Patent ID: 7688987

Claim:
A microphone buffer circuit being adaptable for connection to a power source, the microphone buffer circuit comprising: an input transistor configured to receive and buffer an input signal, the input signal being representative of an audio signal, the input transistor having a first amount of power supply noise that is capable of being coupled thereto; a cascode transistor coupled to the input transistor and a power source, the cascode transistor being configured to receive a current, the current being received directly from the power source and operable to bias the cascode transistor a biasing circuit coupled to and separate from the input transistor and coupled to and separate from the cascode transistor, the biasing circuit operable to cause the cascode transistor and the input transistor to operate within a predetermined operating range, the biasing circuit being disposed between the cascode transistor and an output of the microphone buffer circuit and electrically connecting the cascode transistor to the output of the microphone buffer circuit; such that the cascode transistor is configured to cascode the first amount of power supply noise into a second amount of power supply noise, the second amount of power supply noise being significantly reduced from the first amount of power supply noise; and such that the current drawn from the power source required to bias the cascode transistor does not substantially increase when the cascode transistor reduces the first amount of power supply noise.