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Hello all, i need some help with 2 doubts i got.
I was trying to design a LoRa module matching network but i didnt understand two things
The ST document above shows that they use 4.45 nH and 5.53 pF as part of the matching network. However, these components also seem to form an LC low-pass section, so they indirectly provide some filtering as well.
I calculated the cutoff frequency of this LC section and obtained approximately 1 GHz. Since the operating frequency considered in the ST example is 868 MHz, wouldn't this already introduce some attenuation at 868 MHz?
In other words, are these component values actually supposed to be considered as an independent low-pass filter? If I look only at this LC section, it seems that the signal at 868 MHz would already experience some insertion loss.
Or is this analysis not meaningful because these components are part of the complete impedance-matching network, and therefore I should evaluate the entire network using S11/S22 and S21 rather than analyzing each LC section independently?
I got also a second doubt, this one is for the design of the notch filter, which i have done for my specific circuit ( dont mind the inductor part number, i have typed one wrongly by mistake, the one i chose has a high SRF value and Q of 25 minimum)
I have a question about the notch filter used to suppress the second harmonic. Is my reasoning about its bandwidth correct?
The notch frequency is approximately 1.75GHz ( 868MHz, which Is working frequency x 2 )
The inductor I selected has a self-resonant frequency of 8 GHz and a minimum Q of 25. If I use:
BW=1.75GHz/ Q = 70 MHz ( Here i gotta use the Q value of the inductor right? )
Assuming the bandwidth is centered around the notch frequency, this would give:
fl=1.715GHz and fh=1.785GHz
Therefore, 1.736 GHz falls within this range. Does this mean that the second harmonic is effectively inside the notch bandwidth and should be attenuated?
Thanks for the help for my 2 doubts, in case of any more detailed info let me know and i will give you
I was trying to design a LoRa module matching network but i didnt understand two things
The ST document above shows that they use 4.45 nH and 5.53 pF as part of the matching network. However, these components also seem to form an LC low-pass section, so they indirectly provide some filtering as well.
I calculated the cutoff frequency of this LC section and obtained approximately 1 GHz. Since the operating frequency considered in the ST example is 868 MHz, wouldn't this already introduce some attenuation at 868 MHz?
In other words, are these component values actually supposed to be considered as an independent low-pass filter? If I look only at this LC section, it seems that the signal at 868 MHz would already experience some insertion loss.
Or is this analysis not meaningful because these components are part of the complete impedance-matching network, and therefore I should evaluate the entire network using S11/S22 and S21 rather than analyzing each LC section independently?
I got also a second doubt, this one is for the design of the notch filter, which i have done for my specific circuit ( dont mind the inductor part number, i have typed one wrongly by mistake, the one i chose has a high SRF value and Q of 25 minimum)
I have a question about the notch filter used to suppress the second harmonic. Is my reasoning about its bandwidth correct?
The notch frequency is approximately 1.75GHz ( 868MHz, which Is working frequency x 2 )
The inductor I selected has a self-resonant frequency of 8 GHz and a minimum Q of 25. If I use:
BW=1.75GHz/ Q = 70 MHz ( Here i gotta use the Q value of the inductor right? )
Assuming the bandwidth is centered around the notch frequency, this would give:
fl=1.715GHz and fh=1.785GHz
Therefore, 1.736 GHz falls within this range. Does this mean that the second harmonic is effectively inside the notch bandwidth and should be attenuated?
Thanks for the help for my 2 doubts, in case of any more detailed info let me know and i will give you
