In fact, however, it works quite well, although in a roundabout fashion. Conceptually, an ideal current mirror is simply an ideal inverting current amplifier that reverses. May 29, 2015 this new mirror is well suited for low current biasing applications. To get a good insight of current mirrors current sources read the manual. How accurately does this formula predict the output impedance of the widlar current mirror you constructed. In this lab we are going to investigate the basic building blocks of bjt op amps. Change the circuit in order to obtain a current gain equal to 2. Index termscurrent mirror, widlar current source, bjt memristor circuit, power analysis, noise analysis, total harmonic distortion.
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. Pdf this paper investigates the state of the art compensation techniques and explores. 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. 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. Temperature independent band gap reference voltage using. Current mirrors take a positive current source and generate a negative current sink. Moreover, the proposed circuit applying the idea can achieve good. It may be used as a wilson current source by applying a constant bias current to the input. The diodebiased current mirror current ratio reference current 1 output resistance 1 compliance range 2 using a mirror to bias an amplifier 2 wilson current mirror 3 current ratio 3. Current sources and active loads university of north. Ive designed this widlar current source to deliver 5ma of current.
I was thinking of using a current mirror, but i have not really worked with them before and am not sure if i can chain them together i. Ee105 fall 2014 microelectronic devices and circuits. Current mirrors current mirrors are important blocks in electronics. The reference stage of the current mirror circuit 200 is a feedback loop having a feedback path and a forward path and is comprised of transistors 206, 210, 222, 212, and 208. Widlar current source the widlar current source, a variation of the simple current mirror, was advanced by bob widlar in the mid 1960s. Feb 17, 2018 the npn current mirror, in its most basic form, is, in effect, an inverting current buffer in the sense that it changes current sources of any impedance into current sinks of high impedance. A negative feedback loop is created to ensure that the current does not change with pvt variations, thereby making it a good current source. A novel bandgap reference for minimizing currentmirror mismatch.
Media in category current mirror circuits the following 56 files are in this category, out of 56 total. What is the idea of the current mirror with two emitter. A current mirror is a circuit designed to copy a current through one active device by controlling the current in another active device of a circuit, keeping the output current constant regardless of loading. Chapter 16 analog integrated circuits chapter outline 16. An example application of the current mirror is the transconductance op amp. 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 provided internal clamp diode protects the current mirror output from. Zds1009 current mirror datasheet diodes incorporated. Compliance voltage for current mirrors a measure of the minimum load or output voltage for which the current mirror can maintain a constant current. Current mirrors consist of two branches that are parallel to each other and create two approximately equal currents. To best understand this important circuit building.
The rest of the mirror circuit acts as a feedback to control it. What is current mirror and what are its advantages. A widlar current source is a modification of the basic two transistor 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 transistor is there configured as a diode for a fundamental purposes all to do with current mirrors.
Widlar current mirror design using bjtmemristor circuits arxiv. Instead of the large resistors required to create small currents, the widlar. Also, when compared with basic current mirror, improved one consumes only 14th of the power consumed by the basic current mirror. What are the advantages and disadvantages of using an. It has been demonstrated that the circuit shows improved immunity to current mirrormismatch through the selfcompensated current paths. Circuit ideahow the wilson current mirror equalizes the. Figure 1 shows a pspice circuit to display the iv characteristic of a basic current mirror. A ptat current can be copied from the current mirror and can be adjusted by changing the width of m12 or the resistance of r1. The voltage difference between the two pn junctions is the positivetc voltage. International journal of electrical engineering education 404 designing the widlar current mirror bryan hart leigh on sea, essex, uk abstract the widlar current mirror, a widely used integrated circuit configuration, normally receives only a superficial treatment in electronics texts. Experiment 5 design of an operational ampli er using pspice.
Zetex zds1009 current mirror datasheet battery chargers dc motor control outrush current sensing inrush current sensing wide operating voltage range excellent temperature tracking characteristics simplifies circuit implementation only four connections required created date. Specifics of using current mirrors for highside current. Within the circuit, a third transistor is introduced. The authors established that it is necessary to consider also the temperature dependence of branch current ratio m i2mi1. What links here related changes upload file special pages permanent. A small amount of the current flowing through r provides base current for q3, enabling q3 to conduct current. Passive and active current mirrors analog circuit design 51 chingyuan yang ee, nchu overview zreading b. What is the basic idea behind the bjt current mirror. Now wilson current mirror is less dependent on beta values meaning it is less dependent on transistor parameters but o. Replicate reference current at various places required. Pdf the paper reveals the secret behind the unique feature of the popular wilson current mirror circuit to eliminate the early effect that is inherent. A current mirror is a type of electrical circuit design where the current flow in one section of the circuit is used to regulate the current flow in other sections, so that the output of two or more regions mirror each other in value. An alternative current mirror exhibiting a high output impedance. 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.
These building blocks are not shown and a transistor with a re. The current being copied can be, and sometimes is, a varying signal current. Design a widlar current source that produces an output current of. A low voltage very high impedance current mirror circuit and its. Thus, the current mirror circuit acts to regulate current at a value set by the potentiometer, without regard to load resistance. Each block will be tried out in the lab and also simulated via pspice. The closer to the supply rails the current mirror can operate, the greater the compliance range, the better the performance of the circuit. Another variation of the basic current mirror circuit is referred to as the wilson mirror or wilson current mirror. If this resistance is removed the bias current will grow with temperature causing an equal increase in the output current in case of the conventional current. A wilson current mirror is a threeterminal circuit fig. They are widely used in several applications and chips, the operational amplifier being one of them. First of all, i cannot see where the input signal is fed into the circuit.
