Analog to Digital ConvertersPRASANTH.NM.TECH CIM RA1412004010010

Analog SignalsAnalog signals It is a 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

Stereo Volume increases as you turn the knob.

Digital SignalsDigital Signals: They 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 offDoor to a room is either open or closed

APPLICATIONS OF ANALOG AND DIGITAL SIGNALSANALOG SIGNALSThermometer.photocopiersold land-line telephonesaudio tapesVCRs (same as TV)

DIGITAL SIGNALSPCs, PDAsMobile Phones.

ANALOG TO DIGITAL CONVERTER

An electronic integrated circuit which transforms a signal from analog(continues) to digital(discrete) form. Analog signals are directly measurable quantities.

Digital signals only have two states for digital computer we refer to binary states, 0 and 1.

Digital computers require signals to be in digital form whereas most instrumentation transducers have an output signal in analogue form.

ADC conversion is therefore required at the interface between analogue transducers and the digital computer

Why we need ADC?

Microprocessors can only perform complex processing on digitized signals.When signals are in digital form they are less susceptible to the deleterious effects of additive noise.ADC Provides a link between the analog world of transducers and the digital world of signal processing and data handling.

A/D ApplicationsMicrophones - take your voice varying pressure waves in the air and convert them into varying electrical signals Strain Gages - determines the amount of strain (change in dimensions) when a stress is applied Thermocouple temperature measuring device converts thermal energy to electric energyVoltmetersDigital Multimeters.

A/D CIRCUIT

A/D Converter Types

Flash ADC

Delta-Sigma ADC

Dual Slope (integrating) ADC

Successive Approximation ADC

Flash ADCConsists of a series of comparators, each one comparing the input signal to a unique reference voltage.

The comparator outputs connect to the inputs of a priority encoder circuit, which produces a binary output

Flash ADC Circuit

How Flash WorksAs 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.

FlashAdvantages

Simplest in terms of operational theory

Most efficient in terms of speed, very fast

Disadvantages

Lower resolutionExpensiveFor each additional output bit, the number of comparators is doubled.

DIGITAL TO ANALOG CONVERTER

RESOLUTION= N BITS

Modems require a DAC to convert data to analog signals that can be carried by telephone wires.

Video adapters also require DACs to convert digital data to analog signals that the monitor can process.

TYPES OF D/A CONVERTERSBinary weighted resistorR-2R ladderMultiplier DACNon-multiplier DAC

WEIGHTED RESISTOR COMPONENTSOperational amplifierSwitchesResistorsVoltage sourceGround

Binary Weighted resistors are used to distinguish each bit from the most significant to the least significantBinary weighted resistors Reduces current by a factor of 2 for each bitBinary Weighted resistors is reliable, and simple to doResistorvaluescan becalculated using theweightof the binary number.

CIRCUIT

AdvantagesSimple Construction/AnalysisFast Conversion

DisadvantagesRequires large range of resistors (2000:1 for 12-bit DAC) with necessary high precision for low resistorsRequires low switch resistances in transistors Can be expensive. Therefore, usually limited to 8-bit resolution.

APPLICATIONS

Digital Motor ControlComputer PrintersSound Equipment (e.g. CD/MP3 Players, etc.)Function Generators/OscilloscopesDigital Audio