Analog to Digital Converter (ADC)
An analog-to-digital converter (ADC) measures the maximum amplitude
(or the integrated value) of an analog input pulse and converts that value
to a digital number.
Basic Characteristics
• Number of bits (accuracy)
• Conversion Time (speed)
• Dynamical Range (input sensitivity)
ADC Types
• The Flash ADC
• The Wilkinson ADC
• The Successive-Approximation ADC
ADC – Basic Characteristics
Number of bits
n-bit range: The dynamical input range is divided in 2n subdivisions.
Example: 12-bit means 212 = 22 × 210 = 4k = 4096 subdivisions (0…4095)
ADC speed
The frequency of the conversion.
Example: f=20 MHz means T = 1/f = 50 ns for each conversion.
Dynamical Range
The range (in V) of the analog input the ADC can accept.
Example: DR=(-5,+5) V means for a 12-bit ADC an input sensitivity of
10 V / 4096 div ≈ 2.5 mV / div (±1/2 bit accuracy)
ADC – Types: The Flash ADC
The flash ADC is a stack of
single-channel pulse height
analyzers (comparators) with
equal window widths.
Advantage
• Speed (ns conversion)
Disadvantages
• Large differential nonlinearity
• Limited number of bits
ADC – Types: The Wilkinson ADC
ADC – Types: The Successive-Approximation ADC
CAMAC
CAMAC
CAMAC
Controller
DSP
CC-488
CAMAC
Controller
DSP
CC-488