Eduqas A-Level Electronics Signal conversion and communications: ADC, DAC, multiplexing, modulation and optical fibre

What this module actually demands

Signal conversion and communications is where the analogue and digital worlds meet and where information is sent over a link. It spans Component 1 (conversion and modulation) and Component 2 (digital communications and optical fibre). The examiners reward accurate converter calculations, a clear grasp of the sampling theorem and aliasing, and systems reasoning about how data is multiplexed, modulated and transmitted.

This guide walks through the topics in order and sets out the exam patterns Eduqas repeats. Each topic has a matching dot-point page with practice; this overview ties them together.

Conversion: ADC and DAC

Analogue-to-digital conversion samples and quantises a signal, with resolution $\frac{V_\text{range}}{2^n}$, obeys the sampling theorem $f_\text{sample} \ge 2 f_\text{max}$ to avoid aliasing, and introduces quantisation error. Digital-to-analogue conversion rebuilds an analogue voltage with a binary-weighted summing-amplifier DAC or an R-2R ladder, and smooths the staircase output with a reconstruction low-pass filter.

Communications: data, modulation and fibre

Multiplexing and data transmission compare serial and parallel links, define bit rate and baud, share a channel by time-division or frequency-division multiplexing, and detect errors with parity and checksums. Modulation and wireless transmission explain the need for a carrier, AM and FM with their bandwidth and noise trade-offs, digital ASK and FSK, and the transmitter and receiver chain. Optical communication sends light along a fibre by total internal reflection, with an LED or laser source and a photodiode receiver, and beats copper on bandwidth and interference.

How this module is examined

A typical Eduqas profile for this content:

• Calculations. Converter levels, resolution and output codes, sampling rates from the Nyquist theorem, data rates, and bit rate from baud and bits per symbol.
• Explanation. Sampling, quantisation error and aliasing; the two DAC architectures and reconstruction filtering; AM versus FM; total internal reflection.
• Comparison. Serial versus parallel, TDM versus FDM, ASK versus FSK, and fibre versus copper.
• Systems reasoning. Tracing a conversion or a transmitter-receiver chain end to end.

Check your knowledge

A mix of recall and calculation questions covering the module. Attempt them under timed conditions, then check against the solutions.

1. State how many levels a 10-bit ADC has. (1 mark)
2. An 8-bit ADC covers $0$ to $5.0\ \text{V}$. Find its resolution. (2 marks)
3. State the minimum sampling rate for a signal whose highest frequency is $20\ \text{kHz}$. (1 mark)
4. State the main advantage of an R-2R ladder DAC over a binary-weighted DAC. (1 mark)
5. State which of AM and FM is more noise-immune. (1 mark)
6. State the physical effect that keeps light inside an optical fibre. (1 mark)