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MICASDepartment of Electrical Engineering (ESAT)
February 6th, 2007
Junfeng Zhou
Promotor: Prof. Wim Dehaene
KULeuven ESAT-MICAS
Update of the “Digital EMC project”
MICASDepartment of Electrical Engineering (ESAT)
Part I: AMIS problems on RD2E PCB and Chip
Part II: di/dt measurement
Part III: Improved EMI-Suppressing regulator structure
Part IV: Future work
Outline
MICASDepartment of Electrical Engineering (ESAT)
Part I. AMIS problem 1 – USB module
USB module(with shielding box)
Oscillator inside the USB module
MICASDepartment of Electrical Engineering (ESAT)
AMIS problem 2 – Internal Oscillator
Internal Oscillator
Emission
VDD<1>
VSS
Cause trouble for 1 Ohm method,
Less problematic for di/dt measurement
MICASDepartment of Electrical Engineering (ESAT)
Part II. di/dt measurements
Low Drop-out /Serial Regulator
AMIS digital loadEMI-Suppressing
Regulator (MICAS)
GND
VCCVDD<1..10>
VDD2 = 3.3 V
VCCC =12 V
ii33
ii55 and V and V22
i1
ii44 and V and V11
PC
configurationbits
VCC = 4.5 V ~ 8 V
i2
Setup 1
Setup 2
Setup 3
MICASDepartment of Electrical Engineering (ESAT)
Focus on setup-1 – Some preliminary results
Internal Oscillator
Digital Load(Shift register Shift register output bufferoutput buffer)
GND
VDD2 = 3.3 V
i1
VDD3(separate power supply)
clk
EMI
MICASDepartment of Electrical Engineering (ESAT)
1. The impact of internal oscillator on CurrentCurrent SpectrumSpectrum of VDD2
QP<1>=QP<48>=QP<49>=QP<51>=‘1’Note: internal oscillator Note: internal oscillator disabledisable,, di/dt on VDD2,di/dt on VDD2,
Fig. 1 Fig. 2
QP<1>=QP<48>=QP<49>=‘1’, QP<51>=‘0’, Note: internal oscillator Note: internal oscillator enableenable,, di/dt on VDD2,di/dt on VDD2,
Conclusion: Internal clock may cause some problems
MICASDepartment of Electrical Engineering (ESAT)
2. Comparison of internal and external clock on CurrentCurrent SpectrumSpectrum of VDD2
Fig. 2 Fig. 3 QP<1>=QP<48>=QP<49>=‘1’, QP<51>=‘0’, Note: internal oscillator Note: internal oscillator enableenable,, di/dt on VDD2,di/dt on VDD2,
QP<1>=QP<48>=QP<51>=‘1’, QP<49>=‘0’, QP<50>=‘0’, Note: external clock Note: external clock enableenable,, di/dt on VDD2,di/dt on VDD2, internal oscillator is powered down internal oscillator is powered down Conclusion: Much worse with external clk
MICASDepartment of Electrical Engineering (ESAT)
3. The impact of oscillator inside USB module on CurrentCurrent SpectrumSpectrum of VDD2(no switching activity)
Fig. 4Fig. 2
No big difference
QP<1>=QP<48>=QP<49>=‘1’, QP<51>=‘0’, Note: di/dt on VDD2,Note: di/dt on VDD2, USB module is powered down USB module is powered down and the latch is enabledand the latch is enabled
QP<1>=QP<48>=QP<49>=‘1’, QP<51>=‘0’, Note: internal oscillator Note: internal oscillator enableenable,, di/dt on VDD2,di/dt on VDD2,
MICASDepartment of Electrical Engineering (ESAT)
4. The impact of internal oscillator in USB module on CurrentCurrent SpectrumSpectrum of VDD2(working condition)
Fig. 6Fig. 5
QP<1>=QP<48>=QP<49>=‘1’, QP<51>=‘0’ QP<53>=‘1’, Note:Note: di/dt on VDD2,di/dt on VDD2,
QP<1>=QP<48>=QP<49>=‘1’, QP<51>=‘0’ QP<53>=‘1’, Note: di/dt on VDD2,Note: di/dt on VDD2, USB module is powered down USB module is powered down and the latch is enabled and the latch is enabled
No big difference
MICASDepartment of Electrical Engineering (ESAT)
5. The impact of load on CurrentCurrent SpectrumSpectrum of VDD2
1 DFF chain 2 DFF chains
3 DFF chains
4 DFF chains
5 DFF chains
only clock present
• 4.02 MHz clk from internal oscillator, • Data input from on-chip 21-bit Random Generator.
