ADC Pre-Charge Circuit for Faster Sampling Acquisition
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Solution Overview
Problem
Analog to digital converters (ADCs) face limitations in throughput due to the time required to change the voltage on a sampling capacitor between successive conversions, leading to increased acquisition time and disturbance in the conversion process.
Innovation Solution
A pre-charge circuit, comprising an active device such as an amplifier or voltage follower, is intermittently powered to monitor and adjust the input voltage, reducing charge exchanges between the input and sampling nodes, thereby minimizing disturbance and speeding up the conversion process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the ADC operates in a sample and convert cycle updating the voltage on the sampling capacitor, then the converter can perform successive conversions, but the throughput is limited by the time taken to change the voltage on the sampling capacitor
Solution Approach 1:
The pre-charge circuit performs preliminary action by updating the voltage on the sampling capacitor before the acquire mode begins. The circuit monitors the input voltage and pre-charges the sampling capacitor to match the upcoming input voltage level, so that when the sample switch closes, minimal charge exchange is needed, significantly reducing acquisition time and increasing throughput.
2Productivity
If the pre-charge circuit is continuously powered to maintain voltage matching, then the voltage on the sampling capacitor can be kept ready, but power consumption increases
Solution Approach 1:
The pre-charge circuit employs periodic action by being intermittently powered rather than continuously operated. The circuit is activated only during specific phases of the conversion cycle when voltage pre-charging is needed, and remains powered down during other phases, thereby maintaining throughput benefits while significantly reducing average power consumption.
3Loss of time
If the pre-charge circuit actively monitors and adjusts input voltage, then charge exchanges between input and sample nodes are reduced, but the circuit complexity increases
Solution Approach 1:
The pre-charge circuit acts as an intermediary between the input voltage source and the sampling capacitor. It includes a voltage follower or buffer stage that isolates the input from the capacitor, allowing voltage monitoring and pre-charging without directly disturbing the input network. This intermediary approach reduces charge exchanges and acquisition time while adding only moderate circuit complexity through standard buffer components.
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 pre-charge circuit reduces acquisition time and minimizes power consumption by allowing the ADC to scale power usage with conversion rate, enhancing the overall throughput and accuracy of the ADC.
Implementation Method 1
The precharge circuit comprises an active device such as an amplifier or a voltage follower. The operational amplifier may be arranged as a voltage follower having an input connected to the input node of the analog to digital converter.
Implementation Method 2
The pre-charge circuit is connected to a voltage translation device, such as a capacitor. The pre-charge circuit arranged to monitor an input voltage at an input node and to cause the voltage at the sample node to substantially match the input voltage
Data Source
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AI summary
An analog to digital converter comprising at least one sampling capacitor connected to a sample node, and a pre-charge circuit arranged to cause the voltage on the sample node to substantially match the input voltage prior to the analog to digital converter entering an acquire mode in which the sample node is connected to the input node by a sample switch.