JP2000174625A - Signal detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate a noise without eliminating a signal by digitizing a dither signal into dither data, storing the data to a memory, extracting dither data with a required band from the memory corresponding to a characteristic of an analog signal, converting the dither data into an analog dither signal. SOLUTION: An adder 14 adds a dither signal to an analog signal received from an input terminal 1, a filter circuit 2b passes through the analog signal and the dither signal only, an A/D converter 3 converts them into a digital signal, a data processing control section 10 eliminates frequency bands other than the signal frequency by digital filter processing or the like and outputs the result from an output terminal 7. The dither signal resulting from converting dither data stored in advance in a memory 4 by a D/A converter 5 into an analog signal and eliminating signals other than the dither signal by a filter 2a is applied to the input signal at an adder 14. The data processing control section 10 controls the A/D converter 3 and the D/A converter 5 or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal detecting device capable of detecting even a small input signal using dither.

[0002]

2. Description of the Related Art When digitally processing an input analog signal, if the analog signal becomes a small signal having a size smaller than the resolution of the AD converter, it is difficult to detect the analog signal because it cannot be distinguished from quantization noise.

For example, in a device for detecting a small signal such as a device for simultaneously outputting a multi-wave signal on the transmitting side and detecting a change due to a tag on the receiving side, such as an anti-shoplifting device, an antenna between transmitting and receiving is used. The distance could not be detected unless approached, and the current situation was as narrow as about 90 cm, and customers felt uncomfortable. For this reason, the S / N ratio is improved by averaging the data after AD conversion of the received signal. However, in order to improve this effect, a large amount of data is required, and the customer needs to connect between antennas. The processing result must be output within the passing time, and there is a limit to increasing the number of averaging. Although the S / N is improved by digital filter processing, the signal buried in the noise floor cannot be detected because the bit accuracy of the AD converter is a finite value.

For this reason, a technique for detecting a signal having a resolution equal to or lower than the resolution of an AD converter is desired, and so-called dithering, in which a randomized noise called dither is added to an input signal and digitally processed to detect the signal, is used. Law is being attempted. This is to input a dither signal to an AD converter to suppress harmonics generated by AD conversion, and it is possible to obtain only a signal to be detected by digital filter processing or the like after AD conversion. It becomes.

Conventionally, the input of a dither signal is performed by adding a reference noise to the input signal of an AD converter after a reference noise is generated by a noise diode, the band of the noise is controlled, the level is controlled, and the like. FIG. 5 is a block diagram showing the configuration, wherein 1 is a signal input terminal, 12 is an amplifier circuit, 3 is an AD converter, 15 is a noise source, 6 is a filter, and 7 is a signal output terminal. R1 and R2 are input resistances for adjusting the signal level, and R is a feedback resistance for adjusting the gain of the amplifier circuit 12.

In this way, harmonics generated by the AD conversion of the AD converter can be suppressed, and the repetitive characteristics of the linearity error can be forcibly randomized, so that noise is eliminated and the AD conversion is performed. The generated spurious was suppressed.

[0007]

However, the above-described conventional dithering technique can generate noise with a simple configuration, but over a wide range within a half band of the sampling frequency of the AD converter 3. When a multicarrier signal exists, for example, as shown in FIG.
When carriers are arranged at an interval of 10 kHz within a range of 0.9 MHz to 2.7 MHz, a band overlapping with a diode noise band exists. In that case, if the diode noise is removed by a digital filter, a problem arises that the carrier signal is also removed, and the carrier signal in the overlapping portion cannot be detected.

If the diode noise band is further narrowed in order to avoid this, the randomness is lost and it cannot be used as a noise source, and the analog filter has the characteristic that the amount of rejection is 120 to 140 dB. It is difficult to make things. 2.7 MH
Even if a frequency higher than z is set as a noise band, it is difficult to extract noise in such a frequency band from the diode.

Accordingly, the present invention provides an AD converter which can remove noise without removing a signal even if a multicarrier signal exists over a wide range within a half frequency of the sampling frequency of the AD converter. It is an object of the present invention to provide a signal detection device capable of detecting a signal having a resolution lower than the resolution of the signal.

[0010]

According to a first aspect of the present invention, there is provided a signal detecting apparatus for converting a digital signal into a digital signal by adding a dither signal to the analog signal. Digitizing the dither signal, storing the digitized dither signal in a memory as dither data, extracting dither data of a required band from the memory according to the characteristics of the analog signal, and converting the dither signal into an analog signal to obtain a dither signal. .

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a circuit block diagram of a signal detection device according to the present invention, and an input terminal 1 is shown.
The input analog signal is added to the dither signal by the adder 14, only the analog signal and the dither signal are passed by the filter circuit 2b, converted into a digital signal by the AD converter 3, and subjected to digital filter processing by the data processing control unit 10. For example, a band other than the signal frequency is deleted, and output from the output terminal 7.

