The implementation of the current mirror circuit may seem simple but there is a lot going on. 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. To best understand this important circuit building block and how it makes use of this relationship we need to deconstruct the circuit into input and output sections and examine each in turn.
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. 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. Another feature of the current mirror is a relatively low input resistance which helps to keep the input current constant regardless of drive conditions.
The current being 'copied' can be, and often is, a varying signal current. The current mirror is often used to provide bias currents and active loads in amplifier stages. The ideal block level concept of the current mirror is shown in figure Given a current source as the input, the input section of the current mirror looks like a virtual short circuit and reflects swaps the direction of flow this current to produce a current sink the current exiting the mirror ; as a result, we obtain a current sink figure Conversely, given a current sink as the input, the current mirror reflects this current to control current source figure We can generalize this basic current mirror structure with this first observation: A current mirror consists of a low impedance input stage connected to a high impedance output current stage.
Conceptually, an ideal current mirror is simply an ideal current amplifier with a gain of Accurate current amplifiers are difficult to directly implement using conventional transistor amplifier configurations which are typically voltage amplifiers. For example the MOS transistor is generally modeled as a voltage controlled current source and can not be used directly as a current amplifier. The use of feedback and the current to voltage relationship of two terminal elements such as a resistor are most often used when manipulating currents as signals.
Because in a current mirror the input and output are currents, it is easier to convert the input to a voltage first and then convert a voltage back to a current at the output.
In figure The virtual ground at the negative input of the op-amp provides a very low input resistance. These circuits use the linear relationship between the current in resistor R1 and the voltage across the resistor. However, this linear relationship is not necessarily required. Any element or combination of elements could be used such as the V BE or V GS of a transistor as in b if the output voltage was taken at the gate of M1 output of the op-amp.
Similarly, as an output stage we have the operational amplifier implementation of the voltage to current converter from section 1 of Chapter 4 in figure 1. Here the input voltage is forced across resistor R1 such that the resulting current in R1 flows through transistor M1. Implementing the block diagram of the current mirror shown in figure Note that the second op-amp is not actually necessary because the gates of the two NMOS transistors can be tied directly to each other with the same result.
This is an important simplification of the current mirror concept. The converters might consist of non-linear devices having whatever I to V characteristics that may include another physical quantity such as temperature ; the only requirement is that the characteristics be the inverse of each other.
We can make a second observation: A current mirror consists of two connected stages with inverse transfer functions of each other. The converter circuits in figures A much simpler implementation would be better.
We would like a simple configuration where the active element, a single transistor, serves as the desired current-to-voltage converter. However, the transistor is a unidirectional device, where for the BJT the base emitter voltage controls the collector current or for the FET the gate source voltage controls the drain current.
Producing the opposite where the collector current controls the V BE is not possible in the conventional use of the device as a common emitter amplifier.
Common-Source FET Amplifiers Operation
Referring back to Figure As a result, with this diode connected transistor, the collector current serves as the input quantity while the base-emitter voltage V BE serves as the output quantity with the logarithmic transfer function of the base emitter junction.Transconductance for transfer conductancealso infrequently called mutual conductanceis the electrical characteristic relating the current through the output of a device to the voltage across the input of a device.
Conductance is the reciprocal of resistance. Transadmittance or transfer admittance is the AC equivalent of transconductance. Transconductance is very often denoted as a conductance, g mwith a subscript, m, for mutual. It is defined as follows:. For small signal alternating currentthe definition is simpler:. Transresistance for transfer resistancealso infrequently referred to as mutual resistanceis the dual of transconductance.
It refers to the ratio between a change of the voltage at two output points and a related change of current through two input points, and is notated as r m :. The SI unit for transresistance is simply the ohmas in resistance.
Transimpedance or, transfer impedance is the AC equivalent of transresistance, and is the dual of transadmittance. Typical values of g m for a small-signal vacuum tube are 1 to 10 millisiemens.
The Van der Bijl equation defines their relation as follows:. Typical values of g m for a small-signal field effect transistor are 1 to 30 millisiemens. However, Cartwright  has shown that this can be done without calculus. The g m of bipolar small-signal transistors varies widely, being proportional to the collector current. It has a typical range of 1 to millisiemens.
