Texas Instruments Corporation

Telefonaktiebolaget Lm Ericsson (publ)

Martin Sallenhag

Heino Jean Wendelrup

Kjell Berthold Gustafsson

Martin Isberg

John M Muza

Bjorn Martin Lindquist

Roberto Sadkowski

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

Microphone bias current measurement circuit

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. In another apparatus, the estimated samples of the second-order product signal are produced by a device for averaging a square of a difference between respective digital samples of the in-phase signal and the quadrature signal, thereby determining an amplitude of the amplitude-modulated carrier signal, and a device for combining the amplitude and the digital samples, thereby generating the estimated samples.

Digitally compensated direct conversion receiver

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Lund, Sweden

Martin Sallenhag