EECE 281 Sophomore SeminarAnother kind of Transistor?Bipolar Junction TransistorBJT OperationBJT Water ModelCurrent Gain of BJTMain Rules of npn BJT OperationBiasing a Typical BJT AmplifierGain Analysis of BJTBJT Amplifier in Real LifeOp Amps (Operational Amp)Op Amp Analysis (1)Op Amp Analysis (2)Ch. 6: Logarithmic Unit The DecibelLogarithmic ScaleDefining the Decibel“Extending” the DecibelUsing the DecibelUsing the Decibel (2)What Have We Seen?15/24Ch. 6: Logarithmic Unit The Decibel Notes from EECE 281... "Ch. 6" refers to the EECE 281 book called "Electrical Engineering Uncovered"16/24• Engineers deal with data that can take on values over a HUGErange!!!– Plotting this on a “linear” scale doesn’t show the data well Logarithmic Scalei.e., Plotting Y vs. X– so use “logarithmic” scale(s)•Y on log axis vs. X on linear axis, or •Y on linear axis vs. X on log axis, or•Y on log axis vs. X on log axis, … depends on data– The following plots illustrate this!• Two sets of data that are very different, but you can’t see it on the linear scale!!!17/240 100 200 300 400 500 600100101102103104105106XY1Log Vertical Scale0 100 200 300 400 500 600100101102103104105106Y2XLog Vertical Scale0 100 200 300 400 500 600024681012x 105XY2Linear Vertical Scale0 100 200 300 400 500 600024681012x 105XY1Linear Vertical Scale18/24Logarithmic Scale• Instead of using a logarithmic axis…0 100 200 300 400 500 600104105106Y1Option: Plot data on log axisX0 100 200 300 400 500 60044.555.56log10(Y1)Option: Plot log(data) on linear axisX• log(Y) vs. X, or• Y vs. log(X), or• log(Y) vs. log(X)• First… take log of data; then… plot on linear axis19/24• Building on this log10(data) idea…• Definition: use “decibels” as a logarithmic unitof measure for a ratio between two powersDefining the Decibel–30 dB0.001 = 10-3–20 dB0.01 = 10-2–10 dB0.1 = 10-10 dB1 = 10010 dB10 = 10120 dB100 = 10230 dB1000 = 103P1/P2(dB)P1/P2 (non-dB)Powers of 10 are easy to convert to dB!!Know These443442143421decibelbel2110log10PPP1/P2 = 2 ! ~ 3 dBAnother “Rule” to Know!!20/24• Even though dB is defined for power we can extend it for use with voltages and currents:– assume voltages to be compared are across same resistance“Extending” the Decibel===2110222110102110log20log10log10log102221VVVVPPRVRV===21102221102221102110log20log10log10log10IIIIRIRIPPUse “20” for V & I, but use “10” for P21/24• Comparing two quantities in system(s)Using the DecibelAmplifierP2 = 1mWP3= 10 WCableP1 = 2mWdB 401010log10log103102310==−PPThe Amplifier has a Gain of 40 dBdB 321log10log10101210−==PPThe Cable has a Gain of –3 dBNegative dB gain = loss… “Cable has a 3 dB Loss”dB 3710210log10log103101310=×=−PPThe System has a Gain of 37 dBGains in a “cascade” add in dB: –3 dB + 40 dB = 37 dBlog(ab) = log(a) + log(b)22/24Using the Decibel (2)• Using decibels for amplifier gains– MUST disregard the “negative” for an inverting gain– Recall: Inverting Op Amp Gain = –RF/R1– In dB this is stated as: “20log10(RF/R1) (inverting)”• Comparing a quantity in a system to a reference– Sometimes common arbitrary references are used• 1 W ! 10log10(P/1W) dBW• 1 mW ! 10log10(P/0.001W) dBmW or just dBm– Sometimes a physically meaningful reference is used• See table for sound pressure level23/240.0002Threshold of Hearing0.002Recording StudioQuiet Room0.020.2Normal Speech2Busy Street20Rock Concert/ClubChainsaw200Threshold of Pain2000Jet Plane (@ 30 m)Sound Pressure Level(µBar)Sounds0102030405060708090100110120130140Sound Pressure Level(dB)0002.020log2010For Non-PowerFactor of 10!20 dBNot Power!20log10(SPL/y)What should “y” be?A Reference Level!!Reference Level! 0
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