In this paper we propose a new architecture for enhancing the performance of a transimpedance amplifier (TIA) used for low-currents, and in particular, that used in biosensing. It is usually the first block in biomedical acquisition systems for converting a current in the nanoampere and picoampere range into a proportional voltage, with an amplitude suitable for further processing. There exist two main amplifier topologies for achieving this, current-mode and shunt-feedback mode. This paper introduces a shuntfeedback amplifier that embodies current-mode operation and thereby offers the advantages of both existing schemes. A conventional shunt-feedback amplifier has a number of stages and requires compensation components to achieve stability of the feedback loop. The exemplary circuit described is inherently stable because a high gain is effectively achieved in one stage that has a dominant pole controlling the frequency response. Exhibiting complementary symmetry, the configuration has an input port that is very close to earth potential. This enables the configuration to handle bidirectional input signals such are as met with in electrochemical ampero-metric biosensors. For the 0.35µm process adopted and ±3.3V rail supplies, the power dissipation is 330µW. With a transimpedance gain of 120dBohm the incremental input and output resistances are less than 2ohm and the-3dB bandwidth for non-optical input currents is 8.2MHz. The input referred noise current is 3.5pA/√Hz.

This paper describes the design of a high-transconductance, wide-band, temperature-insensitive bipolar differential voltage-to-current converter, the transconductance of which is determined by a chosen degeneration resistor. Detailed illustrations of current and voltage traces are included to clarify circuit operation. Comparison with previously published designs shows that this converter provides better linearity, with very low temperature sensitivity and excellent transconductance predictability. Simulation results show that the proposed circuit, with a nominal transconductance of 5 mS, has a Total Harmonic Distortion (THD) better than −70 dB at 10 MHz, with a degeneration resistor of 400 over an input voltage range of 350 mV for supply voltages of ±2.5 V. The analysis and simulation comparisons are in good agreement.

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