For the first time, it is revealed that the physical origin of the gate-source voltage (V gs )-dependent drain-source capacitance in short-channel metal-oxide semiconductor field-effect transistors (MOSFETs) comes from the depletion capacitance components between the drain and channel end in the saturation region. On the basis of this origin, it is newly found that the V gs -dependent channel resistance should be connected in series with the drain-source capacitance to model the high-frequency (HF) response of the intrinsic output capacitance. The accuracy of an improved MOSFET model, including the channel resistance, is validated by observing the excellent agreement with the measured S-parameters in the wide range of V gs up to 40 GHz.Introduction: Owing to the rapid growth of wireless communication markets, the demand for radio-frequency (RF) transceivers is increasing. Silicon integrated circuits (ICs) with excellent price competitiveness have been widely used. For the design of an RF CMOS IC, the development of an accurate RF metal-oxide semiconductor field-effect transistor (MOSFET) model in the wide bias range is essential.Since the drain-source capacitance C ds in RF MOSFET equivalent circuit models [1,2] in the saturation region is an important parameter for determining the output admittance, accurate voltage-dependent modelling is required. In the conventional models, C ds is simply defined by the substrate depletion capacitance between the source and the drain because it is assumed to be only determined by the drainsource voltage V ds [1]. However, this definition of C ds is physically unacceptable in the saturation region because the distributed depletion capacitance components (ΔC ds1 , ΔC ds2 and ΔC ds3 ) between the drain and the right end of the channel in Fig. 1 is much larger than the substrate depletion capacitance C dsb below due to the smaller depletion width. Thus, C ds should be newly defined as the capacitance between the drain and the channel end. In this case, C ds is strongly dependent on the gate-source voltage V gs because the pinch-off point voltage is determined by V gs − V th , where V th is the threshold voltage.
Abstract-An accurate large-signal BSIM4 macro model including new empirical bias-dependent equations of the drain-source capacitance and channel resistance constructed from bias-dependent data extracted from S-parameters of RF MOSFETs is developed to reduce S 22 -parameter error of a conventional BSIM4 model. Its accuracy is validated by finding the much better agreement up to 40 GHz between the measured and modeled S 22 -parameter than the conventional one in the wide bias range.
An improved MOSFET output equivalent circuit model is proposed to greatly reduce the Y 22 -parameter error of a conventional one in the high-frequency range more than 10 GHz. In this model, a new parallel RC network is connected in series with the drain-source capacitance to model the ac current crowding phenomenon due to the vertically distributed RC effect in the saturation region. Its accuracy is clearly validated by finding much better agreement up to 40 GHz between measured and modelled Y 22 -parameter than the conventional one.Introduction: Recently, silicon integrated circuits (ICs) with excellent price competitiveness have been widely used for RF applications. For the design of RF CMOS ICs, the development of RF MOSFET equivalent circuit model to simulate high-frequency (HF) characteristics is essential [1,2]. In particular, accurate output admittance Y 22 -parameter modelling is very important to simulate output impedance matching circuits in designing RF ICs.The bias-dependent drain-source capacitance C ds and channel resistance r ch in an RF MOSFET equivalent circuit model of Fig. 1 are crucial parameters for simulating Y 22 -parameter [1]. However, this conventional lumped model does not predict HF Y 22 -parameter accurately, because the vertically distributed RC effect in the saturation region shown in Fig. 2 is not considered. Thus, the valid frequency range of the conventional model should be decided and distributed modelling is required for improving HF accuracy. Therefore, in this Letter, an improved MOSFET model considering the distributed effect is proposed to reduce the error of Y 22 -parameter in the HF region and a direct method to extract the model parameters is presented.
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