261
7
Compact MOSFET Models
for RF Applications
7.1 Introduction
For analog and radio frequency (RF) applications of metal-oxide-semiconductor
field-effect transistors (MOSFETs), it is critical to understand the behavior
of these devices under applied signal. In Chapter 6, the analytical expressions are derived for modeling the terminal charges and capacitances of a
MOSFET device based on the quasistatic (QS) assumption. For analog/RF
applications of MOSFETs, the effect of noise, non-quasistatic (NQS) effect,
and resistive network of these devices must be properly characterized and
modeled for circuit CAD (computer-aided design). This chapter presents
the basic understanding of modeling device noise, high-frequency characteristics such as NQS effect, and the resistive network of the devices.
7.2 MOSFET Noise Models
A careful observation of the drain current of a MOSFET reveals minute random fluctuations, referred to as noise. Noise is inherently present in electronic devices with or without the presence of an applied external signal.
Noise could be in output current as well as in output voltage. In an MOS
(metal-oxide-semiconductor) analog circuits, noise in MOSFET devices can
interfere with weak signals and significantly impact the accurate characterization of circuit performance. Therefore, it is very important to model and
characterize noise in devices [1–3].
The amount of noise depends on the bandwidth of the characterizing system. A common noise characterization technique involves a very narrow
bandwidth, centered on a frequency f. The current noise spectral components within this bandwidth have a certain mean square value. The ratio
of this value to the bandwidth, as the latter is allowed to approach zero,
7
Compact MOSFET Models
for RF Applications
7.1 Introduction
For analog and radio frequency (RF) applications of metal-oxide-semiconductor
field-effect transistors (MOSFETs), it is critical to understand the behavior
of these devices under applied signal. In Chapter 6, the analytical expressions are derived for modeling the terminal charges and capacitances of a
MOSFET device based on the quasistatic (QS) assumption. For analog/RF
applications of MOSFETs, the effect of noise, non-quasistatic (NQS) effect,
and resistive network of these devices must be properly characterized and
modeled for circuit CAD (computer-aided design). This chapter presents
the basic understanding of modeling device noise, high-frequency characteristics such as NQS effect, and the resistive network of the devices.
7.2 MOSFET Noise Models
A careful observation of the drain current of a MOSFET reveals minute random fluctuations, referred to as noise. Noise is inherently present in electronic devices with or without the presence of an applied external signal.
Noise could be in output current as well as in output voltage. In an MOS
(metal-oxide-semiconductor) analog circuits, noise in MOSFET devices can
interfere with weak signals and significantly impact the accurate characterization of circuit performance. Therefore, it is very important to model and
characterize noise in devices [1–3].
The amount of noise depends on the bandwidth of the characterizing system. A common noise characterization technique involves a very narrow
bandwidth, centered on a frequency f. The current noise spectral components within this bandwidth have a certain mean square value. The ratio
of this value to the bandwidth, as the latter is allowed to approach zero,