【滴～～滴滴】电子工程师圣经100条，但你不一定能看懂！

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1Capacitors and resistors have parasitic inductance, about 0.4nH for surface mount and 4nH for a leaded component. 

2If you don"t want a high bandwidth transistor to oscillate place lossy components in at least 2 of the 3 leads. Ferrite beads work well. 

3When taking DC measurements in a circuit and they don"t make sense, suspect that something is oscillating. 

4Opamps will often oscillate when driving capacitive loads. 

5The base-emitter voltage Vbe of a small signal transistor is about 0.65v and drops about 2mV/deg C. Vbe goes down with increasing temp.

6Multiply 0.13nV by the square root of the ohmic value of a resistor to find the noise in a 1Hz bandwidth. Then multiply by the square root of the BW in Hz gives the total noise voltage. 

7Johnson noise current goes down with a increase in resistance.

8The impedance looking into the emitter of a transistor at room temp is 26Ohm/Ie in mA 

9All amplifiers are differential in that they are referenced to ground somewhere. 

10Typical metal film resistor has a temp coef of about 100 ppm/deg C 

11The input noise voltage of a quiet op amp is 1nv/sqrt(Hz) but there are plenty available with 20nV/sqrt(Hz). Op amps with bipolar front-ends have lower voltage noise and higher current noise than those with FET front-ends 

12Using an LC circuit as a power supply filter can actually multiply the power supply noise at the filter"s resonant frequency. Use inductor with low Q to overcome this. 

13Use comparators for comparing and op amps for amplifying and don"t even think of mixing the two. 

14Ceramic caps with any other dielectric other than NPO should only be used for bypass applications. 

15An N-channel enhancement-mode FET needs +ve voltage on the gate-source to conduct form drain-source. 

16Small signal JFETS work very well as low-leakage diodes by connecting drain & source together in log current-to-voltage converters and low leakage input protection. Small signal bipolars with b-c tied together will also make nice low-leakage diodes. 

17With low pass filter use Bessel for least amount of overshoot in the time domain, and Cauer (or elliptic) for fastest rolloff in the freq domain. 

18dB is always 10 times the log of the ratio of 2 powers. 

19At low frequencies, the current in the collector of a transistor is in phase with the applied current at the base. At high frequencies the current at the collector lags by 90deg. You must appreciate this simple fact to understand high frequency oscillators. 

20The most common glass-epoxy PCB material (FR4) has a dielectric constant of about 4.3 To make a trace with a characteristic impedance of 100 Ohm, use a trace thickness of about 0.4 times the thickness of the board with a ground plane on the opposite side. For a 50Ohm trace make it 2 times the thickness. 

21If you need a programmable dynamic current source, find out about operational transconductance amps. Most of the problem is figuring out when you need a programmable dynamic current source. 

22A CMOS output with an emitter follower can drive a 5V relay nicely as the relays normally have a must-make spec of 3.5V. This saves power and require no flyback components. 

23Typical thermocouple potential is 30uV/degC. Route signals differentially, along the same path, avoid temp gradients. DPDT latching relays won"t heat up when multiplexing these signals. 

24You SHOULD be bothered by a design that looks messy, cluttered or indirect. This uncomfortable feeling is one of the few indications that there"s a better way. 

25Avoid drawing any current from the wiper of a potentiometer. The resistance of the wiper contact will cause problems (local heating, noise offsets etc.) 

26Most digital phase detectors have a deadband where the analog output does not change over the small range where the 2 inputs are coincident. This often-ignored fact has helped to create some very noisy PLL"s (Use a high val bleeding resistor to always ensure current flow in the deadband) 

27The phase noise of a phase-locked VCO will be at least 6dB worse than the phase noise of the divided reference for each octave between the comparison frequency and the VCO output frequency. Avoid low-comparison frequencies. 

28You can almost always determine the leads of a bipolar transistor with an ohm meter. b-e and b-c junctions will measure like a diode with the b-c junction reading slightly lower than the b-e junction when forward biased. 

29For low distortion, the drains (or collectors) of a differential amp"s front-end should be bootstrapped to the source (or emitter) so that the voltages on the part are not modulated by the input signal. 

30If your design uses a $3 op amp, and you will be making a thousand of them, you have just spend $3000. Are you smart enough to figure out how to use a $.30 op amp instead? 

31The Q of an LC tank circuit is dominated by the losses in the inductor in terms of series R. Q=omega.L/R 

32Leakage current doubles for every 10degC increase in temp. 

33When inputs to most JFET op amps exceed the common-mode range for the part, the output may reverse polarity. This artifact will haunt the designers of these parts for the rest of their lives, as it should! 

34Understand the difference between "make-before-break" and "break-before-make" when you specify switches. 

353 Terminal voltage regulators in the TO-220 packages are wonderful parts. They are cheap, rugged, thermally protected and very versatile. Use them virtually any place where you need a protected power transistor. They also make nice AM power-modulators. 

36Use step recovery diode where you need fast edges under 100pS (hot-carrier is even faster) 

37The old 723 regulator is still one of the lowest noise regulators around! (2.5uVrms 100Hz-10k) 

38You can make a very simple oscillator with one diac, cap and a resistor. 

39NPN transistors are normally superior to their PNP counterpart in performance. 

