0.3V Tunable OTA and Gm-C Filter in 0.13µm CMOS

Abstract

This paper presents an ultra-low-voltage operational transconductance amplifier (OTA) and Gm-C filter, both working with 0.3V single supply voltage. Using pseudo-differential structure, the common mode rejection is the main challenge in low voltage condition which is overcome by a new common mode feedback circuit. The OTA can be tuned through the gate terminal of body-driven PMOS input transistors. Post-layout simulation shows 23.4 dB differential gain and 47.4 dB CMRR at low frequencies. By changing the tune voltage from 50mV to 0V, the OTA's transconductance can be tuned from 7.9 to 17.4 µA/V . By applying input voltages up to 0.36 Vpp, the THD of output current remains less than -60 dB. The proposed OTA is employed to implement a tunable low-pass Gm-C filter. The cutoff frequency of Gm-C filter can be tuned from 1.13 to 1.9 MHz that makes it applicable in the multi-standard direct conversion receivers as channel selection filter. The power consumption of filter is 111.3 µW and its input referred voltage noise is 168.7 nV/ √ Hz, as results of post-layout simulations. The post-layout simulation shows the IIP3 of 8.5 dBm for the cutoff frequency of 1.9 MHz. Keywords Ultra-low-voltage design • Operational transconductance amplifier • Gm-C filter • layout • tunable IntroductionUsing low-voltage small batteries with longer charge-discharge cycle is essential in todays portable equipements like cell phones, laptops, medical devices and etc [1][2][3][4][5]. Moreover, modern systems fabricated in deep sub-micron CMOS