Ultra-Low-Power Always-On Blocks in GF22nm Technology
H. Fattahi (TU Delft - Electrical Engineering, Mathematics and Computer Science)
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Abstract
Internet-of-Things (IoT) applications require nanowatt (nW) power references that are robust to process, voltage, and temperature (PVT) variations. This thesis presents the design of ultra-low-power (ULP) sub-10nW always-on blocks in GlobalFoundries 22nm (GF22nm) technology, including a Proportional to Absolute Temperature (PTAT) current reference, a bandgap reference, and a Low Dropout Regulator (LDO). These references are optimized to operate over the full automotive temperature range while consuming only 1nA of current per branch.
Given the high cost of GF22nm technology, achieving area efficiency is a critical aspect of this research. To address this, the design incorporates area-efficient components such as switched capacitors and duty-cycled resistors. The PTAT block achieves a line sensitivity of 2%/V and 5% spread (σ/μ) at 27°C consuming 4nW by utilizing MOSFETs in weak inversion and operates with an 800mV supply voltage while occupying a silicon area of 0.001mm2. The bandgap reference is supplied from a battery with an end-of-life (EOL) voltage of 900mV. It achieves a maximum temperature coefficient (TC) of 140.6ppm/°C and a line sensitivity of 0.56%/V at 27°C with a supply range from 900mV to 1.98V. Without resistor trimming, the reference voltage spread due to process and mismatch variations is reduced to 2.9% (σ/μ) by using BJTs. The bandgap reference occupies a silicon area of 0.021mm2 using duty-cycled resistors and has a nominal power consumption of 7.6nW. This voltage is used as the reference voltage for an LDO with unity-gain feedback to prevent multiplication of the reference voltage noise. The LDO maintains an output voltage line sensitivity of less than 1%/V with battery voltage variations from 900mV to 1.98V and load currents ranging from 100nA to 1µA.