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A highly linear common-drain (CD) configuration is designed and measured. The third-order nonlinearity of the transconductance which is a major contributor to the third-order nonlinearity in the CD configuration, is linearised by applying the multiple gated transistor technique. In addition, the harmonic feedback effect in the configur- ation, which limits linearity improvement, is solved by employing an LC resonator as a load impedance. The solution is suggested by the high frequency analysis using the Volterra series. This circuit is implemented with a 0.13 mm CMOS process. Measurement results show a NF of 4.2dB, an IIP3 of 34 dBm, and a gain of 2 4.3dB at 7.2mW of power consumption.
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Introduction: The common-drain (CD) stage widely known as the source follower is one of the key configurations of a CMOS amplifier. The CD stage provides high input impedance and low output impedance which makes it suitable for a voltage buffer amplifier. In the buffer appli- cation, linearity is an important issue because the buffer is usually employed in a rear stage which is required to deliver the performance of the preceding stages to the next stage as same as possible. However, the high frequency linearity characteristics of the CD con- figuration have not been fully discussed compared to its counterparts such as the common-source (CS) and common-gate (CG) configurations which have been researched extensively [1 -5].
In this reported work, high frequency linearity analysis using the Volterra series is conducted for the CD configuration. Based on the analysis, we propose to use the multiple gate transistors (MGTR) tech- nique [2], which is applied to linearise the third-order nonlinearity of a main transistor (MT) using an auxiliary transistor (AT) in the CD con- figuration combined with an LC resonator (LCR) as a load impedance at the output node to remove harmonic feedback components in order to improve the linearity of the CD configuration, as shown in Fig. 1.
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High linearity common-drain configuration: The IIP3 (input referred third-order intercept point) of the CD...