Abstract
This paper proposes a new circuit-based approach to mitigate nonlinearity in open-loop ring-oscillator-based analog-to-digital converters (ADCs). The approach consists of driving a current-controlled oscillator (CCO) with several transconductors connected in parallel with different bias conditions. The current injected into the oscillator can then be properly sized to linearize the oscillator, performing the inverse current-to-frequency function. To evaluate the approach, a circuit example has been designed in a 65-nm CMOS process, leading to a more than 3-ENOB enhancement in simulation for a high-swing differential input voltage signal of 800-mVpp, with considerable less complex design and lower power and expected area in comparison to state-of-the-art circuit based solutions. The architecture has also been checked against PVT and mismatch variations, proving to be highly robust, requiring only very simple calibration techniques. The solution is especially suitable for high-bandwidth (tens of MHz) medium-resolution applications (10–12 ENOBs), such as 5G or Internet-of-Things (IoT) devices.
Highlights
The scaling down of CMOS processes has posed new challenges for analog-to-digital conversion, especially from the analog design perspective
Flash analog-to-digital converters (ADCs) are usually implemented for high-speed analog-to-digital conversion [2]
We propose a new way to mitigate the distortion generated by the nonlinearity of the ring-oscillator, exploiting a circuit design with significantly lower power consumption and area comparing to prior art
Summary
The scaling down of CMOS processes has posed new challenges for analog-to-digital conversion, especially from the analog design perspective. Digital logic consumes less power, occupies less area, and works faster as design processes get smaller. Analog designs have become highly complex due to the low voltage supply and limited devices’ gain, higher noise impact, mismatch, and parasitic effects [1]. The current trend is towards mostly digital implementations. Energy-efficient wide-band ADCs are essential for applications such as portable battery-powered devices or radio-receivers. Flash ADCs are usually implemented for high-speed analog-to-digital conversion [2]. The power consumption increases exponentially with the number of bits, making them less power-efficient for more than
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