On the input common‐mode voltage range of CMOS bulk‐driven input stages

Abstract

SUMMARYIn this paper the response of a bulk-driven MOS Metal-Oxide-Semiconductor input stage over the input common-mode voltage range is discussed and experimentally evaluated. In particular, the behavior of the effective input transconductance and the input current is studied for different gate bias voltages of the input transistors. A comparison between simulated and measured results, in standard 0.35- §m CMOS Complementary Metal-Oxide-Semiconductor technology, demonstrates that the model of the MOS transistors is not sufficiently accurate for devices operating under forward bias conditions of their sourcebulk pn junction. Therefore, the fabrication and the experimental evaluation of any solution based on this approach are highly recommended. A technique to automatically control the gate bias voltage of a bulk-driven differential pair is proposed to optimize the design tradeoff between the effective input transconductance and the input current. The proposed input stage was integrated as a standalone block and was also included in a 1.5-V second-order operational transconductance amplifier (OTA)-C lowpass filter. Experimental results validate the effectiveness of the approach.

0.5‐V bulk‐driven OTA and its applications

“…Thus, for the most critical case: V DD = 0.55 V, T = 70 °C and amplifier inputs shorted to ground, the maximum observed input current was 5.9 μA. However, as it was pointed out in , the simulated input currents in bulk‐driven circuits can be significantly overestimated, when compared to the experimental behavior. This is due to the fact, that in CMOS technologies, process parameters of diodes are usually characterized for reverse bias operation and can be inaccurate for forward bias condition.…”

“…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.…”

A Family of Low-Voltage Bulk-Driven CMOS Continuous-Time CMFB Circuits

“…Thus, the noise contribution of the bulk-driven transistors in the above CMFB networks is negligible as compared to the noise contribution of the input transistors of the FD amplifier. Finally, it is worth to note that the maximum input current of bulk-driven MOS transistors when their parasitic pn source-bulk junction is forward biased can be kept to a very low level [16], as will be shown in Section IV.…”

Bulk linearized CMOS differential pair transconductor for continuous-time OTA-C filter design

“…There are many papers describing gate driven [7][8][9][10][11][12][13] and bulk driven MOS pairs [14][15][16][17][18][19][20][21]. A simple gate driven MOS pair unfortunately has poor linearity of voltage to current conversion, therefore the other voltage to current converters are often used when the linearity is important [7].…”

“…For high frequency applications, numerous circuit techniques to design OTA-C filters have been developed, using the gate-driven differential pair transconductors as input stages of the OTAs [7][8][9][10][11][12][13]. On the contrary, the transconductors with bulk-driven differential pair have been proposed for low frequency OTA-C filter applications [14][15][16][17][18][19][20][21].…”