The output collector conductance is determined by the Early voltage and is proportional to the collector current. A transconductance amplifier g m amplifier puts out a current proportional to its input voltage. In network analysisthe transconductance amplifier is defined as a voltage controlled current source VCCS. It is common to see these amplifiers installed in a cascode configuration, which improves the frequency response. A transresistance amplifier outputs a voltage proportional to its input current.
The transresistance amplifier is often referred to as a transimpedance amplifierespecially by semiconductor manufacturers. The term for a transresistance amplifier in network analysis is current controlled voltage source CCVS. A basic inverting transresistance amplifier can be built from an operational amplifier and a single resistor.Hello friends, I hope you all are doing great. There are three main types of configurations of FET like the BJT which are common emittercommon baseand common collector.
The common source amplifier is the basic field-effect transistor technique that normally works as a voltage amplifier. The simple method to know configuration is either a common drain, gate, or source to find the direction of signal from it entering and leaving. The other terminal remains common. For common source configuration signal enter in the gate and leave from the drain.
While source is common between these two terminals this configuration is known as common source configuration. Thanks for reading. Have a good day. I am a professional engineer and graduate from a reputed engineering university also have experience of working as an engineer in different famous industries.
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Post comment. Skip to content. Facebook page opens in new window Twitter page opens in new window Instagram page opens in new window YouTube page opens in new window. Related Posts. Introduction to Class D Amplifier April 17, Leave a Reply Cancel reply Your email address will not be published.A differential amplifier is a type of electronic amplifier that amplifies the difference between two input voltages but suppresses any voltage common to the two inputs.
Single amplifiers are usually implemented by either adding the appropriate feedback resistors to a standard op-amp, or with a dedicated IC containing internal feedback resistors. It is also a common sub-component of larger integrated circuits handling analog signals.
In practice, however, the gain is not quite equal for the two inputs. A more realistic expression for the output of a differential amplifier thus includes a second term.
As differential amplifiers are often used to null out noise or bias-voltages that appear at both inputs, a low common-mode gain is usually desired. The common-mode rejection ratio CMRRusually defined as the ratio between differential-mode gain and common-mode gain, indicates the ability of the amplifier to accurately cancel voltages that are common to both inputs. The common-mode rejection ratio is defined as:. Note that a differential amplifier is a more general form of amplifier than one with a single input; by grounding one input of a differential amplifier, a single-ended amplifier results.
This circuit was originally implemented using a pair of vacuum tubes. The circuit works the same way for all three-terminal devices with current gain. The long-tailed pair was developed from earlier knowledge of push-pull circuit techniques and measurement bridges. The earliest definite long-tailed pair circuit appears in a patent submitted by Alan Blumlein in DC-coupled circuitry became the norm after the first generation of vacuum tube computers.
A differential long-tailed, [nb 2] emitter-coupled pair amplifier consists of two amplifying stages with common emittersource or cathode degeneration. The two bases or grids or gates are inputs which are differentially amplified subtracted and multiplied by the transistor pair; they can be fed with a differential balanced input signal, or one input could be grounded to form a phase splitter circuit.
An amplifier with differential output can drive a floating load or another stage with differential input. If the differential output is not desired, then only one output can be used taken from just one of the collectors or anodes or drainsdisregarding the other output; this configuration is referred to as single-ended output. The gain is half that of the stage with differential output. To avoid sacrificing gain, a differential to single-ended converter can be utilized.
FET Common Gate Amplifier Circuit
The differential pair can be used as an amplifier with a single-ended input if one of the inputs is grounded or fixed to a reference voltage usually, the other collector is used as a single-ended output This arrangement can be thought of as cascaded common-collector and common-base stages or as a buffered common-base stage.As such the FET common gate circuit is seen used in a limited number of applications, although the common source and common drain configurations are sued far more widely.
Common gate FET configuration provides a low input impedance while offering a high output impedance. As the gate is grounded, this acts as a barrier between input and output providing high levels of isolation, preventing feedback, especially at very high frequencies. Although the voltage gain is high, the current gain is low and the overall power gain is also low when compared to the other FET circuit configurations available.
