Switched Capacitor Pre-Charging for Transient-Resistant ADC Inputs
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Solution Overview
Problem
Analog-to-digital converters (ADCs) in automotive and industrial systems are prone to damage from high voltage transients due to long wiring and proximity to generators, which can lead to noise and transients, compromising their accuracy and operation, despite the use of protection devices like resistors and diodes.
Innovation Solution
A switched capacitor circuit is enhanced by pre-charging a sampling capacitor using a voltage buffer, reducing the input impedance and allowing operation with higher source impedances, thereby protecting the circuit from high electrostatic discharge (ESD) currents and maintaining high linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If protection devices like resistors and diodes are used to suppress high voltages and currents, then the circuit is protected from high voltage transients, but the accuracy and operation of the ADC are compromised
Solution Approach 1:
The capacitor is pre-charged to the reference voltage before the sampling phase, so that when the switch closes, no large transient current is drawn from the ADC input. This preliminary charging action eliminates the need for large protection resistors that would otherwise be required to limit inrush current, thereby protecting the ADC without compromising accuracy
Solution Approach 2:
A dedicated voltage buffer is introduced as an intermediary component between the reference voltage source and the sampling capacitor. This buffer isolates the ADC from direct connection to the capacitor charging process, preventing transient currents from affecting the ADC while still allowing the capacitor to be charged to the correct reference voltage
2Device complexity
If a capacitor is directly connected to the input node for sampling, then the circuit structure is simple, but high ESD currents can damage the circuit
Solution Approach 1:
The capacitor is pre-charged to the reference voltage before sampling begins. This preliminary action ensures that the capacitor is already at the correct potential, so when the switch connects the input node to the capacitor, no large ESD or transient currents flow through the ADC input, thereby protecting the circuit without adding complex protection structures
Solution Approach 2:
The pre-charging phase performs an anti-action against potential ESD damage by establishing the capacitor at the reference voltage before any harmful transients can occur. This preliminary counter-measure neutralizes the effect of ESD currents that would otherwise damage the circuit during normal operation
3Measurement precision
If the voltage buffer fully charges the capacitor before sampling, then the linearity is improved, but the power consumption increases
Solution Approach 1:
The voltage buffer performs a partial charging action during the pre-charge phase, bringing the capacitor close to but not necessarily exactly to the reference voltage. This partial action is sufficient to prevent large transient currents and maintain acceptable linearity, while consuming less power than a full charging cycle would require
Solution Approach 2:
The circuit uses periodic switching between pre-charge and sampling phases. During the pre-charge phase, the buffer charges the capacitor; during the sampling phase, the switch connects the input node. This periodic operation allows the buffer to operate intermittently rather than continuously, reducing overall power consumption while maintaining linearity during the critical sampling window
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 effectively increases the input impedance of the switched capacitor circuit, enabling it to handle higher source impedances and protect against high voltage transients while maintaining high linearity, even when the voltage buffer only partially charges the capacitor, providing power savings and improved performance.
Implementation Method 1
pre-charging a capacitor using a voltage buffer having an input coupled to an input node of the switched capacitor circuit and an output coupled to the capacitor
Implementation Method 2
integrating the first charge using an integrator
Data Source
AI summary
In accordance with an embodiment, a method of operating a switched capacitor circuit includes pre-charging a capacitor using a voltage buffer having an input coupled to an input node of the switched capacitor circuit and an output coupled to the capacitor, coupling the input node to the capacitor, wherein a first charge is collected on the capacitor, and integrating the first charge using an integrator.