ADC Flashcards
The process by which analog signals are converted to their digitized forms.
ANALOG TO DIGITAL CONVERSION
ADC occurs via three steps:
SQE
SAMPLING
QUANTIZATION
ENCODING
The analog signal is sampled at regular intervals of time.
Sampling
The sampling rate must be at least twice the highest frequency of the signal.
Nyquist Criterion
It is defined as the process of converting the continuous sample amplitude into a discrete amplitude.
QUANTIZATION
Quantization
Thus by then, the signal will be discrete in both: T_ and A_.
Time and Amplitude
The difference between the actual analog value and quantized digit value.
QUANTIZATION ERROR
It is the process which assigns ones and zeros (stream of bits) for every quantization level.
Encoding
The number of bits assigned for each level (n) depends on the __ (L); such that L=2^n
levels’ number
The resolution of the ADC is the smallest detectable change in voltage.
Ideal ADC
In an ___, the quantization error is uniformly distributed between
–Δ/2 and Δ/2.
Ideal ADC
Q = Δ = Q_ S_ = FS/LN
Quantization Step
Full scale/Level’s number
Types of ADCs
1. D C ADC
2. SAR ADC
3. I ADC
- SS
- DS
- R ADC
4. S-D ADC (over sampled ADC)
Direct conversion ADC
Successive approximation register (SAR) ADC
Integrating ADCs: single slope, dual slop, and ramp ADC
Sigma-Delta ADC (over sampled ADC)
It is one of the most popular ADCs for 8-16 bits
Successive approximation register (SAR) ADC
It has moderate conversion speeds. The conversion time is around 1µs
Successive approximation register (SAR) ADC
It doesn’t consume a lot of power and its cost is low in comparison with the other types.
Successive approximation register (SAR) ADC
It requires a sample, hold circuit, and it can have missing output codes.
Successive approximation register (SAR) ADC
A ____ works by using a digital to analog converter (DAC) and a comparator to perform a binary search to find the input voltage.
successive approximation ADC
A ____ is used to sample the analog input voltage and hold (e.g. keep a non-charging copy) the sampled value whilst the binary search is performed.
sample and hold circuit (S&H)
The ___ starts with the most significant bit (MSB) and works towards the least significant bit (LSB). For an 8-bit output resolution, 8 comparisons are needed in the binary search, taking a least 8 cycles.
binary search
The ___ samples the analog input on a rising edge of the sample signal. The comparator output is a logic 1 if the sampled analog voltage is greater than the output of the DAC, 0 otherwise.
sample and hold circuit
TYPES OF ADC ERRORS
- OFGA NONTE LOHYREMI
Offset Error
Gain Error
Nonlinearity Error
Temperature-dependent Error
Load-dependent Error
Hysteresis Error
Resolution Error
Missing code Error
Constant component of the error that is independent of the inputs
OFFSET ERROR
Difference between the actual transfer ratio and the ideal ratio
GAIN ERROR
Also called Calibration Error
GAIN ERROR
The deviation of the output quantity from a specified linear reference
NONLINEARITY ERROR
NONLINEARITY ERROR
Worst-case deviation from the ideal transfer characteristic curve
INTEGRAL NONLINEARITY
NONLINEARITY ERROR
Difference between the actual transfer ratio and the ideal ratio
DIFFERENTIAL NONLINEARITY
Change in ambient temperature or temperature variation due to self-heating (temperature stability, temperature coefficient)
TEMPERATURE-DEPENDENT ERROR
Is due to the effect of a load impedance upon the converter or signal source driving it.
LOAD ERROR
The difference between the increasing and decreasing input values that produce the same output
HYSTERESIS ERROR
The error due to the inability to respond to change of a variable smaller than a given increment
RESOLUTION ERROR
