A direct RF sampling GPS receiver front-end is presented in a 130nm BiCMOS process, occupying less than 2mm2 of die area. Downconversion of the GPS L1 signal is achieved by subsampling rather than by mixing. The number of building blocks and the complexity of the subsampling receiver are lower than of a conventional heterodyne GPS receiver with comparable performance metrics. The total power consumption from a supply voltage of 1.2V is less than 9mW. The total receiver NF is 3.8dB, the lowest reported NF of a subsampling receiver at this level of power consumption. The NF penalty due to subsampling is less than 1dB.

A RF filter architecture is presented in a 130nm BiCMOS process, serving as replacement of the off-chip Surface Acoustic Wave filter in a GPS receiver front-end. The on-chip RF filter achieves a 3dB bandwidth of less than 12MHz at the GPS L1center frequency of 1575.42 MHz. It exhibits a steep roll-off characteristic resulting in more than 30dB attenuation at frequencies greater than 30MHz away from the center frequency, matching the performance of most commercial off-chip SAW filters. It is implemented as a single cascode stage and achieves a low power consumption of 8.7mW.

A new instrument has been developed and deployed for sensitive reception of broadband extremely low frequency (ELF) (defined in this paper as 300-3000 Hz) and very low frequency (VLF) (defined in this paper as 3-30 kHz) radio signals from natural and man-made sources, based on designs used for decades at Stanford University. We describe the performance characteristics of the Atmospheric Weather Electromagnetic System for Observation, Modeling, and Education (AWESOME) instrument, including sensitivity, frequency and phase response, timing accuracy, and cross modulation. We also describe a broad range of scientific applications that use AWESOME ELF/VLF data involving measurements of both subionospherically and magnetospherically propagating signals.

A system for detecting magnetic fields in the femtotesla range at low frequencies is developed, including the antenna, transformer, and amplifier. Each component is described with relevant tradeoffs which allow a large variety of receivers to be easily designed for any magnetic field sensing in the very low frequency range. A system using a 1-¿-1-mH impedance antenna is developed further as an example that has been used extensively in measurements all over the world in the frequency range of 50 Hz-30 kHz. It has a gain of 0.58 V/nT and a sensitivity of below 1 fT/Hz1/2above 250 Hz.

We present a method for high-frame-rate reconstruction of a dynamic 2-D scene from two effectively continuous orthogonal projections. A natural application of this technique is in the high-speed imaging of transient luminous events-e.g., sprites, elves, gigantic jets, blue jets-in the Earth's atmosphere, where 1-D multianode photometers are used to improve temporal resolution and optical sensitivity over that offered by traditional video cameras. To characterize the performance of the method, we use sprite-image sequences to produce multicolumn and multirow projection data and then use the projection data to produce 2-D ldquoreconstructedrdquo sprite images at the projection data frame rate to compare with the original sprite-image sequence. We also test the performance limits and the spatial resolution of the algorithm using artificially constructed dynamic images.

A new optical instrument has been developed that captures 2-D images at high speed and high sensitivity using 1-D photomultiplier tube arrays. The arrays are orthogonally aligned, and using a coaligned video-speed imager, fast images can be reconstructed using matrix inversion techniques. The instrument can be used to make measurements of optical signatures of energetic electron precipitation induced by discrete waves (e.g., lightning discharges and very-low-frequency transmitter pulses), as well as measurements of high-speed high-altitude glow discharges in the upper atmosphere known as sprites, halos, and ELVES. In this paper, we introduce the instrument and present some first results of sprites and ELVES, and we discuss how the instrument can improve upon current observations in other experiments.

A new technique for finding the frequency spectrum of a carrier frequency modulated by a periodic signal is presented. The technique is based on the frequency modulation (FM) equation due to Hess, which in the frequency domain is a double convolution equation. The technique reduces the FM spectrum problem to the solution of a set of linear equations in which the FM side-band amplitudes are the unknowns. The results obtained through this new technique can, in most cases, be obtained by other means. However, the technique is simple and as a result its implementation on a standard computer is both simple and fast. Furthermore, it is especially suitable when the modulating signal is in the form of a Fourier series with a large number of terms or requires a large number of terms to approximate it. Numerical results obtained using the technique for a large number of complex modulating signals are presented.