Cirrus Logic Inc.

Frank Cheng

Lingli Zhang

Zhong You

Ruoxin Jiang

Dan Shen

An apparatus measures a speaker impedance. A DAC converts a known digital input signal to an audio frequency first analog voltage signal. Resistors with known resistance attenuate the first analog voltage signal to generate a current. The known resistance effectively determines the current because the known resistance is high relative to the speaker impedance. The current is sourced into the speaker to generate a second analog voltage signal. The known resistance is sufficiently high to cause the second analog voltage signal to be inaudible as transduced by the speaker. An amplifier amplifies the second analog voltage signal with a known gain to generate a third analog voltage signal. An ADC converts the third analog voltage signal to a digital output signal. A processing element calculates the impedance of the speaker proportional to the digital output signal based on the known digital input signal, the known resistance, and the known gain.

Apparatus and method for measuring speaker transducer impedance versus frequency with ultralow inaudible signal

An asymmetric modulation scheme may be used to drive two output nodes coupled to a load. The asymmetric modulation scheme may be one-sided such that the switching rate of a first output node is lower than the switching rate of a second output node. The first output node may be switched only to change a direction of current between the first output node and the second output node, while the second output node is switched to convey the information of an input signal. The asymmetric modulation scheme may be used to drive a speaker to reduce noise at the first output node to improve accuracy of current monitoring through the speaker by a current monitor coupled at the first output node.

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Austin, TX, United States of America

Frank Cheng