In the video, the programmed voltage across q2s collector is reflecting across the q3 collector. This additional component forces the currents in the two branches of the circuit to be unequal. Firstorder temperaturecompensated totalcurrent reference. Without the transistor being there the circuit would make a really poor current mirrorsource. A brief introduction of wilson and widlar current sources and the steps to carry out the lab are given here. Hence, the required v, must be smaller than the threshold voltage v.
Similar to widlar current mirror, but addition of resistor makes output current less dependent of input current. An important currentmirror application is as an active load for a longtail pair, as exemplified in fig. This is why these circuits are called current mirrors. The implementation of the current mirror circuit may seem simple but there is a lot going on. Output current depends on input current and resistor r 2 2 2 1 2 2 2 4 2 2 r r v k w l k w l i ov out. The gate source voltage is set by the diode geometry and the injected input or reference. Types of mirrors there are three types of current mirrors that will be discussed throughout this article. In the final section, we saw some examples of how current mirrors are incorporated into analog integrated circuits.
The above circuit does pose its own voltage headroom limitation. This didactic study consists of a detailed analysis followed by a stepbystep design procedure that. The design uses a high swing super wilson current mirror which has negative feedback. The low swing cascode current mirror with mos transistors. 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 mirror circuits are usually designed with bipolar junction transistors bjt such as the npn transistor, where a positively doped p. With a constant base current and a nearly constant. The widlar circuit may be used with bipolar transistors, mos transistors, and. The npn transistors q1 and q2 shown make up the differential amplifier and q3 and q4 pnp make up the current mirror. Current mirror circuits basics of mos current mirrors application.
Simple current mirror wilson current mirror cascode current mirror simple current mirror. The mirrored current is a precise copy of the input current. A feedback action is used to force the input and output currents to be. Current mirrors have low input impedance, so the reference current can be from a poor current source output impedance 1k ohms and give rise to a mirrored current that is a better current source output impedance 100k ohms. Prof, ece department, ssn college of engg bjt lowlevel mirror the circuit shown in figure is a lowlevel current mirror. The input stage of the current mirror circuit 200 includes an input current source 202 and is representative of any source of electrical reference current iref. A diode is also provided to limit the voltage at the current mirror output. Designing the widlar current mirror designing the widlar. Introduction to electronics ii dedication human beings are a delightful and complex amalgam of the spiritual, the emotional, the intellectual, and the physical. Since multistage amplifier systems often have high gain, bias currents must be small. The current mirror active load is a way to accomplish high gain for a single stage differential amplifier. At first glance, the current mirror circuit shown to the right would seem to be backwards.
Thus, the variation in vrej generated by current mirror mismatch has been much reduced in the proposed bandgap core. Another excellent current mirror circuit is the widlar current source circuit, invented by bob widlar the circuit is exactly the same as the basic current mirror circuit using two bjt transistors. The feedback can be connected in series with the load current feedback or in parallel voltage feedback. The widlar mirror the widlar scaling mirror is often used as fixed scaling current source a can be made as a buffered or a wilson source c a feedback resistor can be added on the input side turning it into a transconductor b a base resistor as shown can provide beta compensation. This configuration provides much higher voltage gain than in the case of a passive resistive load, and also converts a doubleended input to a singleended output. This new mirror is well suited for low current biasing applications. 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. Widlar current mirror design using bjtmemristor circuits.
Pdf eliminating the early effect in the wilson current mirror. The only difference between the two circuits is the introduction of an emitter resistor. 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. This paper presents a description of basic current mirror cm, widlar current mirror, fourth circuit element memristor. Index terms current mirror, widlar current source, bjtmemristor circuit, power analysis, noise analysis, total harmonic distortion. But there is a modification in the output transistor. The widlar mirror the widlar scaling mirror is often used as fixed scaling current source a can be made as a buffered or a wilson source c a feedback resistor can be added on the input side turning it into a transconductor b a base resistor as shown can provide beta compensation i. Jan 30, 2017 structure and characteristics of the bjt widlar current mirror. Pdf compensation in mos current mirror circuits researchgate. The current mirror circuit shown with two npn transistors in the figure above a is sometimes called a currentsinking type because the regulating transistor draws the current from the load to ground sinking current, rather than forcing it to flow from the positive side of the battery to the load sourcing current. The fundamental current mirror with mos transistors 2.
I ran it in pspice, and did a sweep of load resistors from 1 to 2. 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. Robert widlar used a modification of the basic current mirror to realise a sufficiently low bias current for the input pair of an opamp that would otherwise have required a highvalue resistor. This lecture deals with the design of current mirrors as both bias elements and signal processing. E 5 hich is called the proportional to absolute temperature ptat current. Cmos current mirrors with reduced input and output. Index termscurrent mirror, widlar current source, bjtmemristor circuit, power analysis, noise analysis, total harmonic distortion.
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