GB1600117A - Method of an apparatus for improving the signal to noise ratio of signals - Google Patents

Description

(54) METHOD OF AN APPARATUS FOR IMPROVING THE SIGNAL TO NOISE RATIO OF SIGNALS (71) I, WILLIAM JOSEPH MULLAR KEY, of 9, Elgin Avenue, Garswood Ashton-in-Makerfield, WN4 ORH formerly of 52 Peveril Close, Whitefield, Lancashire, a British subject, do hereby declare the invention for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to the improving of the signal to noise ratio of signals. The invention is particularly applicable to the enhancement of signals which may be considered as pulsed or amplitude modulated sinewaves, for instance speech or numerical information, encoded as data by any known modulation technique, e.g. delta modulation or other forms of pulse code modulation.

According to the present invention there is provided a signal processor including a transfer element having an input and an output, the transfer element being such that its output signal has the same sign as its input signal, and has a magnitude which is a power of the magnitude of the input signal, wherein said transfer element consists of: a first circuit comprising a diode and a squarer for passing positive signals; a second circuit comprising a diode and a squarer for passing negative signals, said first and second circuits being connected in parallel; and a summation amplifier receiving on its respective inputs the outputs from the two squarers.

The present invention will now be described in greater detail, by way of example, with reference to the accompanying drawing, wherein: Figure 1 is a block diagram of one preferred form of a signal processor; Figure 2 is a graph showing the transfer function of the transfer element in Figure 1; Figure 3 is a block circuit diagram of one preferred construction for the transfer element; and Figure 4 is a block diagram of a radioreceiver including the processor.

The embodiment shown in Figure 1 includes an input terminal 1 connected to a band-pass filter 2. The output of the filter 2 is connected to a transfer element 3, whose output is in turn connected to a further band-pass filter 4, with substantially the same pass band as the filter 2. The output of the filter 4 appears at a terminal 5.

Figure 2 shows the transfer function of the element 3. The transfer function is time independent and such that the output y is related to the input x by the general equation: Y = a(x ) where a is a signum function of x such that when x > 0, a = +1 x < 0, a = -1 and n is positive and greater than 1.

In the preferred form n = 2, so that y = xlxl.

Consider the receipt for a pulsed sinewave, for instance, a radio signal, by the circuit shown in Figure 1. The wave consists in the frequency domain of a fundamental and side-bands together with a noise distribution which in general will be Gaussian.

The pass-band of the filter 2 is chosen such that it just allows through the side-bands.

The signals then pass through the transfer element 3. This increases the ratio between high and low signals. To take a very simple example, a signal with an amplitude represented by 4 will produce an output repre sented by 16, whereas a signal with an amplitude represented by 5 will produce an output corresponding to 25. Thus, the ratio between he usefu; signal and the noise (the noise is assumed to be low level) is increased. The non-linear transfer function produces harmonics, thus increasing the bandwidth of the signal. The harmonics lying outside the bandwidth of the original signal are removed by the filter 4, which has the same pass-band as the bandwidth of the original signal. Thus, a signal is produced with an improved signal to noise ratio. and the same bandwidth as the original signal.

Figure 3 shows a first physical construction for the transfer element. The circuit comprises two diodes 6 and 7 connected to respective squarers 8 and 9, the outputs of the squarers being connected to a summation circuit 10. The squarers consist of respective logarithmic amplifiers 11 and 12 (x2) multipliers 13 and 14, and antilogarithmic amplifiers 15 and 16. A positive signal is passed by the diode 6. squared and appears at one input to the summation circuit 10. A negative signal is passed by the diode 7, and goes down the other branch of the chain, and appears at the other input to the summation circuit 10. The signal output y from the summation circuit 10 is thus related to the input signal x by the equation: y = xlxl.

A system illustrating a possible use for a processor. such as that shown in Figure 1, is shown in Figure 4. A radio signal is amplified by an R.F. stage 21. treated bv a processor 22 and fed to a demodulator 23.

The processor 22 includes a transfer element of the type shown in Figure 3.

