Investigating packaging effects on bandgap references

Abstract

This thesis investigates packaging effects on precision bandgap voltage references used in LTC switching regulators. Packaging stress causes a mean offset and room temperature distribution widening of the bandgap reference output voltage, as well as inconsistent temperature characteristics. Bandgap references with and without a proprietary stress-relief mechanism were compared to determine the impact of packaging stress on reference performance. References without stress-relief showed a mean offset of -2.3mV and spread of 10mV, while references with stress-relief showed a mean offset of -2.0mV and spread of 3.6mV. References with stress relief exhibited more consistent temperature coefficients than references without stress relief. A test chip was fabricated to allow measurement of VBE and AVBE within the bandgap reference. Parts with stress-relief showed tighter VBE and AVBE distributions, as well as more favorable temperature characteristics. The experiments in this thesis show that stress-relief is effective at improving bandgap reference performance.