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North Carolina Zoo
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North Carolina Zoo
Zoo logo
Zoo entrance
Date opened
August 13, 1974 (Official)[1]
Location
Asheboro, North Carolina, United States
Coordinates
35°37′46″N 79°45′52″W / 35.6295°N 79.7645°W / 35.6295; -79.7645Coordinates: 35°37′46″N 79°45′52″W / 35.6295°N 79.7645°W / 35.6295; -79.7645
Land area
1,371 acres
No. of animals
1,600+.[2]
No. of species
225.[2]
Annual visitors
700,000.[3]
Memberships
AZA[4]
Major exhibits
African Pavilion, Forest Glade, Sonora Desert, Watani Grasslands Reserve
Website
www.nczoo.org
The North Carolina Zoological Park is located in Asheboro in Randolph County, North Carolina in the Uwharrie Mountains near the geographic center of the state, approximately 75 miles (121 km) west of Raleigh, NC, United States. At over 2,000 acres (810 ha), it is the largest walk-through zoo in the world, and one of only two state-owned zoos in the United States.[3] The NC Zoo has over 1,600 animals from more than 250 species primarily representing Africa and North America. The zoo is open 364 days a year and receives more than 700,000 visitors annually.
Contents
[hide]
1 History
2 Future Plans
3 Attractions
3.1 Layout
3.2 North America
3.3 Africa
3.4 Aviary
3.5 Art
4 Research and conservation
4.1 Africa
4.2 North Carolina
4.3 Breeding
5 Organization
6 References
7 External links
History[edit]
In 1967, the North Carolina legislature created the NC Zoological Garden Study Commission to examine the feasibility of a state zoo.[5] The nine-member commission found that a zoo was both feasible and desirable. The next year, the North Carolina Zoological Society was formed with the goal of raising funds and public support for the zoo project.[6] The same year, the legislature created the NC Zoological Authority to oversee the project. The site in Randolph County was selected from 6 sites after a 2-year search by the zoo commission, led by State Representative Archie McMillan of Wake County. After the selection of the site, its 1,371 acres (5.55 km2) were donated to the state.[5] A $2 million bond was passed and Governor Robert W. Scott dedicated the site in spring 1972. Construction of the North Carolina Zoo began in 1974 with the official opening date of August 13, 1976.[1] The first animals, two Galapagos tortoises arrived in 1973 and an interim zoo was opened in 1974. In 1978, Ham the Chimp, the first hominid in outer space, was moved to the zoo from the National Zoo in Washington, D.C. He lived there until his death in 1983 from a heart attack.[7] After construction delays and difficulty securing private funding, an additional $7 million were given by the General Assembly,[8] and the first permanent exhibit opened in 1979.[6]
The zoo has continued to expand ever since. Throughout the 1980s, the exhibits of the Africa region opened and in 1984 the zoo received accreditation from the Association of Zoos and Aquariums (AZA). In 1993, the first of the North America exhibits was completed, showcasing the animals and habitats of the Sonora Desert. The final North America exhibit opened in 1996.
Following the invasion of Afghanistan in 2001, the zoo spearheaded efforts to rebuild and maintain the Kabul Zoo. Beginning in 2002, the zoo helped raise funds, organize animal purchases, and provide expertise in animal care, exhibit reconstruction and renovation, staff training, and business strategy. In 2005 the NC Zoo employed a full-time staff member to live for a year in Kabul to assist with the training and retention of staff.[9] Following the 2003 invasion of Iraq, the NC Zoo once again took the lead in the rebuilding efforts at the Baghdad Zoo.[10] The zoo's exhibits have been replaced and the staff now coordinates with the North Carolina State University College of Veterinary Medicine in a program set up by the zoo.
