Figure 1

Bipolar junction transistor

Bipolar junction transistor (BJT) is a type of transistor using both electrons and electron holes as charge carriers. In contrast, a unipolar transistor, like field-effect transistors (FETs), uses 1 kind of charge carrier. A bipolar transistor lets small current to inject at 1 of its terminals to control much higher currents between the other 2 terminals, making the device able of amplification/switching.

bipolar: device with current carried by 2 charge carrier types (both electrons and holes)

View for other definitions

junction: semiconductor transition part between where conduction is mainly by electorns and where mainly by holes
transistor: semiconductor device acting as a switch/amplifier, controlling electrical current flow via a small input signal
- semiconductor: solid substance with an insulator and metal's conductivities
  - insulator: a substance that won't readily let heat/sound flow
- electron hole/hole: positive charge carriers, representing an electron's absence in the semiconductor material
charge carrier: particle carrying electric charge and let current flow in a material (e,g, electrons, holes)
unipolar: device with current carried only by 1 charge carrier type (e.g., elecrons or holes)

[6] Figure 11

[3] Figure 2

Components

A BJT has 3 parts: the emitter, base, and collector, which makes 2 p–n junctions between 2 semiconductor types: the emitter–base and base–collector junction.

p-n junction: boundary where p and n-type semiconductor materials meet
- boundary: dividing line between 2 regions of different doping

In both NPN and PNP BJTs:

The emitter–base junction is often forward-biased (i.e. to let to reduce the junction's barrier) to let charge carriers flow from emitter to base.
The base–collector junction is often reverse-biased (i.e. to increase the junction's barrier) to block current from base to collector and collect the carriers.

n-type and p-type properties

A n-type (semiconductor) is a material (e.g., silicon) doped with impurities (e.g., phosphorus, arsenic) with extra valence electron (crucial they can be excited to move through the material, allowing it to conduct electricity.), creating a surplus of free electrons acting as majority negative charge carriers, hence "n"
- - to dope (in electronnics): to intentionally introduce impurities into a pure (intrinsic) semiconductor to modify its electrical properties and increase its conductivity
    - intrinsic: material in its purest natural form, prior impurities are added
  - surplus: amount left over if requirements are met
A p-type (semiconductor) is the same material dope with other impurities (e.g., boron, aluminum) but with excess holes (missing electrons), acting as majority positive charge carriers, hence "p"

Note: Negative carriers refer to electrons but, positive carriers don't refer to protons (which are positive subatomic particles), but holes (missing electrons) instead.
The charge carriers (holes/electrons) of the semiconductors don't work the same way as the convential current that flow on a circuit. Thus,

A BJT's terminals' names originate from the type of doping, not the direction of current flow:

In a PNP BJT, true to their names:

Emitter (p-type) “emits” holes (charge carriers not conventional current flow) out of the BJT.
Base (n-type) is called that as it's the “base layer” between the emitter and collector. Small base current in it controls the larger current from emitter to collector.
Collector (p-type) “collects” the holes into the BJT to the base.

Similarly in a NPN BJT:

Collector (n-type) collects the electrons flowing from the emitter and sends it out (Fig. 11).
Small current flows in the base (p-type) controls the larger current from emitter to controller.
Emitter (n-type) emits electrons instead (not holes) into the BJT to the base.

Figure 11 conventional current flow (in red) and charge carrier (in cyan) flow on an NPN BJT circuit.

The opposite direction on a PNP BJT.

The junctions can be made in many ways, like changing the semiconductor material's doping as it is grown, by depositing metal pellets to form alloy junctions, or by such methods as diffusion of n-type and p-type doping substances into the crystal. The superior predictability and performance of junction transistors quickly displaced the original point-contact transistor. Diffused transistors, along with other components, are elements of integrated circuits for analog and digital functions. Hundreds of bipolar junction transistors can be made in one circuit at a very low cost.

Bipolar transistor integrated circuits were the main active devices of a generation of mainframe and minicomputers, but computer systems now use complementary metal–oxide–semiconductor (CMOS) integrated circuits relying on the field-effect transistor (FET). Bipolar transistors are still used for amplification of signals, switching, and in mixed-signal integrated circuits using BiCMOS. Specialized types are used for high voltage and high current switches, or for radio-frequency (RF) amplifiers.

Operation

Formulae and notations

Note: Be careful with what formula to use as certain ones depend on the type of BJT circuits. E.g.,

β or hFE (beta) is the transistor’s current gain: ratio of the collector current IC over base current IB: β = IC/IB.

