Transimpedance amplifiers: Reaching high gain, low noise and high bandwidth

Transimpedance amplifiers are current-to-voltage converters. They are found in a wide variety of applications that require current measurements at high sensitivity, low noise and/or high bandwidth. Inherent to the construction of such an amplifier are certain tradeoffs between bandwidth, amplification, and noise level, requiring a careful design and layout of a transimpedance amplifier for any given task. These design limitations become especially relevant for high-gain, high-bandwidth applications, such as photodiode readout or ion current sensing. In these applications, commercially available amplifiers are often not suited for the task, leading to a low signal-to-noise ratio. This paper discusses the most significant limiting factors of transimpedance amplifiers, and describes their effects, source and possible mitigation options. It presents a novel combination of feedback resistor configuration and shielding layout to improve performance beyond typical single-resistor shielded options. Based on this, a low-cost transimpedance amplifier made with readily available off-the-shelf components reaching 30 kHz bandwidth and 1 GΩ amplification with only 3.898 pA root-mean-square noise was developed, characterized and demonstrated for use in ion mobility spectrometry as one exemplary application requiring high gain, low noise and high bandwidth.