Analog-to-digital conversion is an electronic process in which a continuously variable signal is changed, without altering its essential content, into a multi-level signal.Typically, an ADC is an electronic device that converts an input analog voltage (or current) to a digital number.

An analog-to-digital converter (abbreviated ADC, A/D or A to D) is an electronic integrated circuit, which converts continuous signals to discrete digital numbers. The reverse operation is performed by a digital-to-analog converter (DAC).

A device for converting information in the form of combinations of discrete (usually binary) states or a signal to information in the form of the value or magnitude of some characteristics of a signal, in relation to a standard or reference.

Most often, it is a device which has electrical inputs representing a parallel binary number, and an output in the form of voltage or current.Numbers in base two are called binary number. Consider the binary number 10101. This represents the value 1*24+0*23+1*22+0*21+1*20

The values of the binary number represents the decimal values or total voltage of the circuit.

The fundamental circuit of most D/A converters involves a voltage or current reference; a resistive ladder network that derives weighted currents or voltages, usually as discrete fractions of the reference; and

A set of switches, operated by the digital input, Determines which currents or voltages will be summed to constitute the output.

The binary number which is set by the switches is 1000 or decimal number 8. the binary ladder is tied to the +15 V supply through the resistors in parallel.

The largest number that the four switches can express is 1111 or decimal number 15. In this case a 1 is +15 V, and a 0 is ground.

Therefore, if the binary number is set by the switch 1111 or decimal number 15 for a circuit, the binary ladder is tied to the +15 V supply through all the resistors in parallel.This produces a 15 V output voltage. If all the switches are switched to the 0 position, the output is 0 V or ground,

The voltage increments in the binary ladder can be computed by using the following formula,

where, Vs = voltage supply in volt, N=number of bits in the binary number inputThe output voltage of the binary ladder can be computed by the following formula:

where, Vout=Output voltage of the binary in volt, and N=No.of bits, BN=Binary number input.

What is the voltage increment V for an 8 bits binary ladder with 15 volts as the supply volts.What is the voltage increment V for an 8 bits 2R binary ladder with 15 volts as the supply volts.

It is important to remember that the values of resistors in the binary ladder are divided by 2 for each binary power increase, that is 2 resistor is 8k, 21 resistor is 4k, 22 resistor is 2k, and 23 resistor is 1k. If a fifth bit is added to the binary ladder, the resistor value will be 500 and so on.

Therefore, it could be concluded that the larger the binary number, the smaller the resistor.0

The output voltage of this circuit can also be calculated as follows,

Digital comparator can be used to make a fast analog-to-digital converter.

An analog-to-digital converter produces a binary number which is in direct proportion to an analog voltage input.3bit analog-to-digital converter:7 LM339 voltage comparators

Negative input of each comparator is tied to a resistor voltage divider which divides the 8-volt supply into 1-volt increments.

Each VC has a reference voltage of 1volt greater than the previous comparator

Positive inputs to the VCs are tied together so that the input voltage will increase on all comparators at the same time.

If input voltage increase to 2.5volt, the output of the first two comparators will be logic 1

NAND GATE--------------------A B C0 0 10 10 1 11 1 1

Basic Operation PrincipleWhen all VCs output are at logic 0, the output of their corresponding NAND gates are 1.If the analog input voltage rises to 1.5 volts, the first comparators output goes to logic 1 which will fed to the two-input NAND gates.The other input to this NAND gate is from the inverter which comes off the output of the second comparator.The output of the second comparator will be 0 because the analog voltage is 1.5v and is not yet enough to change the state of the second comparator.Therefore, the 0 is inverted to a 1 and fed to the input of the NAND gate for the first comparator.1 will be the input of the first NAND gate and 0 on its output which is fed to the 2nd NAND gate.Produce a logic 1 or binary number 1 on the output of the 2nd NAND gate.A binary number 1 or 2^0 or logic 1 means for the 1st output NAND gate means that the analog input voltage lies between 1-2 volts.

The successive approximation method is used to determine the correct binary number by using 4-set of 7406 converter, an LM339 voltage comparator and a 2R resistor network.The output of the D-to-A converter is fed to the negative input of a voltage comparator and the positive input comes from the analog voltage.The initial setting of this method is to set the most significant bit of the D-to-A converter to a logic 1.Test the output of the A-to-D converter against the input analog voltage for to identify if the A-to-D output is larger or smaller.If the voltage generated by the A-to-D converter is smallerSet the most significant bite (MSB) at a logic 1If it is larger, bring it LOWSet the MSB at a logic 0