Earl W. McCune

Operating modes of dynamic-power-supply transmitter amplifiers

Any amplifier operated with a varying supply voltage is actually a three-port circuit, having two inputs and one output. When an amplifier is characterized as a three-port for dynamic supply voltage operation, three separate operating modes appear: linear L-mode and the two nonlinear modes C-mode and P-mode. Each of these modes, along with their relationships and differences, are identified, characterized, and discussed. Relations of these modes to the dynamic power supply transmitter techniques of envelope tracking and/or direct polar are presented. Measurements are reported that provide experimental verification for these amplifier operating modes.

Direct digital frequency synthesizer with designable stepsize

The Variable Resolution (VR) technique for direct digital frequency synthesis (DDFS) is introduced. By manipulating the number of phase states available to the DDFS accumulator, it is shown that the frequency resolution can be designed to desired values while keeping binary arithmetic circuit structures. Examples focus on realizing exact decimal resolution and prime rational fractions thereof, such as 1/3. Measurements not only validate this design approach, but also show worst case output spurious signal magnitudes below −73 dBc from initial implementations

Fundamentals of Switching RF Power Amplifiers

How to determine if an amplifier is actually switching, or is just operating in compression, is developed here. While compressed amplifier operation is any deviation from linear operation toward lower output at the highest amplifier output powers, switching has additional requirements that the transistor achieve two steady states within each RF cycle: OFF and ON. Conditions necessary for transistor switching operation to occur at RF signal frequencies are derived, and related to the transistor transition frequency metric fT. The degradation of available amplifier efficiency as the operating frequency approaches fT is evaluated. Testing methods to verify that transistor switching operation is achieved are proposed.

Spurious mechanisms and debugging in direct digital synthesis

While the technique of direct digital frequency synthesis (DDFS) is well known, the mechanisms active in the generation of non-harmonic spurious output signals are not so well known. Here the significant spurious generating processes active in a DDFS design are illustrated. Use of this information in debugging a DDFS design to fundamentally reduce power in spurious signals is discussed. Thus this work specifically excludes dithering, a spurious power spreading process, from the techniques considered.

Multimode Transmitters: Easier with Strong Nonlinearity

Traditionally, multimode transmitters are approached from a linear circuit approach, and then significant work follows to improve their abysmal initial energy efficiency. Here we consider the reverse procedure, where the starting point is the circuit with greatest energy efficiency – a switch – surrounded by system architectures which result in exactly the same output signals. This latter approach necessarily leads to polar signal processing and polar modulation techniques.

Process- and technology-independent power switching transistor figures of merit

It is becoming important to properly choose among the many semiconductor switch technologies available when designing efficient high-speed power switches, due to required circuit energy efficiency improvements. In a world of wide bandwidth and high frequency signals, the desirable operating frequency of switch-mode circuitry increases correspondingly. This paper proposes two figures of merit (FoM) combining FET channel ON resistance with gate-charge and gate-source voltage to perform such comparisons. Beyond just comparison, one FoM is shown to be useful in design and evaluation of high speed, high power switches and their drivers. Using these comparisons, silicon FETs are shown to have a huge disadvantage for high speed switching applications including RF power amplifiers.

An RFIC within a direct open-loop polar multimode transmitter for UMTS/EDGE/GSM

An RFIC within a direct open-loop polar multimode transmitter that supports UMTS, GSM, and EDGE is shown in 0.18 mum CMOS. Design details, and chipset system application are explained. The chip architecture applies phase accurate FLL two-point modulator with SigmaDelta feedback control for AM-PM corrected wideband phase modulation to an LC VCO, and AM-AM corrected envelope drive of multi-stage saturated PA. IC measurement results and chip-set system performance are presented.

Power proportional computing for “Green” servers

Achieving energy-efficient “Green” operations within data centers used for applications such as Cloud Computing requires matching the power consumed to the data processed at each server in real-time. Beyond having a high efficiency in the server power supplies, it is vitally important to only draw power when the server is actually processing data. To operate at maximum energy efficiency, in the times when a server is idle it needs to draw no power for the server farm. By matching power draw to actual data processing activity at logic speeds, the average energy draw of the server farm drops by 50% or more with no reduction in throughput. Drawing on technology developed for efficient radio transmitters, an agile power supply, able to provide tight voltage regulation and still transition between power-off and power-on (or the other way) in nanoseconds without transition overshoot is described. With this nanosecond agility, this also solves the objective for elastic computing. Additionally, the supply pin pairing required by this energy management method provides benefits toward reducing electromagnetic interference (EMI). Proportional reduction in processor operating temperature improves reliability, along with reducing facility cooling loads.

Embrace circuit nonlinearity to get transmitter linearity and energy efficiency

Abstract form only given. Following a review of why the design of transmitter power amplifiers is getting more complicated, a reverse approach to the usual design approach is presented: instead of starting with a linear circuit and then working to improve its energy efficiency, rather begin with a maximally energy efficient circuit and work to make it support all the signals we require from the transmitter. New design methods are introduced to support this inverted development procedure. Gain, stability, power control, and long term ageing results are presented.