Abstract: A microphone is provided in a mobile terminal and is connected to a current source when the flip portion of the mobile terminal is open and is disconnected from the current source when the flip portion of the phone is closed. The mobile terminal can then infer the position of the flip portion of the housing, e.g., opened or closed, based upon the state of the microphone's current supply circuit, for example by detecting the current flowing through the circuit or a voltage drop across a supply resistor. In addition, an on-hook/off-hook button can be provided to a hands-free accessory without increasing a number of signal lines/connections between the hands-free accessory and the mobile terminal. This can be accomplished, for example, by connecting the on-hook/off-hook button to a switch in the microphone signal line. The switch selectively creates an open in the microphone signal line, which can be detected by the mobile terminal, thereby resulting in an off-hook condition.

Abstract: A microphone bias current detection circuit includes: a microphone circuit 18; an amplifier 10 having a first output and a second output, the first output is coupled to the microphone circuit 18 for providing a bias current to the microphone circuit 18, the second output provides a sampled current Is proportional to the bias current; a first switch 30 having a first end coupled to the second output of the amplifier 10; a resistor 38 having a first end coupled to a second end of the first switch 30; and a second switch 32 coupled between the first end of the resistor 38 and a reference current source.

Abstract: A digitally compensated direct-conversion receiver includes devices for generating digital samples of a base-band in-phase signal and a base-band quadrature signal and for detecting the presence of a second-order product signal produced by an amplitude-modulated interfering signal. Also, the apparatus comprises a device for digitally compensating the digital samples by removing the second-order product signal, thereby producing compensated digital samples. In one method of digitally compensating samples of an information signal quadrature-modulating a carrier signal, estimated samples of a second-order product from a switched carrier signal are formed by averaging the digital samples during two time periods and by determining a time of ramps in the in-phase and quadrature signals that occur between the time periods due to the interfering signal. The digital samples may be differentiated and the results smoothed in determining the time of the ramps.