Patent ID: 7787639
Filing Date: 2010-08-31
Classification: H03F,H03G

Abstract:
1. A circuit for suppressing audio noise, having a common node electrically connected to an output terminal of a preamplifier and an input terminal of a postamplifier, comprising: a first pulldown switch, wherein a first terminal of the first pulldown switch is electrically connected to the common node, a second terminal of the first pulldown switch is grounded and a control terminal of the first pulldown switch is electrically connected to a first voltage supply; during a first duration after the first voltage supply is turned on, the first pulldown switch is turned on and the common node is consequently grounded; a second pulldown switch, wherein a first terminal of the second pulldown switch is electrically connected to the common node and a second terminal of the second pulldown switch is grounded; a first control switch, wherein a first terminal of the first control switch is electrically connected to the first voltage supply and the control terminal of the first pulldown switch, a second terminal of the first control switch is electrically connected to a control terminal of the second pulldown switch and a control terminal of the first control switch is electrically connected to a second voltage supply providing power to the preamplifier; during a second duration before the second voltage supply is turned on and the voltage thereof is stable, the first control switch is turned on to control the second pulldown switch turn on and the common node is consequently grounded; and a voltage detecting circuit, electrically connected to the control terminal of the first control switch, controlling the first control switch turn off and the second pulldown switch is consequently turned off during the second voltage supply is turned on and the voltage thereof is stable; wherein, the first voltage supply has the substantially same characteristic before and after the voltage thereof is stable, and the second voltage supply has the substantially same characteristic before and after the voltage thereof is stable.