A signal conditioner is an important electronic device used to convert an electrical signal to a standardized format that can be processed by other equipment. Signal conditioning optimizes the signal to ensure accurate transmission, measurement and conversion to desired output.
When designed as a printed circuit board (PCB), signal conditioners provide additional advantages of compact size, rapid prototyping and ease of manufacturing. PCB-based conditioners are ubiquitous in industrial, automotive, aerospace and consumer applications for interfacing sensors, data acquisition devices and controllers.
This article provides a detailed overview of PCB signal conditioners including:
- Definition and working principle
- Signal conditioning processes
- Types of PCB signal conditioners
- Circuit design and PCB fabrication
- Applications and uses
- Advantages of PCB construction
- Design considerations and challenges
By the end of this article, you will have a comprehensive understanding of what PCB signal conditioners are, their functionality, design, manufacturing and applications across various industries.
What Is a Signal Conditioner?
A signal conditioner is an electronic device used to convert a signal from its original form to a more desirable standardized format. Key elements include:
- Receives input signal from a source such as sensor, transducer, etc.
- Conditions the signal using processes like amplification, filtering, conversion, isolation, etc.
- Converts it into a standardized output signal that is compatible with other equipment
- Transmits the conditioned output signal for further processing, display or control
Block diagram of a generic signal conditioner.
The purpose of signal conditioning is to:
- Change the signal into a suitable voltage/current range
- Filter out noise, interference or unwanted components
- Amplify low-level signals to measurable magnitudes
- Provide electrical isolation between components
- Ensure accurate and repeatable transmission
- Convert between analog and digital signals
- Standardize the output format for compatibility
This processing and conversion of the raw input signal enables reliable transmission, measurement and interpretation of the signal.
Why Use a PCB Signal Conditioner?
Printed circuit boards provide the following advantages for implementing signal conditioners:
- Compact size – PCBs allow construction of small footprint conditioners.
- Rapid prototyping – PCB fabrication is fast and inexpensive for developing prototypes.
- Volume manufacturing – PCB assembly can be automated for high volume production.
- Component density – More components can be accommodated in a small PCB area.
- Flexibility – PCBs enable design flexibility and circuit modifications.
- Reliability – Robust performance with quality electronic components and soldering.
- Cost-effectiveness – Low per-unit PCB costs at high production volumes.
The use of PCB technology enables creation of miniaturized, reliable and affordable signal conditioners that can be rapidly designed and manufactured.
Signal Conditioning Processes
Signal conditioners employ various techniques to convert the raw input signal into the required output form. Major processes include:
- Increases signal amplitude using electronic amplifiers.
- Boosts weak sensor signals to measurable voltage/current levels.
- Maintains signal-to-noise ratio (SNR).
- Uses op-amps and instrumentation amplifiers.
- Removes unwanted signal components like noise.
- Employ low pass, high pass, bandpass filters.
- Prevents aliasing in analog to digital conversion.
3. Electrical Isolation
- Provides galvanic isolation between input and output.
- Uses optical, capacitive or magnetic isolation techniques.
- Prevents ground loops and protects equipment from transients.
4. Analog to Digital Conversion
- Converts analog signals to digital format.
- Required for input to digital systems like computers.
- Uses analog to digital converter (ADC) ICs.
5. Digital to Analog Conversion
- Converts digital signals to analog format.
- Needed for analog outputs like voltage/current.
- Employs digital to analog converter (DAC) ICs.
6. Linearization and Compensation
- Improves output signal linearity and accuracy.
- Compensates for sensor non-linearities.
- Uses linearization techniques like polynomial calibration.
7. Impedance Conversion
- Matches differing impedances between source and destination.
- Uses impedance matching networks.
- Prevents signal reflections and errors.
8. Limiting and Protection
- Limits output signals to specified safety levels.
- Protects against over-voltage and transients.
- Uses clamping diodes, fuses, suppressors.
Proper selection of signal conditioning steps converts the raw input to the standardized output needed by the application. Multiple techniques can be combined in a single conditioner PCB for complete functionality.
Types of PCB Signal Conditioners
PCB construction allows implementation of several types of signal conditioners. Major categories include:
1. Instrumentation Amplifiers
- Amplify small differential input signals from sensors like strain gauges and thermocouples.
- Provide high input impedance, gain stability and common-mode noise rejection.
- Use precision low-drift op-amps with ultra-low offset voltage.
- Available as integrated ICs optimised for amplification.