In the case where wide band signals are to be processed it may be convenient to divide such signals into a number of smaller bandwidth sections by using appropriate bandpass filters. The band-pass filters are arranged in parallel and each feed a respective processor containing identical transfer characteristics such that each section of the signal is processed identically. The various processed signals in the respective bandwidth sections are then recombined to reproduce the original signal having an improved signal to noise ratio.

WHAT I CLAIM IS: 1. A signal processor including a transfer element having an input and an output, the transfer element being such that its output signal has the same sign as its input signal, and has a magnitude which is a power of the magnitude of the input signal, wherein said transfer element consists of: a first circuit comprising a diode and a squarer for passing positive signals: a second circuit comprising a diode and a squarer for passing negative signals, said first and second circuits being connected in parallel; and a summation amplifier receiving on its respective inputs the outputs from the two squarers.

2. A signal processor according to Claim 1, wherein each squarer comprises a logarithmic amplifier, a multiplier and an antilogarithmic amplifier connected in series.

3. A signal processor according to claim 1 or 2, wherein the transfer element has its output signal y related to the unprocessed signal x by the equation: Y = a(x ) where a is a sign function of x such that when x > 0, a = +1 x < 0, a = -1 and n is positive and greater than 1.

4. A signal processor constructed and arranged to operate substantially as herein described with reference to and as illustrated in Figures 1 and 3 of the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. sented by 16, whereas a signal with an amplitude represented by 5 will produce an output corresponding to 25. Thus, the ratio between he usefu; signal and the noise (the noise is assumed to be low level) is increased. The non-linear transfer function produces harmonics, thus increasing the bandwidth of the signal. The harmonics lying outside the bandwidth of the original signal are removed by the filter 4, which has the same pass-band as the bandwidth of the original signal. Thus, a signal is produced with an improved signal to noise ratio. and the same bandwidth as the original signal. Figure 3 shows a first physical construction for the transfer element. The circuit comprises two diodes 6 and 7 connected to respective squarers 8 and 9, the outputs of the squarers being connected to a summation circuit 10. The squarers consist of respective logarithmic amplifiers 11 and 12 (x2) multipliers 13 and 14, and antilogarithmic amplifiers 15 and 16. A positive signal is passed by the diode 6. squared and appears at one input to the summation circuit 10. A negative signal is passed by the diode 7, and goes down the other branch of the chain, and appears at the other input to the summation circuit 10. The signal output y from the summation circuit 10 is thus related to the input signal x by the equation: y = xlxl. A system illustrating a possible use for a processor. such as that shown in Figure 1, is shown in Figure 4. A radio signal is amplified by an R.F. stage 21. treated bv a processor 22 and fed to a demodulator 23. The processor 22 includes a transfer element of the type shown in Figure 3. In the case where wide band signals are to be processed it may be convenient to divide such signals into a number of smaller bandwidth sections by using appropriate bandpass filters. The band-pass filters are arranged in parallel and each feed a respective processor containing identical transfer characteristics such that each section of the signal is processed identically. The various processed signals in the respective bandwidth sections are then recombined to reproduce the original signal having an improved signal to noise ratio. WHAT I CLAIM IS:

1. A signal processor including a transfer element having an input and an output, the transfer element being such that its output signal has the same sign as its input signal, and has a magnitude which is a power of the magnitude of the input signal, wherein said transfer element consists of: a first circuit comprising a diode and a squarer for passing positive signals: a second circuit comprising a diode and a squarer for passing negative signals, said first and second circuits being connected in parallel; and a summation amplifier receiving on its respective inputs the outputs from the two squarers.

2. A signal processor according to Claim 1, wherein each squarer comprises a logarithmic amplifier, a multiplier and an antilogarithmic amplifier connected in series.

3. A signal processor according to claim 1 or 2, wherein the transfer element has its output signal y related to the unprocessed signal x by the equation: Y = a(x ) where a is a sign function of x such that when x > 0, a = +1 x < 0, a = -1 and n is positive and greater than 1.

4. A signal processor constructed and arranged to operate substantially as herein described with reference to and as illustrated in Figures 1 and 3 of the accompanying drawing.