A temporary Australian exhibit opened in 2004 and featured the largest collection of Australian plants on the East Coast until 2006.[5] The North Carolina Zoo is the nation’s first state-supported zoo and remains one of only two state zoos (the other state being Minnesota).[6] In November 2008, the zoo announced that in the first ten months of 2008, its operating revenue had increased 18% from its intake the previous year.[11]
Future Plans[edit]
This section needs to be updated. Please update this article to reflect recent events or newly available information. (April 2017)
On April 1, 2010, the zoo announced it had acquired adjacent forestland to bring the total land tract to over 2,000 acres (8.1 km2).[12] The main exhibits currently occupy about 500 acres (2.0 km2). There are plans for expansion to include animals and plants from Asia, which could include tigers, rhinos, and orangutans with the goal of attracting an additional 300,000 people a year.[3][13] There are also plans for a convention center and a hotel over looking an animal exhibit to establish the zoo as a multi-day destination.[13]
The NC Zoo would be one of many state facilities to receive money from the Connect NC bond referendum, scheduled to be voted on during the March 2015 primary election.[14] A new exhibit complex focused on Africa's aquatic ecosystems is also still in the planning stages.[15] If passed, the bond would provide significant funding for building new exhibits at the zoo and improving existing facilities. The African exhibit may include more animals like the Nile crocodiles, common hippos and other reptiles, primates and mammals from Africa.
Attractions[edit]
A polar bear and its enclosure in the North America section of the zoo.
The zoo is home to 1,600 animals of more than 200 species. It is home to the largest collection of chimpanzees of any zoo in America[15] as well as the largest collection of Alaskan seabirds in the country.
Layout[edit]
The North Carolina Zoo consists of two main areas: "Africa" and "North America" on opposite ends. There are parking lots located on both ends, so during peak season, visitors can start their day from either side. With approximately five miles of walking paths, the zoo also provides trams and air-conditioned buses for visitors.
The North Carolina Zoo was the first American zoo to incorporate the "natural habitat" philosophy – presenting animals together with plants in exhibits that resemble the habitats in which they would be found in the wild. Most animals are kept in large expanses of land, which reduces many of the behavior problems that can be caused by close confinement. The 37-acre (150,000 m2) African Plains exhibit alone is as large as many entire zoos.
North America[edit]
In the North American half, the swamps of the southeast are to be seen in "Cypress Swamp" area, home to alligators, cougars, ducks, and a variety of reptiles and amphibians. "Rocky Coast" depicts the rocky coasts of the Pacific Northwest, with polar bears, California sea lions, harbor seals, Arctic foxes, and the Alaskan seabirds. The streams of North Carolina can be seen in the "Streamside" exhibit with bobcats, otters, and a number of snakes and fish, including the critically endangered Cape Fear shiner. The "Prairie" enclosure shows off the enormous bison and elk of the great plains. The flora and fauna of the American Southwest are on display in the glass-domed "Sonoran Desert," which houses ocelots, coatis, common vampire bats, and a variety of free-flight birds such as white-winged doves, Gambel's quail, and horned larks. Black bears, grizzlies and red wolves also each have their own exhibits.
Several African elephants roam the Watani Grasslands exhibit
Africa[edit]
The "Forest Edge" is a 3.5-acre (14,000 m2), lightly wooded grassland enclosure where zebras, giraffes, and ostriches wander together. The "Watani Grasslands" mimic the great savanna of Africa and are home to rhinos, African elephants, Thomson's gazelle, gemsbok, waterbucks, sitatungas, blesboks, ostriches, and greater kudu. Chimpanzees, lions, western lowland gorilla, red river hogs mandrills and one of the largest baboon troops in the country each have their own exhibit in the African half of the zoo.
