Pchannel mosfet s m2 and m4 act as a current mirror and are in strong inversion and m1 and m3 are in weak inversion region. Your current mirror will pull current out of an external circuit comprised of a 10k. Voltage and current sources rely on the availability of. Difference between simple cascode current source and. Lecture 14 fet current and voltage sources and current. Lowvoltage wilson current mirrors in cmos ieee conference. Bjt current mirror mosfet current mirror multisim live. Also, when compared with basic current mirror, improved one consumes only 14th of the power consumed by the basic current mirror. If we assume that m1 and m2 are matched, the dc current iqdivides equally between the devices so that id1 id2 iq2. We now know how to implement this bias design with mosfetswe use the. Figure 3 shows a small signal model of a wilson current mirror drawn with a test voltage source. A small amount of the current flowing through r provides base current for q3, enabling q3 to conduct current. Current mirrors consist of two branches that are parallel to each other and create two approximately equal currents.
Cmos ptat current source a circuit which uses mosfet s only and one resistor is shown in. I put 100 ohm resisters on the source to ground, and that helped a little. Comparison of cmos current mirror sources citeseerx. The transistors used for implementing different current mirror circuits have been modeled using 0. The advantage of the wilson mirror over the current mirrors examined above is that it has a. For the love of physics walter lewin may 16, 2011 duration. Because the two transistors have their baseemitter junctions in parallel. Transistor m 1 is operating in the saturation or active mode, and so is m 2. Use a resistance r to replace the ideal iref source. The drain current of mosfet depends on its gate voltage v g and drain voltage v d.
Table 1 shows the comparison between different current mirror circuits on the basis of the simulation results obtained. The mirrored current is a precise copy of the input current. Zds1009 current mirror datasheet diodes incorporated. 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. Figure 3 shows the basic current mirror with a third transistor added. Characteristics of mosfet current mirrors we can easily use enhancement mode mosfets to form current mirrors, as shown in the circuit to the right. Najmabadi, ece102, fall 2012 2 17 cascode amplifier is a twostage, cscg configuration. A low voltage selfbiased and bulkdriven mosfet wilson current mirror circuit 1shobhna, 2mrs. If the effect of early voltage is important, it can be minimized by using the slightly more complex wilson current mirror. Finding frequency response of amplifiers capacitors typically divide into two groups.
On the left is a bjt current mirror and on the right is a mosfet current mirror. 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. Pdf analysis and simulation of mosfet differential amplifier. To best understand this important circuit building. Now wilson current mirror is less dependent on beta values meaning it is less dependent on transistor parameters but o. We present experimental results from versions of these three current mirrors that were fabricated in a 0. The simple mosfet current mirror has only the second imperfection because there are no gate currents. The three t2 collectors may be joined to give 3i in. Current mirrors usually employ the same length for all of the transistors. An nchannel mosfet current mirror with a resistor to set the reference current iref. 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.
Transistor m1 is operating in the saturation or active mode, and so is m2. What are the advantages and disadvantages of using an. The implementation of the current mirror circuit may seem simple but there is a lot going on. What is current mirror and what are its advantages. Derive the smallsignal model output impedance, rout, of the simple current source and 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. Browse other questions tagged mosfet test current mirror or ask your own question. Analysis of the modified mos wilson current mirror. Build a mirror using pnp transistors and use the output impedance of the simple mirror to determine the early voltage for the pnp transistor. 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. Circuit ideahow the wilson current mirror equalizes the. Cmos ptat current source a circuit which uses mosfets only and one resistor is shown in. Like the wilson and widler current mirror circuits, this new current mirror can be used as a low current biasing circuit. In this setup, the output current i out is directly related to i ref, as discussed next.
Wilson won and his mirror, in its bipolar form, has been a. Lowvoltage wilson current mirrors in cmos request pdf. High current power mosfet with current mirror and temperature. Current mirrors current mirrors are important blocks in electronics. The wilson current mirror a wilson current mirror is shown in fig. 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 wilson current mirror is a threeterminal circuit fig. A low voltage selfbiased and bulkdriven mosfet wilson. Thus, the drain current can be expressed as, figure 4. Chapter 16 analog integrated circuits chapter outline 16. 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. In the previous article, we discussed about current mirror circuit and how it can be built using transistor and mosfet. The left side, which is the same as that shown in fig. Fet current and voltage sources and current mirrors the building blocks of analog circuits iv in this lecture you will learn.
