Analog to Digital and Digital to Analog converter(simple and best mini project using simulation tool MULTISIM)

CHAPTER 1

INTRODUCTION

1.1  ANALOG TO DIGITAL CONVERTER (ADC) AND DIGITAL TO ANALOG CONVERTER (DAC)

In electronics, an Analog to Digital Converter (ADC) is a device for converting an analog signal (current, voltage etc.) to a digital code, usually binary. In the real world, most of the signals sensed and processed by humans are analog signals. Analog-to-Digital conversion is the primary means by which analog signal are converted into digital data that can be processed by computers for various purposes.

Digital to Analog converter (DAC) is a device that converts digital code into analog signals. There are several DAC architectures; the suitability of a DAC for a particular application is determined by figures of merit including: resolution, maximum sampling frequency and others. Digital-to-analog conversion can degrade a signal, so a DAC should be specified that has insignificant errors in terms of the application. Due to the complexity and the need for precisely matched components, all but the most specialized DACs are implemented as integrated circuits (ICs).

          1.1.1    Scope of the Experiment:

·         To design and implement the ADC and DAC

·         To analyse the circuit

          1.1.2    Objective of the Experiment

·         Draw the pin diagram of the IC’s used

·         Construct the logic circuit of ADC and DAC

·         Simulate using the MULTISIM 11.0

·         Verify the output

CHAPTER 2

ANALOG TO DIGITAL CONVERTER (ADC) AND DIGITAL TO ANALOG CONVERTER (DAC)

2.1 BLOCK DIAGRAM:

2.2 PIN DIAGRAM:

2.2.1 ADC:

2.2.2 DAC:

2.3 CIRCUIT DIAGRAM:

V1- Supply voltage of 5V

Pot- Potentiometer

U2 and U5- Voltmeters

U1-Analog to digital converter(ADC)

U6-Digital to Analog converter(DAC)

U3 and U4-Hexadecimal displays

X1,X2...X8-LED’s

2.4 WORKING:

The ADC is an 8-bit A-to-D converter, having data lines X1 toX8. It works on the principle of successive approximation.  The input control signals Vref + and Vref -  being active-high, are tied to Vcc (5 volts). The input control signal SOC, being active-High, initiates start of conversion at rising edge of the pulse, whereas the output signal EOC becomes high after completion of digitisation. This EOC output is coupled to SOC input, where rising edge of EOC output acts as SOC input to direct the ADC to start the conversion. As the conversion starts, EOC signal goes high. At next clock pulse EOC output again goes low, and hence SOC is enabled to start the next conversion. Thus, it provides continuous 8-bit digital output corresponding to the instantaneous value of analogue input. 

The maximum level of analogue input voltage should be appropriately scaled down ie 5V in binary form, so the resolution is usually expressed in bits. In consequence, the number of discrete values available, or "levels", is usually a power of two. For example, an ADC with a resolution of 8 bits can encode an analogue input to one in 256 different levels, Since 2⁸ = 256. The values can represent the ranges from 0 to 255 (i.e. unsigned integer).

Resolution can also be defined electrically, and expressed in volts. The minimum change in voltage required to guarantee a change in the output code level is called the LSB (least significant bit, since this is the voltage represented by a change in the LSB). The resolution Q of the ADC is equal to the LSB voltage. The voltage resolution of an ADC is equal to its overall voltage measurement range divided by the number of discrete voltage intervals.

Q = E_FSR/N ,

Where, N is the number of voltage intervals and E_FSR is the full scale voltage range, given by,

E_FSR = V_refhi – V_reflow,

Where , V_refhi  and  V_reflow  are the upper and lower extremes respectively, of the voltages that can be coded.

Normally, the number of voltage intervals is given by,

N = 2^m

Where, ‘m’ is the resolution in bits.

