Apparatus and methods for biasing a power amplifier are disclosed. In one embodiment, a method of biasing a power amplifier includes shaping an enable signal using a time-dependent signal generator to generate a control current, amplifying the control current using a current amplifier to generate a correction current, and generating a bias current for a power amplifier using a primary biasing circuit. The primary biasing circuit is configured to use the correction current to correct for a variation in gain of the power amplifier when the power amplifier is enabled.

Apparatus and methods for biasing power amplifiers

Aspects of this disclosure relate to dynamic error vector magnitude (DEVM) compensation. In one embodiment, an apparatus includes an amplifier, a low pass filter, and a bias circuit. The amplifier, such as a power amplifier, can amplify an input signal. The low pass filter, such as an integrator, can generate a correction signal based at least partly on an indication of a duty cycle of the amplifier. The indication of the duty cycle of the amplifier can be an enable signal for the amplifier, for example. The bias circuit can generate a bias signal based at least partly on the correction signal and provide the bias signal to the amplifier to bias the amplifier.

Dynamic error vector magnitude duty cycle correction

A semiconductor die with an integrated circuit providing a signal conditioner (106) for a capacitive transducer (105), comprising: a gain stage (101) configured to receive an analogue transducer signal; an analogue-to-digital converter (102) coupled to receive a signal outputted from the gain stage (101) and to provide a digital signal. A feedback signal is provided via a digital-to-analogue converter (104) and a digital signal processor (103) that receives the digital signal; and the gain stage (101) is configured with a first input (107) and second input (108) coupled to receive the analogue transducer signal and the feedback signal, respectively.

Signal conditioner with suppression of interfering signals

Apparatus and methods for biasing power amplifiers are disclosed herein. In certain implementations, a power amplifier system includes a power amplifier and a bias circuit that generates a bias voltage for biasing the power amplifier. The bias circuit includes an amplifier, a current source for generating a reference current, and a reference transistor having a current therethrough that changes in relation to the bias voltage. The amplifier can control the bias voltage based on an error current corresponding to a difference between the reference current and the current through the reference transistor. The amplifier can be used to control the bias voltage such that the reference current and the current through the reference transistor are substantially equal.

Apparatus for reproducing sound including at least three loudspeakers (5, 6,7) mounted in a substantially sealed enclosure. The three loudspeakers may be mounted to a wall of the enclosure so that they are all directed away from, and evenly spaced around, a common point. Two speakers may be driven with the respective out of phase signals comprising the difference between two stereo channels and another speaker with the sum of those channels.

Apparatus for reproduction of sound

A method and system for providing a mixed-mode (current- and voltage-source) audio amplifier is disclosed. The mixed-mode amplifier includes a voltage sensing feedback path including a first network comprising at least one circuit; and a current sensing feedback path including a second network comprising at least one circuit. According to the method and system disclosed herein, the first and second networks vary an output impedance or transconductance of the amplifier as a function of frequency of the input voltage signal, such that at a first frequency range, the amplifier operates substantially as a current amplifier, and at a second frequency range, the amplifier operates substantially as a voltage amplifier, thereby inheriting distortion reduction of the current amplifier and stability of the voltage amplifier.

John J. Hench

Papers

Mixed-mode (current-voltage) audio amplifier