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Hi, can anybody help me to determine the choke value at 433MHz PA and how large the SRF should be? The file attached is Inductor selection guide from murata.
Your choke impedance should be at least 5 X your output impedance at the operating frequency. The SRF should be higher than your operating frequency. The choke should be of low Q to avoid peaking.
To reduce the Q factor, can I series a low value resitor with the choke?
Now I am working toward a 433MHz 8dBm power amplifier at 2.5V supply under CMOS process. And I am wondering about the optimum load impedance where largest power can be obtained. With some simulations, I found that the optimum load changes with the choke value changes. For example, choke 33nH with Zopt 38-j175 ohm,but choke 100nH with Zopt 166-j435 ohm. Even when the choke value reaches 1uH, the Zopt changes to 1666ohm. I don't know why this will happen.
Added after 5 minutes:
Still another question. Can we still use the equation of Zopt=VDD/(2*Po) under my condition?
If I can use it, the choke has to be as large as 150nH. Actually I get good performance with 33nH choke.
If I should not use this equation to determine the optimum load, which should I choose. Or just through simulation?
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