Analog to Digital Conversion: Principles, Types, and Applications, Slides of Computer Networks

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Presented By:

Amit Kumar Joshi

Presentation Topic:

Analog to Digital Conversion

(ADC)

Analog Signals

Analog signals – directly measurable quantities in terms of some other quantity Examples: Thermometer – mercury height rises as temperature rises Car Speedometer – Needle moves farther right as you accelerate

Digital Signals

Digital Signals – have only two states. For digital computers, we refer to binary states, 0 and 1. “1” can be on, “0” can be off. Examples: Light switch can be either on or off Door to a room is either open or closed

©Alex Doboli 2006

Quantization

 Quantization is the process of converting the sampled continuous-

Valued signals into discrete-valued data

Quantizing

The number of possible states that the converter can output is: N=2n where n is the number of bits in the AD converter Example: For a 3 bit A/D converter, N=23=8. Analog quantization size: Q=(V max -V min)/N = (10V – 0V)/8 = 1.25V

Step 1: Quantizing

Example: You have 0-10V signals. Separate them into a set of discrete states with 1.25V increments. (How did we get 1.25V? (Discussed in previous slide)

Step 2. Encoding

• Here we assign the digital value (binary number) to each state for the computer to read.

©Alex Doboli 2006

Sampling

Collect sufficient data for correctly representing a

continuous-time signal

3 Basic Types

Flash ADC Digital-Ramp/Dual slope/Counter slope ADC Successive Approximation ADC

3 bit Flash ADC Circuit

How Flash Works

• As the analog input voltage exceeds the reference voltage at each comparator, the comparator outputs will sequentially saturate to a high state.
• The priority encoder generates a binary number based on the highest- order active input, ignoring all other active inputs.

Flash

Advantages

• Simplest in terms of operational theory
• Most efficient in terms of speed, very fast  (^) limited only in terms of comparator and gate propagation delays Disadvantages

Lower resolution

Expensive

For each additional output bit, the number of comparators is doubled  i.e. for 8 bits, 256 comparators needed

2-> Dual Slope ADC

• Also known as Counter-Ramp or Digital Ramp ADC
• A dual slope ADC is commonly used in measurement instruments (such as DVM’s). ADC 1. 20