Patent ID: 8073158

Claim:
A circuit for eliminating noise generated by a sound card which is supplied with an audio power, the circuit comprising: a first transistor with a first gate configured to receive a power good signal, a first drain connected to a standby voltage terminal, and a first source connected to ground; a second transistor with a second gate connected to the first drain of the first transistor, a second drain coupled with an audio signal output of the sound card, and a second source connected to ground; a third transistor with a third gate responsive to a power supply on (PSON#) signal, a third drain connected to the first gate of the first transistor, and a third source connected to ground; wherein the power good signal stays at low level during a time when the PSON# signal turns from high to low level in order that the audio power for providing working voltage to the sound card is powered up, thus the first transistor turns off, and the second transistor turns on to ground the audio signal output of the sound card during powering up time so as to eliminate turn-on noise; and wherein the PSON# signal turns from low to high level to turn on the third transistor before the audio power for providing working voltage to the sound card is powered down, thus the first transistor turns off, and the second transistor turns on to ground the audio signal output of the sound card during powering down time so as to eliminate turn-off noise.