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Dark noise charge12/30/2023 The reason is that noise arises from the physical resistance of the channel, which originates from the inversion layer at the source to a region near the drain. It is important to define γ in terms of g ds,ch (the drain-source conductance in the “linear region” of the device) and not g m, which leads to the erroneous conclusion that γ is much larger than 1. A good test for a compact model is a plot of γ versus the drain and gate bias voltage, as shown in Figure 2.13. For short-channel devices it has been observed that γ is larger than 1, which is sometimes attributed to the hot electron effects occurring on the drain end of the transistor. The coupling to the gate through the gate-oxide capacitance also gives rise to a correlated gate noise current. For a long-channel device, it is well known that γ = 2/3, which is derived by considering the thermal noise contribution of an incremental region of the channel to the drain. Where g ds,ch is the channel conductance. The power spectrum equation is defined as However, the power spectrum equation suggests that at frequencies higher than 100 Hz, the level of thermal noise starts to drop off. The thermal noise power is proportional to the bandwidth and is effectively white noise. Elimination of thermal noise is impossible however, it can be reduced by reducing the temperature of operation or reducing the value of the resistance in electrical circuits. Thermal noise occurs due to the vibration of charge carriers within an electrical conductor and is directly proportional to the temperature, regardless of the applied voltage. Hence, thermal noise is also known as Johnson-Nyquist noise, Johnson noise, or Nyquist noise. Johnson in 1926 and later explained by Harry Nyquist. Thermal noise was first detected and measured by John B. Thermal noise is always present in the electrical equipment used and is one of the major sources of noise that can affect the weak levels of biomedical signals at their source.
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