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Comparisons ofComparisons ofNon‐Invasive Stability Measurements
B d Plvs. Bode PlotsAEi SystemsAEi Systems
5777 W. Century Blvd. Suite 1285, Los Angeles, CA 90045310‐216‐[email protected]
© 2014 AEi Systems. All Rights Reserved 1
More Information: https://www.picotest.com/non‐invasive‐stability‐measurement.html
What’s Included HereWhat s Included Here
• Hardware circuitry including Linear Regulators,Hardware circuitry including Linear Regulators, POLs, and Switchers were constructed and bench tested– Non‐Invasive Stability Measurement (‘NISM’) of Stability Margins and Bode Plots were both
d drecorded– In some cases, the circuit were also simulatedThe Stability Margin vs Phase Margin results are– The Stability Margin vs. Phase Margin results are compared and documented
Note: The testing was performed by AEi SystemsNote: The testing was performed by AEi Systems.
© 2014 AEi Systems. All Rights Reserved 2
What is NISM and Why It’s a i i l h lCritical Technology
• Non‐Invasive Stability Measurement is a method of determining control loop stability margins without requiring access to the feedback loop
• In many situations it is not possible to access the control loopIn many situations it is not possible to access the control loop– Examples – POLs, Fixed Voltage Regulators, Voltage References, High BW Opamps– Integrated Switching ICs that do not allow loop access– In other cases it might be impractical to break the control loop because cutting a printed circuit board
trace or lifting components might be requiredtrace or lifting components might be required
• NISM is computed by converting output impedance to group delay. Then the ‘Q’ is derived from the group delay and the stability margin f th Qfrom the Q
• The NISM technology is licensed and promoted by Picotest.com• The measurement capability can be found on various VNAs p y
– OMICRON Lab, Keysight, Copper Mountain, Rhode‐Schwarz
© 2014 AEi Systems. All Rights Reserved 3
NISM is Based on FundamentalsNISM is Based on Fundamentals
• Dr. R.D. Middlebrook popularized the topic of Minor Loop Gain, Tm with his introduction of the extra element theorem which allowed us to assess the stability of power supplies and input filters
• Minor loop gain, based on Nyquist criteria is now one of the most researched electronics topics
• Many articles can be found with an internet search of “forbidden region stability criteria”
• The concept is simple. Break a system into two parts, generally termed a System and a Load and determine the impedance of each part, ZS and ZL