The current mirror with ac grounded output for finding closedloop current gain. The proposed circuit is simulated using hspice for 0. Analogue electronicscurrent mirrorswilson wikibooks, open. The gate source voltage is set by the diode geometry and the injected input or reference current. At first glance, the current mirror circuit shown to the right would seem to be backwards. Floating gate wilson current mirror for low power applications. Set 16 vbe multiplier and complimentary common collector amplifier problems. Wu,uc berkeley current flowing through the channel between the source and drain is controlled by the gate voltage. Frequency response university of california, san diego. 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. It is evident that the dc drain current id, is equal to the current source i, regardless. 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. Eventhough the textbooks claim that the negative feedback in wilson increases the output resistance, the final output resistance for both circuits turn out to be the same.
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. Ee105 fall 2014 microelectronic devices and circuits. We will use absolute limits of f 0 all capacitors open and f. Browse other questions tagged mosfet test currentmirror or ask your own question. Structure and operation of the wilson current mirror and the modified wilson current mirror using mosfet transistors. They are widely used in several applications and chips, the operational amplifier being one of them. A current mirror gives a replica attenuated or amplified, if necessary of a. The simple mosfet current mirror has the second imperfection only because there are no gate currents. Wilson current mirror bjt and mosfet cascoded current mirror bjt and mosfet for best performance, transistors should be matched, temperature should be.
This technique is also useful in reducing the power supply voltage required for a mosfet to operate in a saturation region, which in turn minimizes the dynamic power dissipation. These are circuits that reflect an input current to a load. Measure id3 with either an ammeter, or by measuring the voltage drop across r1 and applying ohms law. The basic current mirror can also be implemented using mosfet transistors, as shown in figure 2. Current ratioing is achieved by only scaling the width of transistors. The cascode and wilson current q1 q2q3 q4 figure 16. Under this condition all three transistors have nearly equal collector currents and therefore. 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. 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. Mosfet current mirror and cs amplifier electronic circuits 1 062 prof. Currentoutput circuit techniques add versatility to your. Pdf compensation in mos current mirror circuits researchgate. Lecture 15 the mosfet university of california, berkeley. Direct scaling of the width also faces difficulties.
May 29, 2015 this new mirror is well suited for low current biasing applications. Start by drawing the smallsignal equivalent circuit. Replicate reference current at various places required. Level 3 using the current mirror from level 2, use. This tutorial will demonstrate the basic idea of a current mirror which is widely used in integrated circuits. There are also other possibilities such as using voltage regulators as current sources.
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. For small signals, we can write the quantities in above. In fact, however, it works quite well, although in a roundabout fashion. Both threetransistor and fourtransistor versions are shown in figure 3. Mar 06, 2017 structure and operation of the wilson current mirror and the modified wilson current mirror using mosfet transistors. Assume that the nmos devices in a single ald1103 package are matched to each other. If the supply voltage, v cc changes, the output current will change.
I think sourcing current over known resistor with pwm and mirroring it to unknown load may work much more reliable than trying to measure current over shunt resistor and trying to set pwm to get the right current. Hi all, ive been going through some current source topologies for my work, and i acnt seem to find the difference between a simple cascode current source and a modified wilson current source see attached figure. The fourtransistor version is more accurate and has a wider dynamic range. It is mirrored into the collector of q1 by dividing by 1. The reference current source is also known as golden current source. The modified wilson current mirror is an attempt to improve performance by increasing the effective output resistance at the drain of the mirror mosfet. 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 two bjts have equal base to emitter voltage vbe, also vb in this case and the two mosfets have equal gate to source voltage vgs, also vg in this case. We can easily use enhancement mode mosfets to form current mirrors, as shown in the circuit to the right. Pdf design and implementation of mosfet based folded. Multiple current sources and sinks with different magnitudes can be synthesized from a single current source. Different current mirror circuits described has been analyzed using pspice simulation.
The mosfet implementation of the wilson current mirror looks like the following. Analogue electronicscurrent mirrorswilson wikibooks. The mosfet substrate gate source drain metaloxidesemiconductor fieldeffect transistor. A new cmos voltage divider based current mirror, compared with the basic and cascode current mirrors presented by m.
It should be noted that the wilson current mirror is not a constant current source. The emitter current in q3 is iothis current is the input to a basic current mirror consisting of q1 and q2. In next videos, we will cover cascode current mirror, wilson current mirror etc. Suppose that the reference current, i ref, is supplied by a resistor to the supply voltage. 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. 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. Cascode current mirror wilson current mirror wideswing current mirror 4. It is of particular interest for current sense applications for feedback purposes. Similarly for a current sink with nmos transistor the drain to source voltage. We thus prefer to employ a unit transistor and create copies by repeating such a device.
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