Multisensor readout circuit using a multiple differential-input operation amplifier with pulse output

Abstract

In this paper, a CMOS multisensor readout circuit is presented. A multiple differential-input operational amplifier (MDI-OPA) with three distinct positive inputs and one common negative input is designed to make one of the three inputs to act as a general differential-input OPA through a built-in multiplexer. A voltage-to-current converter and a current-controlled oscillator are integrated with the MDI-OPA so that the selected analog input voltage can be used to generate a pulse output whose frequency is linearly proportional to the selected input voltage. The linearity of the transfer characteristic is at least 99.99% for input voltages below 1.44 V. An added current-offset structure is used to modify the transfer characteristic that usually varies owing to process variation. The measured output transfer characteristics of three input channels show nearly the same sensitivity of 90 Hz/mV or so with a linearity of at least 99.99% with the assistance of the current-offset mechanism.

CMOS pulse-width-modulation readout circuit with a wide modulation range for ion-sensitive FET-based sensors

“…The effective floatinggate voltage decreases with the increase of pH value of the analyzed solution. 16) Figure 2 shows the simulated signal waveforms for the V sen of 0.8 and 1.05 V with the SW signal of 1 kHz and the RESET pulse signal of 250 Hz. The signal V r is designed to be 1.25 V and is used to compare with the signal V c which is the voltage drop across the capacitor C p .…”

“…[1][2][3][4][5][6][7][8][9][10][11][12] Ion-sensitive FETs (ISFETs) have been widely researched and used in biomedical applications, analytical chemistry and environmental monitoring. [13][14][15][16][17][18][19][20][21][22] The original ISFET is an open-gate MOSFET. Its gate oxide or an extra coated gate insulator such as Si 3 N 4 , Al 2 O 3 , or Ta 2 O 5 is used as a sensing membrane for H + ions.…”

“…Under a bias voltage V ref from an added reference electrode which is usually a silver=silver chloride (Ag=AgCl) electrode and is considered as the gate of the ISFET, the variation in the ion concentration of the analyte is measured as a change in the threshold voltage or a change in the effective floating-gate voltage. [14][15][16] To make the implementation of sensing membrane flexible, an extended metal electrode, on which a sensing film is coated, can be interconnected to the polysilicon gate of a standard MOSFET. 16,23) By using the extended-gate topology, the sensing area will be not constrained by gate size and the ISFET is easily integrated with its readout circuit.…”

“…[14][15][16] To make the implementation of sensing membrane flexible, an extended metal electrode, on which a sensing film is coated, can be interconnected to the polysilicon gate of a standard MOSFET. 16,23) By using the extended-gate topology, the sensing area will be not constrained by gate size and the ISFET is easily integrated with its readout circuit. A native alumina (Al 2 O 3 ) on the extended open aluminum metal layer can be used as a sensing membrane.…”