A third-order complementary metal-oxide-semiconductor sigma-delta modulator operating between 4.2 K and 300 K

Area of Science:

• Cryogenic electronics
• Mixed-signal integrated circuits
• Low-temperature instrumentation

Background:

• Sigma-delta modulators are crucial for high-resolution analog-to-digital conversion.
• Operating electronic components at cryogenic temperatures presents unique challenges, including performance degradation and anomalies.
• Standard CMOS processes are often limited in their low-temperature operational capabilities.

Purpose of the Study:

• To design and implement a third-order switched-capacitor sigma-delta modulator capable of operating across a wide temperature range, from 300 K down to 4.2 K.
• To optimize the modulator's architecture, specifically the operational transconductance amplifier (OTA) in the loop filter, to mitigate cryogenic anomalies.
• To evaluate the modulator's performance, including signal-to-noise-plus-distortion ratio (SNDR) and power consumption, at both room and cryogenic temperatures.

Main Methods:

• Implementation of a third-order switched-capacitor sigma-delta modulator in a standard 0.35-μm CMOS process.
• Design and optimization of an operational transconductance amplifier (OTA) to address cryogenic anomalies below the freeze-out temperature.
• Characterization of the modulator's performance, including SNDR and power consumption, at 300 K and 4.2 K with a 5 kHz signal bandwidth and 500 kHz sampling frequency.

Main Results:

• At 300 K, the modulator achieved a signal-to-noise-plus-distortion ratio (SNDR) of 70.8 dB with a 5 kHz bandwidth and 500 kHz sampling frequency.
• At cryogenic temperature (4.2 K), the modulator maintained a competitive SNDR of 67.7 dB.
• The cryogenic operation at 4.2 K demonstrated low power consumption, drawing only 21.17 μA from a 3.3 V supply.

Conclusions:

• The developed third-order switched-capacitor sigma-delta modulator successfully operates across a broad temperature range, from 300 K to 4.2 K.
• The optimized OTA architecture effectively eliminates cryogenic anomalies, ensuring robust performance at extremely low temperatures.
• This work demonstrates the feasibility of using standard CMOS technology for high-performance mixed-signal applications in cryogenic environments.