Noise

噪聲觀察的一條簡單規則是：（通過智力地）對每個晶體管的柵電壓作很小的變化，而後預計輸出的效果。

套筒式和摺疊式運放：在相對低的頻率時，共源共柵器件產生的噪聲可忽略；

Sources of Noise
1、Shot Noise
Shot noise is always associated with a direct-current flow and is present in diodes, MOS transistors, and bipolar transistors.
The origin of shot noise can be seen by considering the diode of Fig. 11.1a and the carrier concentrations in the device in the forward-bias region as shown in Fig. 11.1b.

The passage of each carrier across the junction, which can be modeled as a random event, is dependent on the carrier having sufficient energy and a velocity directed toward the junction. Thus external current I, which appears to be a steady current, is, in fact, composed of a large number of random independent current pulses. If the current is examined on a sensitive oscilloscope, the trace appears as in Fig. 11.2, where ID is the average current.







White Noise
Amplitude distribution of Shot Noise is Gaussian

2、Thermal Noise
Thermal noise is generated by a completely different mechanism from shot noise. In conventional resistors it is due to the random thermal motion of the electrons and is unaffected by the presence or absence of direct current, since typical electron drift velocities in a conductor are much less than electron thermal velocities.


White Noise
Amplitude distribution of Shot Noise is Gaussian

3、Flicker Noise ( 1/f Noise )


Not White Noise
Amplitude distribution of Flicker Noise is non-Gaussian

4、Burst Noise ( Popcorn Noise )
This is another type of low-frequency noise found in some integrated circuits and discrete transistors. The source of this noise is not fully understood, although it has been shown to be related to the presence of heavy-metal ion contamination. Gold-doped devices show very high levels of burst noise.



Not White Noise
Amplitude distribution of Burst Noise is non-Gaussian

5、Avalanche Noise

Noise Models of Integrated-Circuit Components
1、Junction Diode
Shot Noise：Fig. 11.4.
Thermal Noise: rs is a physical resistor due to the resistivity of the silicon.
any Flicker Noise present can be represented by a current generator in shunt with rd, and can be conveniently combined with the shot-noise generator.


2、Bipolar Transistor
In a bipolar transistor in the forward-active region, minority carriers diffuse and drift across the base region to be collected at the collector-base junction.







3、MOS Transistor




4、Resistors

5、Capacitors and Inductors