Abstract: Direct current (DC) offset in and audio driver can cause a constant drain on power even when there is no sound. Furthermore it can cause an audible pop when the audio driver is enabled. A scaled replica output stage can be employed to perform DC offset cancellation offline during a sampling phase. Once DC offset cancellation is achieved, the audio driver uses a full scale output stage during the operation phase.

Abstract: An integrated audio codec includes a high-pass filter to prevent damage to personal computer speakers and other components. The audio codec may be compliant with HD audio standards and can operate with generic software drivers. Tuning of the high-pass filter is provided through an external pin-out where either an external capacitor or external resistors provide an ability to tune the high-pass filter. In one implementation, a tuning voltage is digitized into a tuning code used by a digital high-pass filter. In addition, multiplexers can be used to insure only the audio path leading to the speakers is filtered.

Abstract: A triangular waveform generator is converted to a free running oscillator controlled by a calibration code. The free running oscillator can be synchronized to an external clock signal by comparing the external clock frequency to the frequency of the triangular waveform and adjusting the calibration code until the discrepancy in frequency is minimized.

Abstract: Class-D amplifiers have evolved from using binary pulse-width modulation (PWM) modulators to three-level PWM modulators. Three-level PWM drivers for audio applications offer the benefits of eliminating costly elements at the output of an audio system. However, they also introduce increased common-mode interference. Three-level PWM generates three states, but one state has two interchangeable representations which can be scrambled in order to shape the common-mode output spectrum.

Abstract: Presently many audio chips suffer from pop issues, which is especially serious for single ended audio drivers. An audio pop is a disturbance in the output caused by a sudden transition of chip power, particularly when a chip is powered on or powered off. Furthermore, compensation networks included in the amplifiers on audio chips for stability offer a significant path for transmitting power disturbances to the output. Hence, circuitry is developed to suppress pops in the output stages of an amplifier.

Abstract: In today's environment class-D amplifiers are used to provide an integrated solution for applications such as powered audio devices due to their advantages in power consumption and size over more traditional analog amplifiers. Due to power output requirements, the output stages of power drivers such as class-D amplifiers require a supply voltage in excess of the technologically allowed voltage for the switches in the output stage. A level shifter is used to ensure voltages supplied to the output switches do not exceed the technological limits. An ideal level shifter should provide the optimal voltage swing to output switches under all process, supply voltage and temperature (PVT) variations. The ideal level shifter should also provide fast transitions when the control signal changes from high to low and low to high.

Abstract: A driver controller comprising a state machine for controlling transitions between a plurality of states. An output switch for providing a low impedance path to ground during transition periods. An output stage for decoupling output signal from driver amplifier during the transition periods.

Abstract: An apparatus for detecting and controlling current. A current detector for generating a first value that represents an amount of current being delivered to a device. A current limit circuit for generating a second value that represents a maximum permitted current level from a current source. A current controller for controlling the amount of current drawn by the device if the first value exceeds the second value.