Abstract
This paper describes a very low level dc current amplifier using switched capacitor (SC) circuit to miniaturize and improve its output response speed, instead of the conventionally used high-oh-mage resistor. A switched capacitor filter (SCF) and an offset controller are also used to decrease vibrations and offset voltage at the output of the amplifier. The simulation results show that the parasitic capacitances that are distributed to the input portion of the amplifier have some effect on offset voltage. From the experimental results, it is seen that the duty ratio of the clock cycle of SC circuit should be in the range from 0.05 to 0.70. It is suggested that the proposed very low level dc current amplifier using SC circuit is an effective way to obtain both a faster output response and its miniaturization.
Highlights
When very small currents are measured by mass spectroscopes and radiation detectors, response speeds of the measuring instruments are limited by those of very low level dc current amplifiers [1]
To evaluate response speed of the very low level dc current amplifier, a square wave current Is with a time period of 5 ms and an amplitude of 10 nA was input to the amplifier
It is found from the experimental results that the duty ratio of the clock cycle should be in the range: 0.05 < d < 0.70
Summary
When very small currents are measured by mass spectroscopes and radiation detectors, response speeds of the measuring instruments are limited by those of very low level dc current amplifiers [1]. This means that the amplifiers are required to observe rapid transient phenomena. The amplifier with high-ohmage resistor has unavoidable effects of the stray capacitances across its terminals. This factor causes the amplifier to have a complicated frequency characteristic, which results in its poor responses [1] [2]. Some shielding techniques [3]-[5] have been reported for the purpose of de-
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