Analog Multiplexer Shared Buffer for High-Voltage Bootstrap Switching
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Solution Overview
Problem
Existing analog multiplexers face challenges in handling high input voltages while maintaining linearity, as they require large and complex buffer designs for overvoltage protection, which increases circuit area and costs, limiting the number of feasible inputs.
Innovation Solution
Implementing a shared buffer configuration where the output of the analog multiplexer is fed back to the bootstrap circuit of each switch, eliminating the need for individual buffers and allowing the shared buffer to provide a buffered version of the input voltage, thus reducing circuit area and enabling handling of voltages beyond the rating of the transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a buffer is added to each analog input to provide buffered voltage to the bootstrap circuit, then linearity is improved and unwanted parasitics are reduced, but device complexity and circuit area increase significantly
Solution Approach 1:
The patent merges multiple individual buffer functions into a single shared buffer that serves all analog inputs. The shared buffer receives the selected input voltage and provides buffered voltage to all bootstrap circuits simultaneously, eliminating the need for separate buffers at each input and reducing overall device complexity while maintaining linearity improvement benefits
Solution Approach 2:
The shared buffer is designed to perform multiple functions: it buffers the selected input voltage, provides overvoltage protection for the bootstrap circuits, and distributes the buffered voltage to all bootstrap circuits. This multi-functional design reduces the total number of components while maintaining the necessary protection and linearity features
2Adaptability or versatility
If overvoltage protection is implemented in each buffer to handle input voltages greater than transistor voltage ratings, then the ability to handle high input voltages is improved, but the buffer design becomes increasingly large and complex
Solution Approach 1:
The patent combines the overvoltage protection functionality from multiple individual buffers into a single shared buffer implementation. By consolidating the protection circuitry into one location, the total area required for overvoltage protection is significantly reduced while still protecting all bootstrap circuits from high input voltages
Solution Approach 2:
The shared buffer acts as an intermediary between the high-voltage input signals and the low-voltage bootstrap circuits. It receives the potentially high-voltage selected input signal, conditions it through buffering and protection circuitry, and provides a safe buffered voltage to all bootstrap circuits, thereby protecting them from overvoltage damage without requiring each circuit to have its own protection mechanism
3Reliability
If a buffer is placed at each analog input to protect against overvoltage, then transistor protection is improved, but the number of feasible inputs is limited due to increased circuit area
Solution Approach 1:
The patent merges the protection functionality into a single shared buffer that protects all analog inputs simultaneously. Instead of having separate protection circuits for each input channel, the shared buffer provides centralized protection, dramatically reducing the total area required while maintaining reliable transistor protection across all inputs
Solution Approach 2:
The shared buffer is designed as a universal protection mechanism that serves all analog input channels. It can handle any of the selected input signals and provide protection to all bootstrap circuits regardless of which input is currently selected, thereby enabling a greater number of input channels within the same area budget
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
This solution reduces unwanted parasitics and leakage, maintains linearity, and allows for more inputs without increasing circuit area, effectively addressing the limitations of traditional buffer designs.
Implementation Method 1
Each analog switch of an analog MUX typically uses a bootstrap circuit to improve linearity by maintaining a fairly constant gate-to-source voltage (Vgs) on the pass transistor of the analog switch
Implementation Method 2
The common MUX output is coupled to an input of a common buffer shared by all of the analog switches, in which an output of the common buffer tracks the output of the analog MUX, thus providing a buffered MUX output
Data Source
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AI summary
An integrated circuit includes a plurality of analog inputs, and an analog multiplexer (MUX). The MUX includes a common output node configured to provide a MUX output, a plurality of analog switches, and a shared buffer. Each switch includes a corresponding bootstrap circuit coupled to a control electrode of a corresponding pass transistor in which the corresponding bootstrap circuit includes a corresponding boosting capacitor. Each analog switch of the plurality of analog switches has a first input coupled to a corresponding analog input of the plurality of analog inputs, a second input, and an output coupled to the common output node. The shared buffer has an input coupled to the common output node and coupled to provide a common buffered MUX output to the second input of each of the plurality of analog switches.