The fundamental current mirror with mos transistors. Metaloxide semiconductor fieldeffect transistor mosfet the metaloxide semiconductor fieldeffect transistor mosfet is actually a fourterminal device. Eliminating the early effect in the wilson current mirror. Transistor m1 is operating in the saturation or active mode, and so is m2. To best understand this important circuit building. It may be used as a wilson current source by applying a constant bias current to the input branch as in fig. This new mirror is well suited for low current biasing applications. It should be noted that the wilson current mirror is not a constantcurrent source.
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. Zds1009 current mirror datasheet diodes incorporated. If the supply voltage, v cc changes, the output current will change. Lecture notes microelectronic devices and circuits. How the wilson current mirror equalizes the input and output currents. Multiple current sources since there is no dc gate current in mosfet, we can tie up multiple current mirrors to single current source. Other current mirrors wilson current mirror is the current mirror circuit named after its inventor george wilson. It is of particular interest for current sense applications for feedback purposes. High current power mosfet with current mirror and temperature sense diodes ixys its diversified product base of specialized power semiconductors, integrated circuits and rf power is utilized by more than 2500 customers worldwide, ranging across industrial, transportation, telecommunications, computer, medical, consumer and clean tech markets. For i use both nmos and pmos to generate sink and source current. Chapter 16 analog integrated circuits chapter outline 16. The amplitude of the current is micro a and the duration of the pulse is micro sec, so i think it might be some special requests for the discrete mosfet. In above wilson current mirror circuit, there are three active components which are bjts and a single resistor r1. 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.
A low voltage selfbiased and bulkdriven mosfet wilson. 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. When there is a current input, there is a current output, which is the exactly mirror or multiple of the input current. Current mirrors current mirrors current mirrors are. This current might come from a resistor connected to the positive rail or a current source realized with a transistor or another current mirror. In this example we will construct a current mirror, where we would like to mirror the current four times the current source.
Conceptually, an ideal current mirror is simply an ideal inverting current amplifier that reverses the. 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. 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. Current mirror texas instruments current regulation. 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. Wilson current mirror 3 current ratio 3 reference current 4 output resistance 4. Mosfet current mirror and cs amplifier electronic circuits 1 062 prof. If one transistor should become hotter than the other, it will pass more collector current than the other, and the circuit will no longer mirror current as expected. The circuit shown in fig 5 shows the circuit configuration if you are using a hexsense current sensing mosfet. Estimate the minimum voltage across m1 if it is to remain in saturation. The current sense resistor value is chosen based on the. Wilson won and his mirror, in its bipolar form, has been a. And even in this case the wilson idea is beneficial.
A low voltage selfbiased and bulkdriven mosfet wilson current mirror circuit 1shobhna, 2mrs. The basic current mirror can also be implemented using mosfet transistors, as shown in figure 2. The emitters of the two transistors are shown connected to ground. The mirrored current is a precise copy of the input current.
In this circuit a fraction of the drain current flows out of the hexsense mosfet current sense pin through the current sense resistor to the kelvin source lead. Assume that the nmos devices in a single ald1103 package are matched to each other. Analogue electronicscurrent mirrorswilson wikibooks. Typical bias of a discrete cs amplifier placing a current mirror in the source circuit will not work. 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. Lowvoltage wilson current mirrors in cmos request pdf.
View notes current mirrors from electrical 468 at northwestern polytechnic university. Use a resistance r to replace the ideal iref source. The current being copied can be, and sometimes is, a varying signal current. Features, specifications, alternative product, product training modules, and datasheets are all available. I put 100 ohm resisters on the source to ground, and that helped a little. How accurately does this formula predict the output impedance of the. Mosfet for mciro current mirror all about circuits. Also, when compared with basic current mirror, improved one consumes only 14th of the power consumed by the basic current mirror. Design a circuit to bias the mosfet in figure shown, so that its drain current is 5. 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.
An example application of the current mirror is the transconductance op amp. In order to justify the name current mirror, in this circuit the output current has to follow exactly the input current. 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. In next videos, we will cover cascode current mirror, wilson current mirror etc. Derive the smallsignal model output impedance, rout, of the simple current source and the modified wilson current source. In addition to the drain, gate and source, there is a substrate, or body, contact. Size the transistors in the mirror for a current gain equal to unity, a 30. Note that the gate voltage of each mosfet is the same i. Yet, we dont, choosing introduction to electronics.
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. Construct the following circuit with the following sizes for the transistors. The circuit consist of negative feedback network to improve the performance. 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. Can we place a current mirror in the source circuit. A wilson current mirror is a threeterminal circuit fig. Suppose that the reference current, i ref, is supplied by a resistor to the supply voltage. An nchannel mosfet current mirror with a resistor to set the reference current iref. For the love of physics walter lewin may 16, 2011 duration. They are widely used in several applications and chips, the operational amplifier being one of them. When building a real current mirror circuit using discrete transistors, the two transistors should be epoxyglued together backtoback so that they remain at approximately. Like the wilson and widler current mirror circuits, this new current mirror can be used as a low current biasing circuit.
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