• Phase margin is determined by setting |Tm| = 1 and solving for phase
Zs ZL
Phase margin is determined by setting |Tm| 1 and solving for phase
© 2014 AEi Systems. All Rights Reserved 4
NISM is Based on FundamentalsNISM is Based on FundamentalsZs ZL
A complication exists in that we cannot pseparate the voltage regulator into two parts, ZS and ZL without cutting a trace or removing the capacitor
• NISM software extracts data from impedance and group delay and allows the ZS and ZL to be mathematically separated so they can be converted to Stability Margin
or removing the capacitor
be mathematically separated so they can be converted to Stability Margin• Practically speaking, impedance is measured with a suitable probe in a 1 or 2 port
configuration• The instrument converts the impedance to group delay and Q• The user positions waveform cursors on the impedance and Q waveforms and the
conversion to phase margin is read out on the instrument’s screen• A video of the process can be viewed here,
https://www picotest com/products NISM software htmlhttps://www.picotest.com/products_NISM_software.html
© 2014 AEi Systems. All Rights Reserved 5
Non‐Invasive Stability Measurement vs. d lBode Plot Measurement
• RH1086 Linear Regulatorg• RH1085 Linear Regulator• LM317 Linear Regulator– Various Configurationsg g• TPS4022 Buck Regulator• TPS7A4501 Linear Regulator• LMR10515 Simple Switcher• TL431 Adjustable Shunt Regulator• VRG8666 (RH3080) Linear Regulator• CLC1007 245MHz Opamp
© 2014 AEi Systems. All Rights Reserved 6
RH1086 Linear RegulatorRH1086 Linear Regulator
NISM Bode Plot PMNISM Bode Plot PM
Measured 59 deg 56 deg
Simulated 63 deg 56 deg
Vout
Vout
Vin
Min = 25mANom = 500mAMax 1A
X2RH1086
1.80V5 00V
R1249
ADJ
C10.1uF
C20.1uF
Vin5
Vout
CoutCinT409G226M015
+/-0.5V
I125m
Vin
3.28%45.24% 45.24%
Max = 1AIN OUT
ADJUST I2AC = 1
557mV
5.00V
R2110
Cadj68n
3.28% 5.87%B1Currentmag(f req)/(2*3.14159265)
R31
f req1 Vf req10V
© 2014 AEi Systems. All Rights Reserved 7
RH1086 Linear RegulatorRH1086 Linear Regulator12
010 100
2 db_v(vout) 5 tgqcurve
10.01.80 x = 91.7k hertz, y = -12.9 db(volts)NIP = 63 degrees
f/Hz TR1 TR2 PM: C 1 52 580k 325 128 504 129 58 904 °
-11010-2
10-1
TR1 TR
2
-30.0
-10.0
10.0
b_v(
vout
) in
db(v
olts
)
1.00
1.40
1.80
tgqc
urve
Plot
1
2
x = 57.9k hertz, y = 456m
Cursor 1 52.580k 325.128m 504.129m 58.904 °Cursor 2 40.777k 302.517m 597.409m
C2-C1 -11.803k -22.611m 93.280m10-3
102 103 104 105 106 107
f/HzTR1: |Mag(Gain)| TR2: |QTg(Gain)|
100 1k 10k 100k 1Meg 10Megfrequency in hertz
-70.0
-50.0d
200m
600m
5
1 ph_v(bodeplot) 2 db_v(bodeplot)
1
0
50
100
0
100
200
1/dB
TR2
0
90.0
180
ot) i
n de
