Shared-Capacitor Bootstrapped Multiplex Circuit for Low-Noise Switching
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Solution Overview
Problem
Conventional multiplex circuits in computer systems suffer from increased circuit area and manufacturing costs due to the use of bootstrap switches, which also introduce potential routing issues and power supply noise, especially as the number of input signals increases.
Innovation Solution
Implementing a bootstrapped multiplex circuit where multiple bootstrap switches share a common capacitor, reducing circuit area and minimizing noise by using a boost voltage to activate the n-channel transistor, thus reducing on-resistance and improving linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If bootstrap switches are used in multiplex circuits, then noise rejection is improved, but circuit area and manufacturing cost increase
Solution Approach 1:
Multiple bootstrap switches share a common bootstrap capacitor, merging what would otherwise be separate components into a shared resource. This reduces the total circuit area while maintaining the noise rejection benefits of bootstrap switches for all channels.
Solution Approach 2:
The single bootstrap capacitor serves multiple bootstrap switches simultaneously, making it a universal component that performs the same function (providing bootstrapping) for multiple signal paths. This multi-functionality reduces overall circuit complexity and area.
2Object-affected harmful factors
If bootstrap switches are used in multiplex circuits, then noise rejection is improved, but manufacturing cost increases
Solution Approach 1:
By merging multiple bootstrap capacitors into a single shared component, the manufacturing cost is reduced due to fewer components requiring placement, testing, and assembly. The noise rejection performance is maintained across all channels through the shared bootstrap mechanism.
3Adaptability or versatility
If more input signals are added to multiplex circuits, then signal selection capability is improved, but circuit area increases
Solution Approach 1:
As more input signals are added to the multiplex circuit, the shared bootstrap capacitor continues to serve all additional switches, preventing proportional increases in circuit area. This merging approach allows enhanced signal selection capability without linearly increasing the footprint.
4Reliability
If n-channel transistors are activated with boost voltage, then on-resistance is reduced, but power supply noise may be introduced
Solution Approach 1:
The bootstrap capacitor is charged to a voltage higher than the power supply voltage before the switch is activated. This preliminary charging action ensures that when the switch turns on, the gate voltage is already sufficiently high to create low on-resistance, and the rapid charging process minimizes the time during which noise could be generated.
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
The solution allows for efficient signal selection with reduced noise injection and circuit area, enhancing the performance and cost-effectiveness of multiplex circuits while maintaining noise benefits associated with bootstrap switches.
Implementation Method 1
a shared capacitor circuit that includes a capacitor, the first and second switch circuits being coupled to the shared capacitor circuit
Data Source
AI summary
A multiplex circuit for computer systems includes multiple bootstrap switches that share a common capacitor for generating a boost voltage. When one of the bootstrap switches is activated, it is coupled to the common capacitor which is used to generate the boost voltage to control a switch transistor in the activated bootstrap circuit. Upon deactivating an active bootstrap switch, the common capacitor is pre-charged prior to the activation of another bootstrap switch.