[9] It's often constant if the BJT is on and in active region (if it changes based on VCE). β ratio is often 20-500.

[9] α (alpha) is the ratio of the DC IC to DC IE: α = IC/IE or α = β/(β + 1). It's a bit less used constant pertaining to BJTs. Usual values is often 0.95 to 0.99+, but often under 1.

For more exercises see: Bipolar junction transistor (BJT) exercises

Basics (normal BJT circuits/fixed-bias):

Note: Voltage values (VC, VB, VE) at a point in a BJT refers to the voltage at the node relative to ground (one probe at the node and to ground); E.g., VC refers to a node's voltage at collector terminal and another one to ground.

VC (collector voltage):
- VC = VCC - ICRC
VB (base voltage):
- VB = VE + VBE
- VB = VCC (R2/(R2 + R1)]
VE (emitter voltage):
- VE = IERE
VCB ()
- VCB = VC - VB
VBC ()
- VBC = VB - VC
VBE ()
- VBE = VB - VE
VCE (collector-emitter voltage)
- VCE = VBC + VBE
- VCE = VC - VE
- VCE = VCC - ICRC
- VCEQ (quiescent collector-emitter voltage) is a crucial parameter defining a BJT's DC operating point (Q-point) alongside the quiescent collector current (VCQ). It's the steady DC voltage between the collector and emitter terminals without AC signal applied, determining where a BJT sits on its characteristic curves and if it amplifies (active region) or acts as a switch (saturation/cutoff).
VBB (base bias voltage): The voltage source supplying a BJT's base and sets IB through RB. The double letter just refers to the terminal it powers.
- VBB = VCC [(R2/(R2+R1)]
- VBB = IBRB + VBE
VCC (collector supply voltage) is the voltage source powering a BJT's collector and provides energy to the IC through RC.
- VCC =

Active/Forward mode voltages (NPN):

Si BJT: VBE ≈ 0.6-0.7 V
Ge BJT: VBE = 0.2-0.3 V
VC < 0 (CB junction reverse-biased)
VCE > VCE (saturation) (often > 0.2 V)

Saturation mode (NPN):

VBE ≈ 0.7 V
VBE = VBE (saturation) ≈ 0.2 V
VBC = 0.5 V (CB junction forward-biased)

Currents:

[9] IB: collective current/current at the collector
- IB = (VCC - VBE)/RB
IC: base current/current at the base
- IC = β*IB

This equation is for current gain as it relates to total beta and total collector current: IC = βIB

[9] Note: Crucial things to note for this equation: BJT must be in active region for this to apply. The rule itself has 2 subrules to heed:

[9] Rule 1: In NPN BJTs, IC must be at least a few 10ths of 1 volt higher than IE. In PNP BJTs, VE must exceed VC by a close amount. Otherwise no current flows through the BJT no matter the VB.
[9] Rule 2: There is a ~0.7 V drop from base to emitter (VBE) in an NPN BJT and a 0.7 V rise of VBE in a PNP.

E.g., In a NPN transistor, this means VB must be at least 0.7 V higher than the VE to overcome the diode drop. Otherwise, the BJT stays off. This expression explains this rule mathematically: VBE = VB – VE = 0.7 V (or -0.7 V for a PNP device)

Emittive current/Emittor's current: IE = IC + IB
Note: Due to IB being much smaller than IC, we often assume IE equals to IE: IC ≈ IE

Voltages

VBE = voltage across the base and emitter

E.g., Consider a NPN BJT: If a small (conventional) current of 3 mA to the BJT's base (B = 3 mA).

If β = 100, then collective Ic would be a 100x times greater than the IB.

Max BJT ratings

Maximum BJT ratings are symbols found on a transistor's datasheet, which are the limits the device can withstand without damage.

Max voltage between C and E with base open: VCEO
Max reverse voltage between C and B with base open: VCBO
Max reverse voltage between E and B with base open: VEBO
Max collector current (also): IC or ICmax
Max power dissipated: PD = ICVCE
Max temperature for an internal silicon junction: TJ or TJ max

Reverse and foward-biased

“Biased” means a voltage is applied to a junction in a way to control how it conducts current flow.

Forward-biased junction: Voltage lets current flow (reduces the barrier).
Reverse-biased junction: Voltage blocks current flow (increases the barrier).

