A frequency generator for generating a large number of closely and evenly spaced frequencies over a large bandwidth including a first digitally controlled oscillator and a second digitally controlled oscillator, and a combiner for mixing the frequencies from said first and second digitally controlled oscillators, wherein the sampling rate of the digitally controlled oscillators differs by a small predetermined amount. Switching speed is extremely rapid.
A method and apparatus for generation of high frequency pulses and for excitation of nuclear magnetic resonance of a sample generates a plurality of modurated high frequency waves having different frequencies from each other, and combines the generated these high frequency waves so as to generate high frequency pulses which provide a frequency spectrum having a predetermined band, thereby a shortening of the high frequency pulse width as well as a narrowing of the frequency band is achieved.
A frequency synthesizer system generates a clock signal having an adjustable, accurate and stable frequency. The synthesizer produces a first reference frequency FR and an adjustable first intermediate frequency F1 equal to the frequency FR divided by a selectable number (N2/N1) which permits course adjustment of the frequency in steps over a prescribed range. The frequencies FR and F1 are then mixed and filtered to produce a second intermediate frequency FR+F1. The system also generates a second reference frequency F3 which is finely adjustable over a range in the order of magnitude of the frequency difference between two successive steps of the first intermediate frequency F1. This second reference frequency is mixed with the second intermediate frequency and the result is filtered to produce a final frequency FR+F1+F3.
A circuit (62, 64) for receiving a periodic input signal at frequency f, and for producing a pseudosinusoidal staircase output signal at a fundamental frequency f from which predetermined harmonics of the fundamental frequency are absent. Also provided are an oscillator in which such a circuit forms the drive circuit for a piezoelectric crystal, and an accelerometer in which such an oscillator is used as the force sensing means. In the accelerometer, the reaction force of a proof mass (40) is sensed by a resonator that comprises a drive circuit (44) for producing a drive signal and a piezoelectric crystal (42) connected between the proof mass and support (46). In response to the drive signal, the crystal undergoes mechanical vibration at a frequency f that varies with the force applied to the crystal. A resonator signal corresponding to the mechanical vibration is produced and input to drive circuit. The drive circuit responds by producing the drive signal in the form of a periodic, pseudosinusoidal staircase function. The staircase function has fundamental frequency f, and has N steps of M discrete nonzero amplitude levels per period. N and M are integers greater than one, with M being less than N. The drive circuit produces the M amplitude levels such that predetermined harmonics of the fundamental frequency f are not present in the drive signal, thereby reducing the possibility of activity dips in the accelerometer output.
A trigger source switching circuit including a first switch system for a high frequency region, and a second switch system for a low frequency region. The first switch system is composed of a plurality of semiconductor switches having good frequency and isolation characteristics, and the adverse effect of the DC shift is eliminated by using a capacitor connected between the outputs of the semiconductor switches and the output terminal of the trigger source switching circuit. The second switch system for the low frequency region is composed of analog switches, and the output terminal of each analog switch is connected to an input terminal of an operational amplifier of a small output offset, thereby reducing the effect of the on-resistance of the analog switches and the adverse effect of the DC shift. The analog switches can be used because the frequency and isolation characteristics required in the high frequency region are unnecessary in the low frequency region.
To harden transmissions, in both directions, between a master station (1) and a slave station (2), a table of communication parameter values is memorized in each station and the table values are then used in accordance with the master station's decision. Each message from one station to the other contains information to allow the receiving station to determine the parameter values to be selected in the table to eliminate values where there is a high risk of jamming.
