Techniques are disclosed relating to DC interference cancelation in received wireless signals. Disclosed techniques may be performed in the digital domain, in conjunction with analog cancelation techniques. In some embodiments, a receiver apparatus operates a local oscillator at a frequency corresponding to a particular pilot symbol in a received wireless signal. In some embodiments the receiver estimates DC interference at the frequency based on the received pilot symbol (this may be facilitated by the fact that the contents of pilot symbols are known, because they are typically used for channel estimation). In some embodiments, the receiver apparatus is configured to cancel the DC interference based on the estimate to determine received data in subsequently received signals at the frequency. Disclosed techniques may allow narrowband receivers to efficiently use more of their allocated frequency bandwidth, rather than wasting bandwidth near the frequency of the local oscillator.

A mixer includes a load portion connected between an input terminal of a first power voltage and an output terminal of the radio frequency transmit signal and configured to adjust a magnitude of the radio frequency transmit signal, a first switching unit connected to an output terminal of the radio frequency transmit signal, and configured to perform a first switching operation in response to a plurality of local oscillation signals, and a second switching unit connected between the first switching unit and an input terminal of a second power voltage, lower than the first power voltage, and configured to perform a second switching operation in response to a plurality of baseband signals, the plurality of local oscillation signals include an I+ baseband signal, an I baseband signal, a Q+ baseband signal, and a Q baseband signal, and the second switching unit includes a first branch performing a switching operation under control of the I+ baseband signal and the Q+ baseband signal, a second branch performing a switching operation under control of the I baseband signal and the Q baseband signal, a third branch performing a switching operation under control of the Q+ baseband signal and the I baseband signal, and a fourth branch performing a switching operation under control of the Q baseband signal and the I+ baseband signal.

A mixer includes a load portion connected between an input terminal of a first power voltage and an output terminal of the radio frequency transmit signal and configured to adjust a magnitude of the radio frequency transmit signal, a first switching unit connected to an output terminal of the radio frequency transmit signal, and configured to perform a first switching operation in response to a plurality of local oscillation signals, and a second switching unit connected between the first switching unit and an input terminal of a second power voltage, lower than the first power voltage, and configured to perform a second switching operation in response to a plurality of baseband signals, the plurality of local oscillation signals include an I+ baseband signal, an I baseband signal, a Q+ baseband signal, and a Q baseband signal, and the second switching unit includes a first branch performing a switching operation under control of the I+ baseband signal and the Q+ baseband signal, a second branch performing a switching operation under control of the I baseband signal and the Q baseband signal, a third branch performing a switching operation under control of the Q+ baseband signal and the I baseband signal, and a fourth branch performing a switching operation under control of the Q baseband signal and the I+ baseband signal.

A radio frequency (RF) front-end receiver having a passive mixer with feed-forward intermodulation distortion cancellation, or at least reduction. An example receiver generally includes a mixer having differential input terminals and differential output terminals and a baseband filter having inputs coupled to the differential output terminals of the mixer. The receiver also includes common-mode sensing circuitry coupled to the differential input terminals of the mixer and configured to sense a common-mode signal of a first differential signal present at the differential input terminals of the mixer. The receiver further includes a conversion circuit coupled to the common-mode sensing circuitry and configured to convert the common-mode signal to a second differential signal presented to the differential output terminals of the mixer and the inputs of the baseband filter.

According to one embodiment, a wireless communication apparatus includes receiver circuitry and transmitter circuitry. The receiver circuitry is configured to receive a first frame addressed to another apparatus, the first frame being transmitted by a first wireless communication apparatus, and estimate a difference between an oscillation frequency of an oscillator of the first wireless communication apparatus and an oscillation frequency of an oscillator of the wireless communication apparatus based on the first frame. The transmitter circuitry is configured to transmit a third frame at a frequency determined based on the difference during a period at least partially overlapping a period during which the first wireless communication apparatus transmits a second frame addressed to a second wireless communication apparatus.

According to one embodiment, a wireless communication apparatus includes receiver circuitry and transmitter circuitry. The receiver circuitry is configured to receive a first frame addressed to another apparatus, the first frame being transmitted by a first wireless communication apparatus, and estimate a difference between an oscillation frequency of an oscillator of the first wireless communication apparatus and an oscillation frequency of an oscillator of the wireless communication apparatus based on the first frame. The transmitter circuitry is configured to transmit a third frame at a frequency determined based on the difference during a period at least partially overlapping a period during which the first wireless communication apparatus transmits a second frame addressed to a second wireless communication apparatus.

A receiver circuit is provided. The receiver circuit includes an antenna configured to receive a radio frequency (RF) signal; a filter configured to filter the RF signal received by the antenna; and a passive mixer circuit configured to adjust a center frequency of the filtered RF signal to a predetermined frequency. The passive mixer circuit includes: a transformer which includes a first coil and a second coil that is separate from the first coil; a first passive mixer which is directly connected to a first end of the second coil; and a second passive mixer which is directly connected to a second end of the second coil and is separate from the first passive mixer.

A receiver circuit is provided. The receiver circuit includes an antenna configured to receive a radio frequency (RF) signal; a filter configured to filter the RF signal received by the antenna; and a passive mixer circuit configured to adjust a center frequency of the filtered RF signal to a predetermined frequency. The passive mixer circuit includes: a transformer which includes a first coil and a second coil that is separate from the first coil; a first passive mixer which is directly connected to a first end of the second coil; and a second passive mixer which is directly connected to a second end of the second coil and is separate from the first passive mixer.

A method for determining amplitude and phase correction coefficients for one or more signal processing paths across a frequency band of interest is provided. The method comprises transforming an input test signal from the time domain to the frequency domain to obtain an input magnitude spectrum and an input phase spectrum for the/each signal processing path. It further comprises transforming an/each respective output test signal from the time domain to the frequency domain to obtain an output magnitude spectrum and an output phase spectrum for the/each signal processing path. It also comprises comparing the/each input magnitude spectrum with its respective output magnitude spectrum to determine an amplitude correction coefficient for the/each signal processing path and/or comparing the/each input phase spectrum with its respective output phase spectrum, to determine a phase correction coefficient for the or each signal processing path.

A magnetic resonance imaging (MRI) system (100, 400, 500) includes a wireless RF station (20, 320, 420, 520, 620) which is associated with one or more RF coils which sense the magnetic resonance (MR) signal emitted from a subject under MRI examination. The wireless RF station communicates digital data representing the sensed MR signal to an MRI controller (124) for further processing, which may include display. An internal clock (2202, 3202) in the wireless RF station is precisely synchronized with the MRI controller clock (108, 2101, 3101), with carrier phase synchronization and code phase tracking of a predefined code sequence such as a pseudo random number (PRN) sequence.