Ralph Oberhuber

A 1 ppm/°C bandgap voltage reference with new second-order Taylor curvature compensation

The industrys most accurate 2.5V bandgap voltage reference is presented with true 16-bit performance: 1 ppm/C temperature coefficient, 100 µV initial accuracy, 1 µV/V line regulation and 15 µV/mA load regulation. This unique accuracy has been achieved by controlling every important parameter with a dedicated feedback loop, using unconditionally stable single-stage amplifiers. A two-temperature trimming procedure, used on packaged parts at the final test, allows to set the reference value at normal temperature and to remove the first-order temperature drift without the need to store a package ID number. Vbe curvature compensation is implemented with a new, enhanced second-order Taylor approximation. The combination of the mentioned techniques results in a unique implementation of a bandgap reference suitable for any system-on-chip design because it is small in chip area, easily manufacturable, and easy to use, and at the same time shows best in class accuracy.

Bandgap yield loss due to dislocations on RFSiGe transceiver ICs: failure analysis, design

New design and layout methods were developed to overcome yield loss from dislocation defects, which are omnipresent in SiGe technologies as a penalty for the higher speed compared to pure Si. This paper presents the failure analysis on bandgap malfunctions in a RF-SiGe transceiver device which is currently ramped to production. The resulting yieldloss was significant. In-circuit fault analysis identified collector-emitter leakage of the SiGe-HBTs as the electrical root cause. All existing failure patterns were explained with SPICE circuit simulation. Isolation and characterization of the bipolar transistor and high resolution TEM showed dislocations originating from the high strain at the STI-moat edge. Design and layout improvements were applied to reduce the sensitivity of the bandgap reference circuit to the defects: a 5V HBT with superior yield performance was introduced, and variations in the sizing of the matched npn were investigated. With these improvements, the bandgap fails were drastically reduced.

Low overshoot, low dropout voltage regulator with level detector

An ultra-small, low power, low dropout (LDO) voltage regulator is presented which tracks the output voltage with threshold voltages of the underlying process technology. The topology of the regulator is extremely simple because it does not use an error amplifier. Instead a common-gate stage feedback loop is used, reducing the number of active transistors to only 10. This results in extremely small chip area as well as very low power consumption. This regulator is suitable for various applications where high precision of the output voltage is not required, such as controlling the interfaces of the various sub-circuits in highly complex system-on chip designs. Moreover, in many applications, the voltage overshoot from the output of the LDO can cause violations of breakdown voltage limitations on transistor terminals in subsequent stages, and thus damages those transistors. Therefore in the second part of this paper, an improved ultra-small regulator circuit will be discussed with reduced output voltage overshoot for sharp input voltage ramps. It also comprises a simple, new level detector circuit which indicates if the regulator is in regulation mode or passive mode.