It looks complicated but it's not. Q1 and Q2 are the pair in diff pair. What's drawn are regular transistors, though they could be FETs or vacuum tubes. What they are doesn't matter. It's how they are connected that does.
V+in is where the + of a balanced cable would go, V-in is where the second, out of phase, input from the cable goes (Remember? There are two signal wires in a balanced cable).
Ignore all the rest of the squiggles and notes.
Focus instead on where Q1 and Q2 are connected directly together—the two arrows are pointing at this junction. See it?
For purposes of our understanding, this connection of the two transistors is all we're interested in.
Whatever signal is placed on either of the two inputs, an identical copy comes out where the respective arrow is (called the emitter).
If the two emitters have the same signal (because the inputs have the same signal), there is no difference between the two, thus, no current flows. Like a teeter totter with two equal weight people, or closer to home, our example of the two wires of a lightbulb placed on the + terminal of a battery. Nothing flows, because there are no differences.
However—and of course you saw this coming—place opposite signals (out of phase: one rising as the other is falling) in the diff pair's inputs, and current flows.
A new difference
It looks complicated but it's not. Q1 and Q2 are the pair in diff pair. What's drawn are regular transistors, though they could be FETs or vacuum tubes. What they are doesn't matter. It's how they are connected that does.
V+in is where the + of a balanced cable would go, V-in is where the second, out of phase, input from the cable goes (Remember? There are two signal wires in a balanced cable).
Ignore all the rest of the squiggles and notes.
Focus instead on where Q1 and Q2 are connected directly together—the two arrows are pointing at this junction. See it?
For purposes of our understanding, this connection of the two transistors is all we're interested in.
Whatever signal is placed on either of the two inputs, an identical copy comes out where the respective arrow is (called the emitter).
If the two emitters have the same signal (because the inputs have the same signal), there is no difference between the two, thus, no current flows. Like a teeter totter with two equal weight people, or closer to home, our example of the two wires of a lightbulb placed on the + terminal of a battery. Nothing flows, because there are no differences.
However—and of course you saw this coming—place opposite signals (out of phase: one rising as the other is falling) in the diff pair's inputs, and current flows.
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