Increase Power Efficiency and Lower Costs


Key areas of expertise include:


Digital Class D Audio Amplifiers 

Pallab and Bill are the original developers of the high fidelity class D audio amplifier technology from Freescale Semiconductor that received a 2006 EDN award for innovation. Digital Class D audio amplifier systems involve algorithms for conversion from digital audio PCM input to digital PWM output.  They can also include asynchronous sample rate conversion, and mixed mode feedback systems to produce high performance audio at the output of the power stage in the presence of power supply noise and power stage nonlinearities.  For ultra high performance audio, a digital class D amplifier also requires a pristine quantization clock with very low jitter.  To meet stringent EMI requirements it may be necessary to slow down the switching edges as well as distribute the switching over a well controlled frequency band.  Both of these result in changes to multiple aspects of the system design.

Class D audio amplifier chipsets are now available commercially.  However, a vast number of applications still use analog class AB amplifiers.  ADX Research, Inc. will help clients provide class D solutions that range in power from under 1 W to in excess of 1 kW with appropriate levels of audio quality.  ADX Research, Inc. has experience with high performance audio having dynamic range in excess of 105 dB un-weighted over the entire audio band.  In the digital domain, the founders of ADX Research, Inc. have invented algorithms for generation of digital PWM that have greater than 120 dB dynamic range and 110 dB linearity and have also invented spread spectrum digital PWM with similar audio performance but with dramatically lower EMI.   ADX Research, Inc. can provide digital PWM algorithms for class D audio amplification that optimize performance and cost for a wide range of applications.


High Performance Switching Power Conversion

Switching frequencies continue to rise as switches become faster and the space available for the power converter becomes smaller. In spite of the increase in the switching frequency, the performance of the power converter is often constrained by the controller. ADX Research provides expertise in agile power converter control such that the performance is constrained only by the power stage and the switching frequency.


Supply Modulation of RF Power Amplifiers  

Class AB RF power amplifiers can be 50 % efficient if they are operated close to saturation.  Therefore, in variable envelope applications, if the power amplifier is provided a variable supply that keeps it close to saturation then improved efficiencies are possible.  Doing this also disturbs the RF power amplifier linearity and takes special expertise to maintain linearity and ultimately meet the RF spectral mask requirements, including the spurs caused by the switcher switching frequency and its harmonics.  The first commercial subscriber application to implement this technology was architected by the founders of ADX Research and introduced in the first Motorola satellite phone.  The resulting system doubled the RF power amplifier efficiency while significantly shrinking system cost by reducing the RF power amplifier requirements.  A larger volume cell-phone application that also involved an RF linearization loop was also implemented.


Switching RF Generation and Amplification

Modulated RF generation and amplification represents a large fraction of mixed mode ICs.  If modulated RF could be generated in the digital domain and amplified by switching amplifiers it would represent a radical change in the communication industry.  As semiconductor switches become faster, this is a goal achievable for niche applications today.  The longer term goal would be more mainstream applications.  Initial results are highly promising and the technology is ready for larger trials.



RF Power Amplifier Linearization

Linear RF power amplifiers are used in applications where the RF signal has a variable amplitude. Nonlinearities cause spectral regrowth that may cause interference. Attempts to improve power amplifier efficiency can further degrade linearity. By appropriately predistorting the input signals it is possible to compensate for the nonlinearity in the RF power amplifier. This linearization process can enable improved power conversion efficiency of the RF power amplifier.