The bias circuit is devoted to supply currents andor. Calculate the parallel resistance of the current mirror and the widlar current source and enter the values in. Ic biasing and bjt current source content current mirrors and current source improvements of current mirror circuits, widlar and wilson current mirror multitransistor current mirror introduction for discrete circuit. Wilson current mirror can be used to increase output resistance and gain. Electronic circuits 1 highspeed circuits and systems laboratory lect.
Alowvoltage mos cascode current mirror for all current. The common terminal is connected to a power supply or ground, and the input current source is connected to the input terminal. Current mirrors are basic building blocks of analog design. The output resistance of wilson current mirror is substantially greater than. The output current is equal to the input current multiplied by a desired current gain. Ecen3250 lab 6 design of current sources using mos transistors. An example application is the 741 operational amplifier, and widlar used the circuit as a part in many designs. The ref200 current mirror uses a full wilson architecture for high. In practical application of current mirror, early voltage is assumed to be. In the final section, we saw some examples of how current mirrors are incorporated into analog integrated circuits. The mirrored current is a precise copy of the input current.
Lecture08 current sources university of california, berkeley. Widlar current source is used when a small current is needed. In the video, the programmed voltage across q2s collector is reflecting across the q3 collector. Applications of current mirrors in circuits operating at higher frequencies req. How does it provide improvement over simple current mirror circuit. In these twobranch mirror combinations it is achieved the temperature compensation of the current flowing through a single branch, treated as output branch. Analog electronics, analog circuits, transistors, current mirror, widlar mirror, transistor current mirror. Current mirror current source also known as ce bjt current source with constant voltage drive. Each of these current mirrors can operate on a low powersupply voltage of a.
Lecture 14 fet current and voltage sources and current. The basic parameter that describes the functionality of a current mirror is its current gain or reflection coefficient. Simple current mirrors the circuits depicted in figure 3 are the simple and the widlar current mirrors. The motivation behind a current mirror is to sense the current from a golden current source and duplicate this golden current to other locations. The output impedance of a widlar current mirror is approximately, where. The current mirror is used to provide bias currents and active loads to circuits. The circuit is exactly the same as the basic current mirror circuit using two bjt transistors. Class ab current biasing simulation bias currents set at i ref and i q by r and emitter resistors r e.
Pdf this paper investigates the state of the art compensation. The current mirrors are particularly useful for the distribution of bias currents in larger circuits. Constant currents are established by current mirrors, current sinks, and current sources, all of which are often collectively. Modify the simple mirror into a widlar mirror as shown in figure. Use a current mirror to control a power supply edn. Transistor current mirror circuits gate study notes for 2019. The only difference between the two circuits is the introduction of an emitter resistor. The proposed circuit is simulated using hspice for 0. V tn 2 i o i ref lecture20 current mirrors 10 mos current mirrors changing the mirror ratio mirror ratio can be changed by modifying wl ratios of the two transistors forming the mirror. Alowvoltage mos cascode current mirror for all current levels bradley a. Ic3 and ic4 are matched to ic1 the control transistor but ic2 is reduced by re2. Current mirror using a common collector stage to balance input and output. Ch 9 cascode stages and current mirrors 47 bad mos current mirror example this is not a current mirror since the relationship between vxand iref is not clearly defined.
Vcc the most basic current mirror with 2 fe in out fe hi. A wilson current mirror is commonly used because of its good accuracy and. Ec8453 important questions linear integrated circuits. Its operation is simple and has been discussed in the lecture. Linear integrated circuit questions and answers operational amplifier internal. Class ab current biasing simulation bias currents set at i ref and i o by r and emitter resistors r e.
An example application of the current mirror is the transconductance op amp. Fet current and voltage sources and current mirrors the building blocks of analog circuits iv in this lecture you will learn. Lecture 8 mosfet current mirror, widlar, reference. Operational amplifiers and linear integrated circuits, 3e. Alowvoltage mos cascode current mirror for all current levels. Current is input to the drain of the third mos transistor. The most basic current mirror with 2 fe in out fe hi i h and an output resistance equal to 2 ce a o c vv r i.
Widlar current source, for which 1 2 2 ln c c ec kt i i qr i. Considering that the baseemitter voltages are equal and assuming the. Section 4 deals with the simulations using pspice and. This additional component forces the currents in the two branches of the circuit.
Ive explained its basic concept also ive given link below in the description related to how we can improve cmrr. Concept of using a current mirror circuit to allow subtraction of collector currents at a simple node by kcl. M use of a current mirror in nchannel mosfet difference amplifier for single ended output and higher common mode rejection. Section 4 deals with the simulations using pspice and the comparative results are shown. A wilson current mirror is a threeterminal circuit that accepts an input current at the input terminal and provides a mirrored current source or sink output at the output terminal.
I also me his brother at the analog aficionado dinner. The main problems of discrete current mirrors, compared to monolithic implementations, as you hint at in your question, are the unequal current density if you use them at a ratio other than 1, and temperature difference between the devices. In a widlar current source, a current much smaller than the reference current can be. 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. Widlar current source the widlar current source, a variation of the simple current mirror, was advanced by bob widlar in the mid 1960s. The output resistance is equal to the output resistance of the q 2 or m 2.
