ASIL-D and AEC-Q100 Grade 0 Compliant Automotive RC Oscillator with Farey Sequence-based Calibration

Abstract

In vehicle electrification, safety remains a top priority. High safety applications must meet AEC-Q1 00 Grade 0 and ASIL-D standards, requiring circuits operating in temperatures from -40°C to 150°C, and employing two physically isolated systems for cross-validation. Battery management systems in electric vehicles consist of multiple battery monitoring ICs (BMICs) [1], each featuring dual isolated systems to validate measurements, communication, and oscillator functions (Fig. 1). Oscillator accuracy, critical for measurement and communication, must satisfy specific standards depending on the communication protocol. Low-speed automotive communication standards like CAN/LinBus accept sub-1% inaccuracy. However, to achieve sub-1% inaccuracy within a wide temperature range and dual-isolated architecture, extensive trimming incurs significant costs that scale with the number of BMICs. Therefore, there's an urgent need to develop oscillators that achieve sub-1% inaccuracy while minimizing trimming efforts. RC oscillator (RCO) is a promising option. Previous closed-loop architectures achieved high accuracy, but required costly high-bit, multi-point trimming [2]-[3]. Alternative open-loop architectures reduced manual trimming burden, but struggled to attain sub-1% inaccuracy [4]-[5]. The current-calibration method [5] can improve accuracy by increasing the current-steering DAC (IDAC) bits at the cost of doubling the area and causing mismatch issues, necessitating extra manual trimming.