MICASDepartment of Electrical Engineering (ESAT)
6. The impact of load on CurrentCurrent TransientTransient of VDD2
1 DFF chain 2 DFF chains 3 DFF chains
4 DFF chains 5 DFF chains
Pk-Pk: 23.8mV Pk-Pk: 45mV Pk-Pk: 66.3mV
Pk-Pk: 86.9mV Pk-Pk: 108.1mV
MICASDepartment of Electrical Engineering (ESAT)
7. The impact of load on di/dtdi/dt TransientTransient of VDD2
In general, as more DFF chains In general, as more DFF chains are on, the di/dt peak increases are on, the di/dt peak increases proportionally. proportionally.
MICASDepartment of Electrical Engineering (ESAT)
Conclusions
On-chip internal oscillator won’t hurt much, which is common for all measurements.
Oscillator inside USB module is not a problem at all, shielding box can do most of the job.
Setup for massive measurements is in preparation Automatic setup shall be ok by this week, Agreement on data to be measured ?
MICASDepartment of Electrical Engineering (ESAT)
• z1 cancel off the p1 • Make the p2 cut-off frequency• This zero is intrinsic for this feedback
topology
sacrifices dynamic sacrifices dynamic noise performancenoise performance
Part III: EMI-Suppressing Regulator possible improvement
Frequency
H(s)-dB
z1 p1p2
peakingPrevious structure problem: di/dt TF: pole-zero tracking !!
MICASDepartment of Electrical Engineering (ESAT)
Cascode compensation (Ahuja, JSSC 12/1983)
1
2• The feed forward path is removed,
• Miller effect still available,
• A2 Cc instead of (1+ A2 Cc ) for miller cap,
• Improved PSRR performance,Improved PSRR performance,
MICASDepartment of Electrical Engineering (ESAT)
Ahuja inspired...
• However, our di/dt TF is other way around !!!
• According to maple simulation, things are getting even worse because the -3dB frequency is shifted to even high frequency.
• The reason is that there is voltage gain from V3 to Vctrl, i.e.:
Vctrl /V3=gm2*Rota
If gm2*Rota <<
1 ??
This trick doesn’t help
!!! One degree of freedom is added !!!
Kill the Vctrl/V3 gain !
MICASDepartment of Electrical Engineering (ESAT)
Some formulas
tan
m
k
G
C
2m
C
g
C
2
2( )m m
C m m
g G
C g G
• p1 :
• p2 :
• z1 :
m
C
G
C
1
tan
m
k
g
C
m
C
G
C
• p1 :
• p2 :
• z1 :
NowNow
PreviousPrevious
(Assume:Assume: )1OTA mG g
MICASDepartment of Electrical Engineering (ESAT)
Maple calculation of the new structure
-3dB
100 kHz
• -3dB frequency moves down to below 40 -3dB frequency moves down to below 40 kHz,kHz,
• At 100 kHz, there is already decent di/dt At 100 kHz, there is already decent di/dt suppression.suppression.
Maple calculation is ready
To Be Done: • Spice simulation to verify Maple calculation ?• Re-design EMI-Suppressing Regulator based on this new structure ?
MICASDepartment of Electrical Engineering (ESAT)
Part IV: Future Work
Continue the digital load measurements,
More analysis for new structure: Stability and Transient, Spice simulation.
MICASDepartment of Electrical Engineering (ESAT)
Questions
Thank you for your attention
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