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Transcript of analog.ppt
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Chapter – analog I/O
Voltage
t
continuous
logical
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voltage
time
Voltage is sampled during these time periods
T = (Sampling Frequency)-1 Sampling time
Sampling is a function of time
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V t
t
where,V t the actual voltage over time= sample interval for A/D converter=t time=
t1 t2
V t1
V t2
Vma x
Vmin
t1 t2, time at start,end of sample=V t1 V t2
, voltage at start, end of sample=Vmin Vmax, input voltage range of A/D converter=
N number of bits in the A/D converter=
Analog Inputs
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R 2N=
where,R resolution of A/D converter=
VI INTVin Vmin–
Vm a x Vm in–------------------------------
R 1– =
VI the integer value representing the input voltage=
VCVI
R 1–-------------
Vm ax Vmi n– Vmin+=
VC the voltage calculated from the integer value=
VERRORVm ax Vmin–
2R------------------------------
=
VERR OR the maximum quantization error=
(1)
(3)
(4)
(2)
Some relationships
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N 10=
R 2N 1024= =
VI INTVin Vmin–
Vm a x Vm in–------------------------------
R 746= =
VC
VIR------
Vm ax Vm in– Vmin+ 4.570V= =
VERROR
Vma x Vm in–2R
------------------------------ 0.0098V= =
Vma x 10V=Vm in 10V–=Vin 4.564V=
Given,
Calculate,
An Example
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Aliasing
fAD 2fsignal where,
fAD sampling frequency=fs ignal maximum frequency of the input=
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Analog Output Relationship
R 2N=
where,R resolution of A/D converter=
VI INTVdesired Vmin–Vma x Vmin–
-------------------------------------
R=
VI the integer value representing the desired voltage=
Voutpu tVIR------
Vma x Vm in– Vm in+=
Voutput the voltage output using the integer value=
VERRORVm ax Vmin–
2R------------------------------
=
VERR OR the maximum quantization error=
(5)
(7)
(8)
(6)
Vdes ired the desired output voltage=
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An ExampleN 8=
R 2N 256= =
VI INTVin Vmin–
Vm a x Vm in–------------------------------
R 160= =
VC
VIR------
Vm ax Vm in– Vmin+ 6.250V= =
VERROR
Vma x Vm in–2R
------------------------------ 0.020V= =
V m ax 10V=V m in 0V=Vdesired 6.234V=
Given,
Calculate,
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Insulated wires
Metal sheath
Insulating cover
Two conductorshielded cablecross section
Electrical Noise
1" or less typical
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