RLCG measurements (imitance)

Transcription

1 RLCG measurements (imitance) Ján Šaliga KEMT FEI TU Košice 2017 Real electronic components Real components are NT ideal (perfect) It they were ideal the would have only one physical property: resistivity, capacity or inductivity Real components have also parasitic properties We have strictly to distinguish components and their required physical properties: Resistor and resistivity Capacitor and capacity Coil (inductor) and inductivity Keramický kondenzátor Cievka s jadrom 2 Physical models Each component has: The main parameter (R or C or L) Parasitic parameters The main and parasitic parameters are the complex property of component and there is no way the disconnect them for measurement task The nominal value of main parameters specified by vendor is valid with some tolerance at specified conditions Real value of main parameter can vary from the nominal one even at keeping the conditions of testing 3 1

2 Imitance: impedance/admitance Reflects the behavior of electronic component for sinewave voltage and current Complex number - real and imaginary part Z( j) 1 Y ( j) Quality Q and dissipation D factors: Q Energy stored 1/ D Energy lost +j X -j R X Z R D U T G B +j Y Z( j) R( ) jx ( ) B Y ( j) G( ) jb( ) Z j exp j Y ( j) exp j arctg X arctan B( ) R G G( ) Q X ( ) 1 G( ) R( ) D D tan90 -j B( ) 4 Fictive models Expression of measurement results according to the chosen fictive (equivalent)! Interpretation of measured imitance!!! Parameters of fictive models can be simple recalculated from one model to other model (interconnection) The values of components in fictive model are valid only for given conditions of measurement (they are function of frequency, voltage amplitude, temperature, ) Four models are used - 2 serial and 2 parallel Z j RS jx S RS jls ; X S LS 1 Z j RS jx S RS j ; C S 1 CS X S Ls Cs Rs Rs Y j GP jbp GP jc p ; BP C p Cp Gp 1 Y j GP jbp GP j ; LP 1 L Lp P BP Gp 5 Example of frequency dependence A: Z A MAX B MAX B: MKR Hz MAG m deg PHASE mdeg A MIN B MIN deg m START Hz STP Hz 6 2

3 Example of voltage dependence Fictive capacity of capacitors can depends on testing voltage amplitude and its offset. DC [%] C V ac Typ I Typ II V dc 7 Temperature sensitivity of capacitors DC [ %] Typ I Typ II T [ C] 8 What has influence on results? Z Analyzer Q : 165 Q =165? Q = 120 LCR meter Q : 120 L =5.231 uh? L =5.310 uh uh LCR meter uh LCR meter 9 3

4 What has influence on results? Condition of measurement and method of measurement: Frequency of test signal Amplitude of test signal Bias Condition in environment (temperature, humidity, pressure,...) Component status (aging, mechanical deformation,...) Fictive model for interpretation of results Errors and uncertainty of measurement 10 Measurement Set-Up Instrument Port Extension Test Fixture R x + jx x Page 11 Which Value Do We Measure? TRUE EFFECTIVE INDICATED +/- % Instrument Test fixture Real world device Page 12 4

5 Sources of Measurement Errors Technique Inaccuracies Complex Residuals Residuals Noise Instrument Port Extension Test Fixture R x + jx x Parasitics Page 13 Actions for Limiting Measurement Errors Instrument Calibration Port Extension LAD Compensation Test Fixture Compensation Guarding R x + jx x EShielding Page 14 Measurement Technique Selection Criteria Frequency Impedance Required measurement accuracy Electrical test conditions Measurement parameters Physical characteristics of the Page 15 5

6 Frequency vs. Measurement Techniques 100KHz Network Analysis RF I-V 1 MHz 1.8 GHz 10KHz 22KHz I-V Resonant 30MHz 110MHz 70MHz 5HZ Auto Balancing Bridge 40MHz K 10K 100K 1M 10M 100M 1G 10G Frequency (Hz) Page 16 Auto Balancing Bridge Theory of peration Virtual ground V 1 H L R 2 V 2 = I 2 R 2 V 1 Z = I 2 = I V 1 R 2 V 2 I = I I 2 V 2 Page 17 Auto balancing bridge (Z x) R ref + U U o=ki DU T ADC Phase sensitive detector (synchronous detector) microcontroller Harmonic oscillator Phase shift0 /90 Display: R x+,jx x 18 6

7 Examples 19 RLCG bridge in laboratory Derived from the basic idea and realized in the form of virtual instrument: Bridge: serial connection of known reference resistor as current sensor and measured component () powered by sinewave from generator Measuring card senses vectors of voltages across the reference resistor and measured component Vectors (waveform) are digitized and amplitudes and phase shifts are calculated. Complex impedance or admittance has been calculated The impedance/admittance is recalculated to the fictive models and parameters (Rs, Ls/Cs; Gp, Cp/Lp; Q; D, ) Digitizing and calculation Front panel Harmonic waveform generator Rref U R j U j Bridge 20 RF I-V Advantages and Disadvantages High frequency, 1MHz < f < 1.8GHz Most accurate method at > 100 MHz Grounded device measurement U 1 R 1 R 2 I U 2 Page 21 7

8 RF I-V Advantages and Disadvantages +High frequency, 1MHz < f < 1.8GHz +Most accurate method at > 100 MHz -Grounded device measurement High impedance Vm U I Vm U I Low impedance R 0 R 0 R G R 0 Vm U U R G U U R 0 Vm U G U G U UU U I UU Z 1 R0 I U I U I R0 U UU UU Z R0 I U I UU U I UU Page 22 R0 R0 Network Analysis (Reflection) Technique Theory of peration V INC V R = V R V INC = Z L - Z Z L + Z Input signal V INC (from generator) Reflected signal(v R ) Transiting signal to Page 23 Teory of reflection Reflection coefficient U Z j j U j Z Z U gen Vm Directional coupler gen U j Z gen j U j Z gen j j Z j gen gen gen ju j ju j Z gen Vm U Z 24 8

9 Network Analysis Advantages and Disadvantages High frequency - Suitable for f > 100 khz - Best for f > 1.8 GHz Moderate accuracy Limited impedance measurement range ( should be around 50 ohms) See more later within the special lecture on network analyzers Page 25 Theory of TDR operation TDR = time domain reflectometry Effect of long wires (transmission lines with distributed parameters): signal propagates in time in the form of waves (E i - incident, E r - reflected) (a delay between ends of line) A part of incident wave energy is reflected at any inhomogeneity of wires, especially at the end of long wires if impedance of load Z L differs from characteristic impedance of wires Z 0 If Z L=Z 0 the load is matched to wires and all energy of incident wave is transferred to the load = the optimal status for many applications. The incident and reflected waves can be measured at the beginning of wires The ratio of incident and reflected waves is the reflection coefficient (usual symbol j or j) 26 Incident and reflected wave 27 9

10 Reflection analysis 28 Reflection analysis. 29 More connections a 30 10

11 scilloscope A complex load V INC V R Z L Step Generator Series R & L = V R V INC = Z - Z L Z + Z L Parallel R & C 0 t Page 31 H TDNA - time domain network analyzer (TDR) Advantages and Disadvantages Reflection and transmission measurements Single and multiple discontinuities or impedance mismatches ("Inside" look at devices) impedance should be around 50 ohms Not accurate for m or M s or s with multiple reflections Good for test fixture design, transmission lines, high frequency evaluations Page 32 11