Lemurs from neighboring Madagascar were added to the Africa section of the zoo in 2010 after a $100,000 refurbishment of the former patas monkey exhibit, one of the first exhibits when the zoo opened in June 1980.[16]
Aviary[edit]
A female eclectus parrot in the Aviary
The R. J. Reynolds Forest Aviary recreates the hot, humid conditions of a tropical forest. It displays more than three thousand tropical plants and allows visitors to walk among 35 species of free-flying tropical bird including, sunbitterns, victoria crown pigeons and Chilean flamingos as well as red-footed and yellow-footed tortoises. Since 2007, the aviary has also been home to four species of poison dart frogs. The Aviary was listed among the top 10 American habitat exhibits in the US by USA Today.[17]
Art[edit]
The zoo is home to a large collection of art, primarily sculpture but also murals, mosaics, and paintings. Primarily depictions of animals and their habitats, the artwork uses a variety of materials including marble, steel, bronze, fiberglass, limestone, glass, cement, and others. The zoo's art is intended to enliven and enrich the zoo experience and help fulfill its mission by "promoting individual discovery and new ways of thinking."[18]
The two largest sculptures are located at the zoo's main entrances. One, "Sum of the Parts" is a pile of large metal cubes, about a yard (1 m) on a side. Most of the cubes are shiny and depict extant species, but a few rusted cubes tumbled off to the side memorialize extinct species. The second, "The Elephant Group" depicts several large elephants in bronze. The works were installed in 1998.
Research and conservation[edit]
Africa[edit]
The NC Zoo is involved in several research and conservation projects. Together with the World Wildlife Fund and the government of Cameroon, the zoo participates in a project to track the movements of elephants through satellite tracking collars in order to expand reserves and parks in a way that protects the most crucial areas of their habitats.[19] The project was recognized in 2008 by the AZA with a Significant Achievement in Conservation Award.[20] Also in Cameroon and its neighbor, Nigeria, the zoo is working on a project to monitor the rare Cross River gorilla, a subspecies that was thought extinct for many years. Its remote habitat is difficult to access, so with the help of satellite imaging and GPS systems, the zoo coordinates with park rangers and other conservation groups to map their habitat and movements and assist efforts to ensure their continued survival.[21] In another project with the Nigerian Conservation Foundation, the zoo has assisted with biodiversity surveys of the southwester region of the country. The surveys mapped suitable habitats, primarily the Omo and Oluwa forest reserves and recorded observed wildlife while documenting the level of human disturbance in the country of 150 million. After completing the survey, the team made several recommendations to maximize preservation of important habitat for forest elephants, chimpanzees, and other animals in the region.[22]
The zoo also operates projects in Uganda. An education project around Kibale National Park has been in place for over ten years and aims to educate young people about the purpose of the park and the value of biological conservation.[23] It also supports research at the Ngogo field research site inside the park. Ngogo researchers study primate plant use and rain forest regrowth after logging among other things, and removes illegal snares from the park which can seriously injure or kill protected animals. Along with Botanic Gardens Conservation International and the Atlanta Botanical Garden, the zoo is also advising in the construction and management of the Tooro Botanical Garden, which is designed to preserve and research the extraordinary biodiversity of the Albertine Rift region, with a special program for medicinal plant research.[24]
North Carolina[edit]
A number of projects are also underway in North Carolina. Protection and research of the hellbender salamander, which is globally recognized as near threatened but is classified as "endangered" in a number of US states including North Carolina, is the target of a project in the Appalachian Mountains. Due to the steep decline in population in the past 30 years, the zoo conducted a thorough survey, with the help of the AZA, into the hellbender populations of western North Carolina.[25]
