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Circuits and Analysis: DFM for Design and Mass-Production with eCAD Tools

Learn about circuits and analysis, including Design for Manufacturing (DFM) principles and tools such as the Pspice Freeware Simulator. Understand passive components like capacitors and inductors, their dynamic characteristics, and their behavior in RC and RL circuits. Explore resonant circuits, different types of capacitors and inductors, and considerations for selecting passive components.

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Circuits and Analysis: DFM for Design and Mass-Production with eCAD Tools

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  1. Circuits and Analysis • DFM = Design for Manufacturing • Design for Mass-Production

  2. eCAD Tools Pspice Freeware Simulator (~6MB download) Includes simple schematic capture & analog simulator http://www.linear.com/designtools/softwareRegistration.jsp Includes full suite of Cadence Tools for Academic Use ONLY! http://www.cse.ogi.edu/CFST/tut/help/pspice_examples.html

  3. Current: Sum of the currents at any node must equal 0. Currents Entering = Currents Exiting Voltage:Sum of the voltages in a circuit loop must equal 0. Voltages Supplied = Voltages Dropped Recall the Basic Kirchhoff’s Circuit Laws

  4. Passive Components

  5. Capacitor Review • Static Characteristics: C = Q/V • Where 1 Farad = 1 Coulomb per 1 Volt • If C is constant and I try to store more charge on C, its voltage will increase proportionally • If C is constant and I want to increase the voltage across it, I need to add more charge • Dynamic Characteristics: I(t) = C dV/dt • where; I(t) = capacitor charging current (Amps) • dV/dt = capacitor voltage change (Volt/Sec) • Note: If I(t) is constant, V(t) is a ramping voltage • Laplace Impedance  1/sC • Complex Impedance  1/jwC • Capacitors Add Directly in Parallel Circuit: CEQ = C1 + C2 +…CN • Capacitors Add Inversely in Series Circuit: CEQ-1 = C1-1 + C2-1 +…CN-1

  6. Dynamic RC Circuit Behavior Review + Where t = RC (time constant)

  7. Inductor Review • Static Characteristics: L = Fm/I • Where 1 Henry = 1 Weber (Mag Flux) per Amp • Note: 1 Henry = 1 Volt per Amp/Sec = 1 Volt-Sec/Amp • Dynamic Characteristics: V(t) = L dI/dt • Where; V(t) = inductor voltage • dI/dt = inductor current change (Amp/Sec) • Note: If DC current thru an inductor is abruptly stopped (circuit opened), the induced voltage V(t) will “spike” very high • Laplace Impedance  sL • Complex Impedance  jwL • Inductors Add Directly in Series Circuit: LEQ = L1 + L2 +…LN • Inductors Add Inversely in Parallel Circuit: LEQ-1 = L1-1 + L2-1 +…LN-1

  8. Dynamic RL Circuit Behavior Review V/R V Current Voltage

  9. Parallel Resonance (Infinite Impedance) Parallel Impedance Z = sL // (sC)-1 Z = (sL)(sC)-1 / (sL + (sC)-1) Z = sL / (s2LC + 1)  jwL / (-w2LC + 1) Note Z  Infinity when w2 = 1/LC  w = (LC)-1/2 (f = 2pw ) Series Resonance (Zero Impedance) Series Impedance Z = sL + (sC)-1 Z = s2LC + 1  -w2LC + 1 Note Z  0 when w2 = 1/LC  w = (LC)-1/2

  10. Electrolytic & Electric Double Layer • Rolled-Wet electrolyte construction • Very Polarized, Low Voltage Range • Ultra High Capacitance Density (5000F available) • High Cost • Used in Power Supplies, Power Backup Systems • Listed on WEEE Restrictions – Item # 15 (2.5x2.5cm) • Reliability Risk for High Temp or High Vibration Apps

  11. Tantalum • Solid Dielectric construction • Polarized • Medium-High Capacitance Density • Low Voltage Range • Used for Board Large (Bulk) Decoupling • Rectangular SMT package • Ceramic • Solid Dielectric construction in single & multilayered • Non-polarized, High Voltage Range • Low Capacitance Density • Low Cost • Used for IC decoupling, low precision timing, filters • Rectangular SMT package