Not 1, but 2 terminals can only be “forward/reverse-biased”, since a BJT comprises of 2 diodes, connected with their matching terminals (anode for NPNs or cathode for PNPs) connected to each other to form the base of the BJT and their opposite terminals (cathodes for NPNs or anode for PNPs) pointing outward diagonally in the shape of a half 'X'. Thus, one is the (upper diode) collector-base diode (call it diodeCB) and one is the (lower diode) emitter-base diode (call it diodeEB).

Note: The diodes are also referred/represented as a junctions.

(NPN and PNP) BJTs have 3 modes (or 4, if counting active mode as 2 individuals modes) they can be in:

active, forward, or forward-active mode
- BE junction: forward
- BC junction: reverse
reverse or reverse-active mode (often counted as a single mode with forward mode)
- BE junction: reverse
- BC junction: forward
cutoff mode
- BE junction: reverse
- BC junction: reverse
saturation mode
- BE junction: forward
- BC junction: forward

An NPN in active mode's diodeCB is always reverse biased and the diodeEB is always forward biased. In a PNP, this is the complete opposite.

If either junction’s bias changes, both PNP or NPN BJT leaves active mode, becoming a switch:

both junctions forward → saturation BJT (fully on state)
both junctions reverse → cutoff BJT (off state); as shown by this table below; and
1 junction forward, one junction reverse → active BJT (amplified on state)

NPN BJT

A NPN BJT is basically comprised of 2 regular diodes with their anodes connected, acting as the base, and their cathodes facing the other way, acting the collector (upper diode) and emitter (lower diode). Whereas, the PNP's diodes are just reversed. In active mode, the base–emitter is forward biased and base–collector reverse biased.

Figure 3

Figure 4

[3] Water pipe analogy (for NPN BJT) In the vertical part (BJT's collector), a horizontal red door controls if water (current) flows down into the lower part (BJT's emitter). A vertical door controling its own water floor there in the horizontal part (BJT's base) of the pipe also controls the red door.

Without pressure on the horizontal door, it holds water.

Like on an NPN BJT: If voltage is used on the emitter and collector and the base isn't forward-biased, current won't flow from the BJT.

Figure 5

Figure 6

[3] If enough water flows into horizontal tube, the vertical door opens. A certain lower water amount won't open door. If the vertical door is open, this is the transistor's active mode (VBE). As the vertical door opens, so will the horizontal door to let water flow.

Same as we apply the BJT's base to emitter voltage, current flows throught the collector to the emitter. This can occurs if voltages as low as 0.7 V and 1 mA current, it's enough to turn the BJT on.

Note: The (conventional) current shown moving (in red in Fig. 6) in the circuit doesn't work like the charge carriers (electrons/holes). The charge carriers flow in the opposite way of both PNP and NPN BJTs.

Thus, when active, a NPN's conventional current flows into the collector and out of the emitter, but vice versa for its charge carriers, which flow into the emitter and out of the collector

Figure 11

Overally, ideally, regardless how much current the collector gets (tube's upper part), if the base receives under the needed current amount, the BJT is stays off (neither the collector or base opens).

The base controls the collector, both for PNP and NPN.

[2.2] If we provide a fixed IB and connect AC voltage to the collector resistor, what we measure on the VCE as shown on this oscilloscope, with the IC as the y-axis, which is constant after ~0.2 V and VCE as the x-axis.

Adjusting the IB moves the graph upside down.

[]

Characteristic curves

[2.2] The full characteristic graph of each IB is drawn as so on the left.

The region after the red dotted line, where IB is almost constant is the active region, where IC only changes based on the VCE.

The region where IC (due to VCE being too low) is the saturation region.

But eventually, pushing VCE too high (in this passing value 12 on the x-axis, IC rises combined to the high voltage overheats and kills the BJT.

[2.2] If we connected the emitter to ground, the collector will turn on and pull in large current from the base to the collector (diode) which should be avoided.

PNP BJT

[2.2] A PNP is like a NPN BJT but with its diodes reversed by connecting their cathodes to be the base and their anode acting in the opposite way of NPNs, as the collector (lower diode) and emitter (upper diode) terminals.

If VBE = -0.6 V pulling current from the base to the emitter, we'll have a IC flowing beta time larger than IB: IC = βIB.

[8.1]

Characteristic curve

A PNP BJT's characteristic curve is similar to a NPN, but reversed.

Figure 7

Figure 8

Figure 9

[3] Water pipe analogy (for PNP BJT) Consider a NPN transistor BC547 (Fig. 10). The tube's upper part for this is the emitter. Its collector is the lower part. The base is the horizontal part. If the tube's horizontal part receives water, it stays closed.

For as a PNP BJT's base connected to positive (Fig. 8), as the base gets positive voltage, it turns off/stays off. Without water at the horizontal part opens the part to let water flow.

Connecting the base to negative voltage (Fig. 9) (causing current flow into the emitter) turns on the BJT as long as the base has lower current (less positive) than the emitter or the emitter has more positive voltage than it (is more positive),

Figure 10

Note: Again, the (conventional) current and charge carrier of a PNP BJT move move in the same direction as in a NPN. If active, a PNP's (conventional) current flows into the emitter and out of the collector, but vice versa for its charge carriers.

Overall, a PNP BJT's emitter connects to positive voltage, and gets the voltage and its collector outputs the current.

But a NPN BJT's emitter connects to positive voltage, and gets the voltage and its collector outputs the current.

[2] We can also use an NPN BJT as a switch by connecting a load between the power supply's positive voltage and the BJT's collector. Using a limiting-current resistor turns the BJT on.

[2] To use a PNP BJT as a switch, connect a load between the power supply's negative voltage and the BJT's base.

Modes

Both PNP and NPN BJTs work in 3 (or 4) different modes/regions: Cuttoff, saturation, and active mode.

[2] Cuttoff mode: BJT is off, with the collector and emitter are reverse bias (no conduction)
Active mode: BJT is on and current is collector current is proportional to base current. I.e., Back to the water pipe analogy, the vertical pipe's water amount is proportional the horizotal pipe's water amount. The relationship between the collector current and base current is defined by the formula: IC = IB x β.
- IC = collector curent
- IC = base current
- β (beta) = current gain; ration of collector current to base current

On active mode, a BJT is used as an amplifier.

Saturation mode: BJT is considered as on but the current flowing in the collector varries little to change in base current. Thus the BJT at this mode is fully on, where output voltage drops to a near 0 value.

To use a BJT as a switch, use it cuttoff and saturation mode. To use it as an amplifier, use it in active region.

Reverse-active mode:

Circuit types

Fixed-bias circuit

A fixed-bias circuit is a BJT circuit with no RE, only 1 RB, and no voltage divider resistors.

Voltage-divider circuit

A voltage divider BJT circuit has both a RC and RE, as well as 2 additional resistors, often notated as R2 and R1 on the opposite side of RC and RE. The formulae used for this circuit are also different:

VB = VCC [R2/(R2+R1)] is for a voltage divider BJT circuit, whereas a normal fixed-bias BJT circuit VB is calculated as: VB = VCC-VBE.

Self-bias circuit

A self-bias circuit BJT circuit has RB and RE used to transistor’s operating point stabilizes automatically. This emitter resistor RE creates negative feedback: If IC rises, VRE rises, and both VBE and IC reduces. This makes the circuit more stable against variations in β or temperature.

IE causes a voltage drop across RE, reducing the VBE, seen by the transistor.

to "see" (in electrical circuit analysis): to be affected by

Since a self-bias BJT's base sees the voltage drop across RE, we must modify the fixed-bias formula of IB (IB = (VCC-VBE)/RB) to add (β+1 )RE, as the denominator, in series to RB:

IB = (VCC-VBE)/[RB+RE(β +1)]

BJT as switches

[9] When designing amplifiers and analog circuits, we often use BJTs as a switch. One can use a transistor as a switch IO a mechanical switch, because of a few reasons.

First, transistors can switch on/off very fast, often a fraction of a micro-second.

They can be driven from other circuits (e.g., a microcontroller) unlike a mechanical switch, which also wear out and contacts bounce while transistors won't. There are more reasons.

This circuit uses a switch to control if current from the 6 V source should be sent to the BJT's base through resistor R1. If the base receives a certain amout of current, the larger current from the same source, across R2, then to the green LED will be allowed throught the BJT's collector terminal

Assuming β = 200

To calculate the voltage the multimeter (labeled 'M') reads (i.e., the VC):

To calculate VC, we must calculate the current per branch.

- Via KVL, we know the voltage in the loop of the voltage source, switch, R1, and the BJT's E terminal must add up to 0 V.
Finding IB: The BJT's base is 0.6 V higher than its emitter, thus VBE ≈ 0.6 V. So the voltage on R1's branch is 6V - 0.6V = 5.4 V, where the current there is: 5.4V/500kΩ = 0.0108 A = 10.8 mA
Finding IC: IC = IB x β = 10.8mA x 200 = 2.16 mA, thus we know that 2.16 mA flows in the branch of R2 and the green LED.
Finding votage at point V: Labelling the voltage before the resistor as 'A' and voltage after it as 'D', then voltage at point D is what we need. So the potential difference of R2 is VA - VD = VR2, rearrenging for VD gives VD = VA - VR2. We've calculated IR2 = 108 mA, then its voltage is VR2 = 2.16mA x 1kΩ = 2.16 V and VD = 6V - 2.16 V = 3.84 V.
Since the average voltage of an LED is 2.2 V, then VC = 3.84V - 2.2V = 1.64 V will be measured by the multimeter.

BJT switches with inductors

[S1] E.g., Consindering this NPN BJT circuit with an inductor instead of a RC. As the transistor turns from on to off, current across the inductor causes a big voltage spike across VCE. The spike easily exceed VCE breakdown voltage, damaging/burning out the transistor.

[S1] In detail, this works as the BJT is on, current flows into the inductor and energy is stored in its magnetic field. As the BJT turns off, the inductor tries to keep the same current flow by, creating a very high voltage (inductive kickback). The voltage spike appears across the BJT's VCE exceed VCE breakdown.

[S1] Thus, a "flywheel"/"protection" diode is a a type of snubber diode to be used across the inductor to provide a discharge path to its current.

The diode works as it gives the inductor a safe current path as the transistor turns off. IO a big voltage spike, current flows into the diode and coil. Voltage is clamped to ~0.7 V, protecting the transistor.

BJT as inverters

Consider this circuit:

If 5 V is at the input, the current flowing across R2 and into the base is: 5V/10kΩ = 0.0005 A (and 9V/1kΩ = 0.009 A across R2 and into the collector), which is the same as the current base needed to drive the BJT (IB needed = IC/β = 0.009A/18 = 0.0005 A), on the edge of driving the BJT to saturation mode, thus dropping the output voltage to near 0.
If 0 V is at the input, the base receives no current, so no current flow across the BJT and R1.

Without current flow across a resistor, no voltage drop occurs across the resistor, the resistor does nothing and 9 V is at the C terminal.

BJT as amplifiers

[S1] Now the input is a sinuisoidal signal. The output signal is now seen across VS. The output signal is seen across VCE. To amplify this input, we need the BJT to work in active mode. Thus base-emitter must be forward biased and base collector must be reverse biased. VCE provides forward bias for base-emitter and establish an appropriate reverse bias for base collector.

To determine the base point, the load line along the collector characteristics is mode illustrative. As IS changes, IC and VCE follow the load dline. Recall the BJT being used as a switch works in cutoff and saturation. When using a BJT as an amplifier, we want the bias point on the active region, at the center of the active region.

The quiescent (Q) point/operating point, is a BJT amplifier's stable DC operating point amplifier in the active region. The Q point is the IC's point and VCE when no AC input signal is used. To use a BJT as an amplifier, the Q-point must be in active region of its characteristic curves. The load line is a graphical representation of all potential combinations of IC and VCE in a zurve. Setting the Q-point appropriately ensures the AC signal amplifies without being distorted (cut off/saturated).

[S5]

[13.1]

[S1] IB without AC signal is: IB = (VBB - VBE)/RB = (4.7V - 0.7V)/100kΩ = 4e-5 A = 40 μA
Ic = β x IB = 107 x 40μA = 4.3 mA
VCEQ (quiescent collector-emitter voltage) is calculated via KVL for the collector-emitter loop with supply voltage VCC being 20 V and collector RC being 2.5 kΩ:

VCEQ = VCC - ICRC = 20V - (4.3mA x 2.5kΩ) = 20V - 10.75V = 9.25 V

[S5]

BJT fixed bias amplifier

This is an akin circuit as the previous one.

This establish a stable DC operating point (Q-point) for the BJT to act as a linear AC amplifier without distortion.

IO 2 power supplies, it only uses VCC. Input and output coupling capacitors (both CC) are added, which block DC and pass AC signals for proper amplification.

The AC input is fed into the BJT's base, which often assumes a small signal input.

