A 40-nm microcontroller featuring voltage stacked memory and logic is presented. This involved connecting the power domains of the memory and logic in series, such that the ground of one power domain is connected to the positive supply rail of the other. In this paper, an ARM Cortex-M0+ and its peripherals are powered from 0 V to V_DD, while its 4-kB ROM and the 16-kB SRAM are powered from V_DD to 2 V_DD. Since the memory and logic will, in general, draw different supply currents, the midrail V_DD is provided by an on-chip switched capacitor voltage regulator (SCVR). To allow a direct comparison of voltage stacking with a conventional single supply, it can be turned off by configuring the SCVR to power both the memory and logic from 0 V and V_DD. Turning on voltage stacking results in 96% power conversion efficiency, while the active converter area is reduced by 2.6 ×. Despite the use of a smaller SCVR, the voltage stacking reduces the supply noise by 3.4 dB and the output voltage drops from 58 to 36 mV.

@en

This paper presents a CMOS 40nm microcontroller where for the first time, stacked voltage domains are used. The system features an ARM Cortex M0+ processor, 4kB ROM, 16kB SRAM, peripherals, and an on-chip switched-capacitor voltage regulator (SCVR). By using voltage stacking the test chip achieves state-of-the-art (96%) power-conversion efficiency and observed power savings run from 23% to 63% depending upon the payload current, while supply voltage variations are reduced from 5.6mV to 3.8mV (RMS).@en