Calculating the output resistance of a widlar current source. Widlar current mirrors,wilson current mirrors and cascoded current mirrors. Specifics of using current mirrors for highside current measurements in detector power supplies george mitev mitev abstract in this article are described novel, current mirror based, highside current measurement circuits for ionizing radiation detector power supplies. The analysis has been performed by comparing a modified configuration with a simple circuit of widlar cm. The q2 re2 combination is a widlar cur rent source. Without the transistor being there the circuit would make a really poor current mirror source. There are many good resources online and in textbooks on current mirrors. To improve the output of basic current mirror circuit, we will discuss to popular current mirror techniques wilson current mirror circuit and. Repeat the same procedure you followed for the simple mirror circuit. A wilson current mirror or wilson current source, named after george wilson, is an improved mirror circuit. The widlar circuit may be used with bipolar transistors, mos transistors, and even vacuum tubes.
A current mirror is a circuit block which functions to produce a copy of the current flowing into or out of an input terminal by replicating the current in an output terminal. Eecs140 analog circuit design lectures on current sources university of california berkeley college of engineering department of electrical engineering and computer science robert w. The focus of analysis were a power dissipation, a total harmonic distortion and a chipsurface. Widlar current mirror design using bjtmemristor circuits. Ive explained its basic concept also ive given link below in the. What is the best one between wilson current source or. Concept of using a current mirror circuit to allow subtraction of collector currents. We thus prefer to employ a unit transistor and create copies by repeating such a device. Therefore, for an ideal current amplifier, the current transfer ratio is an important parameter. The output impedance of a widlar current mirror is approximately, where. Current sources and active loads university of north. I ref i on i op i l pnp widlar current mirror npn widlar current mirror r l 100. Modify the simple mirror circuit by adding the base current compensation transistor q 3 as shown below. The r2 is connected in series with the t2 emitter and ground.
Each has different advantages and their uses are for different purposes. The transistor is there configured as a diode for a fundamental purposes all to do with current mirrors. Pnp widlar current mirror npn widlar current mirror r l 100. One way to limit this is to increase the output impedance of the circuit notice right now. Voltage references and biasing stanford university. The current mirror is used to provide bias currents and active loads to circuits. This lecture deals with the design of current mirrors as both bias elements and signal processing. The basic circuit of the transistor current mirror is shown in the diagram below. Class ab current biasing simulation bias currents set at i ref and i o by r and emitter resistors r e. The closer to the supply rails the current mirror can operate, the greater the compliance range, the better the performance of the circuit. Current sources current mirrors are commonly used for current sources in integrated circuit design. Thus, as in the opamp version of this circuit, the diode provides its own bias current. The cascode and wilson current q1 q2q3 q4 figure 16. This paper presents a description of basic current mirror cm, widlar current mirror, fourth circuit element memristor and an analysis of widlar configuration with integrated memristor.
Current mirrors usually employ the same length for all of the transistors. Pdf widlar current mirror design using bjtmemristor. Widlar current source cs26 i r i o r q 1 q 2 r out i o v. Wilson current source is a current mirror while widlar current source is independent from reference current. Wilson and widlar current mirroring techniques february 2020 to improve the output of basic current mirror circuit, we will discuss to popular current mirror techniques wilson current mirror circuit and widlar current source circuit. Abstract the widlar current mirror, a widely used integrated circuit configuration, normally receives only a superficial treatment in electronics texts. Dawson page 3 notice how this technique solves a thorny problem for using transistors as a current source. Direct scaling of the width also faces difficulties. I ran it in pspice, and did a sweep of load resistors from 1 to 2. An example application is the 741 operational amplifier, and widlar used the circuit as a part in many designs. Temperature independent band gap reference voltage using. Concept of current mirror circuit analog electronics duration. Widlar current mirror a resistor r e is included in the emitter of q 2. The widlar circuit may be used with bipolar transistors, mos transistors, and.
An example application of the current mirror is the transconductance op amp. Passive and active current mirrors analog circuit design 51 chingyuan yang ee, nchu overview zreading b. A wilson current mirror is a threeterminal circuit fig. Instead of the large resistors required to create small currents, the widlar. Learn more about analog design in this introduction to the current mirror, including how this circuit is implemented in analog ics.
