Resistors: History, Classification, and New Trends

1. Lecture 8 Resistors Passive Electronic Components and Circuits (PECC)

2. Resistors Resistors History and new trends Electrical Properties Classification Parameters Marking and Codification Variable resistors

3. History and new trends • 1827 – the first resistor • 1976 – first embedded resistors • General evolution trends: • Performance improvement • Size reducing • Cost reduction

4. History and new trends • Miniaturization

5. History and new trends • Miniaturization

6. Resistors Resistors History and new trends Electrical Properties Classification Parameters Marking and Codification Variable resistors

7. Electrical properties • The mathematical relation which designates the resistance calculation: http://www.8886.co.uk/ref/resistivity_values.htm http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/rstiv.html#c1 http://www.istonline.org.uk/Handbook/40.pdf

8. Electrical properties • The equivalent electrical model • Due to fabrication particularities, every each resistor will have besides its own resistance a parasitic inductance and as well a parasitic capacitance. • The parasitic parameters must be taken into consideration at high frequencies.

9. Electrical properties • Problem: • Please consider the following voltage divider. • What is the dividing factor, if: • R1=1kΩand R2=100Ω; • R1=100kΩ and R2=10kΩ; • R1=100kΩ and R2=1kΩ; • 2. How will this dividing factor modify with the frequency if every resistor has a parasitic capacitance of 2 pF?

10. Resistors Resistors History and new trends Electrical Properties Classification Parameters Marking and Codification Variable resistors

11. Classification • Constructive criteria: • Discrete • Fixed (constant). • Variable. • Integrated • Resistor arias. • Resistor networks. • Embedded (“built in” the structure) • On the PCB level. • On the ceramic substrate level (multichip modules – MCM). • In silicon with the thin film technology. • Inside integrated circuits.

12. Classification • Discrete resistors: • Fixed (R=ct.) • Variable (R≠ct.)

13. Classification • Integrated resistors: • Networks • Arias

14. Classification • Embedded • Fabrication cost reduction. • Thermo-mechanical reliability. • Dimension reducing. • Large scale compatibility between different materials • Values between 10Ω and 200kΩ with under 10% tolerances.

15. Classification • Linearity criteria: • Linear • Non-linear • Thermistors • Varistors • Photo-resistors

16. Classification • Technological criteria: • Film resistors – are being obtained by depositing layers of resistive materials ( agglomerated carbon, crystalline carbon, metal alloys, metal oxides) in a thin pellicle (film – under 10μm) on a insulating support. • Winded resistors – are being obtained by winding a metallic conductive wire on a insulating support. This technology is being used for obtaining high accuracy resistors or high power resistors. • Volume resistors – the resistive element is basically the resistor’s body.

17. Resistors Resistors History and new trends Electrical Properties Classification Parameters Marking and Codification Variable resistors

18. Parameters • Mandatory printed parameters • Nominal resistance. • Nominal value’s tolerance. • Parameters printed only for particular resistors: • The dissipated nominal power. • The temperature coefficient. • The upper limit voltage. • Parameters the are not printed: • The nominal values domain. • The nominal temperature domain. • Noise factor.

19. Parameters • Normalized values series: • In practice, there isn’t a continuous value range for the resistors. • The solution adopted is to use normalized values series. Every series is characterized by a certain tolerance. • The resistance’s nominal values are being obtained from a normalized series value by multiplication with the powers of 10. • A certain series covers almost all the resistances possible values domain, taking into consideration that between two successive values from a series the following formula must apply:

20. Parameters • Normalized values series: • The number of values from a series is dependent of the tolerance by resolving the adjacent equation and taking into consideration the first higher then “n” integer. • The nominal values from a series are in a geometrical progression given by the adjacent relation:

21. Parameters • Normalized values series: • The most important normalized series are: E6(20%); E12(10%); E24(5%); E48(2%); E96(1%); E192(0,5%); • Values from the first three normalized series:

22. Parameters • Choosing a resistor by taking into consideration its tolerance: • When choosing a resistor for a certain application you must take into consideration its tolerance. • The one circuit’s function variation with its components tolerances is called sensitivity.

23. Parameters • Nominal power, Pn: • The nominal power represents the maximum power which can be dissipated by a resistor in a continuous functionality regime, at an environment temperature equal with the nominal temperature, Tnwithout changing its parameters. • This parameter is being printed only for the resistors with the nominal power higher then 2W. • For this parameter, you will find 24 standardized values: 0,05W; 0,1W; 0,125W; 0,25W; 0,5W; 1W; 2W; 3W; 4W; .... 10W; 16W; ... 500W

24. Parameters • Low-power resistors: • For the low-power resistors (below 2W), the nominal power can be deduced watching every resistor’s geometrical dimensions.

25. Parameters • Temperature coefficient: • Is being printed only for high accuracy resistors. • The temperature coefficient is defined as follows: • For most of the resistors this parameter can be considered as a constant.

26. Parameters • The upper-limit voltage, Vn: • Is being printed only for resistors dedicated to function at very high voltages. • For a common resistor, the upper-limit voltage can be calculated as follows:

27. Parameters • Noise factor, F: • The noise factor can be defined as the noise voltage value that appears at the resistor's terminals when applying a 1V DC voltage. • The noise voltage occurs because of the disordered movement of the electrons through the conductive material:

28. Resistors Resistors History and new trends Electrical Properties Classification Parameters Marking and Codification Variable resistors

29. Marking and Codification • Resistors marking • Resistors marking refers at the way the information printed on the resistors is being encoded: • Marking using digits and letters – alphanumeric. • Marking using the resistors color code.

