saulbit
Member level 4
I am designing a wideband receiver circuit. The first IF is about 5100MHz, and the second IF is about 300MHz, consequently the second LO is 4800MHz, which is provided by a 2.4GHz PLL and a *2 multiplier. The input is from 2000MHz to 3200MHz, and the first LO is about 7.2GHz~8300MHz. When the first LO is about 7.6GHz, the power of the 2.4GHz PLL leakage at the first mixer input is about -62dBm, which is terrible for me, for the input level is about -30dBm. This will cause an obvious spur about 32dB. When I measure in the ground using an open-ended cable, of which inner conductor is touched to the ground plane, the power of the 2.4GHz leakage is everywhere in the ground, from -80dBm to -50dBm, to some extent with the different ranges from the PLL. Now how can I suppress the leakage of the PLL. I found it is not transitted from the microwave signal lines, in which there is many amplifiers, providing huge inverse isolations. Each reply is welcome.
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Further more, the whole circuit is a four-layered PCB. The PLL is on the bottom layer, and the main circuit, including the mixers is on the toplayer. The second layer is a whole ground plane. The third one is also a ground plane, in which there are some control lines and some power supply lines.
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Further more, the whole circuit is a four-layered PCB. The PLL is on the bottom layer, and the main circuit, including the mixers is on the toplayer. The second layer is a whole ground plane. The third one is also a ground plane, in which there are some control lines and some power supply lines.