Instrumentation amplifier circuit.
2. Isolation Amplifiers
- Amplify input signal and provide electrical isolation at the output.
- Uses transformer, optical, GI, RF or capacitive isolation techniques.
- Protects sensitive circuits from high voltages and noise.
- Provides patient safety in medical devices.
Isolation amplifier with input protection.
3. Analog Filters
- Remove unwanted interference and noise from signals.
- Types include low-pass, high-pass, band-pass and band-stop filters.
- Used for bandwidth limiting and anti-aliasing before ADC.
- Constructed from resistors, capacitors and op-amps.
4. Digital Isolators
- Isolate digital signals between input and output sides.
- Use magnetic or optical techniques to transmit digital data across an isolation barrier.
- Suitable for isolated serial communication in industrial systems.
Digital isolator with integrated DC-DC converter.
5. Analog Isolators
- Isolate analog signals instead of digital data.
- Based on giant magnetoresistance (GMR) or Hall Effect sensors.
- Used to galvanically isolate analog voltage or current signals.
6. Surge Protectors
- Protect against damaging voltage spikes and transients.
- Use avalanche diode, gas discharge tube, thyristor or MOV techniques.
- Commonly included for input protection in signal conditioners.
7. Limiters and Clamps
- Limit output signal to specified maximum values.
- Use diodes, zener diodes, transistors to clamp voltages.
- Prevent damage to connected instruments from excess signal levels.
8. Analog to Digital Converters
- Convert conditioned analog input signal into digital data.
- Use high resolution delta-sigma converters for precise digitization.
- Enable input to microcontrollers, data loggers, etc.
High speed analog to digital converter.
9. Digital to Analog Converters
- Convert digital input to analog voltage or current output.
- Generated analog output can drive sensors, valves, meters, chart recorders.
- High resolution DACs provide precision analog signal recreation.
The right combination of the above techniques can be implemented on a PCB substrate to realize signal conditioners tailored for specific applications.
PCB Design and Manufacturing
Designing and fabricating a PCB-based signal conditioner involves the following main steps:
1. Define Signal Conditioning Requirements
- Analyze required input and desired output signal parameters.
- Specify conditioning tasks like amplification, filtering, isolation.
- Determine analog/digital conversion needs.
- Set performance metrics like accuracy, response time, temperature stability.
2. Select Electronic Components
- Choose op-amps, specialized ICs, discrete parts meeting requirements.
- Consider factors like gain, bandwidth, noise, offsets.
- Evaluate part electrical characteristics, quality, cost, availability.
3. Design Circuit Schematic
- Create circuit diagram with amplification, filtering, protection stages.
- Simulate circuit performance in software like SPICE.
- Refine design to meet signal specifications.
Signal conditioner circuit schematic example.
4. Layout PCB
- Arrange components and routing for optimal performance.
- Ensure quality power and ground distribution.
- Design for manufacturability and testability.
PCB layout for signal conditioner.
5. Fabricate Prototype PCB
- Generate Gerber files from PCB design software.
- Submit to PCB manufacturer for fabrication.
- May use prototype processes like double-sided FR4.
6. Test Prototype
- Solder components onto fabricated PCB.
- Verify conditioning performance meets requirements.
- Identify any needed design improvements.
7. Manufacture Final Design
- Produce design documentation for volume PCB manufacturing.
- Specify PCB materials, layer count, finishes, tolerances.
- Automated SMT assembly for production efficiency.
- Perform quality assurance testing.
Following these steps results in an application-specific PCB-based signal conditioner solution optimized for the target requirements.
Applications of PCB Signal Conditioners
Due to their versatility, PCB signal conditioners find use across many fields:
- Sensors – Interface sensors like load cells, thermocouples, LVDTs, strain gauges to measurement systems.
- Medical – Process and digitize signals from ECG, EEG, blood pressure sensors. Provide electrical isolation for patient safety.
- Automotive – Condition sensor signals related to pressure, temperature, speed, torque, etc. in engine control and diagnostics.
- Process control – Adapt field signals from process monitoring and control loops.
- Data acquisition – Accept high bandwidth analog signals from experiments for digitization by DAQ systems.
- Avionics – Acquire flight data like vibration, temperature, pressure for aircraft condition monitoring.
- Consumer – Used in devices like weighing scales, fitness trackers, thermometers to interface analog sensors.
- Industrial – Factory automation systems use signal conditioning PCBs to adapt field device signals.
