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Digital Electronics : Sequential Circuits Part 2 ## A quick outline of the topics introduced in this tutorial :

The analog and digital devices work side by side but they cannot work together until there is some means for them to understand their languages. So, for a proper communication between these devices, converters are required that can convert analog into digital and vice versa. These converters are AD and DA converters.

### Analog to Digital Conversion (A to D or ADC or A–D)

There are several different designs of ADCs, which are based on three basically different approaches.

#### • Flash converter

The first is called a flash converter or parallel encoder. These use circuits called comparators. A comparator has two inputs, one is the analogue voltage being converted and the other is a known reference voltage. All we ask of a comparator is to answer a simple question: ‘Is the analogue input voltage higher or lower than our reference voltage?’ It answers by changing its output voltage to logic 1 to mean it is higher and logic 0 to mean it is lower. They are so accurate that the chance of it accepting the two voltages as the same level are extremely slight and doesn’t happen in practice.

#### • Ramp generators

These are a combination of a binary counter that simply counts up from zero to its maximum value, perhaps 1024 like the last type.

#### • Successive approximation

If we were to use a 3-bit digital signal to convert an analog voltage of between 0 V and 4 V we could have the 3 bits representing voltages of 4V, 2 V and 1V.

The tutorial document contains more comprehensive descriptions of these different ADC approaches.

#### Digital to Analog Conversion (DAC)

Changing a group of digital bit values to an analog voltage is basically just the reverse process of the A–D conversion. Most digital to analog converters operate by adding current together then converting the result into an analog voltage. The binary levels are used to switch currents on or off.

### Resolution

This is the number of digital bits used to convert into an analog voltage. Typical values available are from 4 to 18 bits. As the digital input changes by a single bit, say from 1000 to 1001, the resultant voltage or current increases by a discrete step. The size of this step is determined by the number of bits used compared with the maximum value of the output current or voltage.

### Here's a list of all the tutorials we currently have in this area - Introductory Digital Electronic Circuits and Boolean logic

 Introduction to the Number System : Part 1 Introducing number systems. Representation of numbers in Decimal, Binary,Octal and Hexadecimal forms. Conversion from one form to the other. Number System : Part 2 Binary addition, subtraction and multiplication. Booth's multiplication algorithm. Unsigned and signed numbers. Introduction to Boolean Algebra : Part 1 Binary logic: True and false. Logical operators like OR, NOT, AND. Constructing truth tables. Basic postulates of Boolean Algebra. Logical addition, multiplication and complement rules. Principles of duality.  Basic theorems of boolean algebra: idempotence, involution, complementary, commutative, associative, distributive and absorption laws. Boolean Algebra : Part 2De-morgan's laws. Logic gates. 2 input and 3 input gates. XOR, XNOR gates. Universality of NAND and NOR gates. Realization of Boolean expressions using NAND and NOR. Replacing gates in a boolean circuit with NAND and NOR. Understanding Karnaugh Maps : Part 1 Introducing Karnaugh Maps. Min-terms and Max-terms. Canonical expressions. Sum of products and product of sums forms. Shorthand notations. Expanding expressions in SOP and POS Forms ( Sum of products and Product of sums ). Minimizing boolean expressions via Algebraic methods or map based reduction techniques. Pair, quad and octet in the context of Karnaugh Maps. Karnaugh Maps : Part 2Map rolling. Overlapping and redundant groups. Examples of reducing expressions via K-Map techniques. Introduction to Combinational Circuits : Part 1Combinational circuits: for which logic is entirely dependent of inputs and nothing else. Introduction to Multiplexers, De-multiplexers, encoders and decoders.Memories: RAM and ROM.  Different kinds of ROM - Masked ROM, programmable ROM. Combinational Circuits : Part 2 Static and Dynamic RAM, Memory organization. Introduction to Sequential Circuits : Part 1 Introduction to Sequential circuits. Different kinds of Flip Flops. RS, D, T, JK. Structure of flip flops. Switching example. Counters and Timers. Ripple and Synchronous Counters. Sequential Circuits : Part 2ADC or DAC Converters and conversion processes. Flash Converters, ramp generators. Successive approximation and quantization errors.