gree
s
0
40.0
80.0
ot) i
n db
(vol
ts)
ot1
BW = 73.4k hertz, PM = 56.2 degrees
f/Hz TR1/dB TR2/°Cursor 1 52.743k 0.000 55.467
-100
-50
-200
-100
102 103 104 105 106 107
TR
2/°
100 1k 10k 100k 1Meg 10Megfrequency in hertz
-180
-90.0
0
ph_v
(bod
eplo
-80.0
-40.0
0
db_v
(bod
eploPlo
21
© 2014 AEi Systems. All Rights Reserved 8
f/HzTR1: Mag(Gain) TR2: Phase(Gain)
NISM Bode Plot PM
Measured 59 deg 56 deg
Simulated 63 deg 56 deg
RH1085 Linear RegulatorRH1085 Linear Regulator12 100
f/Hz TR1 TR2 PM: Cursor 1 446.684k 579.827m 268.056m > 71°Cursor 2 367.002k 572.428m 299.448m
C2 C1 79 681k 7 398 31 392-210
-110
10 3
10-2
10-1
TR1 TR
2
NISM Bode Plot PM
Measured > 71 deg 94 degC2-C1 -79.681k -7.398m 31.392m 10-3
102 103 104 105 106 107
f/HzTR1: |Mag(Gain)| TR2: |QTg(Gain)|
1
0
50
0
100
200
1/dB
TR
R1249
Vin
V15V
Adj
Vout
Iload
Vout
5
C2TBJD336K010C
R3C1
8
C3TBJD336K010C
R4 C6
+/- 0.25V3.78%
C40.1uF
45.24%
C5
IN OUT
ADJUST
X4RH1085
I2AC = 1
f/Hz TR1/dB TR2/°Cursor 1 186.327k 0.000 94.093
-50
0
-200
-100
0
102 103 104 105 106 107
TR1
R2/° R2
249
Iload25m
1C1TBJD336K010C 1
C71200p
0.01uF
3.78%5.87%
45.24%6.28%6.28%0.01uF45.24%
B1Current
R5
freq1 Vfreq1
© 2014 AEi Systems. All Rights Reserved 9
f/HzTR1: Mag(Gain) TR2: Phase(Gain)
Currentmag(freq)/(2*3.14159265)
1
LM317 Linear Regulator, Cap 1LM317 Linear Regulator, Cap 112
0
10
100
f/Hz TR1/dB TR2 PM: Cursor 1 8.018k -5.024 2.186 24.483 °Cursor 2 8.059k -5.032 2.177
C2-C1 40.224 -7.159m -8.375m30
-20
-10
0
10-2
10-1
TR1/
dB TR2 NISM Bode Plot
Measured 24 deg 25 deg
-30102 103 104 105 106 107
f/HzTR1: Mag(Gain) TR2: |QTg(Gain)|
140
f/Hz TR1/dB TR2/°-20
0
20
50
100
150
200
TR1/
dB
TR2/°
f/Hz TR1/dB TR2/Cursor 1 7.854k 0.000 24.815
-400
103 104 105 106
f/HzMemory 1 : Mag(Gain)Memory 1 : Unwrapped Phase(Gain)
General LM317 configuration used, Cap 1 is a 100uF Tantalum
© 2014 AEi Systems. All Rights Reserved 10
Note: The circuit is from the Picotest VRTS 1 board, https://www.picotest.com/products_VRTS01.html. It was measured using several capacitors in the kit.
LM317 Linear Regulator Cap 4LM317 Linear Regulator Cap 412
5
10
8*10 1100
2*100
f/Hz TR1/dB TR2 PM: Cursor 1 53.625k 8.866 1.707 28.958 °
-5
0
2*10-1
4*10-1
6*10-1
8*10-1
TR1/
dB TR2
Cursor 2 51.136k 8.729 1.738C2-C1 -2.488k -136.574m 31.597m
-10 10-1
104 2*104 4*104 6*104 8*104 105
f/HzTR1: Mag(Gain) TR2: |QTg(Gain)|
1100 100
NISM Bode Plot
Measured 29 deg 30 deg1
0
50
100
0
50
100
R1/
dB
TR2/°
Measured 29 deg 30 deg
Measured on the VTRS 1 board,
f/Hz TR1/dB TR2/°Cursor 1 58.325k 28.422f 29.764
-100
-50
-100
-50
103 104 105 106
T
°
f/Hz
Cap 4 is a 2.2uF Tantalum