The zoo is also involved in project to restore population of endangered Schweinitz's sunflower. In 2001, a road expansion project by the North Carolina Department of Transportation threatened a significant population of the flowers. The zoo partnered with a number of individuals and organizations and successfully managed their transplant to an off-road site, which continues to be managed and monitored by zoo horticulturalists.[26]
Breeding[edit]
Since 1995, the zoo has been a part of the red wolf Species Survival Plan and reintroduction program. The zoo has been home to 48 of these critically endangered animals, including a litter of 5, born at the zoo in 2002, which became the first captive-bred wolves to be adopted by wild parents.[27] The zoo is also involved in the gorilla Species Survival Plan and received two female gorillas in early 2010 as part of the effort.[28] As a result of their successful breeding, two male gorillas (Bomassa and Apollo) were born in August 2012.[29] The Aviary is also known for a number of high-profile hatchings, including the first US hatchings of the golden white-eye,[30] the red-faced liocichla,[31] the African pied barbet,[32] the golden-headed manakin, the horned puffin, the parakeet auklet and the thick-billed murre as well as the second US hatchings of the African grey-headed kingfisher and the African spoonbill.[31]
Organization[edit]
The zoo is part of the North Carolina Department of Natural and Cultural Resources. Its operation and development are overseen by a 15-member Zoo Council appointed by the Governor to six-year terms. The Director of the zoo is Pat Simmons, formerly the Director of Akron Zoo. Simmons took over from long-time Director, Dr. David Jones, who retired in 2015. The zoo's annual operating budget is roughly $18 million. It receives around 60 percent from the state with the remainder being made up of ticket and merchandise sales and donations from the North Carolina Zoological Society, which remains the zoo's fund-raising and membership arm.[3] The Zoological Society is overseen by its Board of Directors.[33] The Chairman of the Board is always a member of the Zoological Council[34] and the two groups meet once annually.[33]
References[edit]
^ Jump up to: a b NC Zoo – North Carolina Zoo : Zoo History 1970's
^ Jump up to: a b "Animals". Retrieved January 9, 2014.
^ Jump up to: a b c d "NC Zoological Park Funding and Organization (PDF)" (PDF). Retrieved April 19, 2012.
Jump up ^ "List of Accredited Zoos and Aquariums". aza.org. AZA. Retrieved July 8, 2010.
^ Jump up to: a b c "Brief History of the North Carolina Zoo" (PDF). Retrieved April 19, 2012.
^ Jump up to: a b c North Carolina Zoological Society Timeline Archived July 11, 2010, at the Wayback Machine.
Jump up ^ Winston Salem Journal
Jump up ^ "Legislators Rescue Money-Plagues Zoo ''The Dispatch''". Google. Retrieved April 19, 2012.
Jump up ^ Update on the Kabul Zoo Story NC Zoo Archived July 14, 2011, at the Wayback Machine.
Jump up ^ N.C. Zoo Vets Continue To Assist Baghdad Zoo NCDENR Archived April 16, 2010, at the Wayback Machine.
Jump up ^ "Support grows for zoo". Philanthropyjournal.org. November 26, 2008. Retrieved April 19, 2012.
Jump up ^ "Zoo expands with acquisition of nature preserve. ''News & Record''". News-record.com. April 1, 2010. Retrieved April 19, 2012.
^ Jump up to: a b "NC Zoo looks beyond cuts and into future". Greensboro News and Record. July 8, 2011. Retrieved August 6, 2011.
Jump up ^ "Connect NC".
^ Jump up to: a b "Exhibits at the North Carolina Zoo (PDF)" (PDF). Retrieved April 19, 2012.
Jump up ^ "Lemur Exhibit Opens". NC Zoo Society News. September 2010.
Jump up ^ "Zoo Tales: A Winter Respite. ''The Pilot''". Thepilot.com. March 7, 2010. Retrieved April 19, 2012.
Jump up ^ "NC Zoo Art Brochure (PDF)" (PDF). Retrieved April 19, 2012.
Jump up ^ "Cameroon Elephant Conservation ''NC Zoo''". Nczoo.org. Retrieved April 19, 2012.
Jump up ^ "North Carolina Zoological Park Field Conservation and Research Programs (PDF)" (PDF). Retrieved April 19, 2012.
Jump up ^ "Cross River Gorilla Conservation ''NC Zoo''". Nczoo.org. Retrieved April 19, 2012.
Jump up ^ "Biodiversity of the Omo Forest, ''NC Zoo''". Nczoo.org. Retrieved April 19, 2012.
Jump up ^ "Unite ''Nc Zoo''". Nczoo.org. Retrieved April 19, 2012.
