Pre-Charging Circuitry for Multiplexer Channel Switching
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Solution Overview
Problem
The existing pre-charging circuits for capacitive nodes in multiplexers face challenges in achieving fast charge settling times due to the need for significant level shifting and power consumption, especially when switching between channels with large voltage differences, which limits multiplexer channel switching times and circuit throughput.
Innovation Solution
The implementation of a pre-charge circuit with capacitors that track signal levels on each multiplexer channel, reducing the level shifting burden on the amplifier and allowing for stable and low-power operation by pre-charging the capacitive load to a level close to the next MUX channel output, using a two-stage pre-charging process with a coarse buffer amplifier and a fine transconductance amplifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a pre-charging amplifier is used to pre-charge the capacitive node to reduce charge settling time, then the charge settling time is reduced, but the amplifier experiences operational difficulties with full range input signals and cannot achieve fast rail to rail output level shifting
Solution Approach 1:
The pre-charging amplifier input stage is segmented into multiple parallel input channels, each with its own capacitor. Each channel is dedicated to tracking a specific MUX input channel, dividing the complex task of handling full-range signals into manageable per-channel operations. This segmentation allows each amplifier input to handle a limited voltage range while collectively covering the full signal spectrum.
Solution Approach 2:
Capacitors are introduced to perform preliminary tracking of MUX input channel voltages before the amplifier processes the signal. These capacitors capture and hold the voltage levels of upcoming MUX channels in advance, so when a channel switch occurs, the amplifier only needs to handle the difference between the stored capacitor voltage and the new channel voltage, rather than the full rail-to-rail range.
2Measurement precision
If a pre-charging amplifier handles full range signal level shifts, then all MUX channels can be pre-charged accurately, but the amplifier consumes more power and operates less stably
Solution Approach 1:
Capacitors are introduced as intermediary elements between the MUX channels and the pre-charging amplifier. These capacitors act as voltage buffers that store the voltage levels of upcoming channels, mediating the signal transmission to the amplifier. By placing these intermediary capacitors in the signal path, the amplifier only needs to amplify small differential voltages rather than large rail-to-rail swings, significantly reducing power consumption while maintaining pre-charge accuracy.
3Adaptability or versatility
If the multiplexer switches between channels with large voltage differences, then the MUX can handle diverse signal ranges, but the charge redistribution time increases, limiting circuit throughput
Solution Approach 1:
Capacitors connected to each MUX input channel continuously track and store the voltage levels of all available channels in advance. Before a channel switch occurs, the appropriate capacitor already holds the voltage level of the upcoming channel, enabling the pre-charging amplifier to quickly adjust the capacitive node voltage without waiting for charge redistribution during the switch transition. This preliminary voltage capture maintains high circuit throughput while handling diverse voltage ranges.
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 approach significantly reduces charge settling times and improves circuit throughput by distributing the level shifting burden among capacitors and optimizing power consumption, enabling faster and more stable pre-charging of capacitive loads.
Implementation Method 1
each pre-charge circuit input channel has a respective capacitor that is able to be switched in and out of series with the respective multiplexer channels, such that the respective capacitors track the signal levels on the respective channels
Implementation Method 2
pre-charge circuitry arranged in use to pre-charge the capacitive load in dependence on a signal on one of the input channels to the multiplexer to be next output to the capacitive load
Data Source
AI summary
A pre-charge circuit is provided for pre-charging the input node of a capacitive component to which the multiplexer output is fed to a charge level that is close to or approximates the signal output level of the multiplexer when its output is next switched. In order to reduce the level shifting burden on the amplifier in the pre-charge circuit, each pre-charge circuit input channel has a respective capacitor that is able to be switched in and out of series with the respective multiplexer channels, such that the respective capacitors track the signal levels on the multiplexer channels. The provision of the corresponding capacitors for each MUX channel reduces the input current to the pre-charge amplifier, and allows for the level shifting burden to be taken by the capacitors, leading to more stable and lower power operation.