© 2014 AEi Systems. All Rights Reserved 11
f/HzTR1: Mag(Gain) TR2: Phase(Gain)
LM317 Linear Regulator Cap 5LM317 Linear Regulator Cap 512
10
20
30
100
f/Hz TR1/dB TR2 PM: Cursor 1 23.846k -2.238 667.879m 55.870 °30
-20
-10
0
10
10-1TR1/
dB TR2
Cursor 2 20.816k -2.447 704.124mC2-C1 -3.030k -209.347m 36.246m
-40
-3010-2
102 103 104 105 106 107
f/HzTR1: Mag(Gain) TR2: |QTg(Gain)|
1100
NISM Bode Plot
Measured 56 deg 53 deg1
0
50
101
102
R1/
dB
TR2/°
Measured 56 deg 53 deg
Measured on the VTRS 1 board,
f/Hz TR1/dB TR2/°Cursor 1 26.183k 0.000 52.690
-100
-50 100
102 103 104 105 106 107
T
°
f/Hz
Cap 5 is a 15uF Tantalum
© 2014 AEi Systems. All Rights Reserved 12
f/HzTR1: Mag(Gain) TR2: |Phase(Gain)|
LM317 Linear Regulator Cap 6LM317 Linear Regulator Cap 612
5
10
f/Hz TR1/dB TR2 PM: Cursor 1 27.861k 12.262 6.130 8.507 °-15
-10
-5
0
5
100
TR1/
dB TR2
Cursor 1 27.861k 12.262 6.130 8.507 Cursor 2 27.227k 11.834 6.591
C2-C1 -634.199 -428.118m 460.477m-20
15
10-1
104 2*104 4*104 6*104 8*104 105
f/HzTR1: Mag(Gain) TR2: |QTg(Gain)|
1100 100
NISM Bode Plot
Measured 9 deg 8 deg1
0
50
0
50
TR1/
dB
TR2/°
Measured 9 deg 8 deg
Measured on the VTRS 1 board,
f/Hz TR1/dB TR2/°Cursor 1 28.377k -28.422f 7.907
-100
-50
-100
-50
103 104 105 106
f/HzTR1: Mag(Gain) Memory 1 : Mag(Gain)
Cap 4 is a 22uF Ceramic
© 2014 AEi Systems. All Rights Reserved 13
g( ) y g( )TR2: Phase(Gain) Memory 1 : Phase(Gain)
TPS40222 Buck RegulatorTPS40222 Buck Regulator12
-10
0
100
101
f/Hz TR1/dB TR2 PM: Cursor 1 118.424k -15.580 1.576 31.318 °-40
-30
-20
10-2
10-1
100
TR1/
dB TR2
Cursor 2 132.332k -16.482 1.791C2-C1 13.909k -901.288m 214.985m
-50 10-3
102 103 104 105 106
f/HzTR1: Mag(Gain) TR2: |QTg(Gain)|
180NISM Bode Plot
100kHz
31.8 deg1
0
20
40
60
80
-200
0
200
R1/
dB
TR2/°
A 5 V I 1 6 A O N S h
Measured 31 deg 32 deg
f/Hz TR1/dB TR2/°Cursor 1 99.702k 0.000 32.581-60
-40
-20
-800
-600
-400
102 103 104 105 106
TR
°
f/Hz
A 5‐V Input, 1.6‐A Output, Non‐Synchronous Buck Converter
http://www.ti.com/lit/ug/slvu153/slvu153.pdf
© 2014 AEi Systems. All Rights Reserved 14
f/HzTR1: Mag(Gain) TR2: Unwrapped Phase(Gain)
TPS7A4501 Linear Regulator 0mATPS7A4501 Linear Regulator 0mA100
f/Hz TR1 TR2 PM: Cursor 1 1.857k 4.080 751.851m 60.918 °
010
10-2
10-1
TR1 TR
2
Cursor 2 2.158k 3.797 781.259mC2-C1 301.588 -282.783m 29.408m
-110
10-3
102 103 104 105 106
f/Hz0mA : |Mag(Gain)| 0mA : |QTg(Gain)|
60
NISM Bode Plot
M d 61 d 54 d
0
20
40
60
100
150
R1/
dB
TR2/°
Measured 61 deg 54 deg
A l i f i 1 5 A l
f/Hz TR1/dB TR2/°Cursor 1 1.775k 14.211f 53.951-60
-40
-20
0
50
102 103 104 105 106
TR
°
f/Hz
A low‐noise, fast‐transient‐response 1.5‐A low‐dropout (LDO) voltage regulator
