Creating the circuit to establish the desired dc voltages and currents for the operation of the amplifier four common ways. It consists of four transistors, two of which are gatedrain connected m2 and m3. Circuit ideahow the wilson current mirror equalizes the. The power mosfet is driven by a pwm signal that provides both the propertiming driving voltage and a negative pulse that generates a switching. 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.
Voltage and current sources rely on the availability of. The drain current of mosfet depends on its gate voltage v g and drain voltage v d. In the circuit below, m1 and m2 are nchannel mosfets with kn 40 mav2, w4um, l2um, and vt 0. Mosfet amplifier design a mosfet amplifier circuit should be designed to. Lowvoltage wilson current mirrors in cmos request pdf. Derive the smallsignal model output impedance, rout, of the simple current source and the modified wilson current source. Dd th n ox out v v r r r l c w i i out depends upon supply, process and temperature. In next videos, we will cover cascode current mirror, wilson current mirror etc.
Analogue electronicscurrent mirrorswilson wikibooks, open. Direct scaling of the width also faces difficulties. Transistor m1 is operating in the saturation or active mode, and so is m2. The simple two transistor implementation of the current mirror is based on the. If we assume that m1 and m2 are matched, the dc current iqdivides equally between the devices so that id1 id2 iq2. The mosfet implementation of the wilson current mirror looks like the following.
It is evident that the dc drain current id, is equal to the current source i, regardless. A simple derivation is given for the dynamic output resistance of the wilson current mirror, which forms a basic building block in many analog integrated circuits. Set 16 vbe multiplier and complimentary common collector amplifier problems. It should be noted that the wilson current mirror is not a constant current source. Currentoutput circuit techniques add versatility to your. Using the bulkdriven technique together with quasifloating gate metaloxide semiconductor. Power voltagecurrent converter using quasicomplementary. The emitter current in q3 is iothis current is the input to a basic current mirror consisting of q1 and q2. Mos wilson current mirror using signal flow graphs sfgs, masons gain. Current mirrors current mirrors are important blocks in electronics. Under this condition all three transistors have nearly equal collector currents and therefore. Assume that the nmos devices in a single ald1103 package are matched to each other.
If the effect of early voltage is important, it can be minimized by using the slightly more complex wilson current mirror. Characteristics of mosfet current mirrors we can easily use enhancement mode mosfets to form current mirrors, as shown in the circuit to the right. To best understand this important circuit building. 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. Using a cascode connection will allow for the output resistance ro2 to be boosted in value one such a design is the modified wilson current source.
Current mirrors made by using active devices have come to be widely used in analog integrated circuits both as biasing elements and as load devices for amplifier stages. The fourtransistor version is more accurate and has a wider dynamic range. In this setup, the output current i out is directly related to i ref, as discussed next. Figure 3 shows a small signal model of a wilson current mirror drawn with a test voltage source. In fact, however, it works quite well, although in a roundabout fashion. In the previous article, we discussed about current mirror circuit and how it can be built using transistor and mosfet. The threshold of the mos transistors placed in close proximity are. High current power mosfet with current mirror and temperature. A low voltage selfbiased and bulkdriven mosfet wilson. Just as we connected collector to base with bipolar junction transistors, we can connect drain to gate of a mosfet to cause the device to operate as a forwardbiased diode. May 29, 2015 a new cmos voltage divider based current mirror, compared with the basic and cascode current mirrors presented by m. The mirrored current is a precise copy of the input current. Measure id3 with either an ammeter, or by measuring the voltage drop across r1 and applying ohms law. The modified wilson current mirror is an attempt to improve performance by increasing the effective output resistance at the drain of the mirror mosfet.
Definition of current by a resistive divider 2 1 2 2 2. The wilson current mirror a wilson current mirror is shown in fig. Analysis of the modified mos wilson current mirror. A small amount of the current flowing through r provides base current for q3, enabling q3 to conduct current. At low frequency this ratio is real and represents an output resistance.
Current mirrors usually employ the same length for all of the transistors. Fet current and voltage sources and current mirrors the building blocks of analog circuits iv in this lecture you will learn. 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. 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. Department of electrical and ecse330b electronic circuits i.
Current mirrors current mirrors current mirrors are. Shown in the figure below is the full wilson current mirror. A new mirroring circuit for power mos current sensing highly. A wilson current mirror is a threeterminal circuit fig. We now know how to implement this bias design with mosfetswe use the. To illustrate this dependence on equal temperature, try grasping one transistor between your fingers to heat it up. A new cmos voltage divider based current mirror, compared with the basic and cascode current mirrors presented by m. It may be used as a wilson current source by applying a constant bias current to the input. A current mirror gives a replica attenuated or amplified, if necessary of a. For the love of physics walter lewin may 16, 2011 duration.
Lecture notes microelectronic devices and circuits. A low voltage selfbiased and bulkdriven mosfet wilson current mirror circuit 1shobhna, 2mrs. Analogue electronicscurrent mirrorswilson wikibooks. Najmabadi, ece102, fall 2012 2 17 cascode amplifier is a twostage, cscg configuration. If vdd 5v, what value of rref will make iout 250ua note. Mosfet current mirror and cs amplifier electronic circuits 1 062 prof. Use a resistance r to replace the ideal iref source. At first glance, the current mirror circuit shown to the right would seem to be backwards. In this paper, we describe three simple lowvoltage cmos analogs of the wilson current mirror that function well at all current levels, ranging from weak inversion to strong inversion. The rout was 5 million ohms, running at 10ma, measured on a fairchild curve tracer. A current mirror gives a replica attenuated or amplified, if necessary of a bias. We thus prefer to employ a unit transistor and create copies by repeating such a device.
