Analogue electronicscurrent mirrorswilson wikibooks. Applications of bipolar junction transistor or bjt history. Ac analysis defining the important parameters of any system. Bjt differential amplifier similarly for bjt a d g m r c. Drain, gate, source 20080724 v1 c e b q1 rbias 10k rload 3k d1 simple diode current sinking mirror current limitor this is a lesser version of the transistor as diode configuration. Current sources and active loads the transistor biasing techniques introduced in earlier sections are not suitable for the design of ic amplifiers since, even for a relatively simple multistage amplification system, many resistors and large capacitors are required. In chapter 8 we explored the transistor and you should recall that the bjt device is a current amplifier of sorts current controlled current source in that the collector current is. There are two types of applications of bipolar junction transistor, switching and amplification. Problems for amplifier section university of california. Vmin always trades with noise lowest possible noise.
In contrast, unipolar transistors, such as fieldeffect transistors, only use one kind of charge carrier. Bjt circuit practice problems you should do a bunch of these to get ready for quizzes, exams, etc. Introduction the ta will show you the emitter, base and collector for the transistor. A bipolar junction transistor bipolar transistor or bjt is a type of transistor that uses both electron and hole charge carriers. Analogue electronicscurrent mirrorswilson wikibooks, open. The first trick to use bipolar junction transistor as a current mirror circuit is to construct an exponential voltage to current converter using the transistor. Every mirror configuration that can be built with npn transistors can also be built with pnp transistors, and the general behavior, advantages, and disadvantages of each configuration will be the same. Bjt transistor modeling 5 the ac equivalent of a transistor network is obtained by. Replacing all capacitors by a shortcircuit equivalent 3. Ee105 fall 2015 microelectronic devices and circuits prof. Scribd is the worlds largest social reading and publishing site. In any practical circuit, you would lay out the diode as a matched, interdigitated, diodetied bjt.
There are also a number of secondary performance issues with mirrors, for example. Lecture20current mirrors 1 ee105 fall 2014 microelectronic devices and circuits prof. The bjt symbols and their corresponding block diagrams are shown on figure 1. A current mirror with a splitcollector bjt to compensate for the base currents 3 although the splitcollector mirror gain is much more accurate than what is achievable with either the basic mirror or the base current compensated structure of fig. Why cant we replace diode connected bjts by simple diodes in a current mirror circuit. Remember that two equal size transistors at the same temperature with the same v gs or v be for a bjt have the same drain current. The bipolar junction transistor bjt as a switch bipolar.
A currentsteering circuit using mosfet courtesy of sedra and. Basic bjt current mirror with multiple outputs youtube. Conceptually, an ideal current mirror is simply an ideal current amplifier with a gain of 1. Jan 06, 2019 this is just one portion of an endless history of bjt. Additionally we have darlington pairs and a pchannel mirror. Explain why an ordinary junction transistor is called bipolar. Transistor and logic gates laboratory instruction today you will learn how to use a transistor to amplify a small ac signal as well as using it as a switch to construct digital logic circuits. Vincent chang current mirror with multiple outputs pnp current mirrors.
Widlar current mirror design using bjtmemristor circuits. Bjt are called bipolar because both holes and electrons are involved in the. Jan 29, 2017 structure and operation of the basic two transistor bjt current mirror as an ic biasing block. Bipolar junction transistors as switches this worksheet and all related. The basic current mirror can also be implemented using mosfet transistors, as shown in figure 2.
Chapter 16 analog integrated circuits chapter outline 16. It may be used as a wilson current source by applying a constant bias current to the input branch as in fig. Because they have relatively low compliance voltages, they also are called wideswing current mirrors. Bipolar junction transistors bjts questions and answers. With discrete parts and for low frequencies, its easier to just throw an opamp at it. This is a common collector amplifier emitter follower. Basic bjt current mirror with multiple outputs duration. Ee105 fall 2014 microelectronic devices and circuits. Sep 18, 2016 a bipolar junction transistor bipolar transistor or bjt is a type of transistor that uses both electron and hole charge carriers. These semiconductor materials can either be a p type positive with an excess of holes, or a n type negative with an excess of. Important attributes for current sources include high output resistance with a wide range of voltage compliance and rejection of external variations such as power supply or temperature. Because the transistor operation is carried out by two types of charge carriers majority and minority carriers, an ordinary transistor is called bipolar.
Applications of bipolar junction transistor or bjt. However, due to the quadratic term, a very good approximation is achieved for much lower values of. The word transistor is derived from the words transfer and resistor it describes the operation of a bjt i. Current mirror circuit designs using bjt and mosfet. It works in active mode actually and the collector current is a function of the base voltage.
Bipolar junction transistors bjts questions and answers q1. Common emitter bjt amplifier design current mirror design. This paper presents a description of basic current mirror cm, widlar current mirror, fourth circuit element. It is a currentdriven device mosfet is voltage driven, the output current is equal to the input current times a factor which is called gain. Bjt transistor modeling 4 a model is a combination of circuit elements, properly chosen, that best approximates the actual behavior of a semiconductor device under specific operating conditions. Ee105 fall 2015 microelectronic devices and circuits. The bjt current mirror operates by the same method as the mosfet version, but with a few key differences. The zds1009 current mirror has been developed specifically for high side, current sense plus level translation applications and as such will find a broad applications base including battery charge management, dc motor control and over current monitoring functions. Npn transistor an implementation on an ic device construction is not symmetric. The examples tab demonstrates current mirrors, however what it fails to expand on is the efficiency of a current mirror. Zds1009 current mirror datasheet diodes incorporated.
