The utility model relates to a power supply circuit with low power supply
noise in an audio
system. One ends of the first, second and third resistors are connected with an input power supply, the other end of the first
resistor and one end of the fourth
resistor are connected with a drain
electrode of the NMOS tube, the other end of the fourth
resistor and one end of the fifth resistor are connected with a positive input end of the
operational amplifier, and a grid
electrode of the NMOS tube is connected with an output end of the
operational amplifier. The negative input end of the
operational amplifier and the other end of the second resistor are connected with the input end of the
numerical control resistor array, the source
electrode of the NMOS tube is connected with the output end of the
numerical control resistor array, and the other ends of the third resistor and the fifth resistor are connected with the power supply end of the digital circuit. And a plurality of resistance value control ends of the
numerical control resistor array are connected to the digital circuit. According to the utility model, by dynamically matching the working current of the high-
noise digital circuit, the current extracted from the power supply is approximately constant, the
voltage noise of the shared power supply is reduced, the
signal-to-noise ratio of the ADC and the DAC is improved, and the
chip packaging volume and cost are reduced.