2.4.1 ADC PROCESS:

The two main steps of ADC process is

1) Sampling and holding

2) Quantising and encoding 

Sampling and Holding:

·        *  Holding signal benefits the accuracy of the A/D conversion

·         * Minimum sampling rate should be at least twice the highest data frequency of the analog signal

Quantizing and Encoding:

·         *  Quantizing: Partitioning the reference signal range into a number of discrete quanta, then matching the input signal to the correct quantum.

·         *  Encoding: Assigning a unique digital code to each quantum, then allocating the digital code to the input signal.

2.4.2 DAC PROCESS:

The above diagram, shows how the Digital signal is converted into analog form.

A DAC converts an abstract finite-precision number (usually a fixed-point binary number) into a physical quantity (e.g., a voltage or a pressure). In particular, DACs are often used to convert finite-precision time series data to a continually varying physical signal.

An ideal DAC converts the abstract numbers into a conceptual sequence of impulses that are then processed by a reconstruction filter using some form of interpolation to fill in data between the impulses. A conventional practical DAC converts the numbers into a piecewise constant function made up of a sequence of rectangular functions that is modeled with the zero-order hold. Other DAC methods (such as those based on delta-sigma modulation) produce a pulse-density modulated output that can be similarly filtered to produce a smoothly varying signal.

As per the Nyquist–Shannon sampling theorem, a DAC can reconstruct the original signal from the sampled data provided that its bandwidth meets certain requirements (e.g., a baseband signal with bandwidth less than the Nyquist frequency). Digital sampling introduces quantization error that manifests as low-level noise added to the reconstructed signal.

2.5 Simulation sample:

2.6 APPLICATIONS:

ADC and DAC are used virtually everywhere where an analog signal has to be processed, stored, or transported in digital form and vice versa.

    *  Some examples of ADC usage are digital voltmeters, cell phone, thermocouples, and digital oscilloscope.

    *   Microcontrollers commonly use 8, 10, 12, or 16 bit ADC'S our ADC is a 8-bit ADC

   *  They also have a wide range of application in the field of MUSIC RECORDING, DIGITAL SIGNAL PROCESSING, ROTARY ENCODERS and SCIENTIFIC INSTRUMENTS

CHAPTER 3

MULTISIM 11.0

NI Multisim (formerly MultiSIM) is an electronic schematic capture and

simulation program which is part of a suite of circuit design programs, along with NI

Ultiboard Multisim is one of the few circuit design programs to employ the original

Berkeley SPICE based software simulation. Multisim was originally created by a

company named Electronics Workbench, which is now a division of National

Instruments. Multisim includes microcontroller simulation (formerly known as

MultiMCU), as well as integrated import and export features to the Printed Circuit

Board layout software in the suite, NI Ultiboard. Multisim is widely used in academia and

industry for circuits education, electronic schematic design and SPICE simulation.

3.1 PROCEDURE FOR USING MULTISIM

·         Click on Multisim in the desktop.

 Open/Create Schematic: A blank schematic is automatically created. To create a

new schematic click on File-New-Schematic Capture.

·         To place components, click on Place/Components. On the Select Component window click on the Group to select the component needed for the circuit. Click OK to place the components on the Schematic.

• To connect the components click on Place/wire, drag and place the wire.
•   To place Digital Source click on Source in Group and Digital Source.
•  Grounding: All circuit must be grounded before the circuit simulation. Click on
• Ground the toolbar to ground the circuit.
•     To simulate the completed circuit click on Simulation/Run or F5

CHAPTER 4

CONCLUSION

In the experiment we basically vary the input voltage with the help of a potentiometer and the voltage values are measured with the help of a voltmeter. The input signals are fed to the analog to digital converter(ADC) as a result the signals are converted to digital form. For each change in the input voltage the corresponding value of Digital signal is measured.

Simultaneously the Digital signals is fed to the digital to analog converter(DAC) as a result the digital signals are converted to analog signals and their value is measured using a voltmeter.

Now the voltage value of the input signal and the output signals are compared. It is observed that the input voltage equals the output voltage indicating the successful conversion of analog signal to digital form and digital signals to analog form.