Another advantage over the basic current mirror is that it has a higher output resistance. Pdf compensation in mos current mirror circuits researchgate. Firstorder temperaturecompensated totalcurrent reference. Constant currents are established by current mirrors, current sinks, and current sources, all. Following that algorithm a current mode all analog circuit with cascode current mirror as basic circuit element is proposed which computes dft using radix4 fft algorithm. The objective in this prelab assignment is to design a current source using two nmos transistors in a current mirror configuration shown in figure 2.
Wilson, an integrated circuit design engineer who worked for tektronix. Design and implementation of low voltage, high bandwidth. I never had the pleasure of meeting bob widlar, but i did learn about his widlar current source at nyu in my undergraduate studies in 1969 see bob widlar cherrybombs the intercom speaker on edn. Specifics of using current mirrors for highside current. An output current is output from the source of a mos transistor for conversion to a voltage by a circuit that receives the current which outputs a reference voltage. The minimum output voltage is very low vcesat of q2.
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. This circuit is named for its inventor, robert widlar, and was patented in 1967. There is much literature available on the design of current mirrors. Suketu naik summary an overriding concern for ic designers is the minimization of chip area or silicon real estate. Bias current source is this a good bias current source. This additional component forces the currents in the two branches of the circuit to be unequal. 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.
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. Linear integrated circuits questions and answers for freshers. For its operation it relies heavily on the parity of parameters and regimes between the two. If the gain is unity, then the input current is reflected to the output. A widlar current source is a modi cation of the basic twotransistor current mirror that incorpo. Pdf widlar current mirror design using bjtmemristor. Ch 9 cascode stages and current mirrors 31 bipolar current mirror circuitry. A wilson current mirror is a threeterminal circuit fig. The maximum variation of output current with frequency for the modified howland circuit was 2. Two of the circuits requires an input voltage of a diode drop plus a saturation. Media in category current mirror circuits the following 58 files are in this category, out of 58 total.
Abstractthis paper presents a description of basic current mirror cm, widlar current mirror, fourth circuit element. The widlar current mirror, a widely used integrated circuit configuration. The collector current of q2 may be much lower than q1 with only a modest value for re. Ee105 fall 2014 microelectronic devices and circuits. The resulting class of sub circuits is called current mirrors. Taking into account its advantages, the low swing cascode current mirror is an often used solution in low voltage biasing circuits.
What will be the value of emitter resistance in widlar current source for. The widlar circuit may be used with bipolar transistors, mos transistors, and even vacuum tubes. How accurately does this formula predict the output impedance of the widlar current mirror you constructed. Pdf a comparison of modified howland circuits as current. Figure 1 shows an ideal current source where the output current iout is independent of the voltage vout across the output terminals. Transistor current mirror circuits download study material. The only way to clearly define vx with iref is to use a diodeconnected mos since it provides squarelaw iv relationship. Eecs240 lecture 8 4 current mirror better approach. View lecture 8 mosfet current mirror, widlar, reference generator, band gap references. But there is a modification in the output transistor. Us20060091940a1 us11262,940 us26294005a us2006091940a1 us 20060091940 a1 us20060091940 a1 us 20060091940a1 us 26294005 a us26294005 a us 26294005a us 2006091940 a1 us2006091940 a1 us 2006091940a1 authority us united states prior art keywords mos transistor current circuit gate drain prior art date 20040211 legal status the legal status is an assumption and. It may be used as a wilson current source by applying a constant bias current to the input branch as in fig. Another excellent current mirror circuit is the widlar current source circuit, invented by bob widlar.
Pdf lowvoltage wilson current mirrors in cmos semantic. The analysis has been performed by comparing a modified configuration with a simple circuit of widlar cm. Ecen3250 lab 6 design of current sources using mos. Us20060091940a1 cmos current mirror circuit and reference. Simple current mirror wilson current mirror cascode current mirror simple current mirror. The widlar circuit may be used with bipolar transistors, mos transistors, and. The ratio of i m2 i m1 is given by w2 w1 for same l early e ect cancelled for v d v.
Widlar current mirror a resistor r e is included in the emitter of q 2 7. The output impedance for both circuits was greater than 100 k for frequencies up to 100 khz. The circuit below shows how to do this with the current mirror. Floating gate wilson current mirror for low power applications. Summing currents at the node where iref enters the circuit yields. What will be the overall gain in darlington circuit, if the individual transistor gain is 200. The active compensation technique has been applied to some of the current mirrors and is presented in section 3. Read on wikipedia edit history talk page print download pdf.
The setups for the ac and parametric sweeps are shown below. The focus of analysis were a power dissipation, a total harmonic distortion and a chipsurface. I ref i qn i qp i l pnp widlar current mirror npn widlar current mirror r l 100. In an analog signal processing circuit there are two. 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. The drain current of the second mos transistor is mirrored by cascode current mirror circuits. Equivalent circuits of the mosfet cascode current mirror for determining r o 4. Procedure 1 current mirror comment a common need in circuit design is to establish a constant dc current for purposes of biasing a transistor, injecting a current offset, or driving a load at a constant value of current. It is a widlar mirror without an emitter degeneration resistor in the follower output transistor. Feb 23, 2019 in this video you will come to know about widlar current source and its working. Widlar current mirror design using bjtmemristor circuits arxiv. I ref i on i op i l pnp widlar current mirror npn widlar current mirror r l 100. The current mirror is an important analog building block that finds application in such diverse areas as dc biasing and.
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