Starting at: $Submit for Price HOME ELECTRONICS COMMUNICATIONS TEST EQUIPMENT HISTORY RESOURCES OPEN SHOPPING Transistor Current Mirror Circuit Transistor current mirror circuits are often used within integrated circuits as well as a number of other areas where they enable current to be balanced between two legs. FOLLOW 18072EZ Available Starting at: $Submit for Price Transistor Circuit Types Include: Transistor circuit types Current mirror amplifier Common emitter Long tailed pair Emitter follower Common base Constant current source Darlington pair Capacitance multiplier Sziklai pair Aven Inc ® Authorized Distributor Two transistor High pass filter onlinecomponents.com See also: Transistor circuit design X Current mirror circuits generally consist two main transistor, although other devices such as FETs can be used. Some current mirror circuits may use more than two transistors to enable the level of performance to be improved. Starting at: $Submit for Price The current mirror circuit gains its name because it copies or mirrors the current flowing in one active device in 18072EZ - Available Starting at: $Submit for Price Aven Inc ® Authorized Distributor OPEN onlinecomponents.com another, keeping the output current constant regardless of loading. OPEN OPEN The current being mirrored can be a constant current, or it can be a varying signal dependent upon the requirement and hence the circuit. Conceptually, an ideal current mirror is simply an ideal inverting current amplifier that reverses the current direction as well or it is a current-controlled current source (CCCS). The current mirror is used to provide bias currents and active loads to circuits. 10 MAY 2022 Current mirror circuit Fact of the day: It was on 10 May 1852 that The basic circuit of the transistor current mirror is shown in the diagram below. It comprises two transistors, one of which has the base and collector connected and the other does not. The base connections of both transistors are then linked, as are the emitters which are also taken to ground. the theory of valence was postulated by English chemist Sir Edward Frankland. This states that any atom can combine with a specific number of other atoms. Quote: When people thought the Earth was flat, Programming current I1 I2 they were wrong. When people thought the Mirrored current Earth was spherical they were wrong. But if you think that thinking the Earth is spherical is just as wrong as thinking the Earth is flat, then your R1 view is wronger than both of them put together. Isaac Asimov TR2 The way things are: TR1 Tell someone that there are 300 billion stars in the universe and they will believe you. Tell them a door has wet paint on it and they will Current mirror transistor circuit have to touch it to be sure. In terms of the operation of the circuit, the base emitter junction of TR1 acts like a diode because the collector and base are connected together. ELECTRONICS NOTES BOOKSHOP The current into TRI is set externally by other components, and as a result there is a given voltage built up across the base emitter junction of TR1. As the base emitter voltage on both transistors is the same, the current in one transistor will exactly mirror that of the second, assuming that both transistors are accurately matched. Therefore the current flowing into TR1 will be mirrored into TR2 and hence into the load R1. Circuit limitations The two transistor current mirror circuit shown above is often quite adequate for most applications. However it has some noticeable limitations under many circumstances: Current varies with change in output voltage: This effect occurs because the output impedance is not infinite. This is because there is a slight variation of Vbe with the collector voltage at a given current in TR2. Often the current may vary by about 25% the output compliance range. Current matching dependent on transistor matching: Check out our book shop for essential reading and reference on electronics related topics: ▶ Electronics Notes Bookshop The current mirroring is dependent upon the matching of the transistors. Often the transistors need to be on the same substrate if they are to accurately SHOPPING ON ELECTRONICS NOTES mirror the current. To overcome some of these issues more advanced current mirror circuits cna be developed and used. Electronics Notes offers a host of products are very good prices Current mirror with emitter resistors from our shopping pages (in association with Amazon). Check out these pages on our website: One solution to the variation of current over the compliance range is to introduce a small amount of resistance ▶ Ethernet Products. into the emitter of each transistor. Typically these resistors are chosen to have a few tenths of a volt drop ▶ Computer Products. across them. ▶ Ham Radio Products. ▶ HDMI Products. Note: Electronics Notes receives a small commission on sales at no cost to you. Programming current I1 I2 Mirrored current EVENTS R1 ▶ PCIM Europe ▶ Dayton Hamvention TR2 ▶ SubCon TR1 ▶ Embedded World ▶ HAM RADIO Friedrichshafen Re More events Re SELECTED VIDEO Current mirror transistor circuit with emitter resistors For this circuit, both emitter resistors and transistors need to be matched. This is obviously easy for the resistors where close tolerance resistors are easily available. Wilson current mirror circuit Another variation of the basic current mirror circuit is referred to as the Wilson mirror or Wilson current mirror. Within the circuit, a third transistor is introduced. This transistor, shown as TR3 in the diagram keeps the collector of TR1 at a voltage equivalent to two diode drops below the rail voltage Vcc. Programming current I2 I1 AM Diode Detector / Demodulator Mirrored current SUPPLIER DIRECTORY R1 For everything from distribution to test equipment, TR3 components and more, our directory covers it. ▶ Check our Supplier Directory TR2 TR1 FEATURED ARTICLES ▶ Need a new TV remote - check our buyers guide ▶ Smart speakers: what to buy Wilson current mirror transistor circuit ▶ Oscilloscope Specifications: buying a scope ▶ What is a Spectrum Analyzer? This overcomes the previous effect. Also the transistor without the short circuit collector base connection ▶ E-readers: which one to buy becomes the programming terminal. Current mirror circuits are very useful, especially within integrated circuits. The components can easily be incorporated into the design for little cost. As such they enable balanced currents to be supplied to circuits like differential pairs and the like and this ensures that their operation is improved further. Current mirrors are not widely used outside IC technology in view of the additional number of components required, but nevertheless the principles are the same in both discrete form and when used within ICs. RETURN TO TRANSISTOR CIRCUIT TYPES More Circuits & Circuit Design: Op Amp basics Op Amp circuits Transistor circuits FET circuits Power supply circuits Transistor design Transistor Darlington Circuit symbols Return to Circuit Design menu . . . Starting at: $Submit for Price OPEN Electronics Notes receives a small commission on sales via Amazon to pay for running the site and providing free information. About Electronics Notes Advertise Privacy Policy Images © electronics-notes.com
