DRIVEN-SHIELD AMPLIFIER FOR THE RECORDING OF BROADBAND, NANO-AMP SCALE, CURRENT TRANSIENTS FROM SOURCES LOCATED INSIDE A VACUUM CHAMBER

摘要

A fast, high-sensitivity amplifier has been developed and successfully used to record transient photoconductivity current of high-impedance, hydrogenated amorphous silicon thin film samples mounted inside a cryostat. The key feature of this amplifier is adjustable, positive feedback to the guard conductor of the input coaxial line. The amplifier circuit is located entirely outside the cryostat. It is characterized by a useful bandwidth from oc to 5 MHz, current to voltage gain in excess of 8 x 10(6) V A(-1), good linearity and low noise. Averaging over several hundred waveforms with the help of digital storage oscilloscope improves signal-to-noise ratios dramatically and allows transient photocurrents of the order of 1 nA to be accurately followed in a microsecond time scale. The amplifier was also successfully used to record the ion current of a Faraday cup in time-of-flight mass spectroscopy. [References: 5]