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@library Given a noisy analog sensor input (like from a thermocouple or strain gauge), how would you design an analog front-end and select an ADC to ensure accurate and stable readings at 16-bit resolution? Suggest components you will use for sampling rate, input impedance, filtering, reference voltage stability, and PCB layout techniques to minimize noise
Below is an overview of one approach to designing a high-accuracy analog front-end for a noisy sensor (e.g., from a thermocouple or strain gauge) that includes considerations for sampling rate, input impedance, filtering, reference voltage stability, and PCB layout. Each suggestion includes example parts that you can search for in the Flux library:
Table
Aspect
Design Approach
Example Component / Technique
Low-Noise Amplification
Use an instrumentation amplifier to boost the very small sensor signal, ensuring high input impedance and excellent noise rejection.
Implement RC low-pass filters to suppress high-frequency noise before the ADC. The resistor and capacitor values should be calculated for a cutoff frequency below the noise floor, yet above the signal bandwidth.
Use standard resistor (R?) and capacitor (C?) values (e.g., 10kΩ and 0.1µF give a cutoff ≈ 160 Hz)
ADC Selection
Choose a precision 16-bit ADC that supports the desired sampling rate (e.g., up to several hundred samples per second) and allows for configuring the data rate and gain.
Use an external, high-accuracy voltage reference IC to ensure that the ADC measurements are stable and repeatable despite fluctuations in supply or ambient conditions.
- Separate analog and digital ground planes. - Use a star grounding scheme to minimize ground loops. - Place decoupling capacitors very near the power and reference pins to reduce noise. - Route sensitive signal traces away from high-speed digital lines.
Follow best layout practices when routing, and incorporate a dedicated analog ground net (e.g., using Ground)
Summary:
Amplification: Start with an instrumentation amplifier ([INA333] or [AD8421]) to boost the sensor output while maintaining high input impedance and rejecting common-mode noise.
Filtering: Add RC filters on the signal path. Calculate the RC values to set a cutoff frequency that removes high-frequency noise without distorting your signal.
ADC: Use a 16‑bit converter like the [ADS1115] to digitize the conditioned signal with sufficient resolution and a configurable sampling rate.
Reference: Incorporate a stable voltage reference (e.g., [ADR4550]) and add local decoupling to ensure the reference voltage remains constant.
Layout: Apply careful PCB layout practices (ground separation, decoupling, route length minimization, and shielded traces) to further minimize pickup of ambient noise.
Feel free to ask if you’d like to incorporate any of these changes into your schematic or need additional guidance on calculations or layout suggestions!
Add Front-End Components
Layout and Decoupling Guidance
Validate RC Filter Values
Review ADC and Sensor Specs
Passive Components
Resistor Power Rating
Beta
Checks that the power traveling across a given resistor is under its rating with 50% headroom.