On-chip measurement of bandgap reference voltage using a small form factor VCO based zoom-in ADC

A robust and scalable technique for measuring the output voltage of a band-gap reference (BGR) circuit is described. The proposed technique is based on an ADC architecture that uses a voltage controlled oscillator (VCO) for voltage to frequency conversion. During production testing, an external voltage reference is used to approximate the voltage/frequency characteristics of the VCO with 5ms test time. The proposed zoom-in ADC approach is manufactured with 0.5μm CMOS process. Measurement results indicate that 12 bits of resolution within the measurement range can be achieved with the zoom-in approach. Worst-case INL for the ADC is less than 0.25LSB (50μV).