Analog to Digital Convertor(ADC)

Analog-to-digital converter

       An analog-to-digital converter (abbreviated ADC, A/D or A to D) is a device that converts a continuous physical quantity (usually voltage) to a digital number that represents the quantity's amplitude(An analog signal is continuous in both time and amplitude, whereas a digital signal is discrete in time as well as in amplitude).

Fig:1 Analog to digital conversion

      In most of the digital system needs to take input from Analog sensor or transducer. Analog signal are most common input signal for embedded system. Sensor or transducer Such as Temperature, Motion, pressure, Humidity are analog. 

 SAMPLING AND QUANTIZATION

     The basic way to convert the analog signal into digital signal by using sampling and quantization techniques

which is show in fig:2,

   Logically, an ADC has to covert an analog signal to an equivalent digital one in two steps: converting the analog signal to a discrete in time signal and converting it into a discrete in amplitude signal. The process of    converting an analog signal to discrete in time signal is called as ‘sampling’ and the process of converting it to a discrete in amplitude signal is called ‘quantization’. These processes can occur in any order.

     

Fig:3 sampling and quantisation

PARAMETERS:
  The important parameters consider in ADC is

•    Resolution
•    Sample rate
•    Error rate

 TYPES OF ADC CONVERSION:

• A direct-conversion ADC or flash ADC
• A successive-approximation ADC  
• Dual-slope or multi-slope ADC
• A delta-encoded ADC

   we use successive approximation technique