xonatan
Newbie level 3
Dear Friends
I made an RF LNA amplifier using Avago MGA-632P8 . The schematic and component values follow description in MGA-632P8 datasheet(). However, in order to match the amplifier to my work frequency, some values were adjusted using AWR microwave office.
Then, to test the proper operation of the circuit, I make a test board. I tested it alone and also connected to a LPF at the output and a BPF at the input. The result was positive, the expected gain, S11, S22, etc... in both situations ok.
now, in my final circuit, I have the same chain as before but between the LNA and the BPF filter (LNA input) I placed a coupler to measure a coupled signal, BDCA1-7-33 from minicircuits (https://www.minicircuits.com/pdfs/BDCA1-7-33+.pdf) and a switch,SWMA-2-50DR+, (https://www.minicircuits.com/pdfs/SWMA-2-50DR+.pdf) to swap different BPF.
so, with this new board, when I measure the RF amplifier with no RF input, I find oscillation in around 4.3 GHz in its harmonics. I have tried to move some components around the amplifier, but the oscillation always occurs. Only it disappears when I replace the coupler by a 50ohms resistor. then the amplifier does not oscillate more.
some of you could help me to know why it seems this coupler (50ohms) is the cause for the oscillation?
Thank you very much for your help.
Regards,
Xonatan
I made an RF LNA amplifier using Avago MGA-632P8 . The schematic and component values follow description in MGA-632P8 datasheet(). However, in order to match the amplifier to my work frequency, some values were adjusted using AWR microwave office.
Then, to test the proper operation of the circuit, I make a test board. I tested it alone and also connected to a LPF at the output and a BPF at the input. The result was positive, the expected gain, S11, S22, etc... in both situations ok.
now, in my final circuit, I have the same chain as before but between the LNA and the BPF filter (LNA input) I placed a coupler to measure a coupled signal, BDCA1-7-33 from minicircuits (https://www.minicircuits.com/pdfs/BDCA1-7-33+.pdf) and a switch,SWMA-2-50DR+, (https://www.minicircuits.com/pdfs/SWMA-2-50DR+.pdf) to swap different BPF.
so, with this new board, when I measure the RF amplifier with no RF input, I find oscillation in around 4.3 GHz in its harmonics. I have tried to move some components around the amplifier, but the oscillation always occurs. Only it disappears when I replace the coupler by a 50ohms resistor. then the amplifier does not oscillate more.
some of you could help me to know why it seems this coupler (50ohms) is the cause for the oscillation?
Thank you very much for your help.
Regards,
Xonatan