Jump up ^ "Tooro Botanical Garden ''NC Zoo''". Nczoo.org. Retrieved April 19, 2012.
Jump up ^ "Hellbender Salamander ''NC Zoo''". Nczoo.org. Retrieved April 19, 2012.
Jump up ^ "Schweinitz's Sunflowers ''NC Zoo''". Nczoo.org. Retrieved April 19, 2012.
Jump up ^ "Red Wolves of Alligator River ''NC Zoo''". Nczoo.org. Retrieved April 19, 2012.
Jump up ^ Two New Gorillas on Exhibit NC Zoological Society Archived May 8, 2011, at the Wayback Machine.
Jump up ^ "Archived copy". Archived from the original on September 19, 2012. Retrieved 2012-11-19.
Jump up ^ "Golden White-Eye" Fox8 WGHP News (video) Archived July 19, 2011, at the Wayback Machine.
^ Jump up to: a b Anonymous. "Zoo Tales – Rare Bird Species ''The Randolph Guide''". Randolphguide.com. Retrieved April 19, 2012.
Jump up ^ "N.C. Zoo's R.J. Reynolds Forest Aviary Reopens May 26 ''NCDENR''". Enr.state.nc.us. May 16, 2000. Retrieved April 19, 2012.
^ Jump up to: a b ""The North Carolina Zoological Park Council and Society's Board of Directors Meet Jointly" Zoo and Aquarium Visitor". Zandavisitor.com. Retrieved April 19, 2012.
Jump up ^ "North Carolina statute creating the Zoological Council (PDF)" (PDF). Retrieved April 19, 2012.
External links[edit]
Wikimedia Commons has media related to North Carolina Zoo.
Official website
Heart of North Carolina Visitors Bureau
Official Visitor Info for the Greater Asheboro Area
North Carolina Zoological Society – the non-profit organization that supports the zoo.
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Common emitter
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This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. Please help to improve this article by introducing more precise citations. (December 2008) (Learn how and when to remove this template message)
Figure 1: Basic NPN common-emitter circuit (neglecting biasing details)
In electronics, a common-emitter amplifier is one of three basic single-stage bipolar-junction-transistor (BJT) amplifier topologies, typically used as the voltage amplifier.
In this circuit the base terminal of the transistor serves as the input, the collector is the output, and the emitter is common to both (for example, it may be tied to ground reference or a power supply rail), hence its name. The analogous FET circuit is the common-source amplifier, and the analogous tube circuit is the common-cathode amplifier.
Contents
[hide]
1 Emitter degeneration
2 Characteristics
2.1 Bandwidth
3 Applications
3.1 Low-frequency voltage amplifier
3.2 Radio
4 See also
5 References
6 External links
Emitter degeneration[edit]
Figure 2: Adding an emitter resistor decreases gain, but increases linearity and stability
Common-emitter amplifiers give the amplifier an inverted output and can have a very high gain that may vary widely from one transistor to the next. The gain is a strong function of both temperature and bias current, and so the actual gain is somewhat unpredictable. Stability is another problem associated with such high-gain circuits due to any unintentional positive feedback that may be present.
Other problems associated with the circuit are the low input dynamic range imposed by the small-signal limit; there is high distortion if this limit is exceeded and the transistor ceases to behave like its small-signal model. One common way of alleviating these issues is with emitter degeneration. This refers to the addition of a small resistor (or any impedance)[dubious – discuss] between the emitter and the common signal source (e.g., the ground reference or a power supply rail). This impedance R E {\displaystyle R_{\text{E}}} reduces the overall transconductance G m = g m {\displaystyle G_{m}=g_{m}} of the circuit by a factor of g m R E + 1.677 {\displaystyle g_{m}R_{\text{E}}+1.677} , which makes the voltage gain
A v ≜ v out v in = − g m R C g m R E + 1 ≈ − R C R E , {\displaystyle A_{\text{v}}\triangleq {\frac {v_{\text{out}}}{v_{\text{in}}}}={\frac {-g_{m}R_{\text{C}}}{g_{m}R_{\text{E}}+1}}\approx -{\frac {R_{\text{C}}}{R_{\text{E}}}},}
where g m R E ≫ 1 {\displaystyle g_{m}R_{\text{E}}\gg 1} .
