Build the current mirror circuit shown to the right. In above wilson current mirror circuit, there are three active components which are bjts and a single resistor r1. Is the ideal output impedance of a wilson current mirror 0. Wilson won and his mirror, in its bipolar form, has been a. Suppose that the reference current, i ref, is supplied by a resistor to the supply voltage. Within the circuit, a third transistor is introduced. Fet current and voltage sources and current mirrors the building blocks of analog circuits iv in this lecture you will learn. Types and applications of current mirrors april 03, 2019 by dr. Also, because the current sources are twoterminal devices, they can be used equally well as current sinks.
Sergio franco the current mirror is an important analog building block that finds application in such diverse areas as dc biasing and currentmode signal processing. When the wilson current mirror is used in cmos circuits, it is usually in the four transistor. Current ratioing is achieved by only scaling the width of transistors. Wooyoung choi various bias techniques for mosfet circuits how do we make. Pdf with the evolution of electronics today, a mosfet transistor is useful in many applications such as computers due to several advantages. Transistor m1 is operating in the saturation or active mode, and so is m2. Lowvoltage wilson current mirrors in cmos request pdf. Pdf eliminating the early effect in the wilson current mirror. Lecture 14 fet current and voltage sources and current. The sections are dielectrically isolated, making them completely independent. Bjt current mirror, bjt current mirror with base current compensation, wilson bjt current mirror, lowlevel bjt current mirror, bjt differential amplifier with current mirror load, mosfet differential amplifier with current mirror load 08.
The performance of each section is individually measured and lasertrimmed to achieve. Chapter 16 analog integrated circuits chapter outline 16. V d bipolar diode exponential diode connected transistor quadratic v t v d i d v ds v gs v t after we reach the point v d v t, the transistor will always be in sat. At first glance, the current mirror circuit shown to the right would seem to be backwards. Chapter 7 building blocks of integrated circuit amplifiers. Lecture20current mirrors 1 ee105 fall 2014 microelectronic devices and circuits prof. A low voltage selfbiased and bulkdriven mosfet wilson current mirror circuit 1shobhna, 2mrs. Implementation and applications of current sources and. The gate source voltage is set by the diode geometry and the injected input or reference. Design of the wilson and improved wilson mos current mirrors. Mosfet differential amplifier twoweek lab background the mosfet is by far the most widely used transistor in both digital and analog circuits, and it is the backbone of modern electronics. Also, what is the order of magnitude of a wilson current mirror.
An example application of the current mirror is the transconductance op amp. We note that q 3 carries the same current as q 2 because they are in series, and q 1, in turn, mirrors the current of q 2, so, the left and right halves of the circuit carry identical currents. The simple mosfet current mirror has the second imperfection only because there are no gate currents. Suketu naik wilson current mirror mosfet based wilson current mirror can be used to increase output resistance and gain. Basic current mirror wilson current mirror design equations. The mos current mirror has a current transfer ratio of wl 2 wl 1.
Current and voltage sources 1 analog design for cmos vlsi systems franco maloberti current mirrors a current mirror gives a replica attenuated or amplified, if necessary of a bias or signal current. A low voltage selfbiased and bulkdriven mosfet wilson. Lecture20current mirrors 9 mos current mirrors dc analysis mosfets m 1 and m 2 are assumed to have identical v tn, k n, l, and wl ratios. The proposed circuit was verified using orcad simulator in 0. I put 100 ohm resisters on the source to ground, and that helped a little.
In fact, however, it works quite well, although in a roundabout fashion. In this paper, we describe three simple lowvoltage cmos analogs of the wilson current mirror that function well at all current levels, ranging. Mosfet current mirror and cs amplifier electronic circuits 1 062 prof. Analogue electronicscurrent mirrorswilson wikibooks, open. The term cascode dates back to the days of vacuum tubes, before any sort of semiconductor devices were. Smallsignal circuits of the modified wilson current mirror. A pedagogical exercise in signal flow graphs, masons gain rule, and drivingpoint impedance techniques ronald g. The mirrored current is a precise copy of the input current. The gate source voltage is set by the diode geometry and the injected input or reference current.
The basic current mirror can also be implemented using mosfet transistors, as shown in figure 2. The drain current of mosfet depends on its gate voltage v g and drain voltage v d. 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. Analysis of the modified mos wilson current mirror 323 fig. One way to add emitter resistance without using actual resistors or generating a large voltage drop is to stack one current mirror on top of another, as shown to the left. Analysis of the modified mos wilson current mirror. Pdf analysis and simulation of mosfet differential. It should be noted that the wilson current mirror is not a constant current source.
The reference current source is also known as golden current source. Voltage and current sources rely on the availability of. An improved nmos wilson current mirror is used as shown in, transistor is to provide r eference current and the circuit is biased at. Eecs140 analog circuit design lectures on current sources simple source cont. Ref200 dual current source and current sink datasheet rev.
V tn 2 i o i ref lecture20current mirrors 10 mos current mirrors. Another variation of the basic current mirror circuit is referred to as the wilson mirror or wilson current mirror. Current mirrors usually employ the same length for all of the transistors. We thus prefer to employ a unit transistor and create copies by repeating such a device.
