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The voltage across R forward biases the emitter junction.
This voltage effectively reverse-biases the emitter junction and little current flows in the device.
The negative supply V is used to forward-bias the emitter junction through R.
Turns out it's very simple, just a diode biasing a base emitter junction on a transistor.
The base emitter junction of the transistor has therefore a low voltage across it and the collector current is negligible.
As R1 doesn't go to 0v the base/emitter junction never gets masses of reverse voltage and hence doesn't breakdown.
This reduction in resistance means that the emitter junction is more forward biased, and so even more current is injected.
C1 charges up via the base/emitter junction of the transistor, providing enough current to turn it on and bypass the 27 ohm resistor.
The charge gradient is increased across the base, and consequently, the current of minority carriers injected across the emitter junction increases.
The RF is then rectified when it flows through the base/emitter junction of a bipolar transistor.
The emitter junctions of these amplifier stages are fed by the collectors of a third differential pair (Q2/Q6).
In audio stages using discrete transistors, this is due to rectification at the base/emitter junctions of transistors after the volume control.
Once you do this you will see a diode in series with a base/emitter junction, which itself is a diode so the diode can go as well.
However if we apply a positive-going voltage to the emitter greater than XVB the emitter junction is now forward-biased and a large emitter-base 1 current flows.
Good results in contacting extremely shallow polysilicon emitter junctions have been obtained using sputtered Ti overlaid with a TiW barrier layer and then with aluminum.
A UJT is operated with emitter junction forward- biased while the JFET is normally operated with the gate junction reverse-biased.
The emitter junction is usually located closer to base-2(B2) than base-1(B1) so that the device is not symmetrical, because symmetrical unit does not provide optimum electrical characteristics for most of the applications.
It was fixed by placing a selenium diode across the base emitter junction of the transistor making it "think" it was a selenium transistor (if there could ever be one).
Because the base region is very lightly doped, the additional current (actually charges in the base region) causes conductivity modulation which reduces the resistance of the portion of the base between the emitter junction and the B2 terminal.
This is very important as it is evident from scanning ion mass spectrometry data that out-diffusion base dopant into the emitter junction is difficult to control, as the base is, in general, very highly doped in order to enhance performance.
The structure of a UJT is similar to that of an N-channel JFET, but p-type (gate) material surrounds the N-type (channel) material in a JFET, and the gate surface is larger than the emitter junction of UJT.