Moreover, the proposed circuit applying the idea can achieve good. Transistor current mirror circuit electronics notes. Mosfet current mirror and cs amplifier electronic circuits 1 062 prof. Pdf a high performance current mirror for low voltage designs. A straightforward implementation of the principle depicted in figure 2 appears in figure 4. Thus, the variation in vrej generated by current mirror mismatch has been much reduced in the proposed bandgap core. Wideswing current mirror with enhanced output impedance a variation of the previous circuit is shown below. This arrangement is known as a cascode current mirror. Current mirrors are very useful elements for performing current mode analog signal processing. The implementation of the current mirror circuit may seem simple but there is a lot going on. Conceptually, an ideal current mirror is simply an ideal inverting current amplifier that reverses the current direction as well or it is a currentcontrolled current.
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. Oct 09, 2019 figure 3 this diagram shows the pspice simulated comportment of the circuit in figure 2. Ideally, the known reference current would be the same as the replicated reference current regardless of the number of loads added to the current mirror circuit. Pdf design and analysis of current mirror circuits on. The current being mirrored can be a constant current, or it can be a varying signal dependent upon the. It is predicted that this current mirror may be more used when power supply voltage is. It is evident that the output impedance of both the current source and the sink are rds of. 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. General description the adl5315 is a wide input current range, precision highside current mirror featuring a stable and useradjustable input.
The current being mirrored can be a constant current, or it can be a varying signal dependent upon the requirement and hence the circuit. Transistors in a current mirror circuit must be maintained at the same temperature for precise operation. To illustrate this dependence on equal temperature, try grasping one transistor between your fingers to heat it up. Nmos and pmos implementations of a cascode current mirror. Current mirrors consist of two branches that are parallel to each other and create two approximately equal currents. I think that the two configurations with appropriate ibias. Multiple current sources and sinks with different magnitudes can be synthesized from a single current source. Im unable to understand the input part of the circuit where the author says producing the opposite where the collector current controls the vbe is not possible in the conventional use of the device as a common emitter amplifier. Current mirror circuit designs using bjt and mosfet. This is why these circuits are called current mirrors. 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.
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. A wilson current mirror is a threeterminal circuit fig. The ds3920 precision current mirror is designed for avalanche photodiode apd and pin photodiode biasing and monitoring applications. The device offers a current clamp to limit current through the apd and a current mir. To best understand this important circuit building. R b serves no purpose except to provide a path for the base current. Wooyoung choi for q 1 and q 2 i o i ref only if v ds1 v ds2 v 0v gs 0 ogs o ref vv ii r mismatches between i ref and i o. The current mirror circuit gains its name because it copies or mirrors the current flowing in one active device in another, keeping the output current constant regardless of loading. Current mirror with multiple outputs pnp current mirrors npn current mirrors s e v v i c i s e be t i. A current mirror is a transistor circuit that regulates the current through a load resistance, the regulation point is set by a simple resistor adjustment.
Needs cmfb circuit for v b4 either singleended or differential outputs can connect counterpart as current mirror to eliminate cmfb folding caused modest deterioration of a v0 and gb energy efficiency modest improvement in output swing v in v in v out v out v dd v ss v ss i t v b4 v b3 v b2 v b1 m 1 m 2 m 7 m 9 m 8 m 10 m 5 m 6 m 3 m 4 i t2. Im trying to understand current mirror circuits and ive been reading this article. Iowa state university ames, ia 50011, usa dallas semiconductor corp. Circuit for pnp current mirror using simple device with dotmodel statement shown figure 1 shows a schematic for a pnp current mirror. Current mirrors current mirrors are important blocks in electronics. Precision wide range 3 na to 3 ma highside current.
A current mirror circuit, mirror or copy the input current of one active device to the other. Vv so, if t gs v v, then the mosfet is in saturation. China 2 school ofelectric and information engineering, wuhan institute oftechnology, wuhan 430073, china email. The term cascode dates back to the days of vacuum tubes, before any sort of semiconductor devices were. In analog circuits current sources act as a large resistor without consuming excessive voltage headroom. How to build a current mirror circuit chapter 5 discrete semiconductor circuits pdf version. But there is a modification in the output transistor. 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. Also, an ideal current mirror will have zero input resistance but high output resistance. Bjt the bjt implementation of the simple current mirror is used as a block in the operational amplifier. Background a simple bipolar current mirror structure is shown in figure 1. In above wilson current mirror circuit, there are three active components which are bjts and a single resistor r1. Current mirror circuit including a current input terminal 2, a current output terminal 6, a common terminal 8, a first transistor t1 arranged between the current input terminal 2 and the common terminal 8, a second transistor t2 arranged between the current output terminal 6 and the common terminal 8, a transconductance stage ts having an input terminal coupled to the. A novel bandgap reference for minimizing currentmirror.
