Microchip Technology SAM Series

Figure 12-1. Analog Ripple Noise Sources
I/O
PIN
AVDD
AVSS
AVDD
I/O
AVSS
I/O LOAD
MCU
R
SERIES
1k
After
I/O
PIN
AVDD
AVSS
AVDD
I/O
AVSS
I/O LOAD
MCU
Before
ioh
iol
o AnalogPeripheralNoiseReductionOptions:
 AddSeriesresistorforlowerI/OpinfrequenciestocreateLPF.
 UselowerI/Opindrivestrengthsettingifavailable.
 ChangeI/Opinslewratecontrolsettingifavailable.
 Combinationsofabove
Figure 12-2. PCB Layout Considerations and Effects of Analog Ground Inductance on Analog Signals
AnalogPCBGroundPlane
AnalogGroundPCBTrace
i
AGND=35ma
i
AGND=35ma
H=PCBboardThickness=1.57mm
T=1ozcopper traceThickness=0.03556mm
W=PCBcoppertraceWidth=0.8mm(31mils)
L=PCBcoppertraceLength=101.6mm(4”)
https://spok.ca/index.php/resources/tools/106‐traceindcalc
H=PCBboardThickness=1.57mm
T=1ozcopper traceThickness=0.03556mm
W=PCBcoppertraceWidth=12.7mm(½”)
L=PCBcoppertraceLength=101.6mm(4”)
Inductance=253.4nh
X
L
=2πfL
=2π10Mhz253.4nh
=15.92Ω
V
GNDDROP
=(3.29ma*15.92Ω)
=52.3mv
HYPOTHETICAL GIVEN:
 AnalogGroundCurrent=35matotal
 9.4%AnalogGroundNoise@10Mhz
=3.29ma
Inductance=15.96nh
X
L
=2πfL
=2π10Mhz15.96nh
=1Ω
V
GNDDROP
=3.29ma*1Ω)
=3.3mv
PCBInductanceCalculator:
ADC
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and its subsidiaries
Manual
DS70005439B-page 53