  12. Polyester Film, Metalized Polyester Film • Solid Dielectric construction in multilayered • Non-polarized, High Voltage Range • Medium Cost • Low Capacitance Density • Used for medium precision timing, filters • Rectangular SMT packages • Polypropylene • Solid Dielectric construction • Non-polarized, High Voltage Range • Medium Cost, Low Capacitance Density • Very Low Leakage • Used for high precision timing, filters, sample-hold • Rectangular SMT packages

  13. Inductors • Air Core , Ferrous Core Stick & Ferrous Core Toroid • Note: Air Core May Induce Large Stray Fields • Shielded and Unshielded • Inductance will Have Resistance • Thru Hole & SMT packages • Rated for Inductance, Max Current, Frequency

  14. Passive Components, R-L-C • Critical Factors: • Ambient Temperature • Thermal Deratings & Variation of Primary Parameter (Temp Co) • Maximum Imposed Voltage and/or Current • Maximum Imposed dV/dT and/or Frequency • Inductive Frequency (high frequency model) • Minimum Analysis & Selection Considerations: • Primary Parameter Tolerances (R, L, C %) • Total Power vs Package Dissipation • Maximum Voltage • Composition, Specific die-electrics, construction, etc

  15. Passive Discretes • Resistors/Inductors: Must specify or account for Tolerance, Power, Package and Temp Coefficient • Derating Guide: ~50% of rated power or current • Std Tolerances: 0.1%, 1%, 5%, 10% and 20% • Constructional Anomalies: Max Voltage, Inductive with High Freq • Capacitors: Must specify or account for Tolerance, WV, Polarization, Dielectric, Temp Co and Package • Derating Guide: ~50% of rated voltage • Std Tolerances: 1%, 2%, 5%, 10%, 20%, 80% • Constructional Anomalies: Charge Leakage, Inductive with High Freq,

  16. + - • Amplifiers

  17. Simple Small Signal Models for the BJT Figure 4.33 Small-signal equivalent circuits for the BJT.

  18. Common Emitter Amplifier & Small Signal Equivalent Circuit Voltage Gain: Av = vO/vIN = - bAC (RC//RL) (rp + (1 + bAC)RE1) Current Gain: Ai = iO/iIN = - bAC RC(R1//R2)/(RC+RL) (rp + (1 + bAC)RE1) + (R1//R2) Input Impedance: Ri = vIN/iIN = (R1//R2)//(rp + (1 + bAC)RE1)

  19. Transistor Amplifier Load Line Analysis VCC/RDC VCC DC or Static Load Line:VCC = ICRC + VCEq + (IC + IB)RE Note IC = (bDC)IB & RE = RE1 + RE2  VCC = IC (RC + RE + RE/ bDC) + VCEq = IC (RDC) + VCEqwhere RDC = RC + RE + RE/ bDC Now put into the form Y = mX + b where Y = IC & X = VCE IC = VCE (-RDC )-1 + VCC (RDC )-1    Y intercept = VCC/RDC X intercept = VCC

  20. Transistor Amplifier Load Line Analysis • AC or Dynamic Load Line: • VCC = ICq (RDC) + iCq (RAC) + vCE + VCEqwhere RAC = RC//RL + RE1 + RE1/ bAC • In the form Y = mX + b  IC = VCE (-RAC )-1 + (VCEq/RAC + ICq ) •   Y intercept = VCEq/RAC + ICq X intercept = VCC - ICq (RDC -RAC) The AC or Dynamic Load Line shows the slope the amplifier will actually operate on with signal swing

  21. Transistor Amplifier Load Line Analysis Yd Ys Q Xd Xs Load Line Comparison: Static: IC = VCE (RDC )-1 + VCC (RDC )-1   Ys = VCC/RDC Xs = VCC Dynamic: IC = VCE (RAC )-1 + (VCEq/RAC + ICq )   Yd = VCEq/RAC + ICq Xd = VCC - ICq (RDC -RAC) Quiescent Point Q will be at Intersection, For Best Q Point - Bisect the AC Load Line End Points Note: For Capacitively Coupled Loads RAC < RDC Therefore Set ICq = VCC/(RDC + RAC)

  22. General Linear Analog Circuits • Amplifiers and Attenuators • Math Functions (add, subtract) • Oscillators (sinusoidal) • Filters • Voltage Regulators • Voltage References