- HVAC – Condition temperature and pressure sensor inputs for building automation and regulation.
PCB construction allows creation of application-specific and cost optimized signal conditioners.
Benefits of Using PCBs
Key advantages of implementing signal conditioners on printed circuit boards:
- Compact – Allows construction of small footprint conditioners.
- Customizability – Can adapt PCB design for specific application needs.
- Reliability – Robust performance with quality electronic components.
- Noise reduction – PCB design techniques optimize signal integrity.
- Cost-effectiveness – Low per-unit costs for high volume production.
- Fast development – Rapid design iteration and prototyping.
- Easy manufacturing – Highly automated PCB assembly.
- Scalability – Simpler to scale production compared to custom designs.
- Integration – Can incorporate signal conditioning into sensor PCBs.
- Standardization – Facilitates interoperability between systems.
PCB implementation enables optimization of size, performance, cost and manufacturability for signal conditioning products.
Design Considerations and Challenges
Some key design aspects and challenges for PCB signal conditioners include:
- Achieving required accuracy and response speed for the application. Careful component selection and circuit design optimization needed.
- Managing trade-offs between cost, size and performance specifications. Improved performance often increases cost and size.
- For isolated designs, providing adequate creepage and clearance distances on the PCB to meet isolation voltage ratings.
- Minimizing introduction of noise and interference through proper PCB layout and grounding techniques.
- Heat dissipation from components requiring thermal design using heat sinks, thermal pads, and air flow.
- Reliability factors like component derating, protection from transients, redundancy.
- Designing for manufacturability – component placement, mounting profiles, test points, etc.
- Meeting application-specific size constraints. Compact PCB construction allows miniaturization.
- Conformal coatings may be needed in exposed environments for circuit protection.
A systematic PCB design process and rigorous testing of prototypes is key to overcoming these challenges.
Key takeaways are:
- A signal conditioner converts the signal from the source into a standardized format compatible with receiving equipment. This enables accurate transmission and measurement.
- Implementing conditioners as PCBs provides benefits like small size, design flexibility, ease of manufacturing and cost efficiency.
- Key conditioning techniques include amplification, filtering, isolation, analog/digital conversion, linearization and protection.
- PCB conditioners are designed using a process involving requirements analysis, component selection, circuit design, board layout, prototyping and testing.
- There are diverse applications in industrial, medical, automotive, aerospace and consumer products. PCBs facilitate customization to meet application needs.
- Benefits of PCB implementation includes size, reliability, noise reduction, rapid development, manfuacturability and cost.
- Careful design is needed to meet accuracy, speed, isolation and environmental requirements while managing trade-offs.
In summary, PCB fabrication enables the creation of high performance yet cost-effective signal conditioning solutions tailored for the target application, making the PCB an highly effective implementation platform for signal conditioners across various industries.
Frequently Asked Questions
Q1. How is a signal conditioner different from an amplifier?
The main difference is that a signal conditioner incorporates additional functions beyond just amplification. These include filtering, electrical isolation, analog/digital conversion, linearization, protection, etc. to convert the raw signal into the desired conditioned output format. An amplifier is just one part of the signal conditioning system.
Q2. What are some common inputs and outputs of signal conditioners?
Typical inputs are directly from sensors like temperature probes, pressure transducers, load cells, etc. that output low level analog voltage or current signals. Outputs are usually standardized analog or digital signals compatible with data loggers, controllers, indicators and recording instruments. Industrial signal levels of 4-20mA, 0-5V, 0-10V are commonly produced.
Q3. What performance characteristics are important in signal conditioners?
Key parameters are accuracy, stability, response time, bandwidth, gain linearity and repeatability, noise and ripple rejection, isolation rating, and environmental withstand capability in terms of temperature, humidity and vibration. Meeting application-specific performance requirements is vital.
Q4. What are some design challenges when developing a PCB signal conditioner?
Major challenges include achieving the required signal conditioning performance within size, cost and manufacturability constraints. Important aspects are minimizing noise through optimal PCB layout, managing trade-offs between competing requirements, component selection, thermal design, and designing for high reliability.
Q5. What types of PCB materials and manufacturing processes are used for signal conditioners?
Most use standard FR-4 PCB material. High frequency designs may utilize RF/microwave substrates for controlled impedance tracks. For robustness in harsh environments, PCB coatings like solder mask, moisture barriers and conformal coatings are applied. Manufacturing is highly automated using SMT assembly for volume production.