A 14-bit high-temperature ΣΔ modulator in standard CMOS

Experimental verification is given for the use of ΣΔ modulation for high-temperature applications (≥approximately 150°C) in a standard CMOS process. Switched-capacitor circuits are used to implement a second-order single-stage and a third-order 2-1 MASH ΣΔ modulator with single-bit quantization. The two modulators have an oversampling ratio of 256 with an input signal bandwidth of 500 Hz. The modulators were fabricated in a 1.5-μm standard CMOS technology. A fully differential signal path and near minimum sized switches are used to mitigate the effect of large junction-to-substrate leakage current present at high temperatures. Experimental results show both modulators are capable of over 14 bits of resolution at 225°C and over 13 bits of resolution at 255°C. Results show that the single-stage modulator is more resistant to high-temperature circuit impairment than is the MASH cascaded structure.