  23. General Non-Linear Analog Circuits • Comparators • Oscillators (non-sinusoidal, square, sawtooth, etc) • Voltage Limiters and Clamps • Rectifiers and Bridges • Math Functions (multiply, divide) • Log and other Non-linear Amplifiers • Sample and Hold Amplifiers • Envelope & Peak Detectors • Phase Detectors • Phased Locked Loops • Switching Voltage Regulators

  24. Small Signal Amplifiers • Critical Factors: • Component Tolerances, particularly gain setting R’s, Transistor B • OpAmp Input Offset Voltage (Vio), worse for high gain • Input Bias Current (Ib), Input Offset Current (Iio) • Finite Diff Gain (Ad) & Variation of Ad with Frequency • Output Slew Rate and Output Vp-p at Maximum Frequency • Typical DFM Analysis: • Total DC Offset error in Volts (1,2,3) • Total Gain Error vs Nominal, Converted to Volts (1,4) • Power Bandwidth for Application (1,5)

  25. Basic Gain in Voltage, Current or CombinationLinear Operation: No New Frequencies Created! • Voltage Amplifiers (Vin >> Vout): Av = Vout/Vin • Current Amplifiers (Iin >> Iout): Ai = Iout/Iin • Transimpedance (Iin >> Vout): Zm = Vout/Iin • Transconductance (Vin >> Iout): Gm = Iout/Vin Additional Parameters • Input Impedance: Zin = Vin/Iin • Output Impedance: Zout = {Vout(NL) – Vout(L)}/Iout • Slew Rate (SR): Min dVout/dT • Slew Rate BW = SR/2pVp where Vp = Peak Voltage

  26. + - Operational Amplifier – Why?Linear, Differential, High Gain Amplifier Advantages Over Single Ended Amplifier Block ?? • Easy to add positive and negative feedback with differential input • Single Ended Application Gains can be tightly controlled with external components and made insensitive to internal transistor gain variations • Inherent noise rejection when noise enters both input terminals

  27. Basic Op-Amp SimplifiedImplementation

  28. + - Operational AmplifierIdeal Assumptions Vp Used for basic analysis, nominal gain analysis Vout • Vout = Ad (Vp – Vn) where Ad is the diff gain • Ad = Infinite • Zin = Infinite, Iin = 0 where Iin is the input current • Vp = Vn because of infinite Ad, Vo may be non-zero under this condition • Iout = Infinite (Often a false assumption) These basic assumptions allow simple circuit analysis to determine Nominal gain applications Vn

  29. + - Operational AmplifierPower Supplies Vcc Vp Power Supplies can be a critical consideration Vout • -Vcc < Vout < Vcc At all times, Vout(max) may be as low as 2 to 5 volts below Vcc depending upon model • Vcc, -Vcc sometimes referred to as “Rails” due to power distribution on some boards resembling tracks • Many applications use “Split” supply Operation • Split Supply means Vcc = |-Vcc| • Some models characterized for 1 supply operation (but ALL will work there) • Single Supply means –Vcc = 0 • Vcc, -Vcc power pins should always be capacitively filtered with 0.1uf (usually ceramic monolithic X7R or similar) Vn -Vcc

  30. Operational AmplifierMany Types Available • Others: • Video • Current Feedback • Power • Chopper Stabilized • Electrometer

  31. + - Operational AmplifierBasic Applications Rf Av = - Rf/Ri Zin = Ri Inverting Voltage Amp Ri Vin Vout Rp

  32. + - Operational AmplifierBasic Applications Ri Av = 1 + Rf/Rp Zin = Ri + Non-Inverting Voltage Amp When Rf=0, Rp=~Infinite…… Av = 1 Vin Vout Rf Rp 8

  33. + - Operational AmplifierBasic Applications Av = 1 Zin = Unity Gain Voltage Amp Vin Vout 8

  34. + - Operational AmplifierBasic Applications Ri Gm = 1/Rp Zin = Ri + Transconductance Amp Vin RL Iout Rp 8

  35. + - Operational AmplifierBasic Applications Rf Zm = - Rf Transimpedance Amp Iin Vout RL

  36. + - Operational AmplifierBasic Applications Ai = -(1 + Ri/Rp) Current Amplifier Iin RL Ri Iout Rp

