Explicit characterization of bandgap references
Dai, Xin (2006) Explicit characterization of bandgap references. Masters thesis, Iowa State University.
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Stable and precision voltage references are an integral part of many analog and mixed-signal integrated circuits. Bandgap references have been widely used for precision on-chip voltage sources in both bipolar and CMOS processes. Conspicuously absent in the literature are explicit relationships between the output voltage and temperature of bandgap references. Temperature characteristics of bipolar junction transistors (BJT’s) are developed to explicitly characterize the I-V relationship of BJT’s. Based on this characterization, an explicit relationship for the output voltage of a popular bandgap reference structure is developed. Within the context of this explicit relationship, temperature stability properties of references are explored. Also included in this work is the introduction of a new digital calibration algorithm for pipeline ADCs and an order-dependent layout strategy that inherently cancels high-order gradient effects. The digital calibration algorithm does not require perturbation of the signal path through the pipeline and requires only code density test data generated from applying a simple non-critical test signal at the input. This calibration algorithm can be used to calibrate a multitude of ADC architectures. As a practical example, this method is used to calibrate a sub-radix pipelined ADC with minimal digital circuit overhead. By incorporating this calibration algorithm as part of the design process, the design requirements of the analog part of an ADC can be relaxed. The nth order central symmetrical layout method provides cancellation of all spatial gradients up to nth order by using 2n unit cells in each element for pair-wise element matching. This method is useful for the layout of matching critical devices in high-precision circuits.
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