The dither signal added by the adder 14 is
The dither data stored in advance in the memory 4 is converted into an analog signal by the DA converter 5, and the filter 2a deletes other than the dither signal and adds it to the input signal.
The writing of dither data to the memory is performed, for example, by
The noise data may be created by a known random number generation program using a personal computer, converted into digital data such as HEX (hexadecimal), and written. However, it is preferable that the random number data is long enough to eliminate the periodicity, and it is preferable that the band is limited by a digital filter process in a bandwidth in which the randomness is maintained.

The data processing controller 10 has a built-in programmed computer, has a digital filter function of removing a band other than the input signal from the signal to which the dither signal is added, and controls the AD converter 3 and the DA converter 5. Or the memory address of the memory 4 is controlled.

If the dither signal extracted from the memory 4 by the data processing unit 10 has a frequency characteristic as shown in FIG.
Even in the case of a multicarrier signal in which carriers are arranged at intervals of 10 kHz in a range of 9 MHz to 2.7 MHz, the output signal of the AD converter can prevent the noise and the carrier from overlapping as shown in FIG.

The dither signal added to the input signal is AD
Any frequency interval other than the band of the digital filter that passes only the converted signal may be used, and the amplitude of the dither signal may be set as large as possible within a range not exceeding the analog input voltage range of the AD converter.

Thus, if the dither data written in the memory 4 is widened and used as a noise source, a dither signal in an arbitrary frequency band can be easily generated. And the dither noise frequency band can be separated, and if the dither signal added by the digital filter etc. is deleted,
Even if the signal is lower than the resolution of the AD converter, it can be detected. Therefore, even if the input signal includes a multi-carrier having a frequency band equal to one-half the sampling frequency, dither noise that does not overlap the signal can be created and added, and only noise can be reduced. .

Further, it is also possible to store dither data having different bands for each address in the memory, so that a dither signal of a necessary band can be taken out according to an input signal and injected to the input side. It is compatible with any signal receiver and can reduce noise.

FIG. 4 shows a second embodiment. This is a block diagram showing an example of a receiver for receiving a radio signal. In this example, an A / D conversion is performed by adding a dither signal to an input signal (reception signal) and then performing an averaging process by an averaging processing circuit 8. The noise is further reduced. The averaging processing circuit 8 can be configured by combining, for example, a gate array, and is preferably configured to control the address of the memory 4 storing the dither data and to control the AD converter 3 and the DA converter 5. 9 is a DS for extracting only a carrier component by a DFT / FFT (Fourier transform) filter.
P is a digital signal processor, 16 is a receiving antenna, 11 filters, 12 is an amplifier, and 13a and 13b are filters.

With this configuration, for example, when the AD converter has 14 bits, the level of the multicarrier that can be detected by the AD converter alone from an experiment is −8.
Although the detection level is 0 dB, the detection level is -110 dB by the 14-bit AD converter and dither, and is -130 dB when the averaging process is further performed 100 times, so that the noise floor can be further reduced. Therefore, even if a small signal of many waves is detected as in a shoplifting prevention device, it can be easily detected, and the interval between the transmitting and receiving antennas can be increased.

[0020]

As described in detail above, according to the first aspect of the present invention, by storing dither data in a memory, a dither signal having a band different from the signal frequency band is generated and added according to a received signal. It is possible to detect a signal having a resolution equal to or less than the resolution of the A / D converter. A dither signal can be created, and only noise can be reliably reduced.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of a signal detection device showing an example of an embodiment of the present invention.

FIG. 2 is a diagram illustrating noise characteristics extracted from the memory of FIG. 1;

FIG. 3 is a diagram showing characteristics of the output of the AD converter of FIG. 1;

FIG. 4 is a circuit block diagram of a signal detection device according to another embodiment.

FIG. 5 is a circuit block diagram of a conventional signal detection device.

FIG. 6 is a diagram illustrating an example of a relationship between generated noise and a signal when a conventional multicarrier signal is provided.

[Explanation of symbols]

1. Input terminal 3. AD converter 4. Memory
5 ··· DA converter, 7 ··· output end, 10 ··· data processing control unit, 14 ··· adder.

Claims (1)

[Claims] When converting an analog signal into a digital signal, a signal detection device that converts a dither signal into a digital signal by adding the dither signal to the analog signal, digitizes the dither signal, stores the digitized dither signal in a memory as dither data, A signal detection device for extracting dither data of a required band from the memory according to the characteristic of the above, and converting the dither data into an analog signal to obtain a dither signal.