40Typical spec in some databooks should read "Seen it once". Always work with the worst spec of the part when doing a design. 

41Don"t just copy circuits from application notes without understanding completely how it operates, and the reason for the choice of values. 

42Dealing with crystals, make sure you understand the difference between series and parallel resonant. In a circuit, crystal frequency can generally be slightly lowered by placing a inductor in series and increased by a capacitor in series. 

43Power MOSFETS on-resistance will have a -ve temp coef and not +ve at low current levels. This is important to remember when paralleling devices. 

44Lowest noise figure of a RF transistor is not normally where the input is perfectly matched. 

45Many un-stable RF devices can be made stable by loading the input or the output by a simple resistor, either in series or parallel. 

46You trade gain for bandwidth. 

47Push-pull power invertors using bipolars are risky and can saturate the core because of hysteresis stepping (use power fets) 

48The Al value of a core will increase up to 50% or more under current transients. 

49Be aware of leakage inductance when switching. V=L(dI/dt) 

50The harder you turn-on a power transistor, the longer it will take to turn off.( the part where you burn the joules in the device) 

51Always remember the Miller guy. 

52In fault-finding a circuit, don"t overlook the obvious. (is there power?) 

53What is a ground loop, and how to avoid it. 

54120 is a better number than 240 when using LM3XX type adjustable regulators. 

55The lower comparator in the old 555 may have quite a long storage time. 

56ZERO-ESR caps may do more harm than good. 

57A correctly configured audio power amplifier will give more distortion in Class-AB, not less, because of the abrupt gain changes inherent in switching from A to B every cycle. 

58Be a STAR when it comes to ground matters. 

59Know when you need to use a Zobel network. 

60Use current mirrors and mirror your current. 

61Heatsink eff decreases with height above sealevel. 

62A matt-black heatsink is much better than a shiny one. 

63Ignoring secondary breakdown can be costly. 

64Understand fuses and fuse ratings, fast and slow. Do you know when to use a semiconductor-fuse? 

65Charge balancing resistors are a must when stacking serie-parallel high voltage capacitor banks. 

66You must understand DC-restoration otherwise you will have a hard time designing Z-modulation in CRT circuits. 

67Display 6 vert div low freq on a scope, increase the freq (make sure the source is constant amplitude) until display drops to 4.2 div. That is the true 3dB BW of the scope. (scope-source impedance should be matched) 

68Doing a measurement with your DMM in the ACV position on your DC circuit will give a quick indication of any excess ripple on the supply when you don"t have a scope at hand. 

69Dly timebase on a scope is very useful once you figured out when, why and how to use it. 

70Know what to expect before you measure, otherwise any measurement is meaningless. 

71Op amps. Output will swing in the direction that will force the inv-input level to try come closer to the non-inv input level. 

72Understand virtual ground, slew-rate, CMRR and PSRR. (CMRR decrease with increase in freq) 

73Making measurements near a spec-analalyzer"s noise floor will give 3dB errors. 

74Understand the phase-noise limitations of the analyzer when making such measurements on oscillators. 

75In a LC oscillator add some C with -ve temp coef to cancel the +ve temp coef of the L for min drift with temp. 

76Less drift will result from making C with a few parallel caps, to reduce the heating effect of the oscillating current when spread out over a larger plate area. 

77You will get more tuning range with the same LC combination in a Clapp than in a Colpitts circuit. 

78High-Q tuned LC filters will have more insertion loss. 

79Williams"s Rule (Guru at Linear Tech) for precision op amp circuits: " Always invert (except when you can"t)" 

80Cuk is not a kind of locomotive. 

81If you don"t know how to make a design better, find out what makes it worse. 

82Sometimes you know just enough to be dangerous. 

83Impedance will reflect back as the square of the turns ratio. 

84If you could design a component with the characteristics of a finger it could cure many design problems and you will be rich. 

85Get nervous when the customer you are trying to help doesn"t even have a scope. 

86Specs quoted by reps always exceed those by Engineering. 

87A bad (Engineer) workman always blames his tools. 

88Don"t believe everything that a SPICE program spits out. 

89It is easy to get the color code of a 1kOhm and 12Ohm resistor mixed up when you are in a hurry. 

90I bet one could write a thesis about the ability of probes to get tangled-up on a bench. 

91DMM can upset sensitive circuits from noise generated inside it. 

92When probing directly on a crystal of a uP, use 10kOhm or so resistor in series with the probe tip to prevent loading from stopping the osc. 

93It is easier to see what is happening on the ports using a scope when you trigger one chan against the cpu clock. 

94National once made a bad op amp many years ago that some Engineers referred to it as "Jelly Beans" 

95The moment you can start to notice distortion on an oscilloscope it is already way past being acceptable. 

96Be big enough to say "I don"t know", people will respect you more. 

97The best designer is often working in the marketing department. 

98Some remarkable discoveries/inventions were made by people that knew very little about the subject. Don"t fall into a groove in you thinking process. 

99The Peter-Principle : Everybody will be promoted up to his own level of incompetence. http://pespmc1.vub.ac.be/PETERPR.html 

100END-Enjoy

作者 : 金至卓

在公众号回复“100条”可获取本文“中英文翻译版本”原文pdf档！

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