Howling reduction by analog phase-locked loop and active noise control circuits

•Howling reduction circuit with PLL and active noise control circuits was proposed.•PLL in the proposed circuit generated a signal with the same frequency as howling.•Active noise control in the proposed circuit controlled signal the amplitude.•The proposed circuit operated just after the howling generation and reduced howling.•Howling margin was significantly large compared with other systems reported so far.

This paper proposes a howling reduction circuit using analog phase-locked loop (PLL) and active noise control (ANC) circuits. The proposed circuit reduces howling by generating a signal opposite in phase to howling. To make a signal with the same frequency as howling, we employed the PLL circuit. The ANC circuit was used to control the amplitude of the signal. In addition, we employed pseudo-lock avoidance and differential switch circuits to avoid noise generation. The results confirm the effects of howling reduction by the proposed circuit.

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