Wilson current mirrors in cmos in 1967, george wilson and barrie gilbert entered into a friendly competition to see who could devise the best current mirror with only three transistors. Simple current mirror bjt and mosfet base current corrected simple current mirror widlar current source wilson current mirror bjt and mosfet cascoded current mirror bjt and mosfet for best performance, transistors should be matched, temperature should be. It is of particular interest for current sense applications for feedback purposes. Direct scaling of the width also faces difficulties.
Transistor current mirror circuit electronics notes. Analogue electronicscurrent mirrorswilson wikibooks. Also, in the formula for the actual output impedance of wilson current formula i. Spencer, member, ieee abstract a pedagogical analysis of the modified mos wilson current mirror using signal flow graphs sfgs, masons gain. Thus, the drain current can be expressed as, figure 4. The simple mos current mirror the simple current mirror can be obtained from the one transistor current source by using a second transistor in diode connection that generates the necessary gatesource voltage of the transistor in the output stage. A small amount of the current flowing through r provides base current for q3, enabling q3 to conduct current. 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. Transconductance op amp, circuit symbol, am modulator example application 09.
Eecs140 analog circuit design lectures on current sources university of california berkeley college of engineering department of electrical engineering and computer science robert w. Zds1009 current mirror datasheet diodes incorporated. Your current mirror will pull current out of an external circuit comprised of a 10k. The modified wilson current mirror is used to compare three analytical. It uses a full wilson type architecture as shown in figure 2, with lasertrimming to ensure high accuracy. To understand the modified wilson approach start with the circuit schematic drawing. This transistor, shown as tr3 in the diagram keeps the collector of tr1 at a voltage equivalent to two diode drops below the rail voltage vcc. Multiple current sources and sinks with different magnitudes can be synthesized from a single current source. Current and voltage sources using fets fet current mirrors cascodecurrent mirror double wilson current mirror active biasing schemes ece 315 spring 2007 farhan rana cornell university motivation. 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. Structure and characteristics of the bjt wilson current mirror. Recent listings manufacturer directory get instant insight into any. The generation of this reference current source is itself very complex and requires complex circuit which should be independent of power supply, temperature and process variation. Conceptually, an ideal current mirror is simply an ideal current amplifier with a gain of 1.
It uses a full wilson type architecture, mirror uses a full wilson architecture for high accuracy. It should be noted that the wilson current mirror is not a constantcurrent source. The proposed design is verified with spice simulation of the current mirror in a cmos 2pm technology. The simple two transistor implementation of the current mirror is based on the fundamental relationship that two equal size transistors at the same temperature with the same v gs for a mos or v be for a bjt have the same drain or collector current. Current mirrors objective design, simulate, layout and test various current mirror circuits.
Transistor m 1 is operating in the saturation or active mode, and so is m 2. Circuit ideahow the wilson current mirror equalizes the. Using a cascode connection will allow for the output resistance ro2 to be boosted in value one such a design is the. Pdf eliminating the early effect in the wilson current. In this setup, the output current i out is directly related to i ref, as discussed next. In next videos, we will cover cascode current mirror, wilson current mirror etc. Wilson current mirror is an attempt to improve performance by increasing the effective output resistance at the drain of the mirror mosfet. This arrangement is known as a cascode current mirror. In the circuit below, m1 and m2 are nchannel mosfets with kn 40 mav2, w4um, l2um, and vt 0.
Introduction current mirrors are fundamental building blocks of analog integrated circuits. A properly designed differential amplifier with its currentmirror. Pdf analysis and simulation of mosfet differential amplifier. Includes current mirror 2 applications sensor excitation biasing circuitry offsetting current loops low voltage references chargepump circuitry hybrid microcircuits 3 description the ref200 combines three circuit buildingblocks on a single monolithic chip. If the supply voltage, v cc changes, the output current will change. Lectures on current sources university of california. The implementation of the current mirror circuit may seem simple but there is a lot going on. Wilson current mirror circuit uses three active devices that accept the current across its input and provide the exact copy or mirrored copy of the current to its output. The paper reveals the secret behind the unique feature of the popular wilson current mirror circuit to eliminate the early effect that is inherent for the simple current mirror. The simple current mirror can be obtained from the one transistor current source by using a second transistor in diode connection that generates the necessary gatesource voltage of the transistor in the output stage.
The ref200 current mirror uses a full wilson architecture for high accuracy. The heart of the current steering circuitry utilized to perform this function is the current mirror. Brodersen eecs140 analog circuit design lectures on. Cascode current mirror wilson current mirror wideswing current mirror 4. For small signals, we can write the quantities in above. Modified wilson current mirror next, we are going to try to improve current mirror performance beyond the simple current mirror.
An nchannel mosfet current mirror with a resistor to set the reference current iref. It may be used as a wilson current source by applying a constant bias current to the input. Gain of a cascode amplifier with a cascode current mirror active load f. Jan 30, 2017 structure and characteristics of the bjt wilson current mirror. Ee105 fall 2014 microelectronic devices and circuits. Measure id3 with either an ammeter, or by measuring the voltage drop across r1 and applying ohms law. Operational amplifiers, operational transconductance amplifiers and biasing networks are examples of circuits that are composed of current. A wilson current mirror is a threeterminal circuit fig. Pdf a new configuration for the design of a current mirror is presented.