雜訊測量及分析實驗
Sources of electronic noises• The two most commonly encountered types of
noise are thermal noises and shot noises.
• Thermal noise arise from the random velocity fluctuation of the charge carriers (electron and/or holes) in a resistive material.
• The mechanism is sometimes said to be the Brownian motion of the charge carriers due to the thermal energy of the materials.
The thermal noise is often referred to as Johnson noises (or Nyquist noise) in recognition of two early
investigators.
• The thermal noise is usually expressed as
Sv(f) = 4kBTR (V2/Hz)
where k is the Boltzmann’s constant (1.38x10-23 J/K), R is the resistance of the conductor, T is the absolute temperature, and Sv is the voltage noise power spectral density.
電壓方均根的雜訊與 4kBTR 正比
• Shot noise occurs when the current flows across a barrier. It was first discovered by Schottky.
• It is often found in solid-state devices when a current passes a potential barrier such as the depletion layer in p-n junction.
• The stream of charge carrier fluctuates randomly about a mean level. The fluctuations (shot noise) are due to the random, discrete nature of the tunneling process.
• The shot noise has a constant spectral density of
Si(f) = 2eIDC (A2/Hz)
where e is the electronic charge and Idc is theaverade current.
• In many devices, however, there is additional noise which varies with frequency as 1/f-, where usually lies between 0.8 and 1.2. This is commonly known as 1/f noise or flicker noise or excess noise.
• The fourth types of noise is sometimes found in transistor and other devices. It is called burst noise or random telegraph noise. It consists typically of random pulses of variable length and equal height.
• External noises due to interference from electrical or magnetic disturbances are a separate topic.
Circuit diagram of a noise measurement system
頻譜分析儀的背景雜訊
頻譜分析儀的背景雜訊 (SR760)
OP 放大器之電路模型與雜訊分析
運算放大器 的背景雜訊
4 nV
雜訊電壓頻譜雜訊電壓頻譜
Noises of superconducting device
Geometrical configuration of dc SQUID
YBa2Cu3Oy
STO
~2, 3, 4, 5 µm ~170 nm
Grain boundary
1 1 0 1 0 0 1 0 0 0
F req u en cy , f (H z)
1 0
1 0 0
1 0 0 0
Flu
x no
ise,
S
1/2 (
/
Hz1/
2 )
1/f
white noise
Noises in superconducting devices
Noises in superconducting devices
Possible sources of low-frequency 1/f noise:
• Critical current fluctuation
• Resistance fluctuation, or
• Motion of flux line
Possible sources of white noise:
Thermal noise
Weak Magnetic Fields
Biomagnetic fields
Environmental fields
10-4
10-4
10-5
10-6
10-7
10-8
10-9
10-10
10-11
10-12
10-13
10-14
10-15
Lung particles
Human heart
Fetal heartHuman eye
Human brain ()
Human brain (response)
B (Tesla)
Earth field
Urban noise
Car @ 50 m
Transistorchip @ 2 m
Transistordie @ 1 m
Flux-gatemagnetometer
SQUID
T
nT
pT
SQUID
0.1 1 10 100
10
100
1000S1
/2( 0/
Hz1
/2)
f(Hz)
without flux dam with flux dam
The noise power spectrum density of SQUIDs magnetometer with and without flux dam.
With flux dam
Without flux dam
20 fT/Hz1/2
Bias current, Ib
Vo
ltag
e,
V
= n 0
= (n+1/2) 0
M agnetic flux, /0
Vo
ltag
e,
V
Ib
V
Ib
(a)
(b)
(c)
Schematic of dc SQUID Electronics
Rf
Oscillator
Lock-in Detector
IB
Vo
IntegratorAmplifier
Modulation coil
Pick-up coil
Input coil
Thanks for your attent
ion!Thanks for your attent
ion!
Hong-Chang
Yang
