CMOS Isolation via Buried Layer for Motor Driver Precision
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Solution Overview
Problem
In motor drivers and other circuit devices that perform switching operations, substrate potential fluctuations due to repeated current on/off cycles affect the precision of chopping current detection, leading to variations in motor rotational speed control.
Innovation Solution
A circuit device is designed with a DMOS transistor on a P-type substrate and a CMOS transistor on an isolated N-type buried layer, surrounded by an N-type plug region, which isolates the CMOS transistor from the P-type substrate, reducing the impact of substrate potential fluctuations and allowing precise control of chopping current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a DMOS transistor is used for motor drive switching operation, then high current driving capability is achieved, but substrate potential fluctuation increases affecting detection precision
Solution Approach 1:
The substrate is segmented into multiple isolated N-type buried layers. The DMOS transistor is formed on a first N-type buried layer while the detection circuit is formed on a second N-type buried layer that is electrically isolated from the first. This segmentation prevents substrate potential fluctuations from the high-power switching circuit from affecting the precision detection circuit, thereby resolving the contradiction between high current driving capability and detection precision.
2Productivity
If chopping operation is performed to control motor speed, then motor rotational speed control is achieved, but substrate potential fluctuation causes detection value variation
Solution Approach 1:
An isolated N-type buried layer acts as an intermediary between the high-power DMOS switching circuit and the precision detection circuit. This intermediary layer electrically isolates the detection circuit from substrate potential fluctuations caused by chopping operations, allowing accurate and consistent chopping current detection values even during motor speed control operations.
3Ease of operation
If reference voltage generation circuit and voltage detection circuit are formed on the substrate, then chopping current detection function is achieved, but these circuits are affected by substrate potential fluctuation
Solution Approach 1:
The detection circuits (reference voltage generation circuit and voltage detection circuit) are segmented from the high-power switching circuit by forming them on a separate N-type buried layer that is electrically isolated from the substrate region containing the DMOS transistor. This segmentation protects the detection circuits from substrate potential fluctuations while maintaining their detection functionality.
Data Source
AI summary
An electronic circuit includes a noise source and an analog circuit and a logic circuit that may be adversely affected by noise. At least a portion of the analog circuit and the logic circuit is formed on a buried impurity layer whose conductivity is different from that of a substrate, and at least a portion of the periphery of that portion is surrounded by an impurity layer that is different from the substrate. Thus, propagation of the noise from the noise source is prevented.