non measurements bdbode plots - picotestwhat is nism and why it’s a crii litical tec hlhnology •...

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.


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


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


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


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


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


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


f/HzTR1: Mag(Gain) TR2: Phase(Gain)

NISM Bode Plot PM


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


-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



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


-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


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


1100 100

NISM Bode Plot

Measured 29 deg 30 deg1

0

50

100

0

50

100

R1/

dB

TR2/°


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




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


1100

NISM Bode Plot


0

50

101

102

R1/

dB

TR2/°




-100

-50 100

102 103 104 105 106 107

T

°

f/Hz

Cap 5 is a 15uF Tantalum


f/HzTR1: Mag(Gain) TR2: |Phase(Gain)|


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


1100 100

NISM Bode Plot


0

50

0

50

TR1/

dB

TR2/°



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


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


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


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


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/°


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


f/Hz0mA : Mag(Gain) 0mA : Phase(Gain)



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


60

NISM Bode Plot

M d 47 d 47 d

0

20

40

60

100

150

R1/

dB

TR2/°


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




f/Hz1mA (10k) : Mag(Gain) 1mA (10k) : Phase(Gain)



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


60

NISM Bode Plot

M d 51 d 53 d

0

20

40

60

100

150

R1/

dB

TR2/°


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




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


-10

0

10

20

30

-50

0

50

100

150

TR1/

dB

TR2/°


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


TR1: Mag(Gain) TR2: Phase(Gain)

VRTS1P5 ‐ TL431 Adj. Shunt RegulatorVRTS1P5 TL431 Adj. Shunt Regulator 12

40

60

100


-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


160 200

NISM Bode Plot


1

0

20

40

0

50

100

150

R1/

dB

TR2/°


-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



https://www.picotest.com/products_VRTS03.htmlhttp://www.ti.com/product/lmr10515

VRG8666 (RH3080) Linear RegulatorVRG8666 (RH3080) Linear Regulator12

-10

0

100


-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


NISM Bode Plot


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



VRG8666 (RH3080) Linear RegulatorVRG8666 (RH3080) Linear Regulator12

-10

0

10

100


-40

-30

-20

10

10-2

10-1

TR1/

dB TR2

NISM Bode Plot


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


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



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


non measurements bdbode plots - picotestwhat is nism and why it’s a crii litical tec hlhnology •...

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