Digital Communication and ADC Basics

Digital Bus

• Digital devices need to communicate with each other
• Information is processed and sent to another device
• These communications are called data buses
• Flight management computer (FMC) can make flight routes
• Inertial reference system (IRS) is often used for navigation and speed
• Controlling computers help pilots control the plane
• Flight/slat electronic unit (FSEU) is an example of a controlling computer
• Informational computers give information like oil and engine temperatures

Analog to Digital Converter

• Sample rate/frequency is measured in samples per second (SPS or S/s)
• Sample rate is 1/T, where T is the period of the sample or the time it takes before sampling again
• Nyquist Theorem states that the sampling rate must be at least twice the highest frequency in the analogue signal to accurately recreate the original signal. FNyquist = “fmax”
• ADC is a 2-bit converter. It divides voltage into 4 parts (00, 01, 10, 11)

Flash ADC

• Also called a parallel converter
• Conversion happens in a single cycle
• Fastest ADC type
• Has a complicated architecture
• Uses 2ⁿ-1 comparators

Pipeline ADC

• Uses multiple steps to convert from analog to digital until complete
• There is no rest

Ramp Generation ADC

• Counts upwards from 0 to a desired value

Digital to Analog Converters (DACs)

• These converters convert digital signals into analog signals

Data Buses

• A bus is a collection of wires used to transfer data within a computer
• A bus's width determines the amount of data that can be transferred at once (e.g., 16 bits or 32 bits)
• Simplex bus transmits in one direction only
• Half-duplex bus transmits in both directions but not simultaneously
• Full-duplex bus transmits in both directions simultaneously

Network Topologies

• Topology describes the network layout
• Star topology: every node connects to a central hub (coaxial, twisted-pair, or fiber optic)
• Advantages: centralized management, easy maintenance
• Disadvantages: single point of failure (hub failure causes network failure)
• Bus topology: all devices connect along a single cable
• Advantages: simple setup (good for small networks)
• Disadvantages: vulnerable to cable failures
• Ring topology: data travels in a loop
• Advantages: signal travels all the way if a cable fails
• Disadvantages: vulnerable to cable failure
• Tree topology: one central node with other nodes branching off
• Advantages: expandability (nodes can easily be added)
• Disadvantages: central node failure impacts all other nodes

Parity Checking

• Adds a parity bit to ensure an odd or even number of 1s in the data

ARINC (Aeronautical Radio, Incorporated)

• Develops and operates systems and services for aviation and travel industries
• Standardizes equipment for efficiency, operation, and performance

32-bit Words

• Two wire (twisted pair)
• Bipolar RZ format
• Low speed: 12.5 kbps
• High speed: 100 kbps
• Up to 20 receivers
• Odd parity (normally)

Logic Circuits

• Positive and Negative Logic
• Fan-in and fan-out
• Fan-in = maximum amount of digital inputs
• Fan-out = maximum amount of digital outputs
• AND gate operations

Integrated Circuits

• Half adder combines two binary digits
• Produces a carry output
• AND gate is added in parallel; it doesn't receive a carry input

Counters

• Counters are used to count and measure events
• Synchronous counters have input clocks that are synchronised
• Asynchronous counters do not have synchronised input clocks
• Different types of counters like decade and ripple counters

Registers

• Used to store and transfer data within a computer
• Parallel registers transfer data simultaneously
• Serial-to-parallel converts serial data to parallel, and vice versa
• Shift registers move bits to the left or right to shift numerical values.

Multiplexing

• Combining multiple signals into one channel
• Frequency division multiplexing (FDM) combines signals of different frequencies
• Time division multiplexing (TDM) combines signals by dividing time

Fiber

• Signals are transmitted as light, not electricity
• Converts electric signal to optic, sends it, then back to electrical signal
• Single mode is faster and for longer distances, used for long-distances
• Multimode is slower, used for shorter distances

Connectors

• Threaded coupling mechanism and butt-type connector with ceramic terminals
• Type-B connector is frequently connected and disconnected, suitable for over torque
• Type-C: push-pull coupling mechanism
• Optical sources and transmitters transmit data via fibers

Light Emitting Diodes (LEDs)

• LEDs emit light when current passes through
• They produce colors like red, green, yellow, blue, and infrared.

Laser Diode

• Laser diodes emit light by stimulated emission

Electrostatic Discharge (ESD)

• ESD is the transfer of electrical charges between objects
• Positive charges lose electrons
• Negative charges gain electrons
• Human Body Model (HBM) simulates a human touching a component
• Charged Device Model (CDM) simulates assembly line components

Software Management Control

• Firmware, operational software, and databases

Electromagnetic Environment

• Electromagnetic (EM) field
• Radio Frequency Interference (RFI)
• High Intensity Radiated Field (HIRF)
• Non-ionizing electromagnetic energy external to the aircraft can cause adverse effects on the aircraft systems.

Background

• Problems like countdown issues
• Radio interference issues (eg. HIRF)
• Methods for interference reduction include bonding and shielding (using metallic screening etc)

Aircraft Systems

• Integrated modular avionics (IMA)
• Core processing input/output module (CPIOM)
• Avionics full-duplex switched ethernet (AFDX)
• Aircraft data network (ADN)
• General processing module (GPM)
• Line replaceable modules (LRMs)
• Cabin core system (CIDS, or CSSC)
• Flight attendant panel (FAP)
• Information systems for cabin/flight management
• Health management systems, like AHM
• Electronic flight bag (EFB)