A 0.5 V bulk-input OTA with improved common-mode feedback for low-frequency filtering applications

Abstract

This paper presents the design of a two-stage pseudo-differential operational transconductance amplifier (OTA) and its application in low-frequency continuous time filters. The OTA was designed in a 0.18 lm, 0.45 V V T CMOS process. An improved bulk-mode commonmode feedback (CMFB) circuit has been designed which does not load the OTA compared to prior art. A self cascode load structure and partial positive feedback provide higher gain. The bulk terminals of all transistors have been biased to lower their threshold voltages (V T ) and maximize signal swing. The OTA operates at a supply voltage of 0.5 V and consumes only 28 lW of power. Rail-to-rail input is made possible by using the transistor's bulk terminal as the input. For a load of 20 pF the OTA has a measured DC gain of 63 dB and a gain-bandwidth product of 570 kHz. To demonstrate the use of the OTA in practical circuits, three active RC filters were designed: a 10 kHz Butterworth filter, a 10 kHz Bessel filter, and a 2.5 kHz Tschebycheff filter.

A 0.5 V bulk‐driven voltage follower/DC level shifter and its application in class AB output stage

“…In recent years, many low‐voltage circuits utilizing bulk‐driven transistors have been presented, showing improved performance in a low‐voltage environment . In this work, another example of a low‐voltage bulk‐driven circuit is addressed.…”

0.5‐V bulk‐driven OTA and its applications

“…One of the techniques which could facilitate the design of ultra‐low‐voltage OTAs and op‐amps is based on the application of bulk‐driven MOSFETs . In such solutions, the bulk terminal is used as an input rather than the gate.…”

0.5‐V bulk‐driven differential amplifier

“…[8], Kinget et al . [9], and Trakimas and Sonkusale , in which two bulk‐driven amplification stages with local common‐mode feedback loops are used. The proposed amplifiers operate at a supply voltage less than 0.5 V; the reduction in the supply voltage is mainly achieved by the elimination of the tail current source.…”

“…Thus, alternative analog design techniques and topologies capable for low supply voltages have emerged to achieve large signal-tonoise ratios and small nonlinearity. In the last years, the bulk-driven approach has been proposed in the implementation of extremely low voltage analog circuits [3][4][5][6][7][8][9][10][11][12][13][14][15][16]. On the basis of this approach, the input signal, that is applied to the bulk terminal of MOS devices, results in a large input common-mode range while an appropriate gate overdrive voltage maintains the device in the conductance region.…”