Input Multiplexer RC Filter for Faster PGA Settling
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Solution Overview
Problem
The switching speed of input multiplexer systems in data acquisition is limited by the slew rate capability of the programmable gain amplifier, leading to slowed down input signals and reduced accuracy in signal digitization.
Innovation Solution
The implementation of a pull-up or pull-down circuit during the break-before-make time and the use of a switch in parallel with a resistor to form an RC filter between the MUX output and the PGA input, allowing for faster switching by charging the capacitor more quickly when the switch is closed, thereby improving switching speed without compromising accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the input MUX switches quickly, then the switching speed is improved, but the amplifier cannot settle within its safe-operating region leading to reduced accuracy
Solution Approach 1:
The patent applies preliminary action by pulling the MUX output voltage to a known state (via pull-up or pull-down circuits) before the amplifier switches to the next input channel. This pre-positioning of the output voltage ensures the amplifier starts from a predictable state, enabling faster switching while maintaining settling accuracy within the safe-operating region.
Solution Approach 2:
The patent changes the voltage state parameter of the MUX output by actively pulling it to defined voltage levels during the break-before-make transition. This parameter control prevents the amplifier from operating in undefined regions, allowing faster switching speeds while ensuring the amplifier settles accurately within its safe-operating region before the next conversion.
2Reliability
If the amplifier operates with limited slew rate, then it remains within safe-operating region, but the switching speed of the input MUX system is limited
Solution Approach 1:
The pull-up and pull-down circuits perform preliminary action by establishing the MUX output voltage at defined levels before the amplifier needs to settle. This ensures the amplifier transitions between channels while remaining within its safe-operating region, enabling faster switching speeds without compromising reliability.
Solution Approach 2:
The patent implements a break-before-make switching scheme where the MUX output is pulled to a defined state during the transition interval. This allows the system to skip through the unsafe region quickly and settle accurately within the safe-operating region, effectively rushing through the problematic transition period while maintaining reliability.
3Measurement precision
If the input signal is slowed down for amplifier settling, then accuracy is maintained, but the overall data acquisition speed is reduced
Solution Approach 1:
The pull-up and pull-down circuits perform preliminary voltage establishment before the amplifier settling phase. This ensures the signal is already in a stable, defined state when the amplifier begins settling, reducing the required settling time while maintaining accuracy, thereby increasing overall data acquisition speed.
Solution Approach 2:
The break-before-make switching with active pulling allows the system to rush through the transition period quickly by establishing the output voltage before the amplifier needs to settle. This reduces the time the system spends in transition, maintaining settling accuracy while increasing productivity by reducing the total acquisition cycle time.
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 enables high-speed switching of the input MUX system while maintaining accuracy, avoiding the triggering of anti-parallel diodes and reducing settling time for the PGA, thus enhancing the overall performance of the data acquisition system.
Implementation Method 1
a switch in parallel with a resistor to form an RC filter between the MUX output and the PGA input, allowing for faster switching by charging the capacitor more quickly when the switch is closed
Implementation Method 2
a switch in parallel with a resistor to form an RC filter between the MUX output and the PGA input
Data Source
AI summary
An integrated circuit includes a multiplexer circuit configured to provide an output signal on a conductive line, a programmable gain amplifier having a non-inverting input connected to the conductive line to receive the output signal from the multiplexer, a slew rate adjust circuit connected at a first node on the conductive line between the multiplexer circuit and the programmable gain amplifier, a first switch including a first terminal connected to the first node and a second terminal connected to the input of the programmable gain amplifier, and a low pass filter connected between the first and second terminals of the first switch.