Speaker Impedance Measurement

An integrated circuit for processing audio and voice signals in a telephone, comprising:

• an audio output port having a first and a second output terminal for connection to a first and a second input terminal, respectively, of a speaker;
• an audio input port having a first and a second input terminal for connection to a first and a second output terminal of an audio input source;
• at least one audio output path having a digital input port and an analog output port with at least one analog output terminal;
• an audio input path having an analog input port, comprising a first and a second input terminal, and a digital output port;
• and
• a test impedance, such as a resistor, (RT) having a first and a second terminal, wherein the first terminal is connected to a reference-voltage node of the integrated circuit;
• wherein the integrated circuit is configured such that:
• in a work mode of the integrated circuit
• one of the at least one audio output paths is arranged to supply an audio output signal to the audio output port via the analog output port of that one of the at least one audio output path;
• and
• the audio input path is arranged to receive an audio input signal from the audio input port via the analog input port of the audio input path;
• and
• in a measurement mode of the integrated circuit
• the at least one analog output terminal of the analog output port of one of the at least one audio output path is operatively connected to the first output terminal of the audio output port for supplying a test signal to the speaker;
• the second terminal of the test impedance (RT) is operatively connected to the second output terminal of the audio output port;
• and
• the first and second input terminal of the analog input port of the audio input path are operatively connected to the first and the second output terminal, respectively, of the audio output port for measuring an electrical impedance of the speaker.

A method of measuring an electrical impedance of a speaker connected to the audio output port of the integrated circuit according to any preceding claim, comprising:

• a) setting the integrated circuit in the measurement mode;
• b) applying a digital signal, such as a digital sinusoidal signal, of a given frequency to the digital input port of said one of the at least one audio output path, the at least one analog output terminal of the analog output port of which is operatively connected, in the measurement mode, to the first output terminal of the audio output port for supplying said test signal to the speaker;
• and
• c) determining a digital value representing said electrical impedance for said given frequency based a digital output signal of the audio input path.