30. Marking and Codification • Marking using digits and letters - alphanumeric • The nominal value marking can be done using digits and letters as multipliers. The letter’s position marks the decimal point position in the nominal value. Multiplicatori: R=1; K=1.000 (kilo); M=1.000.000 (mega); G=1.000.000.000 (giga) • Tolerance marking can be done either by clearly printing the tolerance value (5%, 1%, etc.) or the tolerance can be encoded using letters. B0,1%; C0,25%; D0,5%; F1%; G2%; H2,5%; J5%; K10%; M20%

31. Marking and Codification • Marking using digits and letters - alphanumeric • The avoid confusion between the letters that designate the positon of the decimal point and the letters that designate the tolerancethere is a space between the tolerance and the other letters (or event the tolerance is printed in a row below). Nominal value 2700Ω, 5% tolerance Nominal value 330kΩ, 20% tolerance Nominal value 0.33Ω, 10% tolerance • Nominal power and temperature coefficient marking can also be done for the special resistors.

32. Marking and Codification • Marking using digits and letters – alphanumeric – for SMD resistors • For the SMD resistors which are generally smaller then THD resistors, the encoding of the parameters uses the following values – EIA-96 code:

33. Marking and Codification • Marking using the resistors color code • This procedure of encoded marking, although is more difficult to decode, has the advantage that the printing area covers most of the resistor’s body and is visible indifferently of the position of the resistor on a PCB. • The decoding procedure starts with the colored ring (or a group of colored rings) which is closest from one terminal. • For resistors with nominal values from E6, E12, E24, E48 normalized series, the color code contains 4 colored rings (bands). • For resistors with nominal values from E96, E192 normalized series, that have lower tolerances, the color code contains 5 colored rings (bands).

34. Marking and Codification • Marking using the resistors color code

35. Marking and Codification • Observations: • Some colors don’t have a tolerance code (orange, yellow and white). • For the 4 band color code, the tolerance is encrypted using only the following colors: red (2%), gold (5%) or silver (10%). • When the color ring designating the tolerance is missing, that means that resistor has a 20% tolerance value. Thus, the color code will contain only 3 colored rings. Brown, Black, Red + Gold = 10*100, 5% tolerance = 1kΩ, 5% tolerance

36. Marking and Codification • Codification: • Generally, in the electronic circuits besides the resistor symbol you will find its reference (R1, R45, etc.) and its nominal value (1k, 3k3, etc.). The dissipated power or its tolerance are being specified only for specific applications. • Those information regarding the codification procedures are being printed only on the assembly layers of every PCB board.

37. Resistors Resistors History and new trends Electrical Properties Classification Parameters Marking and Codification Variable resistors

38. Variable Resistors • Classification: • Divided in 2 major categories: • Semi-adjustable • Potentiometers

39. Variable Resistors • Use: • Potentiometer circuit: • Rheostat circuit:

40. Variable Resistors • Classification: • By the resistive element manufacturing technology: • Metallic film resistors • Carbon film resistors • Metal-ceramic (cermet) resistors • Winded resistors

41. Variable Resistors • Classification: • By the resistive elements number: • Simple – with only one resistive element • Multiple – with more then one resistive element. Can work in tandem or independently.

42. Variable Resistors • Classification: • By the resistance variation equation dependent with the cursor position: • By destination: • Bulk (commercial use) • Linear • Logarithmic • Accurate (with parameters tolerances lower and very high reliability) • Inverse logarithmical • Exponential • Inverse exponentially

43. Variable Resistors • Parameters: • They are being characterized by the same parameters as the fixed resistors. • The potentiometers tolerances doesn’t have very low values because the exact position of the cursor cannot be technologically set in a very accurate way. To obtain high accuracy potentiometers, multi-turn potentiometers are being used

44. Variable Resistors • Specific parameters: • The residual resistance, r0– represents the value of the resistance measured between the cursor and one of the terminals when the cursor is positioned at that end of the resistor. Ideally, this parameter should be zero. • Contact resistance, rk– represents the value of the resistance measured between moving cursor and the resistive element. Again, this parameter should be as low as possible. • The limit cursor current, In– represents the maximum value that can pass through the resistive element.

45. Variable Resistors • Specific parameters: • The resistance variation equation: • Linear • Logarithmical • Inverse logarithmical

46. Variable Resistors • Mechanical parameters: • The mechanical endurance – represents the minimum number of cursor movements during which the potentiometer keeps its designed parameters. This parameter has values between 10000 and 25000 for the common potentiometers and 100-200 for trimmers. • Pressure force – represents the force with witch the cursor pressures the resistive film.

47. Resistors • Problem 1: • For a 100Ω resistor a tolerance t=10% at the reference temperature T0=20°C has been determined. The resistor has a temperature variation coefficient αT=20ppm/°C. The environment temperature in which the resistor is designate to work is between [-30°C;+90°C]. Considering that due to its dissipated power, the resistor’s body heats up with 50°C, what is the global tolerance in which the nominal value of the resistor can be found?

48. Resistors • The dividing factor for R1=1kΩ and R2=100Ω:

49. Resistors • The dividing factor for R1=100kΩ and R2=10kΩ:

50. Resistors • The dividing factor for R1=100kΩ and R2=1kΩ: