Analog Electronics In A Day Analog Electronic Design Bipolar Junction Transistor BJT Comes in two flavors nPn and PnP · High input current Excellent bandwidth Silicon, germanium, and gallium-arsenide Input circuit looks like a diode Output circuit is high impedance Excellent high speed switches 1-27 The bipolar junction transistor is often shortened to BJT. The Bjt was the workhorse of the semiconductor industry until the field effect transistor (FET manufacturing process was perfected. Since then the FET has been taking sockets from the BJT, but there are many applications, such is high frequency amplifiers, where the BJT still excels. Also, the BJT manufacturing process can be simple and inexpensive, and this, coupled with the BJTs long list of captured sockets, insures that the BJT will be around for a long time
1-27 Analog Electronics In A Day Analog Electronic Design 1-27 • Comes in two flavors: NPN and PNP • High input current • Excellent bandwidth • Silicon, germanium, and gallium-arsenide • Input circuit looks like a diode • Output circuit is high impedance • Excellent high speed switches The bipolar junction transistor is often shortened to BJT. The BJT was the workhorse of the semiconductor industry until the field effect transistor (FET) manufacturing process was perfected. Since then the FET has been taking sockets from the BJT, but there are many applications, such as high frequency amplifiers, where the BJT still excels. Also, the BJT manufacturing process can be simple and inexpensive, and this, coupled with the BJT’s long list of captured sockets, insures that the BJT will be around for a long time
Analog Electronics In A Day Analog Electronic Design BJT Description Collecto Collector Base Base N P B NPN B PNP E 1-28 BJT transistors have three areas that are doped differently to produce different transistor actions these three areas are called the base emitter, and collector. The base and collector are doped to have the same polarity which can be positive or negative. The BJT, like most transistors, come in two types called NPn or PNP P stands for positive, N stands for negative, and the positive or negative regions gain their name from the doping of the semiconductor material making up the base, collector and emitter areas of the bjt An npn transistor looks like two diodes with the anodes connected. the anodes connection is called the base. one cathode is the collector and the other cathode is called the emitter. Although this illustration would not work, it does have a basis in fact because if the width of the base junction were decreased enough, the back-to-back diodes would function as transistor Using the back-to-back diode model, transistors are commonly checked for short circuits and open circuits with an ohmmeter. It then is no surprise that the base-emitter circuit of a BJT looks like a forward biased diode and the base-collector looks like a reverse biased diode
1-28 Analog Electronics In A Day Analog Electronic Design 1-28 NP N PN P Base Emitter Collector Base Emitter Collector B C E B PNP C E NPN BJT transistors have three areas that are doped differently to produce different transistor actions. These three areas are called the base, emitter, and collector. The base and collector are doped to have the same polarity which can be positive or negative. The BJT, like most transistors, come in two types called NPN or PNP. P stands for positive, N stands for negative, and the positive or negative regions gain their name from the doping of the semiconductor material making up the base, collector and emitter areas of the BJT. An NPN transistor looks like two diodes with the anodes connected. The anodes connection is called the base, one cathode is the collector, and the other cathode is called the emitter. Although this illustration would not work, it does have a basis in fact because if the width of the base junction were decreased enough, the back-to-back diodes would function as a transistor. Using the back-to-back diode model, transistors are commonly checked for short circuits and open circuits with an ohmmeter. It then is no surprise that the base-emitter circuit of a BJT looks like a forward biased diode, and the base-collector looks like a reverse biased diode
Analog Electronics In A Day Analog Electronic Design BJT Model o Collector ↓② The model input looks like a forward biased diode, and the input impedance equation is ZiN=Te=1c/26. The base-emitter junction must be forward biased, thus there is a forward voltage drop of vBe. VBE approximately 0.6 volts in a silicon transistor, and 0.2 volts in a germanium transistor. The input current is called IB Since the collector-base junction is reverse biased, the collector current flows from the collector to the emitter. The collector current equation is Ic B(B) where p is the current gain of the transistor. The impedance of the collector-emitter junction is called rc, and rc is very high(in the MQ range) Current gain and the forward voltage drop are a function of the manufacturing process, temperature, and several other items, hence they are not a stable parameter BJT circuits which depend on p and beare not stable; thus, in well designed BJT circuits, the external components stabilize these parameters with feedback
