adjust the values meeting standards. If necessary, the trap filters are added to
suppress every higher harmonic.
7.3.2.
Addition of impedance conversion circuit (if necessary)
Addition of the trap filter may cause that the load impedance becomes lower and the transmission power becomes less
than 0dBm. It is necessary to add the impedance conversion circuit and convert the antenna load impedance to higher
value and adjust the transmission power to 0dBm. LAPIS technology recommends the high pass filter type impedance
conversion circuit. It is possible to protect mixing the frequency elements of switching regulator and clock signal. If it is
necessary to adopt high pass filter type conversion circuit, add enough AC coupling capacitor(100pF). DC voltage of
RF_PA_OUT2 pin is decided by the internal circuit. It is not influenced by the matching circuit.
