Douglas A. Teeter

Average current reduction in (W)CDMA power amplifiers

Statistical average current consumption of conventional CDMA and WCDMA [(W)CDMA] power amplifiers is compared to that obtained by using DC-DC converters, analog bias control, and low power efficiency enhancement (LPEE) techniques. A discussion of theoretical limits, strengths, and weaknesses for each approach is presented

GaAs HBT ESD Diode Layout and its Relationship to Human Body Model Rating

Different GaAs HBT ESD diode configurations are analyzed and compared using human body model (HBM) and transmission line pulse (TLP) measurements. A common diode stack test circuit consisting of 3 series forward and reverse diodes is used to analyze ESD ruggedness dependence on layout and area. Both base emitter and base collector junction ESD ruggedness is compared and analyzed. To our knowledge, this is the first time data has been presented for GaAs HBT diodes that calculates the ratio of HBM voltage to maximum TLP current

Implications of thermal instability on HBT power amplifier reliability

Abstract Thermal stability is one of several important performance requirements for RF power amplifier modules used for cellular applications. In this work, the conditions for thermal instability in an HBT array for shared and individual ballast configurations are evaluated using experimental results from RF biased life test (RFHTOL) and ADS simulations. The instability is modest under nominal operating conditions, but becomes more severe at elevated temperatures which are frequently used in accelerated reliability tests such as RFHTOL. Thermally unstable power cells exhibit current crowding where one or two cells hog most of the current, resulting in localized hot spots from increased power dissipation density. This paper discusses the link between reliability failures during RFHTOL reliability testing and the thermal stability of HBT arrays used in a power amplifier. Shared ballast arrays are shown to be less thermally stable than individually ballasted arrays and thus have more failures during RFHTOL testing. Electro-thermal results indicate the layout aspects of power amplifier module also play an important role in determining junction temperatures for various stages.

RF induced communication errors in RFFE MIPI controlled Power Amplifiers

As the number of RF components increases inside mobile devices, the industry has rapidly adopted and utilized MIPIs RFFE serial bus specification [1] to communicate with these devices and reduce the amount of control line routing between components. However, the use of a serial bus within the RF front end increases the risk that RF energy, particularly from the Power Amplifier (PA), can corrupt the RFFE bus communication. RF coupling to areas such as the RFFE serial clock (SCLK) signal seen within the PAs RFFE state machine can result in communication errors with the PA. This coupling can be to the SCLK signal itself, or to the PAs CMOS controllers ground reference. PA designers must pay special attention to the positioning and design of the CMOS controller and the internal routing of signals to the controller to avoid these problems. This paper provides a detailed analysis of how RF energy coupling to the internal CMOS controller can create “glitches” on the SCLK signal that cause communication errors. A simple example is provided to illustrate how choices in PA module layout can significantly impact these issues. A natural extension of these concepts applies to phone or radio board layouts, too.