The FET common gate circuit is not as widely used as other FET configurations, as it often provides very few advantages over other configurations. There are some areas where it proves to be very useful.
The table below gives a summary of the major characteristics of the common gate amplifier circuit. FET common gate features Common gate FET configuration provides a low input impedance while offering a high output impedance.
The other salient feature of this configuration is that the input and output are in phase. The configuration also improves stability which is a key issue. The gate, being grounded provides isolation between the input and output, thereby considerably reducing the possibility of feedback. One application is for moving-coil microphones preamplifiers - these microphones have very low impedance levels.
Common gate amplifier characteristics summary The table below gives a summary of the major characteristics of the common gate amplifier circuit.
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We recommend our premium football predictions to be used as singles. Joshua has released a list of bleak predictions for the New Year 2016, particularly directed towards the continent of Africa. Known for his unconventional antics, Mr. We are supposed to produce a large quantum of food for the world. This is our natural resource base. Mishandling of electoral processes will create a conducive atmosphere for terrorists.
But there will be overwhelming pressure which he will not be able to resist. Nigerians, support and pray for your leader. Despite the worrisome nature of his predictions, Mr. Joshua posted a sermon about the dangers of offence on YouTube, a topic he further addressed in the live broadcast.
Joshua counted several African leaders among his followers, including the newly elected President of Tanzania, John Magufuli, who has been unanimously lauded for the positive strides the East African nation has taken since the start of his presidency. His television station, Emmanuel TV, was added to the DSTV bouquet in November 2015, bringing the Nigerian cleric to an even wider audience across Africa.
According to an announcement on Facebook, Mr.Vendors are innovating with various form factors and technologies such as PCIe, NMVe and 3D XPoint. NVMe is a much-needed update to data transport mechanisms created in an era when Internet users were happy with 28k dial-up connections, This brings the communication channels around storage closer to the velocity of modern processors and flash architectures.
NVMe also excites Jeff Boudreau, president, Dell EMC Storage Division. He notes that although we are still in the early days of real NVMe usage in storage, it will become the industry standard in five years. Storage class memory (SCM) is a general term that may include specific vendor offerings such as 3D XPoint, ZSSD and others.
It is also referenced sometimes as persistent memory (PMEM). This memory technology promises to be 10 times denser and up to 1000 times faster than conventional flash. Jeff Baxter, chief evangelist for ONTAP at NetApp, agrees that the new possibilities offered by SCM and NVMe are disrupting the market and fueling innovation.
NetApp has been developing NVMe-over-Fabrics technology over existing 32 GB FC SAN infrastructure from Brocade directly to NetApp AFF all-flash arrays running the NetApp ONTAP data management system.
It has also introduced SCM technology as a cache directly within an AFF storage controller, providing three times the IOPS with the same release of ONTAP, same controller and same workload.
These technological breakthroughs are the news of today. But in a few years, they will enter the mainstream. Users can expect to pay more for products containing SCM and other technologies for a while. Eventually, however, they will become the norm.
These will be based on server designs with intelligent storage software on top, and less on dedicated storage controller design. When Rob Commins, vice president of marketing at Tegile looks into the crystal ball, he sees one large shared memory pool as opposed to a shared storage pool.
Eric Herzog, vice president of worldwide storage channels, IBM, concurs with other experts that we can expect NVMe and 3D XPoint to become increasingly more prevalent.
He also called attention to recent discussions and presentations centered around RRAM as yet another wave of high performance, non-volatile storage media. At the same time, he foresees flash moving down the food chain. Whereas disk or even tape is regarded as the best home for secondary storage currently, Herzog thinks flash will gradually take over large chunks of these markets.
Perhaps there will be a price premium for the very latest flash technologies like SCM. But otherwise, the idea that all-flash arrays are more expensive than high-performance hard drive based systems is a myth, according to Herzog. On cost per GB, he thinks they are on par. Once you factor in the extensive abilities for data reduction, they can be less expensive per GB. This will spur further development in the software and analytics fields. Boudreau pointed to machine learning as a key enabler.