CMOS Contact Potential Clamping to Block Substrate Current
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Solution Overview
Problem
CMOS circuits in airbag ignition systems are prone to malfunction due to the formation of parasitic bipolar transistors when external connections are subjected to unintended potentials, leading to substrate currents that can cause airbag failures.
Innovation Solution
A device is implemented in the CMOS circuit to monitor the potential of external contacts and connect them to a leakage circuit node when the potential falls below a reference value, draining current through parasitic bipolar structures to prevent substrate currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If n-well structures are used to implement digital logic circuits in CMOS technology, then circuit functionality is achieved, but substrate current injection occurs through parasitic bipolar lateral structures causing latch-up and circuit malfunction
Solution Approach 1:
The patent introduces a potential detection circuit and control circuit as intermediary components between the n-well structure and substrate. These intermediaries detect potential differences and control the activation of protection circuits, preventing direct harmful current injection while maintaining normal circuit operation. The intermediary structures enable indirect control of substrate current flow without disrupting the primary digital logic functionality.
Solution Approach 2:
The protection circuit is designed to automatically activate when substrate current injection is detected, using self-contained potential detection and control mechanisms. The system monitors its own operational state through potential difference detection and autonomously activates protection measures without external intervention, ensuring continuous reliability while preventing latch-up conditions.
2Reliability
If protection circuits are activated to prevent substrate current injection, then substrate current is blocked, but the complexity of the circuit increases
Solution Approach 1:
The protection mechanism is applied locally only where substrate current injection is most critical, rather than throughout the entire CMOS circuit. The potential detection circuit and protection switches are strategically positioned at specific n-well regions prone to latch-up, maintaining overall circuit simplicity while providing targeted protection where needed most.
Solution Approach 2:
The protection circuit is designed to activate preemptively based on detected potential differences before harmful substrate current can fully develop. By monitoring potential conditions and activating protection switches in advance, the system prevents latch-up conditions without requiring complex real-time response mechanisms, thereby reducing overall circuit complexity.
3Reliability
If potential detection and control circuits are added to activate protection when needed, then substrate current injection is prevented, but the device complexity increases
Solution Approach 1:
The potential detection circuit and control logic are designed to serve multiple functions: detecting potential differences, determining when protection activation is needed, and controlling the protection switches. This multi-functional approach consolidates what could be separate complex circuits into integrated structures, reducing overall device complexity while maintaining reliable substrate current prevention.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Prevents substrate currents from disrupting the functioning of adjacent electronic components by effectively managing parasitic bipolar transistor activation, ensuring reliable operation of airbag ignition circuits.
Implementation Method 1
They detect the potential of a contact (PDH, PDL) of the integrated CMOS circuit, compare the value of the detected potential with a reference value
Implementation Method 2
connect the contact (PDH, PDL) to a leakage circuit node (ABK) to drain the current, so that it does not flow through the parasitic bipolar lateral structure
Data Source
Figure 1a
Figure 1b~1c
Figure 2
AI summary
The invention relates to various devices and methods for preventing the injection of a substrate current into the substrate sub of a CMOS circuit. For this purpose, the devices implement different methods for preventing such injection. They detect the potential of a contact (PDH, PDL) of the integrated CMOS circuit, compare the value of the detected potential with a reference value, and connect the contact (PDH, PDL) to a leakage circuit node (ABK) to drain the current, so that it does not flow through the parasitic bipolar lateral structure, i.e., not into the substrate. The leakage circuit node can be connected, for example, to the reference potential line (GND) or to another line that has a higher potential than that of the reference potential line (GND). This electrical connection is then activated or...initiated when the value of the contact potential (PDH, PDL) is below or equal to a reference value, where this reference value is below the potential of the substrate Sub and/or below the potential of the reference potential line (GND) or the other line mentioned above.