In a DC analysis (understandinghow a circuit responds to DC signals), the capacitors are treated as open circuits (removing them to be a break in the wire). IB, IC, VCC determine the Q-point parameters: IC, IB, VCE.
In a AC analysis (understanding how a circuit responds to AC signals), DC sources grounded, capacitors treated as short circuits (offers 0 resistance). The circuit's external resistors and BJT's internal AC parameters determine the amplifier performance characteristics (voltage gain, input impedance, and output impedance).

The same equations is applied as previous ones:

IB = (VBB - VBE)/RB
Ic = β x IB

VCE = VCC - ICRC

[S5] The fixed bias circuit highly dependent on βDC.

[2.3]

[14]

Characteristic curves

A BJT's characteristic curve tells how IC versus VCE behave at various IB values, each represented as individual curve, where IC is the y-axis, which is dependent on VCE, the x-axis. [7.2] To generate these curves we drive the base with a fixed current source establishing IB. . A DC power supply connects from the collector to emitter, then swept from 0 volts to some upper value, establishing VCE. Meanwhile, we track the resulting IC and plot the result. The IB then increases and the supply swept again for a second trace. Repeating this process results in Fig. 4.3.1.

trace: individual curve on a plot

The bottom is when IB = 0 and corresponding IC = 0 with tiny leakage current, called the collector-emitter current with the base terminal open (ICEO), i.e., no base current. Above curves are higher IB values, all at a fixed amount per subsequent trace (0 μA, 10 μA, 20 μA, 30 μA, etc).

[7.2] The curves have 3 parts vertically:

The leftmost part is the saturation region where current rises rapidly. It's used in transistors switching applications.
The breakover point (VCE (sat)) is small, just a volt's few tenths and is located at the leftmost side of the graph with the the breakdown point on the rightmost.
The breakdown region (collector to emitter voltage with an opense base BVCEO) is where current rises rapidly again, the same effect of individual diodes. Devices don't opreate in this region as damage are likely. For general purpose devices. that's in the range of 30-60+ V.
The active region is between these 2 extremes, where IC is constant, where we use the BJT for applications like linear amplifiers.

[7.2] A curve tracer device is used to generate these curves.

[7.2] To calculate β via the curves:

E.g., If a BJT operates at IC = 4 mA and VCE = 30 V. Assume the IB rises 10 μA per trace.

Find the circuit's IC and VCE, and the point on the graph and the nearest line to the point (in this case (30, 4)).
From VCE's intersection to the trace, track back to the x-axis (a bit higher than 4 mA, at ~4.2 mA) to find the IC's value for that trace.
Determine the IB's step size to find its corresponding value: Here, the VCE intersects the 5th trace, where the bottom horizontal one is when IB = 0, so this trace is IB = 40 .
- step size: increment IB rises between each trace.
Then divide IB by IC values to get β: β = IC/IB = 4.2mA/40μA = 105

[7.2] IC rises as VCE as does, is because VCE is responsible for an increase in VCB (VCE = VCB + VBE), the revrese-bias potential on the collector base PN junction.

As this reverse potential rises, IB depletion region widens, penetrating more into the base and narrowing it, thus reducing chances of recombination, thus reducing IB and increasing β.

[7.2] If we extend the coonstcurrent region traces back into the 2nd quadrant they intersect at a point called the Early Voltage (for James Early) and denoted as VA.

https://youtu.be/2uowMENwiHQ

History

[1] The bipolar point-contact transistor was invented in December 1947 at the Bell Telephone Laboratories by John Bardeen and Walter Brattain under the direction of William Shockley. The junction version known as the bipolar junction transistor (BJT), invented by Shockley in 1948, was for three decades the device of choice in the design of discrete and integrated circuits. Nowadays, the use of the BJT has declined in favor of CMOS technology in the design of digital integrated circuits. The incidental low performance BJTs inherent in CMOS ICs, however, are often utilized as bandgap voltage reference, silicon bandgap temperature sensor and to handle electrostatic discharge.

Bipolar junction transistor

Components

n-type and p-type properties

Operation

Formulae and notations

Reverse and foward-biased

NPN BJT

Characteristic curves

PNP BJT

Characteristic curve

Modes

Circuit types

Fixed-bias circuit

Voltage-divider circuit

Self-bias circuit

BJT as switches

BJT switches with inductors

BJT as inverters

BJT as amplifiers

BJT fixed bias amplifier

Characteristic curves

History

Types

References

Textbook

Quiz

See also

Site navigation

Main Site

Science Site

Math Site

Computer Science Site

Usual headlines

Definition structures

Headlines for references

Webcull - to store all links

Legend: