Isolated Analog Input Circuit for Stable AD Conversion Under Noise
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Solution Overview
Problem
Conventional analog input devices experience unstable AD conversion due to external noise, particularly switching noise from power sources, which cannot be temporarily stopped, leading to fluctuations in the amplitude value held by the sample-and-hold circuit.
Innovation Solution
An analog input device configuration that includes an amplifier with a capacitor in a negative feedback loop and a timing control mechanism to control the switches of the isolating transformers, allowing the secondary side switch to open before the primary side switch, ensuring stable pulse-like signal integration and reduction of noise effects, enabling high precision digital signal output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sample-and-hold circuit is used to hold the instantaneous amplitude value of the pulse-like signal, then the AD conversion can be performed, but the held amplitude value fluctuates when receiving induction of external large noise, causing unstable AD conversion data
Solution Approach 1:
The secondary side switch is opened before the primary side switch to preemptively isolate the amplifier from incoming noise signals. This preliminary action prevents noise from being captured and amplified, thereby stabilizing the amplitude value held by the sample-and-hold circuit and ensuring stable AD conversion data even in noisy environments
Solution Approach 2:
A capacitor is connected to the negative feedback loop across the input and output of the amplifier. This feedback mechanism stabilizes the amplifier's operation by filtering out high-frequency noise components and maintaining a stable gain, which prevents noise-induced fluctuations in the held amplitude value and improves AD conversion stability
2Object-affected harmful factors
If the digital circuit is stopped temporarily to avoid the effect of noise produced from the digital circuit, then the internally generated noise can be avoided, but it cannot exclude influences of external noise that cannot be stopped temporarily such as switching noise of a power source
Solution Approach 1:
The harmful noise influence is extracted and removed by opening the secondary side switch before the primary side switch operates. This isolation mechanism selectively removes external noise signals from reaching the amplifier while allowing the digital circuit to continue operating normally, thereby addressing both internal and external noise sources without requiring digital circuit shutdown
Solution Approach 2:
The secondary side switch acts as an intermediary element between the isolating transformer and the amplifier. By controlling this intermediate switch to open before the primary side switch, the system can prevent external noise from being transmitted to the amplifier while maintaining normal digital circuit operation, thus achieving broader noise source coverage without sacrificing functionality
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 proposed configuration effectively reduces noise influence by averaging it through signal integration, resulting in high precision digital signal output even under large external noise conditions that cannot be stopped temporarily.
Implementation Method 1
a capacitor connected to a negative feedback loop across the input and output of the amplifier
Implementation Method 2
an isolating transformer while a secondary side switch connected to the secondary side of the isolating transformer
Data Source
AI summary
An amplifier for amplifying a pulse-like signal output from a secondary side of an isolating transformer, a capacitor connected to a negative feedback loop across the input and output of the amplifier, and a timing control circuit for controlling an FET into a closed state, then controlling a switch into a closed state, and after that controlling the switch into an open state at timing simultaneously with the FET or earlier than the FET are provided, and when the switch is controlled into the open state, an AD converter converts the output signal of the amplifier to a digital signal.