Implementation and applications of current sources and. It has been demonstrated that the circuit shows improved immunity to current mirrormismatch through the selfcompensated current paths. In the video, the programmed voltage across q2s collector is reflecting across the q3 collector. This work was supported, in part, by dallas semiconductor corp.
When building a real current mirror circuit using discrete transistors, the two transistors should be epoxyglued together backtoback so that they remain at approximately the same temperature. But often the current mirror configuration is used. An alternative current mirror exhibiting a high output impedance. Wilson current mirror this is another type of current mirror. C1, the bypass capacitor on the power supply line, is usually necessary for stable. The reference current source is also known as golden current source. For a 50a current sink, use the circuit shown in figure 4. Important attributes for current sources include high output resistance with a wide range of voltage compliance and rejection of external variations such as power supply or temperature. What is current mirror and what are its advantages. A constantcurrent source byu department of physics and.
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. Differences between current sources transistor and current. Edn use a current mirror to control a power supply. Current mirrors are one of the most common buildings blocks both in analog and mixedsignal vlsi circuits. A current mirror circuit has lots of primary and secondary dependencies and that is the main concern to characterize current mirror circuit. We know that for a mosfet in saturation, the drain current is equal to. An ideal current mirror is a two port circuit that accepts an input current i in and produce an output current i out i in. Hence, for low voltage analog circuit structures, low voltage current mirrors are mandatory. Vv v ogs t assuming q 1, q 2 have same properties k n, vv dd gs r. An example application of the current mirror is the transconductance op amp. Voltageto current conversion functional block diagram voltage reference current limiting comm vset nc inpt ipd current mirror 1.
Concept of current mirror circuit analog electronics youtube. Simple current mirror two implementations exist for the simple current mirror. Pdf a high performance current mirror for low voltage. The mirrored current is a precise copy of the input current.
This circuit is an nchannel implementation of the well known wilson current mirror 7. Chapter 16 analog integrated circuits chapter outline 16. 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. Since a current mirror output must equal its input, 50a flows in the input to ground, and the output is a 50a current sink. An ideal current mirror is simply an ideal inverting current amplifier that reverses the current direction as well or it is a current controlled current source cccs. The above circuit does pose its own voltage headroom limitation. 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. Here, the wellknown lm2596 is controlled by the offtheshelf current mirror bcv61. The current mirror is used to provide biasing current and active loads to circuits. Voltagetocurrent conversion functional block diagram voltage reference current limiting comm vset nc inpt ipd current mirror 1. It may be used as a wilson current source by applying a constant bias current to the input. A 100a current source is tied to the mirror common. A current mirror circuit is designed to replicate a known reference current in one branch of a circuit and apply the replicated reference current into another branch of the circuit. If compliance closer to the negative rail is needed for either.
Note that q2 in previous circuit is split to q2 and q5 in this circuit. The cascode mos current mirror the cascode current mirror is derived from the simple current mirror by cascoding both branches of the circuit. Pdf applications of current mirrors in analog signal processing. They are widely used in several applications and chips, the operational amplifier being one of them. Vbn relative to 3 current mirror ota same g m, gbw, and sr a v increased by cascode g mc r oc factor approximately same noise. The current being copied can be, and sometimes is, a varying signal current. Mosfet current mirror and active load electronic circuits 1 2 prof. The sections are dielectrically isolated, making them completely independent. Current mirror is a fundamental unit, widely used for current amplification, biasing and active load in various analogmixed mode integrated circuits. Discretecircuit c e c c2 c c1 c e c c2 c c1 bias with single supply bias with two supplies. A current mirror is a circuit designed to copy a current through one active device by controlling. Zds1009 current mirror datasheet diodes incorporated. 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. Figure 4 here is a designedtowork application of the principle of figure 2.
Ee105 fall 2014 microelectronic devices and circuits. 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. Current mirrors are basic building blocks of analog design. This lecture deals with the design of current mirrors as both bias elements and signal processing components. Current mirror examples, proper scaling, bipolar current mirrors duration. 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. The device offers a current clamp to limit current through the apd and a. Voltage and current sources rely on the availability of. A pnp current mirror converts current sinks into current. A novel bandgap reference for minimizing currentmirror mismatch.
Pdf current mirrors are one of the most common building blocks both in analog and mixedsignal vlsi circuits. Mar 06, 2017 operation of the basic mosfet current mirror. A current mirror is a circuit block which functions to produce a copy of the current flowing into or out of an input. The schematic of the resulting structure is given in figure 4.
When using discrete transistors, you may glue their cases together to do this. Common emitter bjt amplifier design current mirror design. 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. Summing currents at the node where iref enters the circuit yields. Also, because the current sources are twoterminal devices, they can be used equally well as current sinks. Figure 3 this diagram shows the pspice simulated comportment of the circuit in figure 2. Transistor current mirror circuits gate study notes for 2019.
333 58 1491 2 804 733 1280 669 508 227 705 1150 615 122 1219 645 1112 445 645 1488 210 252 409 1270 1050 1435 360 180 238 1195 572 23 377 981 1304