Abstract
Designing low-noise current readout circuits at high speed is challenging. There is a need for preamplification stages to amplify weak input currents before being processed by conventional integrator based readout. However, the high current gain preamplification stage usually limits the dynamic range. This article presents a 140 dB input dynamic range low-noise current readout circuit with a noise floor of 10 fArms/sq(Hz). The architecture uses a programmable bidirectional input current gain stage followed by an integrator-based analog-to-pulse conversion stage. The programmable current gains setting enables one to achieve higher overall input dynamic range. The readout circuit is designed and in 0.18 μm CMOS and consumes 10.3 mW power from a 1.8 V supply. The circuit has been verified using post-layout simulations.
Highlights
There is a growing need to sense very low levels of current in many biosensors and diagnostics applications [1,2,3]
The resistance is inversely proportional to the input current, which leads to a variable current gain and bandwidth applications [9]
This paper presents a low-noise current readout circuit using programmable gain setting switches to process a wide input range of currents of 140 dB
Summary
There is a growing need to sense very low levels of current in many biosensors and diagnostics applications [1,2,3]. If a TIA is employed, the feedback resistance must be large enough (i.e., gigaohms range) to obtain high gain and there is a trade-off between achieving high dynamic range and achieving low input-referred current noise. Such a large feedback resistor cannot be reliably realized on-chip and must be externally connected. For a programmable gain amplifier, the dynamic range will be measured as a ratio of highest input signal level (at lowest gain setting) and the largest referred input noise ever measured for any of the gain settings. The circuit is designed in a 0.18 μm CMOS process and validated using post-layout simulations
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