How to optimize carrier loop filtering in a concentrator?

The concentrator carrier communication loop has specific filtering requirements, needing to suppress interference while ensuring the transmission quality of the carrier signal (e.g., 270kHz). Optimizing the filtering requires targeted design of the bandpass characteristics. A common-mode inductor CML3225A-510T (51μH) is connected in series on the primary side of the coupling transformer. It has high high-frequency impedance but low impedance at the carrier frequency. A resonant LC network at the carrier frequency (e.g., a 1μH inductor and a 330nF capacitor in series) is connected in parallel to enhance the signal.

A bandpass filter consisting of an inductor and capacitor is added to the receiver (RX) of the carrier chip, with a center frequency at the carrier frequency and a bandwidth of ±10%. A three-terminal filter (e.g., a BLM series ferrite bead) is used in conjunction with a capacitor on the power supply pin. During PCB routing, the carrier signal line is impedance controlled at 50Ω and clamped with a ground wire. After optimization, the carrier receiver sensitivity can be improved by 6dB, while out-of-band noise is suppressed by more than 30dB, improving communication reliability.