1/Capacitors and resistors have parasitic inductance, about 0.4nH for surfacemount and 4nH for a leaded component. 2/If you don"t want a high bandwidth transistor to oscillate place lossycomponents in at least 2 of the 3 leads. Ferrite beads work well. 3/When taking DC measurements in a circuit and they don"t make sense,suspect that something is oscillating. 4/Opamps will often oscillate when driving capacitive loads. 5/The base-emitter voltage Vbe of a small signal transistor is about 0.65v anddrops about 2mV/deg C. Vbe goes down with increasing temp. 6/Multiply 0.13nV by the square root of the ohmic value of a resistor to find thenoise in a 1Hz bandwidth. Then multiply by the square root of the BW in Hzgives the total noise voltage. 7/Johnson noise current goes down with a increase in resistance. 8/The impedance looking into the emitter of a transistor at room temp is 26Ohm/Iein mA 9/All amplifiers are differential in that they are referenced to groundsomewhere. 10/Typical metal film resistor has a temp coef of about 100 ppm/deg C 11/The input noise voltage of a quiet op amp is 1nv/sqrt(Hz) but there are plentyavailable with 20nV/sqrt(Hz). Op amps with bipolar front-ends have lowervoltage noise and higher current noise than those with FET front-ends 12/Using an LC circuit as a power supply filter can actually multiply the powersupply noise at the filter"s resonant frequency. Use inductor with low Qto overcome this. 13/Use comparators for comparing and op amps for amplifying and don"t eventhink of mixing the two. 14/Ceramic caps with any other dielectric other than NPO should only be used forbypass applications. 15/An N-channel enhancement-mode FET needs +ve voltage on the gate-source toconduct form drain-source. 16/Small signal JFETS work very well as low-leakage diodes by connecting drain& source together in log current-to-voltage converters and low leakage inputprotection. Small signal bipolars with b-c tied together will also make nicelow-leakage diodes. 17/With low pass filter use Bessel for least amount of overshoot in the timedomain, and Cauer (or elliptic) for fastest rolloff in the freq domain. 18/dB is always 10 times the log of the ratio of 2 powers. 19/At low frequencies, the current in the collector of a transistor is in phasewith the applied current at the base. At high frequencies the current at thecollector lags by 90deg. You must appreciate this simple fact to understandhigh frequency oscillators. 20/The most common glass-epoxy PCB material (FR4) has a dielectric constant ofabout 4.3 To make a trace with a characteristic impedance of 100 Ohm, use atrace thickness of about 0.4 times the thickness of the board with a groundplane on the opposite side. For a 50Ohm trace make it 2 times the thickness. 21/If you need a programmable dynamic current source, find out about operationaltransconductance amps. Most of the problem is figuring out when you need aprogrammable dynamic current source. 22/A CMOS output with an emitter follower can drive a 5V relay nicely as therelays normally have a must-make spec of 3.5V. This saves power and require noflyback components. 23/Typical thermocouple potential is 30uV/degC. Route signals differentially,along the same path, avoid temp gradients. DPDT latching relays won"t heatup when multiplexing these signals. 24/You SHOULD be bothered by a design that looks messy, cluttered or indirect.This uncomfortable feeling is one of the few indications that there"s abetter way. 25/Avoid drawing any current from the wiper of a potentiometer. The resistance ofthe wiper contact will cause problems (local heating, noise offsets etc.) 26/Most digital phase detectors have a deadband where the analog output does notchange over the small range where the 2 inputs are coincident. Thisoften-ignored fact has helped to create some very noisy PLL"s (Use a highval bleeding resistor to always ensure current flow in the deadband) 27/The phase noise of a phase-locked VCO will be at least 6dB worse than the phasenoise of the divided reference for each octave between the comparison frequencyand the VCO output frequency. Avoid low-comparison frequencies. 28/You can almost always determine the leads of a bipolar transistor with an ohmmeter. b-e and b-c junctions will measure like a diode with the b-c junctionreading slightly lower than the b-e junction when forward biased. 29/For low distortion, the drains (or collectors) of a differential amp"sfront-end should be bootstrapped to the source (or emitter) so that thevoltages on the part are not modulated by the input signal. 30/If your design uses a $3 op amp, and you will be making a thousand of them, youhave just spend $3000. Are you smart enough to figure out how to use a $.30 opamp instead? 31/The Q of an LC tank circuit is dominated by the losses in the inductor in termsof series R. Q=omega.L/R 32/Leakage current doubles for every 10degC increase in temp. 33/When inputs to most JFET op amps exceed the common-mode range for the part, theoutput may reverse polarity. This artifact will haunt the designers of theseparts for the rest of their lives, as it should! 34/Understand the difference between "make-before-break" and"break-before-make" when you specify switches. 35/3 Terminal voltage regulators in the TO-220 packages are wonderful parts. Theyare cheap, rugged, thermally protected and very versatile. Use them virtuallyany place where you need a protected power transistor. They also make nice AMpower-modulators. 36/Use step recovery diode where you need fast edges under 100pS (hot-carrier iseven faster) 37/The old 723 regulator is still one of the lowest noise regulators around!(2.5uVrms 100Hz-10k) 38/You can make a very simple oscillator with one diac, cap and a resistor. 