Some Methods to Calculate the Values of Passive Components from the - - PowerPoint PPT Presentation

Some Methods to Calculate the Values of Passive Components from the Measurements Made with an 1149.4 Compliant Device

2nd IEEE International Workshop on Board Test

Teuvo Saikkonen, Juha-Veikko Voutilainen, and Markku Moilanen Department of Electrical and Information Engineering, University of Oulu, Oulu, Finland

Purpose

• Describe and develop calculation methods

alleviating the problems encountered when using low cost instruments

• Study 1149.4 applications
• Discuss the preconditions and limitations

Outline

• Test circuits
• Calculation methods
• Experimental results
• Discussion

Introduction

• The first general purpose 1149.4 IC was

introduced at ITC 2001 by Sunter et al.

• Duzevik presented preliminary results of

passive component measurement methods using that IC at BTW02

• The same IC is used also in our research
• Goal: measure the component values with a

low cost instrumentation without phase measuring capability

Simple Test Circuit

AT1 Rsense Function generator AT2 Voltmeter V AB2 AB1 To analog ground ABM1 ABM2 ABM3 ABM4

~

ABM1 Zx

Test Board

• Adjustable gain LF bandpass filter
• TAP, AT1, AT2, inputs for external signals and

components

• Access to selected nodes on the board
• Sense resistor Rsense
• Several parallel RC circuits

– resistances defined by DC measurement – capacitances defined by AC measurement when resistances are known

Delta Connection

R1 R2 R3 ABM ABM ABM ABM A01 A0 A2 A23 AT1 AT2 AT2 AT1 V1, V5 V3 V2, V4 V6 I1 I2

Equivalent Circuits

RG Rsw U4 U3 U2 U1 Zx Rsense Rx Cx

Equivalent Circuits

RG Rsw U4 U3 U2 U1 Rsense Rx Cx

Zx Purely Resistive

RG Rsw U4 U3 U2 U1 Rsense Rx

sense x

R U U U U R

2 1 4 3

− − =

Zx Purely Capacitive

U1 U2 U3 URG U Cx//Cin = Ux URG+Rsw URG+Rsw+Rsense

= U4

2 4 2 3 2

U U U x − =

2 2 2 2 x R R

U U U

sw G

− =

+ 2 2 1 2 x R R R

U U U

sense sw G

− =

+ +

Condition: 1) Cin<< Cx or 2) 2πfRGCx<<1

Zx Purely Capacitive

U1 U2 U3 URG U Cx//Cin = Ux URG+Rsw URG+Rsw+Rsense

= U4

in sense x

C R U U U U U U C − − − − − − = ω 1 1

2 4 2 3 2 2 2 4 2 3 2 1

Zx a Parallel Connection of R and C

U1 U2 U3 URG+ZR+Rsw URG+ZR+Rsw+Rsense URG+ZR URG=U4 UZC =Ux

) arctan( ) ( 1 ) ( 1 ) ( 1

2 2 2 2 x x x x x x x x x x x x x

C R C R R C R C R j C R R Z ω ω ω ω ω − ∠ + = + − + =

If RG<< ZR or RG+ ZR<< ZC , U4 can be neglected And if: 1) Cin<< Cx or 2) 2πfRGCx<<1, we get

Zx a Parallel Connection of R and C

U1 U2 U3 URG+ZR+Rsw URG+ZR+Rsw+Rsense URG+ZR URG=U4 UZC =Ux

ω 2 1 2 2 2 sin 2 3 2 2 sin 2 3 1 x R sense R A U U A U U x C − − − − =

                       

in x x

C C C − = ′

A = arctanωRxCx

Delta Connection

2 6 5 5 4 3 3 2 2 1 1

) ( ) ( R V V V V R V V V V R − − = − − =

) ( ) ( ) )( ( ) )( (

3 2 2 6 4 1 6 5 3 2 6 4 3 1 2

V V I V V I V V V V V V V V R − − − − − − − − =

) ( ) ( ) )( ( ) )( (

6 5 1 3 1 2 6 5 3 2 6 4 3 1 3

V V I V V I V V V V V V V V R − − − − − − − − =

sense s s

R V V I

2 1 1

− =

sense s s

R V V I

4 3 2

− =

Capacitance Measurement Results

STA - LCR [%]

• 4,00
• 3,00
• 2,00
• 1,00

0,00 1,00 2,00 3,00 4,00

• 5
• 4
• 3
• 2
• 1

1 2 3 4 5 n 4.27 nF 19.6 nF 47.6 nF 226 nF 453 nF 971 nF

f = (2πRsenseCnom)-1 ⋅10(n/10)

Capacitance Measurement Results

• Errors increase when measuring small

capacitances – conditions Cin<< Cx or 2πfRGCx<<1 not completely fulfilled (Cin = 100 pF) – inaccuracy of the voltmeter increases above 100 kHz – loading effect of the voltmeter – bandwidth limitations of the 1149.4 IC

• Solution: use higher Rsense ⇒ lower f

Capacitance Measurement Results

• Errors increase also when measuring large

capacitances – reasons still need more consideration

RC Circuit Measurement Results

• R values: error 0.12 % or less (DC measurement)

C Values: STA - LCR [%]

• 1,00

0,00 1,00 2,00 3,00 4,00 5,00 6,00 1 2 3 4 nF f = 5 kHz f = 10 kHz f = 50 kHz f = 100 kHz

RC Circuit Measurement Results

• The accuracy of measurements deteriorates

at low frequencies – Zx approaches a pure resistance ⇒ impossible to define the reactance accurately

Delta Network Measurement Results

R Values: STA - REF. [%]

• 10,00
• 5,00

0,00 5,00 10,00 15,00

1,E+01 1,E+02 1,E+03 1,E+04 1,E+05 1,E+06 1,E+07

R [ohm]

R1(R2) R1(R3) R2 R3

R1 ≈ R2 ≈ R3

Rsense = 1 kΩ

Delta Network Measurement Results

• When R1, R2 and R3 differ significantly from

each other (~2 orders of magnitude or more), quite large errors can be found (Table 9) – Analog ground (V3 and V6) values measured through AT2 erroneous – When voltages are probed directly from pins, results are more accurate

Discussion

• Several conditions have to be fulfilled when

selecting fmeas and Rsense – Based partly on the system under test – And partly on the measurement instruments and the 1149.4 IC – And also on the assumptions made to simplify the calculations

• If there is no phase measuring capability prior

knowledge of the nature of the reactance (L

• r C) is necessary

Conclusion

• The lack of elaborate instruments can be

compensated for by calculations

• Familiarity with the system under test is a

necessity – the consequences of choosing improper measurement conditions were shown

• Calculation methods are worth development if

considered cost-effective