What does the Systems and Signal Processing module cover?

It takes a whole-system view of electronics. The input-process-output model treats any system as a chain of blocks: an input block (a sensor), a process block (the circuit that decides or amplifies) and an output block (a transducer), drawn as a block diagram. The module compares analogue and digital signals, stating the advantages of digital and how to convert between the two. It also covers feedback in control systems, distinguishing negative from positive feedback and describing a closed-loop example such as a thermostat.

What is the input-process-output model?

It is a way of understanding an electronic system as three connected blocks rather than a tangle of components. The input block is a transducer that senses a quantity, the process block is the circuit that acts on the signal (for example a comparator, amplifier or logic), and the output block is a transducer that produces a useful effect such as light, sound or movement. Drawing the system as labelled blocks makes its overall behaviour clear before any detailed circuit is designed.

What are the advantages of digital signals over analogue ones?

Digital signals use only two well-separated levels, so they are far more robust against noise and can be transmitted, copied and stored without the gradual degradation that affects analogue signals. They can be processed by logic circuits and computers, corrected for errors, and compressed. The trade-off is that real-world quantities are analogue, so converting between analogue and digital (using an analogue-to-digital or digital-to-analogue converter) is needed at the edges of a digital system.

What is the difference between negative and positive feedback?

Feedback feeds some of a system's output back to its input. Negative feedback opposes the change, pulling the system back towards a set value, which gives stability and steady control, as in a thermostat that switches a heater off as the room reaches the target temperature. Positive feedback reinforces the change, pushing the system further in the same direction, which can produce rapid switching or oscillation. Most control systems rely on negative feedback for stable regulation.

SingaporeElectronics

Systems and Signal Processing: O-Level Electronics module overview of the input-process-output model, analogue versus digital signals and feedback in control systems

An O-Level Electronics overview of the Systems and Signal Processing module. The input-process-output systems model and block diagrams, the comparison of analogue and digital signals and converting between them, and feedback in control systems including negative and positive feedback, with links to every dot point.

Generated by Claude Opus 4.85 min readSEAB O-Level Electronics: Systems and Signal ProcessingUpdated 2026-06-14

Reviewed by: AI editorial process; not yet individually human-reviewed

Jump to a section

What this module is about
The input-process-output model
Analogue versus digital signals
Feedback in control systems
A worked systems example
How this module is examined
Check your knowledge

What this module is about

Systems and Signal Processing steps back from individual components to view electronics as whole systems. It gives you the input-process-output model and block diagrams as a way to describe any system at a glance, compares analogue and digital signals and the advantages of going digital, and explains feedback, the idea that lets a system regulate itself. These framing ideas tie the rest of the course together: the sensors, processing circuits and output transducers you have met all slot into the input-process-output picture, and feedback connects directly to the op-amp and control circuits.

This overview ties the module together and links to every dot point, each with its own worked answers and practice questions. See the full set at /sg-o-level/electronics/syllabus/systems-and-signal-processing.

The input-process-output model

The input-process-output model describes any electronic system as three connected blocks: an input transducer that senses, a process block that decides or amplifies, and an output transducer that acts. Drawing this as a labelled block diagram makes the system's behaviour clear before any detailed circuit work, and helps you locate a fault to a particular stage.

Analogue versus digital signals

Analogue versus digital signals compares the two signal types. An analogue signal varies continuously; a digital signal uses two levels. Digital signals are more robust against noise and can be stored, copied and processed without degradation, which is why so much modern electronics is digital, with converters at the edges to move between the two domains.

Feedback in control systems

Feedback in control systems explains how feeding the output back to the input lets a system control itself. Negative feedback opposes the change and gives stable regulation, as in a thermostat; positive feedback reinforces the change and can cause rapid switching or oscillation. A closed-loop system uses feedback, while an open-loop system does not.

A worked systems example

Block diagram of a temperature alarm

A temperature alarm sounds a buzzer when a room gets too hot. Describe it using the input-process-output model and state where feedback would be used in the related heating control.

Step 1: Identify the input block

The input is a thermistor, whose resistance falls as the room warms; placed in a potential divider it produces a voltage that rises with temperature.

Step 2: Identify the process block

The process block is a comparator. It compares the thermistor divider voltage with a fixed reference set to the alarm temperature, and switches its output high when the room is too hot.

Step 3: Identify the output block

The output is a buzzer (driven through a transistor), which converts the electrical signal into sound when the comparator output goes high.

Step 4: Note where feedback applies

In a related heating controller, negative feedback would be used: the same temperature reading is fed back to switch the heater off as the room reaches the set value, holding the temperature steady in a closed loop.

How this module is examined

Draw clear block diagrams. Label the input, process and output blocks and the signal flow between them; this is the core skill examined.
State digital advantages precisely. Robustness against noise, and storage and copying without degradation, are the marks to secure.
Distinguish the feedback types. Negative feedback opposes the change and stabilises; positive feedback reinforces it. Name the type and its effect.

Check your knowledge

Work through the quiz for this module to test the input-process-output model, analogue and digital signals, and feedback in control systems, then review the worked explanations.

Sources & how we know this

Singapore Examinations and Assessment Board (SEAB) — Singapore Examinations and Assessment Board (2026)
Subjects and syllabuses, Ministry of Education Singapore — Ministry of Education, Singapore (2026)