The voltage gain depends almost exclusively on the ratio of the resistors R C / R E {\displaystyle R_{\text{C}}/R_{\text{E}}} rather than the transistor's intrinsic and unpredictable characteristics. The distortion and stability characteristics of the circuit are thus improved at the expense of a reduction in gain.
(While this is often described as "negative feedback", as it reduces gain, raises input impedance, and reduces distortion, it predates the invention of negative feedback and does not reduce output impedance or increase bandwidth, as true negative feedback would do.[1])
Characteristics[edit]
At low frequencies and using a simplified hybrid-pi model, the following small-signal characteristics can be derived.
Definition
Expression (with emitter degeneration)
Expression (without emitter degeneration, i.e., RE = 0)
Current gain
A i ≜ i out i in {\displaystyle A_{\text{i}}\triangleq {\frac {i_{\text{out}}}{i_{\text{in}}}}\,} β {\displaystyle \beta \,} β {\displaystyle \beta }
Voltage gain
A v ≜ v out v in {\displaystyle A_{\text{v}}\triangleq {\frac {v_{\text{out}}}{v_{\text{in}}}}\,} − β R C r π + ( β + 1 ) R E {\displaystyle {\begin{matrix}-{\frac {\beta R_{\text{C}}}{r_{\pi }+(\beta +1)R_{\text{E}}}}\end{matrix}}\,} − g m R C {\displaystyle -g_{m}R_{\text{C}}}
Input impedance
r in ≜ v in i in {\displaystyle r_{\text{in}}\triangleq {\frac {v_{\text{in}}}{i_{\text{in}}}}\,} r π + ( β + 1 ) R E {\displaystyle r_{\pi }+(\beta +1)R_{\text{E}}\,} r π {\displaystyle r_{\pi }}
Output impedance
r out ≜ v out i out {\displaystyle r_{\text{out}}\triangleq {\frac {v_{\text{out}}}{i_{\text{out}}}}\,} R C {\displaystyle R_{\text{C}}\,} R C {\displaystyle R_{\text{C}}}
If the emitter degeneration resistor is not present, then R E = 0 Ω {\displaystyle R_{\text{E}}=0\,\Omega } , and the expressions effectively simplify to the ones given by the rightmost column (note that the voltage gain is an ideal value; the actual gain is somewhat unpredictable). As expected, when R E {\displaystyle R_{\text{E}}\,} is increased, the input impedance is increased and the voltage gain A v {\displaystyle A_{\text{v}}\,} is reduced.
Bandwidth[edit]
The bandwidth of the common-emitter amplifier tends to be low due to high capacitance resulting from the Miller effect. The parasitic base-collector capacitance C CB {\displaystyle C_{\text{CB}}\,} appears like a larger parasitic capacitor C CB ( 1 − A v ) {\displaystyle C_{\text{CB}}(1-A_{\text{v}})\,} (where A v {\displaystyle A_{\text{v}}\,} is negative) from the base to ground.[2] This large capacitor greatly decreases the bandwidth of the amplifier as it makes the time constant of the parasitic input RC filter r s ( 1 − A V ) C CB {\displaystyle r_{\text{s}}(1-A_{\text{V}})C_{\text{CB}}\,} where r s {\displaystyle r_{\text{s}}\,} is the output impedance of the signal source connected to the ideal base.
The problem can be mitigated in several ways, including:
Reduction of the voltage gain magnitude | A v | {\displaystyle \left|A_{\text{v}}\right|\,} (e.g., by using emitter degeneration).
Reduction of the output impedance r s {\displaystyle r_{\text{s}}\,} of the signal source connected to the base (e.g., by using an emitter follower or some other voltage follower).
