Radio-frequency (RF) receivers having bandpass sigma-delta analog sigma analog-to-digital converters (ADC) designed to digitize signals in the RF domain are described. Such bandpass ADCs utilize one or more of the following techniques to enhance noise immunity and reduce power consumption: generation of in-phase (I) and quadrature (Q) paths in the digital domain, n.sup.th order resonant bandpass filtering with n>1, and signal sub-sampling in an i.sup.th Nyquist zone with i>1. Compared to RF receivers in which the I and Q paths are generated in the analog domain, these RF receivers exhibit higher IRRs because they are not susceptible to in-phase/quadrature (IQ) mismatch. Using n.sup.th order resonant bandpass filtering with n>1 attenuates unwanted image tones. The bandpass ADC-based RF receivers described herein exhibit enhanced immunity to noise, achieving for example image rejection ratios (IRR) in excess of 95 dB.

A device, system and method for improvement of analog/digital conversion. An improved delta sigma-converter including a phase or frequency modulation and demodulation, is used. The improved delta sigma-converter obtains higher gains than traditional Delta Sigma converter, preserving or improving the oversampling and noise shaping gains of these converters.

Apparatuses and methods for power amplification and signal transmission using complex delta-sigma modulation are disclosed. In one embodiment, a complex delta sigma modulator unit comprising a complex polar quantizer within an integrator loop is disclosed. The complex polar quantizer quantizes the envelope of a complex integrated signal and produces a complex quantized output signal of substantially constant envelope. The complex quantized output signal is used in deriving a complex feedback signal within the integrator loop of the complex DSM. The complex quantized output signal may be used in driving a power amplifier substantially at saturation. In some embodiments, an adjacent channel power ratio (ACPR) enhancement technique is used to reduce the quantization noise in the complex quantized output signal.

Provided are a wireless access system provided with a remote unit capable of handling a high-frequency region without being made complicated, and a control method for the same. A wireless access system according to the present invention is provided with: a center unit (1); and a remote unit (3) that converts a baseband signal generated by the center unit (1) into a high-frequency signal and emits the high-frequency signal from an antenna (12). The center unit (1) includes a 1-bit modulator (5) that converts the baseband signal into a 1-bit signal on the basis of a generated clock signal and outputs the 1-bit signal. The remote unit (3) includes: a local generation unit (10) that extracts the clock signal from the 1-bit signal output from the center unit (1), and generates a local signal using the extracted clock signal as a reference signal; a filter (13) that extracts a desired band component from the 1-bit signal; and an up-converter (14) that converts, using the local signal, an output signal of the filter into a high-frequency signal.

In the present invention, an all digital, multi channel RF transmitter is utilized for a parallel magnetic resonance imaging (MRI) device, MRI signal generation, modulation and amplification are employed entirely digitally in the proposed RF transmitter, which enables each transmit channel to be easily and individually reconfigured in both amplitude and phase. Individual channel control ensures a homogeneous magnetic field in the multi channel RF coil in MRI. Besides the homogeneous magnetic field generation, multi-frequency MRI signal generation is made easy by the present invention with very high frequency resolution. Multi-frequency enables faster image acquisition which reduces MRI operation time. Digital Weaver Single Side Band (SSB) modulation is also incorporated into the all digital transmitter to suppress unwanted bands of Double Side Band (DSB) MRI signals. The power amplifier in the MRI transmitter does not amplify the unwanted band so that SSB modulation leads to higher power efficiency.

Provided are a wireless access system provided with a remote unit capable of handling a high-frequency region without being made complicated, and a control method for the same. A wireless access system according to the present invention is provided with: a center unit (1); and a remote unit (3) that converts a baseband signal generated by the center unit (1) into a high-frequency signal and emits the high-frequency signal from an antenna (12). The center unit (1) includes a 1-bit modulator (5) that converts the baseband signal into a 1-bit signal on the basis of a generated clock signal and outputs the 1-bit signal. The remote unit (3) includes: a local generation unit (10) that extracts the clock signal from the 1-bit signal output from the center unit (1), and generates a local signal using the extracted clock signal as a reference signal; a filter (13) that extracts a desired band component from the 1-bit signal; and an up-converter (14) that converts, using the local signal, an output signal of the filter into a high-frequency signal.

A system for acquiring images by means of heterodyne digital holography comprises an image sensor having at least one photodiode coupled to an oversampling analog-digital converter.

In the present invention, an all digital, multi channel RF transmitter is utilized for a parallel magnetic resonance imaging (MRI) device, MRI signal generation, modulation and amplification are employed entirely digitally in the proposed RF transmitter, which enables each transmit channel to be easily and individually reconfigured in both amplitude and phase. Individual channel control ensures a homogeneous magnetic field in the multi channel RF coil in MRI Besides the homogeneous magnetic field generation, multi-frequency MRI signal generation is made easy by the present invention with very high frequency resolution. Multi-frequency enables faster image acquisition which reduces MRI operation time. Digital Weaver Single Side Band (SSB) modulation is also incorporated into the all digital transmitter to suppress unwanted bands of Double Side Band (DSB) MRI signals. The power amplifier in the MRI transmitter does not amplify the unwanted band so that SSB modulation leads to higher power efficiency.

A signal processing circuit has a first signal loop with a first signal processing block and a first feedback path that extends around the first signal processing block, the first signal processing block having a frequency dependence that causes the first signal loop to generate a passband. A second signal processing block is downstream of the first signal loop. A second feedback path extends from downstream of the second signal processing block to upstream of the first signal processing block. In operation, the first feedback path reinforces a signal in the passband and the second feedback path conditions the signal at an output downstream of the first signal processing block.

An exemplary apparatus for converting fluctuations in periodicity of an input signal into proportional fluctuations in the amplitude of an output signal includes: an input line for accepting an input signal; a delay element with an input coupled to the input line and an output; a detector having a first input coupled to the input line, a second input coupled to the output of the delay element, and an output; an integrator having an input coupled to the output of the detector and an output; and an output line coupled to the output of the integrator. The delay element introduces a time delay which is greater than zero and less than twice the nominal oscillation period of the input signal. The detector performs a differencing operation. The integrator has a time constant of integration that is smaller than twice the delay applied by the delay element.