Browse other questions tagged mosfet test current mirror or ask your own question. Descriptiona wilson current mirror, with all relevant branch current. Current ratioing is achieved by only scaling the width of transistors. Thus, the drain current can be expressed as, figure 4. Riviere avoltage current converter is described having a quasicomplementary classab architecture that is particularlysuited to implementation using discrete power mosfets. Suppose that the reference current, i ref, is supplied by a resistor to the supply voltage. And even in this case the wilson idea is beneficial.
The left side, which is the same as that shown in fig. A relatively complex circuit is used to generate a stable reference current i ref i ref is then copied to the different current sources of the. Wilson won and his mirror, in its bipolar form, has been a. Despite the fact that basic current mirror circuit can be constructed using two simple active components, bjts and mosfets or using an amplifier circuit, the output is not perfect, as well as it has certain limitations and dependencies on the external things. Careful layout and transistor design must be used to minimize this source of error.
They are widely used in several applications and chips, the operational amplifier being one of them. Power voltage current converter using quasicomplementary mosfet current mirrors r. Biasing by fixing v g and connecting a resistance in the source 3. Estimate the minimum voltage across m1 if it is to remain in saturation. The simple mosfet current mirror has the second imperfection only because there are no gate currents. Chapter 9 ee105 spring 2008 lecture 20, slide 1prof. What is current mirror and what are its advantages. The implementation of the current mirror circuit may seem simple but there is a lot going on. In order to justify the name current mirror, in this circuit the output current has to follow exactly the input current. We can easily use enhancement mode mosfets to form current mirrors, as shown in the circuit to the right. 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. A lowvoltage, highperformance, selfbiased, cascode bulkdriven current mirror is proposed. Transistor m 1 is operating in the saturation or active mode, and so is m 2. Ee105 fall 2014 microelectronic devices and circuits.
I put 100 ohm resisters on the source to ground, and that helped a little. Abstracta pedagogical analysis of the modified mos wilson current mirror using signal flow graphs sfgs, masons gain rule, and drivingpoint impedance. An example application of the current mirror is the transconductance op amp. The proposed design is verified with spice simulation of the current mirror in a cmos 2pm technology. Chapter 16 analog integrated circuits chapter outline 16. View notes current mirrors from electrical 468 at northwestern polytechnic university. Design of the wilson and improved wilson mos current mirrors. The basic current mirror can also be implemented using mosfet transistors, as shown in figure 2. I was hoping that having 2 mosfets on the same chip would be close enough, but i guess not. 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.
Start by drawing the smallsignal equivalent circuit. Jan 31, 20 in this region, the power mosfet operates in the saturation region and the mirrored current i mirror is not dependent on the drainsource voltage and is only related with the mirroring factor k. 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. The use of feedback and the current to voltage relationship of two terminal elements such. Table 1 shows the comparison between different current mirror circuits on the basis of the simulation results obtained. Excess populations and minimum carrier lifetime, photoconductivity. Two identical transistor m 1 and m 2, whose sources are connected together, are biased by a constant current source i q which is. Comparison of cmos current mirror sources citeseerx. Consider the single stage cs amplifier with an ideal current source load shown in fig. The gate source voltage is set by the diode geometry and the injected input or reference current.
The use of feedback and the current to voltage relationship of two terminal elements such as a. Your current mirror will pull current out of an external circuit comprised of a 10k. This would help counter the body effect of q1 an q4, which have their v t increased. The reference current source is also known as golden current source. If the supply voltage, v cc changes, the output current will change. 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. Both threetransistor and fourtransistor versions are shown in figure 3. An nchannel mosfet current mirror with a resistor to set the reference current iref.
Different current mirror circuits described has been analyzed using pspice simulation. Cascode current mirror wilson current mirror wideswing current mirror 4. How the wilson current mirror equalizes the input and output currents. Mar 06, 2017 structure and operation of the wilson current mirror and the modified wilson current mirror using mosfet transistors. Similarly, a diode connected enhancement mode mos fet gate tied to drain will. It may be used as a wilson current source by applying a constant bias current to the input branch as in fig. The threshold requirement is removed by the use of fig 6 b, which allows for. Lecture 14 fet current and voltage sources and current.
The overflow blog have better meetingsin person or remote. Level 3 using the current mirror from level 2, use additional. Design a circuit to bias the mosfet in figure shown, so that its drain current is 5. Pdf solutions design a simple current mirror using a current of 1. Multiple current sources and sinks with different magnitudes can be synthesized from a single current source. Structure and operation of the wilson current mirror and the modified wilson current mirror using mosfet transistors. A small signal input voltage v in is applied to the gate and output is taken at drain v o. The transistors used for implementing different current mirror circuits have been modeled using 0. It is mirrored into the collector of q1 by dividing by 1. Build a mirror using pnp transistors and use the output impedance of the simple mirror to determine the early voltage for the pnp transistor. Request pdf lowvoltage wilson current mirrors in cmos in this paper. The current mirror with ac grounded output for finding closedloop current gain. Pdf design and implementation of mosfet based folded.
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. Figure 3 shows a small signal model of a wilson current mirror drawn with a test voltage source, v test. 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. 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. Dynamic output resistance of the wilson current mirror.
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