An optical communication apparatus includes a level detector, an FIR filter, and a adjustor. The level detector detects level information that discriminates a change in a multi-value level based on an input signal used in a multi-value amplitude modulation system. The FIR filter compensates a signal band of the input signal in accordance with tap coefficients of a plurality of multipliers. The adjustor corrects the tap coefficient of each of the multipliers included in the FIR filter based on the level information detected in the level detector.

A signal density modulation (SDM) encoder includes a first subtractor, a sigma circuit and a multi-bit quantizer. The first subtractor is used for receiving an input signal. The sigma circuit is coupled to the first subtractor. The multi-bit quantizer, coupled to the first subtractor and the sigma circuit, is configured to generate an output signal. The sigma circuit or the multi-bit quantizer produces a first feedback signal to the first subtractor. The first subtractor performs a subtraction operation according to the first feedback signal and the input signal, and generates a delta signal. The sigma circuit performs an operation on the delta signal, such that the SDM encoder has a noise transfer function having a high pass filtering effect. The noise transfer function is a ratio of a quantization error brought by the multi-bit quantizer with respect to the input signal. The output signal has more than two levels.

An optical communication apparatus includes a level detector, an FIR filter, and a adjustor. The level detector detects level information that discriminates a change in a multi-value level based on an input signal used in a multi-value amplitude modulation system. The FIR filter compensates a signal band of the input signal in accordance with tap coefficients of a plurality of multipliers. The adjustor corrects the tap coefficient of each of the multipliers included in the FIR filter based on the level information detected in the level detector.

A digital filter and a method for filtering a pulse density modulation (PDM) signal are presented. The digital filter has a first filter circuit to receive an input signal with input values at successive time steps to provide a filtered input signal with filtered values at successive time steps. The digital filter does not require sample-rate or data format conversions. Also, the digital filter is area and power efficient when implemented in hardware. Optionally, the digital filter has a sigma-delta modulator including the quantiser, the sigma-delta modulator being used to receive the filtered input signal and to process the filtered input signal before and/or after being quantised by the quantiser. This digital filter does not require sample-rate or data format conversions. This digital filter is area and power efficient when implemented in hardware.

An analog-to-digital converter (ADC) includes a modulator configured to oversample an input signal generated from an output signal of a transducer; and a filter configured to perform a decimation operation on an output from the modulator and a frequency characteristics correction operation according to a filter control signal on the output from the modulator, wherein the frequency characteristics correction operation is performed to complement a frequency characteristics of the output signal of the transducer such that overall frequency characteristics of the transducer and the filter be flat in a signal band.

A digital filter and a method for filtering a pulse density modulation (PDM) signal are presented. The digital filter has a first filter circuit to receive an input signal with input values at successive time steps to provide a filtered input signal with filtered values at successive time steps. The digital filter does not require sample-rate or data format conversions. Also, the digital filter is area and power efficient when implemented in hardware. Optionally, the digital filter has a sigma-delta modulator including the quantiser, the sigma-delta modulator being used to receive the filtered input signal and to process the filtered input signal before and/or after being quantised by the quantiser. This digital filter does not require sample-rate or data format conversions. This digital filter is area and power efficient when implemented in hardware.

Most of the AC-DC converters have an analog control loop, which costs additional pins for the compensator, and there are limited options to change settings when, for example, the output voltage needs to change. This specification discloses systems and methods, where a delta-sigma ADC (analog-to-digital converter) is used to digitize the input voltage. The filter after the delta-sigma ADC can give a big delay, which reduces the phase margin of the control loop. To minimize the delay, this invention ensures that, when the setpoint is reached, the input of the delta-sigma modulator is in the middle of the input range. In some embodiments, a digital control loop can be implemented using a delta-sigma modulator together with a PI controller (proportional-integrator controller).

A radio frequency (RF) transmitter includes a set of input ports to receive baseband samples of a signal to be transmitted on a set of disjoint frequency bands, a set of filter banks, there is one filter bank for each input port, each filter bank includes a plurality of digital polyphase interpolation filters to sample a shifted phase of the corresponding sequence of baseband samples and to interpolate the sampled phases to produce a plurality of sequences of interpolated baseband phased samples with the shifted phase, and a set of oscillators banks, each oscillator bank includes a plurality of polyphase Digital Direct Synthesizer (DDS) corresponding to the plurality of digital polyphase interpolation filters to generate a plurality of sequences of samples of digital waveform. The RF transmitter includes a set of mixer banks to mix corresponding sequences of samples of digital waveform and interpolated baseband phased samples to up convert each sequence of interpolated baseband phased samples to the effective frequency, a parallel digital combiner to combine in-phase sequences of interpolated baseband phased samples of different frequency bands to produce a plurality of sequences of multiband upconverted samples, and a pulse encoder to modulate and encode the plurality of sequences of multiband upconverted samples to produce a plurality of encoded multi-band signals. The RF transmitter converts the plurality of encoded multi-band signals into a RF bitstream and radiate the RF bitstream as an analog signal.

An analog-to-digital converter (ADC) includes a modulator configured to oversample an input signal generated from an output signal of a transducer; and a filter configured to perform a decimation operation on an output from the modulator and a frequency characteristics correction operation according to a filter control signal on the output from the modulator, wherein the frequency characteristics correction operation is performed to complement a frequency characteristics of the output signal of the transducer such that overall frequency characteristics of the transducer and the filter be flat in a signal band.

A radio frequency (RF) transmitter includes a set of input ports to receive baseband samples of a signal to be transmitted on a set of disjoint frequency bands, a set of filter banks, there is one filter bank for each input port, each filter bank includes a plurality of digital polyphase interpolation filters to sample a shifted phase of the corresponding sequence of baseband samples and to interpolate the sampled phases to produce a plurality of sequences of interpolated baseband phased samples with the shifted phase, and a set of oscillators banks, each oscillator bank includes a plurality of polyphase Digital Direct Synthesizer (DDS) corresponding to the plurality of digital polyphase interpolation filters to generate a plurality of sequences of samples of digital waveform. The RF transmitter includes a set of mixer banks to mix corresponding sequences of samples of digital waveform and interpolated baseband phased samples to up convert each sequence of interpolated baseband phased samples to the effective frequency, a parallel digital combiner to combine in-phase sequences of interpolated baseband phased samples of different frequency bands to produce a plurality of sequences of multiband upconverted samples, and a pulse encoder to modulate and encode the plurality of sequences of multiband upconverted samples to produce a plurality of encoded multi-band signals. The RF transmitter converts the plurality of encoded multi-band signals into a RF bitstream and radiate the RF bitstream as an analog signal.