Abstract
This paper presents the small-signal operation of a $g_{\mathrm {m}}$ -boosted inverter-cascode transimpedance amplifier which has not been reported previously and whose comprehensive analysis is not available in any reported article or text-book. A simplified sequential equivalent-circuit method is employed which eliminates the need for complicated circuit analysis techniques. The analysis shows that the gain and the gain-bandwidth of the $g_{\mathrm {m}}$ -boosted inverter-cascode transimpedance-amplifier is enhanced by the gain of the $g_{\mathrm {m}}$ -boosting amplifier. This is due to the increased output impedance of the TIA, and, the reduced input-referred miller-effect capacitance through miller-effect trade-off employing the $g_{\mathrm {m}}$ -boosting loop. To verify the actual performance improvement achieved, circuit simulation results as well as measured experimental results are also provided.
Highlights
Transimpedance amplifiers (TIAs) are today one of the most crucial front-end analog conditioning circuits for meeting the challenging current-sensing specifications in electronic systems, sensor and biomedical applications with nano- and pico-ampere sensed currents
When a single DNA molecule passes through the nanopore, the individual nucleotide bases are identified by the variation of the current through the nanopore due to the particular base passing through the nanopore, which is sensed by the TIA
Considering only thermal-noise of resistors and the drain-current noise of the MOSFET devices, the noiseinserted [21], [22] gm-boosted inverter-cascode TIA with noise-current-spectral-densities associated with all the devices is shown in the Fig. 5, where the drain-current-noise can be expressed by a current-source connected across the drain and the source of the MOSFET devices operating in the saturation region [13]
Summary
Transimpedance amplifiers (TIAs) are today one of the most crucial front-end analog conditioning circuits for meeting the challenging current-sensing specifications in electronic systems, sensor and biomedical applications with nano- and pico-ampere sensed currents. AC coupling can be employed at the input in the form of Quasi-floating-gate inputs for separating the DC-bias circuits for the PMOS and the NMOS inverter sections This is done in order to maintain higher overdrive dynamic range for these inverter devices to operate in saturation and achieve linear small-signal currentto-voltage transimpedance gain. This AC-equivalent circuit is co-incident for both the biasing options as the resistance at the input is dominated by the feed-back resistor RF with the pseudo-resistor having a very high resistance value in the range of several Mega-ohms. Inspecting (24), (27) and (30) it is clear that gm-boosting reduces all the time constants resulting in an overall bandwidth improvement
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