  37. + - Operational AmplifierIdeal Assumptions Vp Used for basic analysis, nominal gain analysis Vout • Vout = Ad (Vp – Vn) where Ad is the diff gain • Ad = Infinite • Zin = Infinite, Iin = 0 where Iin is the input current • Vp = Vn because of infinite Ad, Vo may be non-zero under this condition • Iout = Infinite (Often a false assumption) These basic assumptions allow simple circuit analysis to determine Nominal gain applications Vn

  38. + - Operational AmplifierReal Characteristics Ip Vp Vout Used for more accurate Gain Characterization Iout Vio • Vout = Ad(Vp – Vn) + Ac(Vp + Vn)/2 + Vio Ad is the diff gain, Ac is the common mode gain, Vio = offset voltage • CMRR = Common Mode Rejection Ratio = 20log(Ad/Ac) • Ib = Bias Current (Ave Current = [Ip + In]/2) • Iio = Offset Current (Diff Current = Ip – In) • Iout = Finite, Split between gain set components and load • Vio = Input Diff Voltage reflected back from Vo under the condition the Vp = Vn = 0 Use superposition to understand contributions In Vn

  39. + - Operational AmplifierReal Characteristic Effects Basic Strategy Vp • Consider the Effect Separately, then combine results • Show Ib and Iio as input current sources • Show Vio as diff voltage on Vp-Vn • Use amended opamp in std application circuit, Vin=0 (grounded). • Find Vout, all Vout will be Verror due to Offset and Bias Vout Vn

  40. + - Inverting ConfigurationOffset Error Contribution 1 Rf Ii = (0-Vio)/Ri If = (Vio-Vo)/Rf Ii = If Vo = Vio(1 + Rf/Ri) = Verr Inverting Voltage Amp Error Voltage due to Vio Ri If Vout Vio Ii Rp

  41. + - Non-inverting ConfigurationOffset Error Contribution 1 Ri Ii = (0-Vio)/Rp If = (Vio-Vo)/Rf Ii = If Vo = Vio(1 + Rf/Rp) = Verr Non-Inverting Voltage Amp Error Voltage due to Vio Vin Vout Vio Rf If Rp Ii

  42. Op-Amp Technologies (EDN)Offset Voltage Comparisons IO

  43. Op-Amp Technologies (EDN)Input Bias Current ~10 deg C

  44. + - Inverting AmplifierOffset Error Contribution 2 Rf At V+: Iio = Ib + V+/Rp V+ = Rp(Iio-Ib) At V-: -V-/Ri = (V--Vout)/Rf + Ib + Iio Sub V+ into above equation Vo = Verr = Rf(Ib-/+Iio) - [((RfRp)/Ri + Rp)(Ib+/-Iio)] Note if Iio = ~0 and Rp = Rf//Ri, then Verr = 0 Verr is always minimized when Rp = ~Rf//Ri Inverting Voltage Amp Error Voltage due to Ib, Iio Ri If Vin Vout Iio Ii Ib Ib Rp

  45. + - Non-Inverting AmplifierOffset Error Contribution 2 Rf At V+: Iio = Ib + V+/Ri V+ = Ri(Iio-Ib) At V-: -V-/Rp = (V--Vout)Rf + Ib + Iio Sub V+ into above equation Vo = Verr = Rf(Ib-/+Iio) - [((RfRi)/Rp + Ri)(Ib+/-Iio)] Note if Iio = ~0 and Ri = Rf//Rp, then Verr = 0 Verr is always minimized when Ri = Rf//Rp Non-Inverting Voltage Amp Error Voltage due to Ib, Iio Rp If Vout Iio Ip Ib Ib Ri Ii Vin

  46. + - Inverting AmplifierGain Error Rf Av (nom) = - Rf/Ri But Assume Vout = Ad(V+ - V-) Find expressions for V+ & V- Substitute into above Vout Solve for Vout/Vin = Av Av = -(RfAd)/(RiAd + Ri + Rf) Av = Av(nom)/CF CF = Correction Factor CF = 1 + 1/Ad + Rf/(RiAd) |Av| < |Av (nom)| Inverting Voltage Amp Ri If Vin Vout Ii Rp Don’t Forget to Factor in Res Tol% !

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