Noise generator

百度黎氏秋恒表示，越南具有足够“历史和法律依据”，可证明对西沙和南沙两个群岛（越称黄沙和长沙）拥有“主权”。

A noise generator is a circuit that produces electrical noise (i.e., a random signal). Noise generators are used to test signals for measuring noise figure, frequency response, and other parameters. Noise generators are also used for generating random numbers.^[1]

Theory

There are several circuits used for noise generation. For example, temperature-controlled resistors, temperature-limited vacuum diodes, zener diodes, and gas discharge tubes.^[2] A source that can be switched on and off ("gated") is beneficial for some test methods.

Noise generators usually rely on a fundamental noise process such as thermal noise or shot noise.

Thermal noise generator

Thermal noise can be a fundamental standard. A resistor at a certain temperature has a thermal noise associated with it. A noise generator might have two resistors at different temperatures and switch between the two resistors. The resulting output power is low. (For a 1 kΩ resistor at room temperature and a 10 kHz bandwidth, the RMS noise voltage is 400 nV.^[3])

Shot noise generator

If electrons flow across a barrier, then they have discrete arrival times. Those discrete arrivals exhibit shot noise. The output noise level of a shot noise generator is easily set by the DC bias current. Typically, the barrier in a diode is used.^[4]

Different noise generator circuits use different methods of setting the DC bias current.

Vacuum diode

One common noise source was a thermally-limited (saturated-emission) hot-cathode vacuum tube diode. These sources could serve as white noise generators from a few kilohertz through UHF and were available in normal radio tube glass envelopes. Flicker ( $\ {\tfrac {1}{\ f\ }}\$ ) noise limited application at lower frequencies; electron transit time limited application at higher frequencies. The basic design was a diode vacuum tube with a heated filament. The temperature of the cathode (filament) sets the anode (plate) current that determines the shot noise; see Richardson equation. The anode voltage is set large enough to collect all the electrons emitted by the filament.^[5]^[6] If the plate voltage were too low, then there would be space charge near the filament that would affect the noise output. For a calibrated generator, care must be taken so that the shot noise dominates the thermal noise of the tube's plate resistance and other circuit elements.

Gas-discharge tubes

Long, thin, hot-cathode gas-discharge glass tubes fitted with a normal bayonet light bulb mount for the filament and an anode top cap, were used for SHF frequencies and diagonal insertion into a waveguide.^[7] They were filled with a pure inert gas such as neon because mixtures made the output temperature-dependent. Their burning voltage was under 200 V, but they needed optical priming (pre-ionizing) by a 2 Watt incandescent lamp prior to ignition by an anode voltage spike in the 5 kV range.

For lower frequency noise bands glow lamps filled with neon have been used. The circuit was similar to the one for spike / needle pulses.

One miniature thyratron found an additional use as a noise source, when operated as a diode (grid tied to cathode) in a transverse magnetic field.^[8]

Forward-biased semiconductor diode

Another possibility is using the collector current in a transistor.^{[clarification needed]}

Reverse-biased semiconductor diode

Reverse-biased diodes in breakdown can also be used as shot noise sources. Voltage regulator diodes are common, but there are two different breakdown mechanisms, and they have different noise characteristics. The mechanisms are the Zener effect and avalanche breakdown.^[9]

Zener diode

The Zener effect is primarily exhibited by reverse-biased diodes and bipolar transistor base-emitter junctions that breakdown below about 7 volts. The breakdown is due to internal field emission, since the junctions are thin, and the electric field is high. Zener-type breakdown is shot noise. The flicker ( $\ {\tfrac {1}{\ f\ }}\$ ) noise corner can be below 10 Hz.^[10]

The noise generated by Zener diodes is a simple shot noise.

Avalanche diode

For breakdown voltages greater than 7 volts, the semiconductor junction width is thicker and primary breakdown mechanism is an avalanche. The noise output is more complicated.^[10] There is excess noise (i.e., noise over and above the simple shot noise) because there is avalanche multiplication.

For higher power output noise generators, amplification is needed. For broadband noise generators, that amplification can be difficult to achieve. One method uses avalanche multiplication within the same barrier that generates the noise. In an avalanche, one carrier collides with other atoms and knocks free new carriers. The result is that for each carrier that starts across a barrier, several carriers synchronously arrive. The result is a wide-bandwidth high-power source. Conventional diodes can be used in breakdown.

