We demonstrate how it is possible to increase the sensitivity of current noise measurement systems by exploiting the
properties of a differential transconductance amplifier coupled with a four channels measurement system. In particular, it
is demonstrated that, in proper conditions and by a proper elaboration of the acquired signals, the noise contribution
coming from the active and passive devices that make up the transresistance amplifier can be virtually eliminated. The
method is validated by means of actual measurements in order to demonstrate the effectiveness of the approach we
propose.
KEYWORDS: Diodes, Resistance, Solid state physics, Temperature metrology, Remote sensing, Transistors, Interference (communication), Control systems, Signal attenuation, Amplifiers
In this paper we demonstrate that by exploiting the non linear characteristic of low noise PN junction diodes, a very low
noise, high stability voltage reference can be obtained starting from a conventional solid state series voltage reference. In
order to obtain such a result, a series connection of N identical diodes is supplied in the forward region of the I-V
characteristic by means of a proper resistance. While the DC voltage drop across the diodes can be a large fraction of the
voltage supplied by the reference, the noise introduced by the reference itself is reduced by a much larger factor because
of the low value of the small signal equivalent resistance of the diodes. In its simplest implementation, such a voltage
source would suffer from a relatively high temperature dependence of the supplied voltages because of the intrinsic
properties of PN junctions. However, by resorting to a proper temperature control circuit, high stability can be obtained.
As an example, by employing an AD586 voltage reference and with N=4, a 2.560 V reference has been obtained with a
stability over temperature better than 50 μV/°C and a voltage noise as low as 2×10-15, 6×10-17 and 1.5×10-17 V2/Hz at
100 mHz, 1 Hz and for frequencies larger than 10 Hz, respectively.
An indirect approach for estimating the long term stability of DC electrical sources from low frequency noise measurements is presented and discussed. In particular, it is demonstrated that once the unity frequency magnitude and the frequency exponent of the flicker noise component are determined, an overestimate of the variance of repeated measurements of the source output (averaged over a time interval τ) taken ΔT seconds apart can be readily obtained. The proposed approach is validated with reference to actual experimental data.
KEYWORDS: Amplifiers, Resistance, Field effect transistors, Interference (communication), Resistors, Reliability, Oxides, Power supplies, Signal detection, Data acquisition
Low frequency noise measurements (f<10Hz) are a powerful tool for the investigation of the quality and reliability of electron devices and material. In most cases, however, the application of this technique is made quite difficult both because of the effect of external interferences (temperature fluctuations, EMI, mechanical vibrations, etc.) and because of the high level of flicker noise of the commercial instrumentation. In this paper the most remarkable results we obtained by using low frequency noise measurements for the characterization of the reliability of VLSI metallic interconnections and thin oxides are resumed. Moreover, we discuss the effects of the several sources of noise and interferences which contribute to reduce the sensitivity of the measurement chain. In particular, we demonstrate that by means of a proper design, dedicated instrumentation can be built which allows for a considerable reduction of the overall background noise. Examples will be given with reference to voltage and transresistance amplifiers (both AC and DC coupled), to programmable biasing systems (both current and voltage sources), to thermal stabilization systems and to data acquisition systems. Finally, we will discuss methods which may allow, in proper conditions, to accurately measure noise levels well below the background noise of the input preamplifiers coupled to the device under test. As the systems we discuss are characterized by moderate complexity and employ components readily available on the market, we trust that this paper may also serve as a simple guideline to anyone interested in exploiting the possibility of using very low frequency noise measurements by building his own instrumentation.
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