Timeback Systems, Inc.

Other

Digital Fidelity, Inc.

Royalty Funding Ltd.

Robert G Nelson

Onkar S Modgil

James D Awtrey

Thomas F Crandell

Margaret S Reif

A closed-loop power control system includes an analog input and an analog output. An analog signal applied to the analog input is summed with an analog signal derived from the analog output to produce a difference signal representative of the polarity of the difference between the analog input signal and the derived analog output signal. A digital signal is produced representative of the polarity of the difference signal. The system includes at least two switching networks, having high energy outputs, and which are responsive to the digital signal to reduce the levels of the difference signal in a frequency band of interest at the source of the digital signals. A low-pass filter is included between the high energy outputs and the means to produce the digital signal to attenuate high frequency noise. The phase lag created by a low-pass passive filter at the output of the high energy outputs is, in one embodiment, reduced by a high-pass filter to maintain stability. Instability that may occur in the presence of large amplitude signals is avoided by the use of a clipping circuit.

Stabilization of closed-loop power controllers

A power controller includes a closed-loop system having a summer to sum an input signal with a derived output signal to produce a difference signal. A comparator compares the difference signal with a reference signal to produce a digital signal representative of the polarity difference between the difference signal and the reference signal. Two switching networks respond to the digital signal to produce high energy outputs representative of the digital signal which are used to reduce the level of the difference signal in a frequency band of interest at the comparator. A low pass filter between the high energy outputs and the comparator attenuates high-frequency noise. A low-pass filter of at least the third order, connected in the closed loop, enhances the signal-to-noise ratio. In a specific application the power controller is a power amplifier and the input signal is in the audio frequency range.

Closed loop power controller

An analog-digital converter includes a source of high frequency pulses comprising a variable frequency oscillator having an output frequency f which is a function of an analog condition. Also included is a source of a reference signal, preferably pulses, having a fixed frequency whose value is a fraction of the value of the frequency of the variable frequency oscillator. The first named souce also includes a counter-divider to which the output of the variable frequency oscillator is applied. The counter-divider has an output which is either f/N or f/N-M where N and M are whole integers and M is less than N. A phase comparator is responsive to the reference signal and to the output from the counter-divider for measuring the phase difference between the reference signal and the output pulses from the counter-divider. The dividing ratio of the counter-divider is under control of means responsive to the measure of phase difference such that the counter-divider is adjusted to bring the pulses from the counter-divider toward an in-phase relationship with the reference signal as seen at the phase comparator. The selection of the dividing ratio is carried out by a logic means which responds to the output of the variable frequency oscillator and the output of the source of the reference signal to provide for a selection of the counter-divider division ratio for each cycle of the reference signal. The output or measure of phase difference is in the form of a single-bit digital function and this function is applied to a digital low-pass filter to produce a binary word.

Methods and apparatus for analog-to-digital conversion

A system with improved signal-to-noise ratio for digitizing a representation of an analog condition comprises two oscillators for generating high frequency digital pulse signals, the frequencies of which are harmonically related one to the other. One of the oscillators responds to the analog condition to cause a shift in phase in its digital signal to cause phase differences between the digital pulse signals. The phase differences include quantizing errors having energy from D.C. to one half the frequency of said digital signals. A phase detector detects the phase differences. The detected phase differences are applied to a low-pass filter to produce a signal representative of phase error in a frequency band of interest. A phase modulator modulates the phase shifted digital signal in response to said signal representative of phase error to enhance the phase difference in said frequency band of interest. The phase modulated digital signal is compared with the other digital signal by a D flipflop to obtain a measure of the phase shift. The measure of the phase shift utilized to adjust the phase of the digital pulse signals toward an in-phase condition.

Method of and apparatus for reducing quantizing noise in analog to

The disclosure is directed to an analog-digital converter which includes a source having an output of fixed frequency time-spaced pulses. An oscillator having an output of time-spaced pulses, harmonically related to pulses from the source, is comprised of a plurality of digital gates connected serially in a loop. At least one of the digital gates includes impedance means such as a resister or capacitor, responsive to an analog condition to form a modulator. Change in the value of the impedance changes the time constant of the modulator to effect a change in the time-spaced pulses related to the instantaneous amplitude of the analog condition. The outputs of the source and the oscillator are applied to a comparator. Means responsive to the comparator is employed to correct the oscillator time-spaced pulses toward an in phase state relative to the time-spaced pulses from the source. A digital signal is produced whose value is proportional to the correction made to the oscillator time-spaced pulses and is thus representative of the instantaneous value of the analog condition.

Analog to digital converter

Methods and apparatus are described for generating a digital representation of an analog condition. In one method high-frequency digital signals are generated with the frequency of each signal being constant and the frequencies bearing a harmonic relationship one to the other. A representation of the analog condition is applied to cause a shift in phase in at least one of the digital signals. The digital signals are then compared to obtain a measure of the phase shift which is utilized to adjust the phase of the phase shifted signal toward its original phase condition. As a result of the measure of phase shift, there is generated a single weighed digital function which is representative of the amplitude of the adjustment utilized to return the phase shifted signal toward its original phase shifted condition. The single weighed digital function is applied to a low-pass digital filter to produce a multi-bit digital word representative of the instantaneous value of the analog condition. Apparatus of invention comprises a pair of oscillators whose frequencies are constant, harmonically related to one another and whose outputs are time spaced digital pulses. An analog condition responsive means has applied thereto the aforesaid pulses to effect a relative phase shift between the digital pulses and a phase comparator measures the relative phase shift. Means are provided responsive to the measure of the relative phase shift to return the digital pulses toward an in-phase relationship, and in so doing, there is produced a single weighed digital function representative of the measure of the relative phase shift. A new and improved geophone is described.

Growing community of inventors

Dallas, TX, United States of America

Robert G Nelson