http://www.ti.com/lit/ug/slvu259a/slvu259a.pdf
© 2014 AEi Systems. All Rights Reserved 15
f/Hz0mA : Mag(Gain) 0mA : Phase(Gain)
TPS7A4501 Linear Regulator 1mATPS7A4501 Linear Regulator 1mA100
f/Hz TR1 TR2 PM: Cursor 1 3.366k 2.412 998.434m 47.117 °
010
10-2
10-1
TR1 TR
2
Cursor 2 3.540k 2.408 1.041C2-C1 173.818 -3.697m 42.108m
-110
10-3
102 103 104 105 106
f/Hz1mA : |Mag(Gain)| 1mA : |QTg(Gain)|
60
NISM Bode Plot
M d 47 d 47 d
0
20
40
60
100
150
R1/
dB
TR2/°
Measured 47 deg 47 deg
A l i f i 1 5 A l
f/Hz TR1/dB TR2/°Cursor 1 3.413k 42.503m 46.698-60
-40
-20
0
50
102 103 104 105 106
TR
°
f/Hz
A low‐noise, fast‐transient‐response 1.5‐A low‐dropout (LDO) voltage regulator
http://www.ti.com/lit/ug/slvu259a/slvu259a.pdf
© 2014 AEi Systems. All Rights Reserved 16
f/Hz1mA (10k) : Mag(Gain) 1mA (10k) : Phase(Gain)
TPS7A4501 Linear Regulator 5mATPS7A4501 Linear Regulator 5mA100
f/Hz TR1 TR2 PM: Cursor 1 6.165k 1.264 811.220m 51.214 °
010
10-2
10-1
TR1 TR
2
Cursor 2 5.782k 1.259 835.934mC2-C1 -382.160 -5.214m 24.714m
-110
10-3
102 103 104 105 106
f/Hz5mA : |Mag(Gain)| 5mA : |QTg(Gain)|
60
NISM Bode Plot
M d 51 d 53 d
0
20
40
60
100
150
R1/
dB
TR2/°
Measured 51 deg 53 deg
A l i f i 1 5 A l
f/Hz TR1/dB TR2/°Cursor 1 7.153k 45.204m 53.384-60
-40
-20
0
50
102 103 104 105 106
TR
°
f/Hz
A low‐noise, fast‐transient‐response 1.5‐A low‐dropout (LDO) voltage regulator
http://www.ti.com/lit/ug/slvu259a/slvu259a.pdf
© 2014 AEi Systems. All Rights Reserved 17
f/Hz5mA (2.37k) : Mag(Gain) 5mA (2.37k) : Phase(Gain)
LMR10515 ‘Simple Switcher’ POLLMR10515 Simple Switcher POL1 2
-12*10
-14*10100
m
f/Hz TR1/Ohm TR2 PM: Cursor 1 59.128k 463.831m 900.331m 49.754 °Cursor 2 69 431k 436 216m 1 017
-24*10
-26*10
-28*10-110
10-2
10-1
TR1/
Ohm TR
2
Cursor 2 69.431k 436.216m 1.017C2-C1 10.303k -27.615m 116.502m
-22*10
10
103 104 105 106 107
f/HzTR1: |Mag(Impedance)| TR2: |QTg(Impedance)|
140 200
NISM Bode Plot
Measured 50 deg 51 deg
-10
0
10
20
30
-50
0
50
100
150
TR1/
dB
TR2/°
Measured 50 deg 51 deg
A 5V 3 3P POL
f/Hz TR1/dB TR2/°Cursor 1 46.290k 1.926m 50.514
-40
-30
-20
-10
-200
-150
-100
-50
103 104 105 106 107
T
f/Hz
A 5V to 3.3P POL (Simple Switcher Step‐Down Buck Regulator)
https://www.picotest.com/products_VRTS03.htmlhttp://www.ti.com/product/lmr10515
© 2014 AEi Systems. All Rights Reserved 18
TR1: Mag(Gain) TR2: Phase(Gain)
VRTS1P5 ‐ TL431 Adj. Shunt RegulatorVRTS1P5 TL431 Adj. Shunt Regulator 12
40
60
100
f/Hz TR1/dB TR2 PM: Cursor 1 6.530k -8.714 1.383 35.899 °-40
-20
0
20
10-2
10-1
TR1/
dB TR2
Cursor 2 6.545k -8.711 1.383C2-C1 14.293 2.782m 93.097µ
-60
40
10-3
101 102 103 104 105 106 107
