A semiconductor device includes a carrier transit layer including a first region and second and third regions having a density of a donor impurity element higher than that of the first region, an In.sub.XAl.sub.YGa.sub.(1-X-Y)N (0<X<1, 0<Y<1, 0<X+Y1) carrier supply layer provided over the carrier transit layer and having a density of a donor impurity element lower than that of the second and third regions, a source electrode provided over the second region, a drain electrode provided over the third region, and a gate electrode provided over the carrier supply layer between the source electrode and the drain electrode.

A compound semiconductor device includes: a first layer of nitride semiconductor, the first layer being doped with Fe; a channel layer of nitride semiconductor above the first layer; and a barrier layer of nitride semiconductor above the channel layer, wherein the channel layer includes: a two-dimensional electron gas region in which the two-dimensional electron gas exists; and an Al-containing region between the two-dimensional electron gas region and the first layer, an Al concentration in the Al-containing region being 510.sup.17 atoms/cm.sup.3 or more and less than 110.sup.19 atoms/cm.sup.3.

The present invention relates in one aspect to a class D audio amplifier with improved output driver topology supporting multi-level output signals such as 3-level, 4-level or 5-level pulse width or pulse density modulated output signals for application to a loudspeaker load. The present class D audio amplifiers are particularly well-suited for high-volume consumer audio applications and solutions.

A radio-frequency module comprises a low-noise amplifier including a common source transistor having a gate node that receives a radio-frequency input signal and a drain node that transmits a combined radio-frequency output signal, and a correction signal input path configured to receive a correction signal and provide the correction signal to a source node of the common source transistor to generate, at least in part, the combined radio-frequency output signal.

A biosignal apparatus is described including an amplifier and a sampler. The amplifier is configured to alternate between an operating state and a low power state based on a periodically changing control signal. The sampler is configured to sample a signal output from the amplifier in response to the amplifier being in the operating state and maintain the sampled signal in response to the amplifier being in the low power state.

A radio frequency receiver comprises a plurality of parallel receiving paths, wherein each path can receive a radio frequency signal in one of a plurality of radio frequency bands and amplify the received signal in a low noise amplifier. The amplified signals from the plurality of parallel paths are combined to one combined radio frequency signal in a common summation node and down-converted to a lower frequency signal in a mixer circuit. Each low noise amplifier comprises a low noise transconductance circuit providing a current signal to drive the common summation node, and an automatic gain control circuit in each path compensates for variations in signal strength independently of signal strengths of signals received by the other receiving paths. The receiver is suitable for simultaneous multiple band reception, where received signal strength can vary between the frequency bands.

A system for amplifying a signal with active power management according to one embodiment includes a first digital to analog converter (DAC) circuit configured to provide a modulated carrier signal; a amplifier circuit coupled to the first DAC, where the amplifier circuit is configured to amplify the modulated carrier signal; an output stage circuit coupled to the amplifier circuit, where the output stage circuit is configured to provide the amplified signal to a network; a second DAC circuit configured to provide a full wave rectified envelope of the modulated carrier signal; and a switching regulator circuit including a voltage reference input coupled to the second DAC circuit, where the switching regulator circuit is configured to provide a supply voltage to the output stage circuit and the supply voltage is modulated in response to the envelope received at the voltage reference input.

An amplifier (100) adapted for noise suppression comprises a first input (102) for receiving a first input signal and a second input (104) for receiving a second input signal, the first and second input signals constituting a differential pair. A first output (106) delivers a first output signal and a second output (108) delivers a second output signal, the first and second output signals constituting a differential pair. A first transistor (M.sub.CG1) has a first drain (110) coupled to the first output (106) such that all signal current, except parasitic losses, flowing through the first drain (110) flows through the first output (106), and the first transistor (M.sub.CG1) further having a first source (112) coupled to the first input (102). A second transistor (M.sub.CS1) has a second gate (116) coupled to the first input (102), a second drain (118) coupled to the second output (108) such that all signal current, except parasitic losses, flowing through the second drain (118) flows through the second output (108), and the second transistor (M.sub.CS1) further having a second source (120) coupled to a first voltage rail (122). A third transistor (M.sub.CS2) has a third gate (124) coupled to the second input (104), a third drain (126) coupled to the first output (106) such that all signal current, except parasitic losses, flowing through the third drain (126) flows through the first output (106), and the third transistor (M.sub.CS2) further having a third source (128) coupled to the first voltage rail (122). A fourth transistor (M.sub.CG2) has a fourth drain (130) coupled to the second output (108) such that all signal current, except parasitic losses, flowing through the fourth drain (130) flows through the second output (108), and the fourth transistor (M.sub.CG2) further having a fourth source (132) coupled to the second input (104). A first load (Z.sub.L1) is coupled between the first output (106) and a second voltage rail (136). A second load (Z.sub.L2) is coupled between the second output (108) and the second voltage rail (136). A first inductive element (L.sub.1) is coupled between the first input (102) and a third voltage rail (138), and a second inductive element (L.sub.2) is coupled between the second input (104) and the third voltage rail (138). Transconductance of the first transistor (M.sub.CG1) is substantially equal to transconductance of the fourth transistor

Provided is a terrestrial broadcast wave reception-use antenna device having performance that is equivalent to or better than that of a conventional device in frequency bands at or below an FM band even if an antenna element length is shortened to approximately 55 [mm]. An amplifier (12-A) is configured so as to include a compound semiconductor HEMT for amplifying a received wave having a frequency at or below a resonant point of an antenna element (10) among received waves of the antenna element (10), the compound semiconductor HEMT having an equivalent noise resistance of 2 [] or smaller for the received frequency so that a noise figure (NF) is approximately constant over a wide frequency band at or below the FM band.

Methods and apparatus for Class-D amplifier circuits with improved power efficiency. The circuit has an output stage with at least first and second switches and a modulator that receives an input signal to be amplified, S.sub.IN, and a first clock signal f.sub.SW. The modulator controls the duty cycles of the first and second switches, within a switching cycle based on the input signal, wherein the switching cycle has a switching frequency based on the first clock signal. A frequency controller controls the frequency of the first clock signal in response to an indication of the amplitude of the input signal so as to provide a first switching frequency at a first input signal amplitude and a second, lower, switching frequency at a second, lower, input signal amplitude. A lower switching frequency can be tolerated at low signal amplitudes and varying the switching frequency in this way thus maintains stability whilst reducing switching power losses.