1. DATA CONVERTERS (Linear Circuits) S.Senthil Kumar, Dept. of Aero, KCT

2. Data Conversion
Basically we have two types of data in nature: Analog and Digital.
Data transmission – Electrical wires (for analog) and databus (for digital).
Most of the real-world physical quantities are in analog form.
Data storage and processing – Analog versus Digital. (That’s the idea for data conversion!!!)

3. Data Conversion
Digital data processors – Microprocessors, DSPs, FPGAs etc.
So, when a data conversion needed? – When digital devices interface with analogue devices and vice versa.
Can we locate a place in an airplane where digital systems interface with analogue systems? –YES !!!
A most critical system – Flight Control System (FCS).

4. FBW Flight Control System
Basic components of a FBW flight control system

5. Flight Control Computer (FCC)
FCC used in LCA Flight Control Computer
(Courtesy: DRDO, India) (Courtesy: Curtiss-Wright
Controls Defense Solutions, US)

6. Data Conversion Circuits
Digital-to-Analog (D/A) and Analog-to-Digital (A/D) converters (DAC and ADC).
Application of A/D and D/A converters
Today, both ADC and DAC are available in IC form.

7. ADC and DAC
Applications – digital audio recording and playback, computers, data acquisition, digital multimeter, digital control, digital signal processing, microprocessor based instrumentation.
Since most of the ADCs use DACs in their inside, we have to discuss DAC first.

8. Digital-to-Analog Converter
DAC – Current or Voltage outputs (Unipolar and Bipolar), Multiplying type.
DAC’s current or voltage analog output is proportional to the weighted sum of digital inputs (characteristic of a linear circuit).
Schematic of a DAC

9. Digital-to-Analog Converter
For a voltage output DAC,
Binary Weighted Resistor DAC
R-2R Ladder DAC Types of DAC
Inverted R-2R Ladder DAC
In order to understand the above DACs, we have to know the basics of an Operational Amplifier

10. Operational Amplifier (Op-Amp)
(a) Op-amp circuit symbol (b) Ideal op-amp
(c) Open loop circuit

11. Op-Amp – Inverting Amplifier
Inverting Summing Amplifier

12. Binary Weighted Resistor DAC
A simple binary
weighted
resistor DAC

13. R-2R Ladder DAC A 3-bit R-2R Ladder DAC (Voltage mode) A 3-bit
Inverted R-2R
(Current mode)

14. R-2R Ladder DAC – Equation
3-bit R-2R Ladder DAC (Voltage mode)

15. Analog-to-Digital Converter
A-to-D conversion is a quantization process.
ADC has two techniques of conversion
Comparing a given analog signal with the internally generated equivalent signal (Types: Successive Approximation, Counter and Flash type)
Changing an analog signal into time or frequency and comparing these new parameters with known values.
(Types: Integrator and Voltage-to-Frequency
(V2F) converters)

16. Successive Approximation ADC
Block diagram of a 4-bit successive approximation ADC

17. Successive Approximation ADC
Flowchart of
successive approximation
A-to-D conversion

18. Cycles in Successive Approximation ADC
Conversion process in a successive approximation ADC

19. Reference(s)
Tony R. Kuphaldt, Lessons in Electric Circuits, Volume IV – Digital, Design Science License, Fourth Edition, 2002.
D. Roy Choudhury and Shail B. Jain, Linear Integrated Circuits, New Age International Publishers, Second Edition, 2003.
Anil K. Maini, Digital Electronics Principles, Devices and Applications, John Wiley & Sons, 2007.