michael chiang eecs 713 12/05/2013 presenting: capacitors
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MICHAEL CHIANGEECS 713
12/05 /2013
Presenting: Capacitors
Objective:
Lab exercise for CapacitorsUnderstand bypass/decoupling capacitor
selection.Calculate the capacitors for specific rise
time/knee frequency of a HSDC.Measure characteristics of capacitor
What is a capacitor?
Capacitor is a two terminal electrical component used to store electric charge with conductors separated by an insulator.
d
AC
Capacitor Applications:
Capacitors are used in applications such as energy storage, power systems, noise suppression and coupling.
In a high speed digital device, capacitors are used for uniform voltage distribution (bypass) and shunt current to the return path (decoupling) to provide low impedance path between power and ground or ground connections between gates.
Every capacitor has a parasitic series inductance (lead inductance, package inductance, or mounting inductance – ESL), parasitic series resistance (equivalent Series resistance – ESR) which is real impedance, and self-resonate frequency (SRF):
Circuit Issues
For uniform voltage distribution, a shunt capacitor is connected to the power supply in the frequency range where wired inductance can be a problem.
This bypass capacitor provides low impedance between ground and power plane. Bypass capacitor loses effectiveness at high frequency where it becomes inductance.
This problem is resolved by an assortment of capacitors (large and smaller) used to provide low impedance power source for every logic device across various operating frequency range.
Measuring Capacitor Characteristics
Using Test JigUsing Impedance Analyzer
Test Jig Setup
Materials Oscillocope: Tektronix DPO 4054 Pulse Gen: SYSTRON 101 Pulse Generator Resistors:
100Ω, 0805, 1% 10Ω, 0805, 1%
Capacitor: 1µF, 0603, X5R, 10V
Cu Board Analyzer Probes
Test Jig: Cu Board
Test Jig: Lead Inductance
Rs = source resistance of test jig, Ω = 4.35ΩA = area under spike, Vs = 844.5pVs∆V = Open-circuit Step Voltage of test jig, V = 0.996VL = lead inductance, H
Open Circuit test Load: 1µF Capacitor
Test Jig: ESR
Rs = source resistance of test jig, Ω = 4.35Ω
X = measured step voltage after spike, V = 0.064V
∆V = Open-circuit Step Voltage of test jig, V = 0.996V
Test Jig: Capacitance
∆V = Open-circuit Step Voltage of test jig, V = 0.996V
Rs = source resistance of test jig, Ω = 4.35Ω
X = measured step voltage after spike, V = 0.064V
dV/dt = charge rate of ramp, V/s = 0.236V/998ns = 236472.9V/s
C = capacitance, F
Impedance Analyzer: Resonance Frequency
Materials Impedance Analyzer: HP 4194A Bread board Capacitors:
0.1µF, 0603, X7R, 16V 1µF, 0402, X5R, 10V 1µF, 0603, X5R, 10V 10µF, 0603, X5R, 6.3V
Impedance Analyzer: Resonance Frequency
Impedance Analyzer: Results
1µF, 0603, X5R, 10VLs @ 5MHz ESR @1.93MHz Cs @ 1MHz
8.102nH 10.1Ω 1.47µF
Resonance ESR1000pF, 0603, X7R, 50V 51.5MHz 9.44Ω0.1µF, 0603, X7R, 16V 4.7MHz 7.53Ω1µF, 0402, X5R, 10V 1.9MHz 10.1Ω1µF, 0603, X5R, 10V 1.53MHz 1.18Ω
10µF, 0603, X5R, 6.3V 534kHz 6.81Ω
Resonance Frequency:
When the frequency is below the SRF it behaves capacitive.
When the frequency is above the SRF it behaves inductively.
The inductance in systems induces voltage change between the logic components and supply or ground plane that introduces noise.
Therefore, a capacitor selected must behave capacitively.
1µF Ceramic Capacitor (0603)
From Test Jig
From Impedance Analyzer
Reference:
Johnson, Howard, et al. “High Speed Digital Design: A Handbook of Black Magic” . Pearson Education, New Delhi, 1993, p253-255 & 275-299.
http://www.farnell.com/datasheets/1525783.pdf
http://people.eecs.ku.edu/~callen/713/713_Vias-F13.ppt
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