It is funny how amplifier circuit models look really scary in the beginning, but then after you have been working with them for a while they suddenly start to look incredibly simple.
I believe this is the best explanation and interpretation of electronics circuits. Thank you so much sir for this valuable knowledge you have provided.
00:51 Developing a circuit model for the bipolar transistor 04:29 Transconductance measures the strength of a bipolar device in translating a voltage change to a current change 10:19 Transistor can act as a current source and its values can change. 13:47 Finding IC as a function of time 19:59 Dependent current source placement in simplest bipolar transistor model 22:21 Modeling the base current using a diode 28:04 Transistor model replacement and circuit simplification 31:10 Analyzing large-signal and small-signal operation of Razavi Electronics 37:26 Nonlinear functions require mathematical labor in bipolar transistor circuits. 40:27 Analysis of voltage and current in the circuit with a sinusoidal microphone signal 47:45 Large signal operation allows for signals of any amplitude, leading to complex exponential expressions for IC. 50:57 Small-signal operation assumes input signal is small compared to the bias voltage. 57:35 Small signal operation leads to sinusoidal behavior of collector current. 1:00:42 GM times input voltage equals current fluctuation
At 1:03:02, why (Ic0/Vt) can be equal to gm, isn't gm = Ic0/V0? since Vt = 26mA @300K. ok i probably get it. gm = dIc / dVbe = dIc0 / dV0, which means the equation isn't derived from the previous one, it is a new way of expressing it.
Because If we replace that by current source, Voltage across that would be Vbe and if we change Vbe , then current also...so it would not be a current source....Collector emitter junction has Vce voltage....and by changing that voltage , Ic is constant thats why that is Voltage controlled current source...base emitter junction is not current source.
Over a long time I have been thinking that BJT is a current controlled device, and now this man says it to be voltage controlled. How come everybody modifies electronics as they like?
It really depends wether you are ok if it's linear or not. If it's a current controlled device, then you just have the relation Ic=B*Ib. If you say its a voltage controlled device, then you have that non-linear function. In the end, even the beta isn't constant with magnitude of the currents or temperature. So the system is non-linear and thermically dependent. The good thing is that there are techniques to tie things, so you get an amplifier which is almost beta independent.
Same problem here. I think that it need to be calculated as same except Vt in the breckets because we are taking that Vt out of breckets. Please someone give a explanation for that step.
e^x = x+1 will hold if x is much much smaller than 1, say x=0.1, using your caculator is approximately 1.1(1+0.1something something), try also x=. 2,.3, etc.. and notice that as you approach 1 that expression will no longer hold. For small swing razavi considered vm to be small as compare to vt to produced a linear output, and that will hold only for small input signal because in the graph of Ic vs Vbe which is exponential by nature, you can still find a straigh line if you consider a small part of which will correspond to gm as slope of that small part of the curve, hope that will help.
