Enhancing resolution in analog-to-digital conversion by adding statistically controlled noise to the analog input signal

Claim 3

A method as in claim 1 wherein the step of generating a noise signal includes selecting an amplitude probability density function of the noise signal which is substantially zero except substantially over the interval from -2.sup..sup.-(N.sup.+1) to +2.sup..sup.-(N.sup.+1) times the full scale amplitude of the analog input signal, where the digitized samples are in binary code and N is the number of bits of each digitized sample.

Claim 4

A method as in claim 2 wherein the step of generating a noise signal includes selecting an amplitude probability density function of the noise signal over the nonzero interval which is approximately 2.sup.N divided by the amplitude of the full scale analog input signal.

Claim 5

A method as in claim 3 where the step of generating a noise signal includes selecting a power density spectrum of the noise signal which is substantially zero over substantially the frequency intervals KF(s)-F(m) to KF(s) + F(m) for K = 0,1,2 . . . .

Claim 6

A method as in claim 4 wherein the sampling step includes sampling at a rate which is at least four times the maximum frequency of interest in the analog input signal.

Claim 9

An apparatus as in claim 6 wherein the means for generating digitized samples includes means defining a plurality of quantization steps and wherein the amplitude probability of the noise signal is within an envelope surrounding the analog input signal and having an amplitude dimension which is approximately one quantization step peak-to-peak.

Claim 10

An apparatus as in claim 6 wherein the sampling rate is at least four times the maximum frequency of interest of the analog input signal.

Claim 11

An apparatus as in claim 6 wherein the generating means comprise means for generating a digital noise signal having a repeating plurality of amplitude levels, means for generating a white noise smoothing signal whose average amplitude is substantially less than the digital noise signal, and means for combining the two last recited signals to form said noise signal.

Claim 12

An apparatus as in claim 9 wherein the means for generating the digital noise signal comprise means for generating a clock signal at the sampling rate, means for generating time subdivided clocks at half and one-quarter the rate of said clock signals, and means for combinding said time subdivided clocks to form said digital noise signal, wherein the digital noise signal has a repeating sequence of four different amplitude levels.

Claim 15

A method as in claim 11 wherein the sampling rate is at a defined frequency, and wherein the noise signal has a power spectrum which is substantially outside the power spectrum of the sampling rate frequency.

Claim 16

A method as in claim 12 wherein the quantum levels are uniformly distributed, and wherein the width of the noise signal amplitude band is approximately equal to the difference in amplitude between two adjacent quantum levels.

Claim 17

An analog-to-digital conversion system including an analog-to-digital converter having an input terminal for receiving an input signal, means for sampling the signal at the input terminal at a defined sampling frequency, means for converting each sample to a digital signal representing a corresponding one of a succession of quantum levels, and an output terminal providing said digital signal, wherein the improvement comprises: means for providing an unknown analog signal having a defined frequency range of interest; means for generating a noise signal having a selected power spectrum which is substantially outside the power spectrum of the frequency of interest in the analog signal and having an amplitude probability distribution that is substantially uniform within an amplitude band whose width is related in a selected manner to the amplitude difference between adjacent quantum levels of the analog-to-digital converter; means for combining the analog signal and the noise signal to provide a combined signal; means for applying the combined signal to the input terminal of the analog-to-digital converter to be sampled thereby and converted to said digital signal; and averaging means connected to the output terminal of the analog-to-digital converter for receiving said digital signal, for averaging it over selected averaging intervals, and for providing output signals representing the amplitude level of the unknown analog signal at each averaging interval.

Claim 18

An analog-to-digital conversion system including an analog-to-digital converter having an input terminal for receiving an input signal, means for sampling the signal at the input terminal at a defined sampling frequency, means for converting each sample to a digital signal representing a corresponding one of a succession of quantum levels, and an output terminal providing said digital signal, wherein the improvement comprises: means for providing an unknown analog signal having a defined frequency range of interest; means for generating a noise signal having a selected power spectrum which is substantially outside the power spectrum of the frequency of interest in the analog signal and having an amplitude probability distribution that is substantially uniform within an amplitude band whose width is related in a selected manner to the amplitude difference between adjacent quantum levels of the analog-to-digital converter; means for combining the analog signal and the noise signal to provide a combined signal; means for applying the combined signal to the input terminal of the analog-to-digital converter to be sampled thereby and converted to said digital signal; and averaging means connected to the output terminal of the analog-to-digital converter for receiving said digital signal, for averaging it over selected averaging intervals, and for providing output signals representing the amplitude level of the unknown analog signal at each averaging interval.

Claim 19

A system as in claim 14 wherein the noise signal is a digital signal having a repeating sequence of at least four different amplitude levels and combined with a low-level white noise signal for smoothing.

Claim 22

A method as in claim 16 wherein the sampling is carried out at a defined sampling frequency and wherein the power spectrum of the noise signal is substantially outside the power spectrum of the sampling signal frequency.

Claim 23

A method as in claim 17 wherein the amplitude probability distribution is a function of the difference in amplitude between adjacent quantum value signals.

Claim 24

A method as in claim 18 wherein the analog signal has a defined full scale value and wherein the amplitude probability distribution of the noise signal is a function of the full scale value of the analog signal.

Claim 25

A method as in claim 16 wherein the analog signal has a defined full scale value and wherein the amplitude probability distribution of the noise signal is substantially uniform within a band whose width is a function of the full scale value of the analog signal and of the quantum value signals to which each sample is converted, and the amplitude probability of the noise signal is substantially zero outside said band.

Claim 26

A method as in claim 16 wherein the noise signal is in the form of a digital signal having a repeating sequence of at least four different amplitude levels and combined with a low level white noise signal for smoothing.