Using a cascode configuration, which inserts a low input impedance current buffer (e.g. a common base amplifier) between the transistor's collector and the load. This configuration holds the transistor's collector voltage roughly constant, thus making the base to collector gain zero and hence (ideally) removing the Miller effect.
Using a differential amplifier topology like an emitter follower driving a grounded-base amplifier; as long as the emitter follower is truly a common-collector amplifier, the Miller effect is removed.
The Miller effect negatively affects the performance of the common source amplifier in the same way (and has similar solutions).When an AC signal is applied to the transistor amplifier it causes the base voltage VB to fluctuate in value at the AC signal. The positive half of the applied signal will cause an increase in the value of VB this turn will increase the base current IB and cause a corresponding increase in emitter current IE and collector current IC. As a result, the collector emitter voltage will be reduced because of the increase voltage drop across RL. The negative alternation of an AC signal will cause a decrease in IB this action then causes a corresponding decrease in IE through RL.
It is also named common- emitter amplifier because the emitter of the transistor is common to both the input circuit and output circuit. The input signal is applied across the ground and the base circuit of the transistor. The output signal appears across ground and the collector of the transistor. Since the emitter is connected to the ground, it is common to signals, input and output.
The common- emitter circuit is the most widely used of junction, transistor amplifiers. As compared with the common- base connection, it has higher input impedance and lower output impedance. A single power supply is easily used for biasing. In addition, higher voltage and power gains are usually obtained for common- emitter (CE) operation.
Current gain in the common emitter circuit is obtained from the base and the collector circuit currents. Because a very small change in base current produces a large change in collector current, the current gain (β) is always greater than unity for the common-emitter circuit, a typical value is about 50.
Applications[edit]
Low-frequency voltage amplifier[edit]
A typical example of the use of a common-emitter amplifier is shown in Figure 3.
Figure 3: Single-ended npn common-emitter amplifier with emitter degeneration. The AC-coupled circuit acts as a level-shifter amplifier. Here, the base–emitter voltage drop is assumed to be 0.65 volts.
The input capacitor C removes any constant component of the input, and the resistors R1 and R2 bias the transistor so that it will remain in active mode for the entire range of the input. The output is an inverted copy of the AC component of the input that has been amplified by the ratio RC/RE and shifted by an amount determined by all four resistors. Because RC is often large, the output impedance of this circuit can be prohibitively high. To alleviate this problem, RC is kept as low as possible and the amplifier is followed by a voltage buffer like an emitter follower.
Radio[edit]
Common-emitter amplifiers are also used in radio frequency circuits, for example to amplify faint signals received by an antenna.[dubious – discuss] In this case it is common to replace the load resistor with a tuned circuit. This may be done to limit the bandwidth to a narrow band centered around the intended operating frequency. More importantly it also allows the circuit to operate at higher frequencies as the tuned circuit can be used to resonate any inter-electrode and stray capacitances, which normally limit the frequency response. Common emitters are also commonly used as low-noise amplifiers.
See also[edit]
Electronics portal
Common base
Common collector
Common gate
Common drain
Common source
Open collector
Two-port network
References[edit]
Jump up ^ "Distortion and Feedback". sound.whsites.net. Retrieved 2016-01-27. Although it is commonly accepted that emitter ... degeneration is feedback, this is only partially true. ... it has no effect on effective bandwidth or output impedance. Harold Black invented negative feedback, not degeneration (which pre-dated his invention).
Jump up ^ Paul Horowitz and Winfield Hill (1989). The Art of Electronics (2nd ed.). Cambridge University Press. pp. 102–104. ISBN 978-0-521-37095-0.
External links[edit]
Simulation of The Common Emitter Amplifier Circuit or simulation of Common Emitter Transistor Amplifier
Basic BJT Amplifier Configurations
NPN Common Emitter Amplifier – HyperPhysics
ECE 327: Transistor Basics – Gives example common-emitter circuit with explanation.
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