1-29 Analog Electronics In A Day Analog Electronic Design 1-29 Collector r βIB=IC C Emitter VBE IB re Base The model input looks like a forward biased diode, and the input impedance equation is ZIN = re = IC/26. The base-emitter junction must be forward biased, thus there is a forward voltage drop of VBE. VBE is approximately 0.6 volts in a silicon transistor, and 0.2 volts in a germanium transistor. The input current is called IB. Since the collector-base junction is reverse biased, the collector current flows from the collector to the emitter. The collector current equation is IC = β(IB) where β is the current gain of the transistor. The impedance of the collector-emitter junction is called rc, and rc is very high (in the MΩ range). Current gain and the forward voltage drop are a function of the manufacturing process, temperature, and several other items, hence they are not a stable parameter. BJT circuits which depend on β and VBE are not stable; thus, in well designed BJT circuits, the external components stabilize these parameters with feedback
Analog Electronics In A Day Analog Electronic Design Junction field effect transistor JFET Comes in two flavors: P-channel and N-channel Low input current · Excellent bandwidth Input circuit looks like a diode Output circuit is high impedance Excellent input amplifiers 1-30 The junction field effect transistor is called the JFET, and it comes in two flavors, P-channel and n-channel. It has a high input impedance, so it is often used as the input circuit for amplifiers. The JFET has a high bandwidth, but circuit topologies and restrictions do not enable it to achieve the same high bandwidth, high voltage swing circuits of the BJT Very often the JFET is used as the input stage to achieve high input impedance, and it can achieve high bandwidth with small signal swings of the input circuit JFETS and BJTs can be made with the same process, thus they are often combined to make a high input impedance, high bandwidth amplifier. The JFET output impedance is high in the off state and low in the on state
1-30 Analog Electronics In A Day Analog Electronic Design 1-30 • Comes in two flavors: P-channel and N-channel • Low input current • Excellent bandwidth • Input circuit looks like a diode • Output circuit is high impedance • Excellent input amplifiers The junction field effect transistor is called the JFET, and it comes in two flavors, P-channel and n-channel. It has a high input impedance, so it is often used as the input circuit for amplifiers. The JFET has a high bandwidth, but circuit topologies and restrictions do not enable it to achieve the same high bandwidth, high voltage swing circuits of the BJT. Very often the JFET is used as the input stage to achieve high input impedance, and it can achieve high bandwidth with small signal swings of the input circuit. JFETs and BJTs can be made with the same process, thus they are often combined to make a high input impedance, high bandwidth amplifier. The JFET output impedance is high in the off state and low in the on state
Analog Electronics In A Day Analog Electronic Design JFET Description Drain Source Source N-Channel P-Channel 1-31 The JFET can be visualized as a bar of doped silicon that has a diode junction made in the middle of the bar. If the silicon bar is doped N, then the JFET is called a N-channel device. When the n-channel gate negative with respect to the source the diode is biased off, the bar is depleted of carriers, and the source to drain resistance is quite high (several MQ2). When the n-channel gate is positive with respect to the source the diode is biased on the bar is flooded with carriers thus causing a low source to drain resistance(as low as mQ2). The converse is true for a P-channel JFET
1-31 Analog Electronics In A Day Analog Electronic Design 1-31 N-Channel P-Channel Source Drain Gate Source Drain Gate The JFET can be visualized as a bar of doped silicon that has a diode junction made in the middle of the bar. If the silicon bar is doped N, then the JFET is called a N-channel device. When the n-channel gate is negative with respect to the source the diode is biased off, the bar is depleted of carriers, and the source to drain resistance is quite high (several MΩ). When the n-channel gate is positive with respect to the source the diode is biased on, the bar is flooded with carriers thus causing a low source to drain resistance (as low as mΩ). The converse is true for a P-channel JFET