A low-transconductance OTA with improved linearity suitable for low-frequency Gm-C filters

A low voltage low power operational transconductance amplifier (OTA) based on a bulk driven cell and its application to implement a tunable Gm-C filter is presented. The linearity of the OTA is improved by attenuation and source degeneration techniques. The attenuation technique is implemented by bulk driven cell which is used for low supply voltage circuits. The OTA is designed to operate with a 0.9 V supply voltage and consumes 58.8 μW power. A 600 mVppd sine wave input signal at 1 MHz frequency shows total harmonic distortion (THD) better than -40 dB over the tuning range of the transconductance. The OTA has been used to realize a tunable Gm-C low-pass filter with gain tuning from 5 dB to 21 dB with 4 dB gain steps, which results in power consumptions of 411.6 to 646.8 μW. This low voltage filter can operate as channel select filter and variable gain amplifier (VGA) for wireless sensor network (WSN) applications. The proposed OTA and filter have been simulated in 0.18 μm CMOS technology. Corner case and temperature simulation results are also included to forecast process and temperature variation affects after fabrication.

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A 0.9 V Supply OTA in 0.18 μm CMOS Technology and Its Application in Realizing a Tunable Low-Pass Gm-C Filter for Wireless Sensor Networks

Summary

A low voltage bulk-driven operational transconductance amplifier (OTA) and its application to implement a tunable Gm-C filter are presented. The linearity of the proposed OTA is achieved by nonlinear terms cancelation technique, using two paralleled differential topologies with opposite signs in the third-order harmonic distortion term of the differential output current. The proposed OTA uses 0.8 V supply voltage and consumes 31.2 μW. The proposed OTA shows a total harmonic distortion of better than −40 dB over the tuning range of the transconductance, by applying 800 mVppd sine wave input signal with 1 MHz frequency. The OTA has been used to implement a third-order low-pass Gm-C filter, which can be used for wireless sensor network applications. The filter can operate as the channel select filter and variable gain amplifier, simultaneously. The gain of the filter can be tuned from −1 to 23 dB, which results in power consumptions of 187.2 to 450.6 μW, respectively. The proposed OTA and filter have been simulated in a 0.18 µm CMOS technology. Simulations of process corners and temperature variations are also included in the paper. Copyright © 2014 John Wiley & Sons, Ltd.

A 0.8‐V supply bulk‐driven operational transconductance amplifier and Gm‐C filter in 0.18 µm CMOS process

A low-voltage low-power CMOS fully differential linear transconductor with mobility reduction compensation

\n\nOperational Transconductance Amplifier (OTA) plays an essential role\nin many analog and mixed-signal applications that encourages the researchers to contribute their\nwork to design suitable structures of OTA for their applications with acceptable performance\nparameters.\n\n\n\nThe linearity of an OTA is one of its key performance parameters, which affects the performance\nof the overall system whereas the transconductance value of OTA (Gm) contributes to decide\nits application area. Low transconductance OTA finds its application in biomedical and neural\nnetworks while OTA with higher transconductance is suitable for wireless communication. In any\nsystem, it is desirable to obtain a linear voltage-to-current conversion, i.e., OTA, hence various linearization\ntechniques have been reported to linearize the OTA.\n\n\n\nIn the last two decades, various OTA structures have been reported with linear voltage-tocurrent\nconversion. Some researchers used attenuation by means of different circuit approaches to\nlinearize the OTA or some used cancellation of nonlinearity terms by using different circuit implementation\ntechniques. Researchers used some other methods also to linearize the OTA viz\nsource degeneration, square root technique and mobility compensation.\n\n\n\n The purpose of this paper is to provide a brief survey of various popular linearization\ntechniques reported in the past.\n

Hong Yang

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