This document discusses analog and digital signals and data conversion between the two. It explains that analog signals can take on a continuous range of values while digital signals are discrete. It then discusses analog and digital circuits, with analog circuits having analog inputs and outputs and digital having digital. Digital circuits offer advantages like reliability, easy design and storage. The document goes on to discuss digital signals on aircraft, which take on discrete binary values, and examples like whether the plane is on the ground. It also discusses different types of computers on aircraft like interactive, reference, storage and controlling computers. It finishes with explanations of analog to digital and digital to analog converters, their specifications and examples like temperature sensors.

1. Module 5: Digital Techniques and
Electronic Instrument Systems
5.3 Data Conversion

2. Analog and digital signals
Analog signal:
can take all possible
values.
-2
-1
0
1
2
0 5 10
Digital Signal: can take
specific values (discrete
values).
0
1
2
3
4
0 5 10
0
2
4
6
0 2 4 6 8 10
0
2
4
6
0 5 10 15
2

3. Analog and digital circuits
3
 Analog circuits: Input and output signals are
analog.
 Digital circuits: Input and output signals are digital.
-2
-1
0
1
2
0 5 10
-1
0
1
2
0 5 10
0
2
4
6
0 5 10 15
0
2
4
6
0 5 10 15

4. Digital circuits advantages
4
 High reliability
 Easy design
 High flexibility
 Easy storage

5. Digital signals on the Aircraft
 Digital signals on the aircraft:
 Discrete values, usually binary
values: on / off, high / low.
 Examples:
 Is the aircraft on the ground or on the
earth?
 The Air Data Computer calculates the
airspeed, the altitude, the temperature
etc. from data sensor inputs. These
inputs are send to a digital bus
(ARINC) in a series of binary
numbers. These output serves as an
input for cockpit instruments, such as
the PFD.

6. Types of Computers
 Interactive Computers:
 The plane crew interfaces with the
computer.
 Example: Control Display Unit
(CDU).
 Reference Computers:
 Provides information used by
other computers.
 Example: Inertial Reference
System. (IRS – calculates
airspeed, heading, attitude etc.).
Information is provides to other
systems, such as Auto-throttle
computer, FMC etc.

7. Types of Computers
 Storage Computers:
 Store information such as flight
roots, total fuel, overspeed
threshold, etc.
 Controlling Computers:
 Control a specific device.
 e.g. Flap Electronic Unit (FEU).
Takes input from the Flap Lever
and gives input to the mechanism
that extends or detracts the
flaps, when the airspeed is within
the allowable values.
 Informational
Computes:
 Provide information
to the crew.
 e.g. ECAM
(Electronic
Centralized
Aircraft
Monitoring).

8. A/D & D/A Converters
 Temperature is an analogue value. It must be converted to
discrete value, to be displayed in a digital computer.
 The user input signal to drive a flight control surface is digital.
However, the signal that will drive the control surface must be
analog.

9. D/A Converters
 The circuit is called “Binary Weighted Ladder”.
3-bit
Digital
Input
Analog
Output

10. A/D: Sampling
 Resolution of A/D
conversion depends on:
 Sampling rate
 Number of bits used in
conversion and output
voltage range.
 An mp3 of 44000HZ
and 192kbps.
 Sampling rate: 44000
samples per sec.
 192Kbps: Affects the size
of the discrete areas.

11. D/A & A/D Converters Specifications
 Accuracy:
 The actual output vs. the converted output.
 E.g. if the maximum output of the converter is 10V and the
error is ±1%, then the maximum error for any voltage output is
10mV.
 Resolution of A/D converters:
 The number of steps the input is divided into. Is expressed in
power of 2. A 12-bit A/D converter divides the analog signal in
212 steps.
 Sample and Hold A/D converters:
 Freezes the analog input at the moment a new sample is taken.
 Throughput:
 The maximum number of bits “produced” or “consumed” per
second (the bit rate).