Current-to-voltage converter with low noise, wide bandwidth and high dynamic range.

摘要

The design of a current-to-voltage converter with a uniform transfer function in its feedback loop (12) is proposed. It employs a very large, double-shielded measuring resistance (13) and a two-stage setup to perform a fully linear I/V conversion with a conversion factor of 10<1><0> V/A and a bandwidth of 1 MHz. With the low noise level attained, and with the bandwidth and conversion factor mentioned, it will be possible to monitor events involving as few as 300 electrons. The current-to-voltage converter comprises a differential input amplifier (8), a current source (11) for supplying said differential amplifier (8), at least one operational amplifier (10,14), and a high-valued measuring resistance (13) the voltage drop across which is being taken as a measure of the current to be detected. The measuring resistance (13) is arranged in a feedback loop (12) associated with said differential amplifier (8). The measuring resistance (13) is double-shielded from the remainder of the current/voltage converter circuitry through its arrangement inside a cylindrical capacitor C which acts as a first shield, and which is in turn connected to a casing (15, 25) surrounding the differential amplifier (8) and the feedback loop (12) and which constitutes a second shield.