One way to limit this is to increase the output impedance of the circuit notice right now. Wilson current source is a current mirror while widlar current source is independent from reference current. The only difference between the two circuits is the introduction of an emitter resistor. Thus, as in the opamp version of this circuit, the diode provides its own bias current. The schematic of the circuit is illustrated in figure 6.
Widlar current mirror design using bjtmemristor circuits. Instead of the large resistors required to create small currents, the widlar. 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. This additional component forces the currents in the two branches of the circuit. The results has shown that the presence of the memristor decreases the distortion of the signal in the circuit from the fundamental frequency waveform. Pnp widlar current mirror npn widlar current mirror r l 100. Each has different advantages and their uses are for different purposes. The widlar circuit may be used with bipolar transistors, mos transistors, and even vacuum tubes. 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. A low voltage selfbiased and bulkdriven mosfet wilson. Replicate reference current at various places required. Its operation is simple and has been discussed in the lecture.
The mirrored current is a precise copy of the input current. The analysis has been performed by comparing a modified configuration with a simple circuit of widlar cm. Current mirrors usually employ the same length for all of the transistors. Pdf widlar current mirror design using bjtmemristor. Specifics of using current mirrors for highside current. Voltage references and biasing stanford university. Widlar current source cs26 i r i o r q 1 q 2 r out i o v.
Widlar current source the widlar current source, a variation of the simple current mirror, was advanced by bob widlar in the mid 1960s. 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. The circuit consists of an input diff amp and four wilson current mirrors. I ref i on i op i l pnp widlar current mirror npn widlar current mirror r l 100. 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. Compliance voltage for current mirrors a measure of the minimum load or output voltage for which the current mirror can maintain a constant current.
The main design criteria for this project is to achieve psrr above 60db and a variation less than 3% resulting from temperature changes. Lectures on current sources university of california. What are the advantages and disadvantages of using an. Now wilson current mirror is less dependent on beta values meaning it is less dependent on transistor parameters but o. 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. Ive explained its basic concept also ive given link below in the. The focus of analysis were a power dissipation, a total harmonic distortion and a chipsurface. Calculating the output resistance of a widlar current source.
Current mirrors are basic building blocks of analog design. 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. An important feature of the current mirror is a relatively high output resistance which helps to keep the output current constant. An ai using a conventional current mirror ccm and widlar current source have been implemented in the 0. The basic circuit of the transistor current mirror is shown in the diagram below. Learn more about analog design in this introduction to the current mirror, including how this circuit is implemented in analog ics.
An example application is the 741 operational amplifier, and widlar used the circuit as a part in many designs. A widlar current source is used in analog integrated circuit design to produce a small driving current without the use of large resistors. This additional component forces the currents in the two branches of the circuit to be unequal. The transistor is there configured as a diode for a fundamental purposes all to do with current mirrors. The output impedance of a widlar current mirror is approximately, where. The q2 re2 combination is a widlar cur rent source. Index termscurrent mirror, widlar current source, bjt memristor circuit, power analysis, noise analysis, total harmonic distortion. In this video you will come to know about widlar current source and its working. Current sources and active loads university of north. 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. Current mirror circuit designs using bjt and mosfet. Fet current sources figure 1a shows two fet current sources, one which uses an nchannel depletion mode mosfet and the. An ideal current mirror circuit is an ideal current amplifier with the inverting configuration that can reverse the current direction. Dawson page 3 notice how this technique solves a thorny problem for using transistors as a current source.
The closer to the supply rails the current mirror can operate, the greater the compliance range, the better the performance of the circuit. Direct scaling of the width also faces difficulties. Widlar current mirror a resistor r e is included in the emitter of q 2. Abstract the widlar current mirror, a widely used integrated circuit configuration, normally receives only a superficial treatment in electronics texts.
The current mirror is an important analog building block that finds application in such diverse areas as dc biasing and currentmode signal processing. The circuit is same as the two transistors current mirror circuit without the r2. Since multistage amplifier systems often have high gain, bias currents must be small. Eecs140 analog circuit design lectures on current sources university of california berkeley college of engineering department of electrical engineering and computer science robert w. I ran it in pspice, and did a sweep of load resistors from 1 to 2.
We thus prefer to employ a unit transistor and create copies by repeating such a device. Brodersen eecs140 analog circuit design lectures on. 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. Concept of current mirror circuit analog electronics duration. The performance of the tunable ai using widlar current source are compared with the same using a simple current mirror.
A wilson current mirror or wilson current source, named after george wilson, is an improved mirror circuit. Ive designed this widlar current source to deliver 5ma of current. It comprises two transistors, one of which has the base and collector connected and the other does not. The widlar circuit may be used with bipolar transistors, mos transistors, and even. Therefore, for an ideal current amplifier, the current transfer ratio is an important parameter. Temperature independent band gap reference voltage using. 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.
Class ab current biasing simulation bias currents set at i ref and i o by r and emitter resistors r e. To improve the output of basic current mirror circuit, we will discuss to popular current mirror techniques wilson current mirror circuit and. Chapter 16 analog integrated circuits chapter outline 16. Widlar current mirrors,wilson current mirrors and cascoded current mirrors. 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. Tunable cmos active inductor using widlar current source. 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 cascode and wilson current q1 q2q3 q4 figure 16. A negative feedback loop is created to ensure that the current does not change with pvt variations, thereby making it a good current source.
The r2 is connected in series with the t2 emitter and ground. The widlar circuit may be used with bipolar transistors, mos transistors, and. 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. The current mirror is used to provide bias currents and active loads to circuits. This section covers other current sources that are often seen. Various types of current mirror circuits are discussed in sectionii,sectioniii describes low voltage bulkdriven mosfet current mirror for cmos technology. A wilson current mirror is a threeterminal circuit fig. Repeat the same procedure you followed for the simple mirror circuit.
This lecture deals with the design of current mirrors as both bias elements and signal processing. An example application is the 741 operational amplifier, and widlar used the circuit. Current ratioing is achieved by only scaling the width of transistors. What is the best one between wilson current source or.
There are many good resources online and in textbooks on current mirrors. A current mirror circuit, mirror or copy the input current of one active device to the other active devices output. Wilson, an integrated circuit design engineer who worked for tektronix. Analysis of the modified mos wilson current mirror. Lecture20 current mirrors 1 ee105 fall 2014 microelectronic devices and circuits prof. Current sources current mirrors are commonly used for current sources in integrated circuit design. Ee105 fall 2014 microelectronic devices and circuits. Concept of using a current mirror circuit to allow subtraction of collector currents.754 64 1411 1077 872 1476 513 544 973 1219 1688 81 826 1440 438 333 42 227 979 664 1206 1405 1188 61 889 1598 542 1144 924 948 318 381 184 375 1214 1374 544 105 736 241 280 1380 411