f/HzTR1: Mag(Gain) TR2: |QTg(Gain)|
160 200
NISM Bode Plot
Measured 36 deg 35 deg
1
0
20
40
0
50
100
150
R1/
dB
TR2/°
f/Hz TR1/dB TR2/°Cursor 1 6.535k 0.000 34.584
-60
-40
-20
-200
-150
-100
-50
101 102 103 104 105 106 107
T
°
f/Hz
An Adjustable Shunt Regulator with 2.5V Reference
h // i / d VRTS03 h l
© 2014 AEi Systems. All Rights Reserved 19
f/HzTR1: Mag(Gain) TR2: Phase(Gain)
https://www.picotest.com/products_VRTS03.htmlhttp://www.ti.com/product/lmr10515
VRG8666 (RH3080) Linear RegulatorVRG8666 (RH3080) Linear Regulator12
-10
0
100
f/Hz TR1/dB TR2 PM: Cursor 1 6.617k -8.221 4.200 11.232 °-40
-30
-20
10-2
10-1
TR1/
dB TR2
180 200
Cursor 2 6.407k -8.493 4.931C2-C1 -209.985 -271.359m 730.706m
-50 10-3
102 103 104 105 106 107
f/HzTR1: Mag(Gain) TR2: |QTg(Gain)|
NISM Bode Plot
Measured 11 deg 11 deg
0
20
40
60
50
0
50
100
150
TR1/
dB
TR2/° Vin
Vout
SET
VcBodeInj
43
1
X1VRG8666
V15
C2330u C3
330uI125m
25mA @ 2.5V
f/Hz TR1/dB TR2/°Cursor 1 6.652k 28.422f 10.780
-60
-40
-20
-200
-150
-100
-50
102 103 104 105 106 107
T
f/Hz
2
R1250k
C11u
330u 25m
© 2014 AEi Systems. All Rights Reserved 20
TR1: Mag(Gain) TR2: Phase(Gain)
VRG8666 (RH3080) Linear RegulatorVRG8666 (RH3080) Linear Regulator12
-10
0
10
100
f/Hz TR1/dB TR2 PM: Cursor 1 14.818k -21.472 2.546 20.497 °-50
-40
-30
-20
10
10-2
10-1
TR1/
dB TR2
NISM Bode Plot
Measured 20 deg 21 deg
180
200
Cursor 2 15.304k -21.510 2.696C2-C1 485.650 -38.053m 150.007m
-60
-50
10-3
102 103 104 105 106 107
f/HzTR1: Mag(Gain) TR2: |QTg(Gain)|
0
20
40
60
80
50
0
50
100
150
TR1/
dB
TR2/°
VinVout
SET
VcBodeInj
43
1
X1VRG8666
V15
C2330u C3
330uI125m
R219
150mA @ 2.5V
f/Hz TR1/dB TR2/°Cursor 1 14.330k 0.000 21.222-40
-20
0
-200
-150
-100
-50
102 103 104 105 106 107
T
f/Hz
2
R1250k
C11u
19
© 2014 AEi Systems. All Rights Reserved 21
TR1: Mag(Gain) TR2: Phase(Gain)
CLC1007 245MHz OpampCLC1007 245MHz OpampUsing the Keysight E5061B VNA, with the NISM software, we were able to test the stability of this 245 MHz opamp. The big WOW is that we obtained the (very poor) phase margin from the impedance measurement using NISM (just about 2 degrees). This is a great capability; to be able to accurately assess stability at 100's of MHz or higher without lifting any wires (which would interfere with the measurement). While there is no loop “correlation” for this NISM test, The measured phase margin of 2.36° is not acceptable because signals near the 163MHz bandwidth would become very distorted and fast transitions would see oscillations at this high frequency.
NISM Bode Plot
Measured 2 deg N/A
245 MHz opamp
© 2014 AEi Systems. All Rights Reserved 22