39/NPN transistors are normally superior to their PNP counterpart in performance. 40/Typical spec in some databooks should read "Seen it once". Alwayswork with the worst spec of the part when doing a design. 41/Don"t just copy circuits from application notes without understandingcompletely how it operates, and the reason for the choice of values. 42/Dealing with crystals, make sure you understand the difference between seriesand parallel resonant. In a circuit, crystal frequency can generally beslightly lowered by placing a inductor in series and increased by a capacitorin series. 43/Power MOSFETS on-resistance will have a -ve temp coef and not +ve at lowcurrent levels. This is important to remember when paralleling devices. 44/Lowest noise figure of a RF transistor is not normally where the input isperfectly matched. 45/Many un-stable RF devices can be made stable by loading the input or the outputby a simple resistor, either in series or parallel. 46/You trade gain for bandwidth. 47/Push-pull power invertors using bipolars are risky and can saturate the corebecause of hysteresis stepping (use power fets) 48/The Al value of a core will increase up to 50% or more under currenttransients. 49/Be aware of leakage inductance when switching. V=L(dI/dt) 50/The harder you turn-on a power transistor, the longer it will take to turnoff.( the part where you burn the joules in the device) 51/Always remember the Miller guy. 52/In fault-finding a circuit, don"t overlook the obvious. (is there power?) 53/What is a ground loop, and how to avoid it. 54/120 is a better number than 240 when using LM3XX type adjustable regulators. 55/The lower comparator in the old 555 may have quite a long storage time. 56/ZERO-ESR caps may do more harm than good. 57/A correctly configured audio power amplifier will give more distortion inClass-AB, not less, because of the abrupt gain changes inherent in switchingfrom A to B every cycle. 58/Be a STAR when it comes to ground matters. 59/Know when you need to use a Zobel network. 60/Use current mirrors and mirror your current. 61/Heatsink eff decreases with height above sealevel. 62/A matt-black heatsink is much better than a shiny one. 63/Ignoring secondary breakdown can be costly. 64/Understand fuses and fuse ratings, fast and slow. Do you know when to use asemiconductor-fuse? 65/Charge balancing resistors are a must when stacking serie-parallel high voltagecapacitor banks. 66/You must understand DC-restoration otherwise you will have a hard timedesigning Z-modulation in CRT circuits. 67/Display 6 vert div low freq on a scope, increase the freq (make sure the sourceis constant amplitude) until display drops to 4.2 div. That is the true 3dB BWof the scope. (scope-source impedance should be matched) 68/Doing a measurement with your DMM in the ACV position on your DC circuit willgive a quick indication of any excess ripple on the supply when you don"thave a scope at hand. 69/Dly timebase on a scope is very useful once you figured out when, why and howto use it. 70/Know what to expect before you measure, otherwise any measurement ismeaningless. 71/Op amps. Output will swing in the direction that will force the inv-input levelto try come closer to the non-inv input level. 72/Understand virtual ground, slew-rate, CMRR and PSRR. (CMRR decrease withincrease in freq) 73/Making measurements near a spec-analalyzer"s noise floor will give 3dBerrors. 74/Understand the phase-noise limitations of the analyzer when making suchmeasurements on oscillators. 75/In a LC oscillator add some C with -ve temp coef to cancel the +ve temp coef ofthe L for min drift with temp. 76/Less drift will result from making C with a few parallel caps, to reduce theheating effect of the oscillating current when spread out over a larger platearea. 77/You will get more tuning range with the same LC combination in a Clapp than ina Colpitts circuit. 78/High-Q tuned LC filters will have more insertion loss. 79/Williams"s Rule (Guru at Linear Tech) for precision op amp circuits:" Always invert (except when you can"t)" 80/Cuk is not a kind of locomotive. 81/If you don"t know how to make a design better, find out what makes itworse. 82/Sometimes you know just enough to be dangerous. 83/Impedance will reflect back as the square of the turns ratio. 84/If you could design a component with the characteristics of a finger it couldcure many design problems and you will be rich. 85/Get nervous when the customer you are trying to help doesn"t even have ascope. 86/Specs quoted by reps always exceed those by Engineering. 87/A bad (Engineer) workman always blames his tools. 88/Don"t believe everything that a SPICE program spits out. 89/It is easy to get the color code of a 1kOhm and 12Ohm resistor mixed up whenyou are in a hurry. 90/I bet one could write a thesis about the ability of probes to get tangled-up ona bench. 91/DMM can upset sensitive circuits from noise generated inside it. 92/When probing directly on a crystal of a uP, use 10kOhm or so resistor in serieswith the probe tip to prevent loading from stopping the osc. 93/It is easier to see what is happening on the ports using a scope when youtrigger one chan against the cpu clock. 94/National once made a bad op amp many years ago that some Engineers referred toit as "Jelly Beans" 95/The moment you can start to notice distortion on an oscilloscope it is alreadyway past being acceptable. 96/Be big enough to say "I don"t know", people will respect youmore. 97/The best designer is often working in the marketing department. 98/Some remarkable discoveries/inventions were made by people that knew verylittle about the subject. Don"t fall into a groove in you thinkingprocess. | 
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发表于 2008-5-4 11:44:26
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