Showing papers by "Fred L. Walls published in 1989"
TL;DR: In this article, the authors describe the design, schematics, and performance of a very low-noise FET cascode input amplifier, which has noise performance of less than 1.2 nV/(Hz)1/2 and 0.25 fA/( Hz) 1/2 over the 500 Hz to 500 kHz frequency range.
Abstract: We describe the design, schematics, and performance of a very low‐noise FET cascode input amplifier. This amplifier has noise performance of less than 1.2 nV/(Hz)1/2 and 0.25 fA/(Hz)1/2 over the 500 Hz to 500 kHz frequency range. With modest changes it could be extended to a wide variety of uses requiring low‐noise gain in the 1 Hz to 30 MHz frequency range.
23 citations
31 May 1989
TL;DR: In this article, the combination of the digital filter and the Allan variance corresponds to a novel variance, which is described and compared to the well-known modified Allan variance, and can be identified by Allan variances.
Abstract: Digital noise generators are described as is their use to generate sample series that simulate frequency samples as given by a counter. Applying the Allan variance to the samples of six generators (white phase, flicker phase, white frequency, flicker frequency, frequency random walk, filtered flicker frequency) yields the expected theoretical slopes. The method used consists in filtering the f/sup -1/ and f/sup 0/ phase noise by means of a digital filter in the time domain, (using the Z transform), which yields f/sup -3/ and f/sup -2/ noises, which thus can be identified by Allan variances. The combination of the digital filter and the Allan variance corresponds to a novel variance, which is described and compared to the well-known modified Allan variance. >
7 citations