AoE Chapter 3 - circuit ideas A (high-input-impedance follower)
Also here:
and at the end of the post.
1) How do you go about analyzing this circuit? how do you approach it? I ca n do the DC analysis fine but the AC analysis is a bit difficult.My approach was to assume all caps are shorts then assume a voltage wiggle at n007 (where R4 and R5 meet) and then try to calculate the currents. I ca n figure out most of the currents but it's hard for me to figure out what d rives the changes in the BJT collector current, given that the base and emi tter sorta move in sync. Of course I can't really understand why the circui t behaves the way it does, but simulation confirms that the input current i s incredibly small. It appears that the difference between emitter/collecto r current and the current in the emitter resistor that ends up being really small.
2) How would the circuit designer arrive at such a circuit? Just plain inge nuity or are there specific building blocks?I appreciate the insights, I'm trying really hard to get better at analyzin g transistor circuits and I understand the basics of transistors but can't pull this off.
------------------------------------------------------------------------- Version 4 SHEET 1 880 680 WIRE 64 -192 -96 -192 WIRE 352 -192 64 -192 WIRE 544 -192 352 -192 WIRE 544 -144 544 -192 WIRE -96 -112 -96 -192 WIRE 64 -112 64 -192 WIRE 544 -32 544 -64 WIRE 64 0 64 -32 WIRE 128 0 64 0 WIRE 240 0 192 0 WIRE 64 16 64 0 WIRE -336 80 -416 80 WIRE -208 80 -272 80 WIRE 16 80 -208 80 WIRE 352 112 352 -192 WIRE -416 144 -416 80 WIRE -208 144 -208 80 WIRE 64 160 64 112 WIRE 288 160 64 160 WIRE -208 240 -208 224 WIRE -96 240 -96 -32 WIRE -96 240 -208 240 WIRE -416 256 -416 224 WIRE -96 256 -96 240 WIRE 128 256 -96 256 WIRE 240 256 240 0 WIRE 240 256 192 256 WIRE 352 256 352 208 WIRE 352 256 240 256 WIRE 64 272 64 160 WIRE -96 400 -96 336 WIRE 64 400 64 352 WIRE 352 400 352 336 FLAG -96 400 0 FLAG 64 400 0 FLAG 352 400 0 FLAG 544 -32 0 FLAG -416 256 0 SYMBOL npn 288 112 R0 SYMATTR InstName Q1 SYMATTR Value 2N3904 SYMBOL njf 16 16 R0 SYMATTR InstName J1 SYMATTR Value 2N4416 SYMBOL res 48 -128 R0 SYMATTR InstName R1 SYMATTR Value 10k SYMBOL res 336 240 R0 SYMATTR InstName R2 SYMATTR Value 1k SYMBOL res -112 -128 R0 SYMATTR InstName R3 SYMATTR Value 2.2meg SYMBOL res -112 240 R0 SYMATTR InstName R4 SYMATTR Value 1meg SYMBOL res -224 128 R0 SYMATTR InstName R5 SYMATTR Value 10meg SYMBOL cap 128 272 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName C1
SYMBOL cap 128 16 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName C2
SYMBOL cap -336 96 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName C3 SYMATTR Value 1000p SYMBOL res 48 256 R0 SYMATTR InstName R6 SYMATTR Value 10k SYMBOL voltage 544 -160 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value 9 SYMBOL voltage -416 128 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V2 SYMATTR Value SINE(0 1m 1meg) TEXT -450 424 Left 2 !.tran 20u
-------------------------------------------------------------------------