Tunable Linear MOS Resistors Using Quasi-Floating-Gate Techniques
A family of tunable MOS resistors based on quasi-floating-gate (QFG) transistors biased in the triode region is analyzed in this paper. From the study results, a new device that outperforms previous implementations, is presented. By means of a capacitive divider, the ac component of the drain-to-source voltage scaled with a factor alpha les 1 is added to the gate-to-source voltage leading to a cancellation of the nonlinear terms. The effect of alpha on resistor linearity is analytically studied. Simulation results are also provided for different technologies. Finally, a complete transconductor has been built which preserves the linearity of the MOS resistor. Three versions of the transconductor have been fabricated for different values of alpha (alpha = 0, 0.5, and 1) in a 0.5 mum CMOS technology with plusmn1.65-V supply voltage. Experimental results show (for alpha = 1 ) a THD of - 57 dB (HD2=-70 dB) at 1 MHz for 2-V peak-to-peak differential input signal with a nominal ac-transconductance of 200 muA/V and a power consumption of 3.2 mW.
Available from: Anil Kumar Gupta
- "Several FG based applications can be found out of which few are related to design of multiplier, transconductor, filter, I-V converter, CM with wide dynamic range and enhanced bandwidth and many other concerned to low voltage applications such as CM with enhanced bandwidth , CM with enhanced characteristics . Taking advantage of capacitor divider property, some QFG based transistors were used for design of very linear programmable CMOS OTA  which further used to implement tunable MOS resistors  and also GM-C filter . Other recent published articles are based on current conveyor , CM having low input compliance voltage . "
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ABSTRACT: A low voltage current mirror based on quasi-floating gate MOSFET (QFGMOS) is presented. The use of QFGMOS eliminates the limitations associated with floating-gate MOSFET (FGMOS) structures like increased silicon area, initial charge trapped in the floating gates and gain-bandwidth product degradation. The proposed current mirror based on QFGMOS has a current range up to 500 μA with offset of 10 pA, exhibits high bandwidth of 640 MHz, input resistance of 480 Ω, output resistance of 1.67 GΩ, unity current transfer ratio and dissipates 1.5 mW power. A resistive compensation has also been employed to increase the bandwidth up to 1.3 GHz.
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ABSTRACT: This paper presents an ultra low-voltage, rail-to-rail input/output stage Operational Transconductance Amplifier (OTA) which uses quasi floating gate input transistors. This OTA works with Â±0.3v and consumes 57Â¿w. It has near zero variation in small/large-signal behavior (i.e. transconductance and slew rate) in whole range of the common mode voltage of input signals. Using source degeneration technique for linearity improvement, make it possible to obtain -42.7 dB, HD3 for 0.6v<sub>P-P</sub> sine wave input signal with the frequency of 1MHz. The used feedback amplifier in input stage also enhances common mode rejection ratio (CMRR), such that in DC, CMRR is 146 dB. OTA is used for implementation of a wide-tunable third-order elliptic filter with 237 KHz-2.18 MHz cutoff frequencies. Proposed OTA and filter have been simulated in 0.18Â¿m TSMC CMOS technology with Hspice.
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