The avalanche breakdown also has multistate noise. The noise output power randomly switches among several output levels. Multistate noise looks somewhat like flicker ( $\ {\tfrac {1}{\ f\ }}\$ ) noise. The effect is process dependent, but it can be minimized. Diodes may also be selected for low multistate noise.^[10]

A commercial example of an avalanche diode noise generator is the Agilent 346C that covers 10 MHz to 26.5 GHz.^[11]

References

^ "Sylvania 6D4 Quick Reference Data" (PDF). sensitive research (SR-IX). Retrieved 1 June 2022.
^ Motchenbacher & Fitchen 1973, p. 289
^ Google Calculator result for 1 kΩ room temperature 10 kHz bandwidth
^ Ott 1976, pp. 208, 218
^ Motchenbacher & Fitchen 1973, pp. 289–291
^ Standard noise sources K81A, K50A, K51A (PDF) (data sheet). Philips. Retrieved 14 June 2013 – via tubedata.milbert.com.
^ Catalog. Hewlett-Packard. 1981. p. 437. The 347A waveguide sources are argon gas discharge tubes carefully mounted in waveguide sections for frequencies from 3.95 to 18 GHz. Model 349A also uses an argon tube in a coaxial configuration for frequencies from 400 to 4000 MHz.
^ 6D4 Miniature triode thyratron (PDF) (data sheet). Sylvania. Retrieved 25 May 2013 – via tubedata.milbert.com.
^ Motchenbacher & Fitchen 1973, p. 180
^ ^a ^b ^c Motchenbacher & Fitchen 1973, p. 181
^ 346C Noise source, 10 MHz to 26.5 GHz. Keysight (catalog).

Motchenbacher, C. D.; Fitchen, F. C. (1973), Low-Noise Electronic Design, John Wiley & Sons, Bibcode:1973lned.book.....M, ISBN 978-0-471-61950-5
Ott, Henry W. (1976), Noise Reduction Techniques in Electronic Systems, John Wiley, ISBN 0-471-65726-3

[1] "Sylvania 6D4 Quick Reference Data" (PDF). sensitive research (SR-IX). Retrieved 1 June 2022.

[2] Motchenbacher & Fitchen 1973, p. 289

[3] Google Calculator result for 1 kΩ room temperature 10 kHz bandwidth

[4] Ott 1976, pp. 208, 218

[5] Motchenbacher & Fitchen 1973, pp. 289–291

[6] Standard noise sources K81A, K50A, K51A (PDF) (data sheet). Philips. Retrieved 14 June 2013 – via tubedata.milbert.com.

[HP-347A-7] Catalog. Hewlett-Packard. 1981. p. 437. The 347A waveguide sources are argon gas discharge tubes carefully mounted in waveguide sections for frequencies from 3.95 to 18 GHz. Model 349A also uses an argon tube in a coaxial configuration for frequencies from 400 to 4000 MHz.

[8] 6D4 Miniature triode thyratron (PDF) (data sheet). Sylvania. Retrieved 25 May 2013 – via tubedata.milbert.com.

[9] Motchenbacher & Fitchen 1973, p. 180

[MF181-10] Motchenbacher & Fitchen 1973, p. 181

[11] 346C Noise source, 10 MHz to 26.5 GHz. Keysight (catalog).

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[9]

[10]

[11]

为什么现在	脑梗挂号挂什么科室	皮肤容易过敏是什么原因	鸡蛋炒什么	周武王叫什么名字
egc是什么意思	阴茎是什么	跟腱炎什么症状	飞刀是什么意思	pf什么意思
佐餐是什么意思	尿频繁吃什么药最见效	孕妇梦见下雨是什么意思	翩翩起舞是什么意思	生物制剂是什么
龙代表什么象征意义	泰坦尼克号女主角叫什么	左肺结节是什么意思	人为什么会起鸡皮疙瘩	肝主什么

小腿麻木是什么原因hcv8jop7ns5r.cn	饮料喝多了有什么危害luyiluode.com	75是什么意思hcv8jop9ns0r.cn	一个女一个以念什么hcv7jop9ns5r.cn	脚干裂用什么药膏hcv9jop0ns2r.cn
胃不好喝什么茶hcv9jop1ns8r.cn	软化灶是什么意思bjcbxg.com	香蕉人是什么意思hcv7jop9ns3r.cn	市委讲师团是什么级别hcv8jop7ns2r.cn	社保卡是什么样的图片hcv9jop1ns4r.cn
游泳比赛中wj是什么意思hcv9jop0ns4r.cn	晚上八点多是什么时辰cj623037.com	黎字五行属什么hcv7jop6ns1r.cn	急性肠胃炎吃什么消炎药aiwuzhiyu.com	颈椎病吃什么药最好效果hcv8jop3ns1r.cn
胆固醇高是什么病hcv8jop3ns0r.cn	雪碧喝多了有什么害处hcv8jop0ns8r.cn	1976年是什么命hcv9jop3ns4r.cn	有人的地方就有江湖什么意思xinmaowt.com	冰丝和天丝有什么区别hcv8jop9ns8r.cn

花木兰是什么剧种