The only difference between the two circuits is the introduction of an emitter resistor. A widlar current source is used in analog integrated circuit design to produce a small driving current without the use of large resistors. A negative feedback loop is created to ensure that the current does not change with pvt variations, thereby making it a good current source. Current mirrors usually employ the same length for all of the transistors. Pnp widlar current mirror npn widlar current mirror r l 100. Widlar current mirror design using bjtmemristor circuits. The analysis has been performed by comparing a modified configuration with a simple circuit of widlar cm. Compliance voltage for current mirrors a measure of the minimum load or output voltage for which the current mirror can maintain a constant current. An example application is the 741 operational amplifier, and widlar used the circuit. The current mirror is an important analog building block that finds application in such diverse areas as dc biasing and currentmode signal processing. This additional component forces the currents in the two branches of the circuit. An example application of the current mirror is the transconductance op amp.
What are the advantages and disadvantages of using an. 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. Current sources and active loads university of north. Each has different advantages and their uses are for different purposes. The focus of analysis were a power dissipation, a total harmonic distortion and a chipsurface. 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. Widlar current source the widlar current source, a variation of the simple current mirror, was advanced by bob widlar in the mid 1960s. Various types of current mirror circuits are discussed in sectionii,sectioniii describes low voltage bulkdriven mosfet current mirror for cmos technology. Concept of using a current mirror circuit to allow subtraction of collector currents. To improve the output of basic current mirror circuit, we will discuss to popular current mirror techniques wilson current mirror circuit and.
Widlar current mirror a resistor r e is included in the emitter of q 2. The basic circuit of the transistor current mirror is shown in the diagram below. Current sources current mirrors are commonly used for current sources in integrated circuit design. Calculating the output resistance of a widlar current source. Widlar current source cs26 i r i o r q 1 q 2 r out i o v. Lectures on current sources university of california. The main design criteria for this project is to achieve psrr above 60db and a variation less than 3% resulting from temperature changes. 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.
In this video you will come to know about widlar current source and its working. A low voltage selfbiased and bulkdriven mosfet wilson. Temperature independent band gap reference voltage using. The cascode and wilson current q1 q2q3 q4 figure 16. Index termscurrent mirror, widlar current source, bjt memristor circuit, power analysis, noise analysis, total harmonic distortion. Specifics of using current mirrors for highside current. Current mirrors are basic building blocks of analog design. All is well until the student encounters a circuit with mul tiple feedback loops like the modified wilson current mirror 2. 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.
Modify the simple mirror circuit by adding the base current compensation transistor q 3 as shown below. Class ab current biasing simulation bias currents set at i ref and i o by r and emitter resistors r e. Tunable cmos active inductor using widlar current source. Ive designed this widlar current source to deliver 5ma of current. 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.
Eecs140 analog circuit design lectures on current sources university of california berkeley college of engineering department of electrical engineering and computer science robert w. Now wilson current mirror is less dependent on beta values meaning it is less dependent on transistor parameters but o. I ref i on i op i l pnp widlar current mirror npn widlar current mirror r l 100. Thus, as in the opamp version of this circuit, the diode provides its own bias current. Analysis of the modified mos wilson current mirror. 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. This additional component forces the currents in the two branches of the circuit to be unequal. Learn more about analog design in this introduction to the current mirror, including how this circuit is implemented in analog ics. Widlar current mirror design using bjtmemristor circuits arxiv.
Widlar current mirrors,wilson current mirrors and cascoded current mirrors. Replicate reference current at various places required. Pdf widlar current mirror design using bjtmemristor. Concept of current mirror circuit analog electronics duration.
Abstract the widlar current mirror, a widely used integrated circuit configuration, normally receives only a superficial treatment in electronics texts. Its operation is simple and has been discussed in the lecture. The widlar circuit may be used with bipolar transistors, mos transistors, and even. Fet current sources figure 1a shows two fet current sources, one which uses an nchannel depletion mode mosfet and the. Dawson page 3 notice how this technique solves a thorny problem for using transistors as a current source. The mirrored current is a precise copy of the input current. 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. Voltage references and biasing stanford university. This section covers other current sources that are often seen. 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. The r2 is connected in series with the t2 emitter and ground. In the below image, a widlar current source circuit is shown.
The current mirror is used to provide bias currents and active loads to circuits. Ic3 and ic4 are matched to ic1 the control tran sistor but ic2 is reduced by re2. An ideal current mirror circuit is an ideal current amplifier with the inverting configuration that can reverse the current direction. It may be used as a wilson current source by applying a constant bias current to the input branch as in fig. A current mirror circuit, mirror or copy the input current of one active device to the other active devices output. Instead of the large resistors required to create small currents, the widlar.
The transistor is there configured as a diode for a fundamental purposes all to do with current mirrors. This lecture deals with the design of current mirrors as both bias elements and signal processing. Lecture20 current mirrors 1 ee105 fall 2014 microelectronic devices and circuits prof. There are many good resources online and in textbooks on current mirrors. Therefore, for an ideal current amplifier, the current transfer ratio is an important parameter. 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.
An ai using a conventional current mirror ccm and widlar current source have been implemented in the 0. Repeat the same procedure you followed for the simple mirror circuit. Current mirror circuit designs using bjt and mosfet. The widlar circuit may be used with bipolar transistors, mos transistors, and. We thus prefer to employ a unit transistor and create copies by repeating such a device.
What is the best one between wilson current source or. The output impedance of a widlar current mirror is approximately, where. I ran it in pspice, and did a sweep of load resistors from 1 to 2. A wilson current mirror or wilson current source, named after george wilson, is an improved mirror circuit. An example application is the 741 operational amplifier, and widlar used the circuit as a part in many designs. It comprises two transistors, one of which has the base and collector connected and the other does not. The results has shown that the presence of the memristor decreases the distortion of the signal in the circuit from the fundamental frequency waveform. The widlar circuit may be used with bipolar transistors, mos transistors, and even vacuum tubes. The schematic of the circuit is illustrated in figure 6. Wilson current source is a current mirror while widlar current source is independent from reference current. One way to limit this is to increase the output impedance of the circuit notice right now. Direct scaling of the width also faces difficulties. 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. The performance of the tunable ai using widlar current source are compared with the same using a simple current mirror.
Passive and active current mirrors analog circuit design 51 chingyuan yang ee, nchu overview zreading b. An important feature of the current mirror is a relatively high output resistance which helps to keep the output current constant regardless of load conditions. The closer to the supply rails the current mirror can operate, the greater the compliance range, the better the performance of the circuit. The circuit is same as the two transistors current mirror circuit without the r2.
Without the transistor being there the circuit would make a really poor current mirror source. An important feature of the current mirror is a relatively high output resistance which helps to keep the output current constant. The circuit consists of an input diff amp and four wilson current mirrors. Since multistage amplifier systems often have high gain, bias currents must be small. Chapter 16 analog integrated circuits chapter outline 16. The q2 re2 combination is a widlar cur rent source. Ee105 fall 2014 microelectronic devices and circuits. A wilson current mirror is a threeterminal circuit fig. Current ratioing is achieved by only scaling the width of transistors. Wilson, an integrated circuit design engineer who worked for tektronix. Simple current mirrors the circuits depicted in figure 3 are the simple and the widlar current mirrors. Brodersen eecs140 analog circuit design lectures on.
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