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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