Mar 15, 2020 as we will go through the topic, we will know about the transistor, mainly bipolar junction transistor or bjt. Small signal models are only useful for forward active mode and thus, are derived under this condition. A current mirror is a circuit designed to copy a current through one active device by controlling. The bjt is biased in the active region using the necessary biasing components. This work was supported, in part, by dallas semiconductor corp. Bipolar junction transistors also known as bjts can be used as an amplifier, filter, rectifier, oscillator, or even a switch, which we cover an example in the first section. It is of particular interest for current sense applications for feedback purposes. The bjt is fabricated with three separately doped regions. A wilson current mirror is a threeterminal circuit fig. How to use bjt bipolar junction transistor beginners. Bjt bipolar junction transistor are widely used an amplifier, oscillator, switch etc. Early effect can be combated by using the 4transistor improved wilson current mirror configuration. Bipolar junction transistors are widely used for current mirroring. Current mirrors basic bjt current mirror current mirrors are basic building blocks of analog design.
It is a current driven device mosfet is voltage driven, the output current is equal to the input current times a factor which is called gain. Structure and operation of the basic two transistor bjt current mirror as an ic biasing block. We can easily use enhancement mode mosfets to form current mirrors, as shown in the circuit to the right. The transitors have been replaced by the smallsignal tmodel, which has then been drawn as a largesignal bjt, with the smallsignal output resistances, r o in parallel. Structure and operation of a basic bjt current mirror with multiple pnp and npn outputs. Implementation using discrete transistors the bjt di erential pair is an integral part of op amp integrated circuits. Current sources and active loads university of north. It is not very widely known, but the collector current of the bjt actually depends not on base current, but on the voltage across be junction. If a voltage is applied to the bjt baseemitter junction as an input quantity and the. Electronic circuits 1 highspeed circuits and systems laboratory lect. Characteristics of mosfet current mirrors playhookey.
Generally speaking, this version is preferred over the bjt method if using discrete parts. There are only two differences in using pnp rather than npn transistors in current mirrors. Najmabadi, ece65, winter 2012 simplified physical structure. This is done by providing a voltage across the baseemitter junction of the bjt and. The mirrored current is a precise copy of the input current.
Use a bjt to boost up supplies to multiple base currents. For switching applications transistor is biased to operate in the saturation or cutoff region. The same relationship can be obtained using the equivalent circuit shown in fig. Ref, is the input to the current mirror at the collector of the diodeconnected transistor q. Setting all dc sources to zero and replacing them by a shortcircuit equivalent 2. For its analysis, we assume identical transistors and neglect the early e. The transistor will operate as an amplifier or other linear circuit if the transistor is biased into the linear region. The npn device has one p region between two n regions and the pnp device has one n region between two p regions. The bipolar junction transistor transistor basics 2 the ideal bipolar junction transistor because the current gain. The bjt mirror has two important differences from that of the mosfet. This is problematic for a couple of reasons, most importantly the.
Jan 29, 2017 structure and operation of a basic bjt current mirror with multiple pnp and npn outputs. In addition to the replication, the current drop associated with cmos vs ttl is not clearly explained. In this setup, the output current i out is directly related to i ref, as discussed next. Figure 3 shows a mirror using negative feedback to increase output resistance. The output resistors in q1 and q2 are present in this model, but they are greyed out as they do not play a part in the analysis. Bjt field effect transistor bipolar junction transistor. Ece 255, current sources, mirrors etc purdue engineering. As we will go through the topic, we will know about the transistor, mainly bipolar junction transistor or bjt. Transistor m 1 is operating in the saturation or active mode, and so is m 2. In this experiment, we will make up the circuit using discrete.
Bjt wilson mirror a wilson current mirror is shown in fig. In addition to the replication, the current drop associated with. Check out the hybridpi model for more insight, and try some sims with a small base voltage added to one of the transistors. An oftenused circuit applying the bipolar junction transistor is the socalled current mirror, which serves as a simple current regulator, supplying nearly constant current to a load over a wide range of load resistances. Circuit ideahow the wilson current mirror equalizes the. The emitter current in q3 is io this current is the input to a basic current mirror consisting of q1 and q2. Bipolar junction transistors tlt8016 basic analog circuits 20052007 3 basic operation in the active region figure 4. Because of the op amp, these circuits are sometimes called gainboosted current mirrors.
Discretecircuit bias c e c c2 c c1 c e c c2 c c1 bias with single supply bias with two supplies. Lecture08 current sources university of california, berkeley. Small signal model of a bjt just as we did with a pn diode, we can break the bjt up into a large signal analysis and a small signal analysis and linearize the non linear behavior of the ebers moll model. Therefore voltage across r 3 varies as the collector current is passing through it. Just as we connected collector to base with bipolar junction transistors, we can connect drain to gate of a mosfet to cause the device to operate as a forwardbiased diode. An example application of the current mirror is the transconductance op amp.
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