Lecture on Analog to Digital Conversion Definitions Digital
- Slides: 22
Lecture on Analog to Digital Conversion
Definitions • Digital source produces a finite set of possible values. • Analog source produces a infinite set of possible values. • Signal is a measurable quantity (e. g. , voltage) which bears information. • Noise is a measurable quantity which carries undesired interference.
Why Digital? • • • Less expensive circuits Privacy and security Small signals (less power) Converged multimedia Error correction and reduction
Why Not Digital? • More bandwidth • Synchronization in electrical circuits • Approximated information
Analog to Digital Conversion • Sampling: Obtaining values at discrete points in time. • Quantization: Non-linear transformation that maps continuous values to discrete values. Analog Signal - Continuous time - Continuous value Sample Quantize - Discrete time - Continuous value Digital Signal - Discrete time - Discrete value
Sampling w(t) t 1 t 2 t 3 t 4 t 5 t
“sampler” ws(t) w(t) t 1 t 2 t 3 t 4 t 5 t
Gated Samples
Gated Sample and Hold
Impulse Samples
Sample and Hold
Quantization V output w 2(t) -V V input w 1(t) -V Region of operation For M=2 n levels, step size : = 2 V /2 n = V(2 -n+1)
Quantization Error, e V output w 2(t) -V V input w 1(t) -V /2 - /2 Error, e input w 1(t)
Error is symmetric around zero. 0
Noise Types of Noise • Quantizing noise (during A/D conversion) • Environment noise (e. g. , EM interference) • Filtering noise (low pass filtering at decoder) Types of Quantization Noise • Overload noise (input too large) • Random noise (input too small) • Granular noise (non uniform error jump) • Hunting noise (too long of quite time)
Non-uniform Quantizer Used to reduce quantization error and increase the dynamic range when input signal is not uniformly distributed over its allowed range of values. allowed values for most of time input time
Digital to Analog Converter Circuit
Analog to Digital Converter Circuit
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