data converters ADC AND DAC, Slides of Analog Electronics

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DATA CONVERTERS

(Linear Circuits)

S.Senthil Kumar, Dept. of Aero, KCT

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!!!)

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

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

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.

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

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

Op-Amp – Inverting Amplifier Inverting Amplifier Inverting Summing Amplifier i 1 1 v i R o 1 f v  i R 1 1 f o f i R v i R v R     1 o^ f CL i v^ R A v R    Vout^ ^  V 1 ^ V 2 V 3 

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

R-2R Ladder DAC – Equation 3-bit R-2R Ladder DAC (Voltage mode) 3 2 1 2 4 8 R R R in V V V V d d d          3 2 1 2 2 2 4 8 f f (^) R R R o in R R (^) V V V V V d d d R R      (^)         1 2 3 3 2 1 2 2 2 f o R R V V d d d R          1 2 3 3 2 1 2 2 2 f o R If R R V V d d d        

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

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

Reference(s)

(1) Tony R. Kuphaldt, Lessons in Electric Circuits, Volume IV

- Digital , Design Science License, Fourth Edition, 2002. (2) D. Roy Choudhury and Shail B. Jain, Linear Integrated Circuits , New Age International Publishers, Second Edition, 2003. (3) Anil K. Maini, Digital Electronics Principles, Devices and Applications , John Wiley & Sons, 2007.