The only difference between the two circuits is the introduction of an emitter resistor. Now wilson current mirror is less dependent on beta values meaning it is less dependent on transistor parameters but o. Index termscurrent mirror, widlar current source, bjt memristor circuit, power analysis, noise analysis, total harmonic distortion. The class ab circuit, over most of its input signal range, operates as if either the q n or q p transistor is conducting and the q p or q n transistor is cut off. Various types of current mirror circuits are discussed in sectionii,sectioniii describes low voltage bulkdriven mosfet current mirror for cmos technology. An ai using a conventional current mirror ccm and widlar current source have been implemented in the 0. An example application is the 741 operational amplifier, and widlar used the circuit. Widlar current source the widlar current source differs from the basic current mirror in one important way a resistor r 2 is added to the emitter circuit of transistor q 2. A low voltage selfbiased and bulkdriven mosfet wilson. A widlar current source is used in analog integrated circuit design to produce a small driving current without the use of large resistors.
The circuit consists of an input diff amp and four wilson current mirrors. Replicate reference current at various places required. A widlar current source is a modification of the basic twotransistor current mirror that incorporates an emitter degeneration resistor for only the output transistor, enabling the current source to generate low currents using only moderate resistor values. The circuit is same as the two transistors current mirror circuit without the r2.
An important feature of the current mirror is a relatively high output resistance which helps to keep the output current constant. Fet current sources figure 1a shows two fet current sources, one which uses an nchannel depletion mode mosfet and the. Ee105 fall 2014 microelectronic devices and circuits. The mirrored current is a precise copy of the input current. When combined with other blocks such as the differential pair and the current mirror, it can be used in the design of operational amplifiers, operational transconductance amplifiers, and other such circuits. The widlar circuit may be used with bipolar transistors, mos transistors, and even. This section covers other current sources that are often seen. Current mirrors are basic building blocks of analog design. The performance of the tunable ai using widlar current source are compared with the same using a simple current mirror.
This additional component forces the currents in the two branches of the circuit to be unequal. Analysis of the modified mos wilson current mirror. A negative feedback loop is created to ensure that the current does not change with pvt variations, thereby making it a good current source. Brodersen eecs140 analog circuit design lectures on. Simple current mirrors the circuits depicted in figure 3 are the simple and the widlar current mirrors. An ideal current mirror circuit is an ideal current amplifier with the inverting configuration that can reverse the current direction. A current mirror circuit, mirror or copy the input current of one active device to the other active devices output. Specifics of using current mirrors for highside current. The widlar current source differs from the basic current mirror in one important way a resistor r2 is added to the emitter circuit of transistor q2.
Since multistage amplifier systems often have high gain, bias currents must be small. Its operation is simple and has been discussed in the lecture. Tunable cmos active inductor using widlar current source. Ive designed this widlar current source to deliver 5ma of current. All is well until the student encounters a circuit with mul tiple feedback loops like the modified wilson current mirror 2.
What are the advantages and disadvantages of using an. It may be used as a wilson current source by applying a constant bias current to the input branch as in fig. The results has shown that the presence of the memristor decreases the distortion of the signal in the circuit from the fundamental frequency waveform. Lectures on current sources university of california.
In this video you will come to know about widlar current source and its working. Ic3 and ic4 are matched to ic1 the control tran sistor but ic2 is reduced by re2. Compliance voltage for current mirrors a measure of the minimum load or output voltage for which the current mirror can maintain a constant current. This additional component forces the currents in the two branches of the circuit. Current ratioing is achieved by only scaling the width of transistors.
Widlar current source the widlar current source, a variation of the simple current mirror, was advanced by bob widlar in the mid 1960s. Summary of key concepts voltage source easily synthesized from reference current source using mosfet in diode configuration current source easily synthesized from current source using current mirror circuit. Wilson, an integrated circuit design engineer who worked for tektronix. The main design criteria for this project is to achieve psrr above 60db and a variation less than 3% resulting from temperature changes. Widlar current mirrors widlar current mirrors resemble classical mirrors but the gatesource voltage of the input transistor in diode connection is distributed between the vgs of the output transistor and a series degeneration resistor. Widlar current mirror design using bjtmemristor circuits arxiv. Lecture20 current mirrors 1 ee105 fall 2014 microelectronic devices and circuits prof. The current mirror is an important analog building block that finds application in such diverse areas as dc biasing and currentmode signal processing.
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