JP4905725B2 - converter - Google Patents

Description

  The present invention relates to a converter that converts an analog signal into a digital signal or converts a digital signal into an analog signal.

  In an audio signal transmission system, the transmission side converts an audio analog signal into a digital signal by an A / D converter and transmits it, and the reception side converts the received digital signal into an audio analog signal by a D / A converter. Various means have already been proposed and put into practical use. Further, due to advances in semiconductor technology and the like, A / D converters that convert analog signals into 24-bit digital signals and D / A converters that convert 24-bit digital signals into analog signals have been realized. Therefore, a low distortion audio signal transmission system and recording / reproducing system can be configured.

  When a digital signal is transmitted using such a 24-bit A / D converter or D / A converter, a system is known that compresses 24 bits to form an 11-bit configuration in order to improve transmission efficiency. It has been. For example, as shown in FIG. 8, an audio input analog signal is input to an A / D converter 102 via an LPF (low-pass filter) 101, and converted into a 24-bit linear code digital signal. The most significant bit is a sign bit indicating polarity. The low-order 9 bits corresponding to the low-level portion of the analog signal are discarded by the signal conversion unit 103 from the 24-bit digital signal, and the digital signal is composed of a 1-bit sign bit and 14 bits. input. The code conversion unit 104 is a kind of I.V. Recommendation J.A., which is a kind of broken line code having a total of 11 bits including 1 polarity bit, 3 segment bits, and 7 step bits. It performs compression encoding according to the 41 conversion rule to produce a digital signal having an 11-bit configuration, and sends it in a format according to the transmission method of the transmission path.

The digital signal having an 11-bit configuration received via the transmission path is converted by the code conversion unit 114 into J.P. The signal is converted into a digital signal with a 15-bit linear characteristic according to the 41 conversion rule, and is converted into a digital signal with a 24-bit structure by adding the lower 9 bits of all “0” by the signal converter 113. To enter. The most significant bit in this case is a polarity bit. Then, the signal is converted into an analog signal by the D / A converter 112, the harmonic component is removed by an LPF (low pass filter) 111, and an audio signal is output. In A / D converter and D / A converter in analog signal transmission and recording / reproducing system, encoding and decoding are performed according to the characteristics analysis of analog signal, and pseudo-random code is converted to the least significant bit of digital signal. In addition, means for decoding and reproducing low distortion analog signals has been proposed (see, for example, Patent Document 1).
Japanese Patent No. 3459417

  As mentioned above, J.M. When compression encoding is performed by applying the 41 conversion rule, the lower 9 bits of a 24-bit digital signal are discarded, and a linear code digital signal having a 1-bit code bit and a 14-bit digital signal is broken by a broken line. The A / D converter 102 converts the analog signal into a 24-bit digital signal, the signal conversion unit 103 truncates the lower 10 bits to obtain a 14-bit digital signal, The 14-bit digital signal is converted by the code conversion unit 104 into J.P. In accordance with the 41 conversion rule, it is compressed and encoded into a digital signal having an 11-bit line code. It should be noted that the most significant bit of a digital signal having an 11-bit configuration by broken line coding indicates a polarity bit and the least significant bit indicates a value of 0.5. Therefore, even when 9 bits between the most significant bit (polarity bit) and the least significant bit (value of 0.5) indicate “0”, the signal level dropped in the signal conversion unit 103 is in a low range. The change of the corresponding low-order 10-bit polarity over time is also stored for a digital signal having an 11-bit configuration as it is, so even when the signal level indicates 0, the amplitude corresponding to 0.5 by the least significant bit. The frequency component of the level, that is, the noise component is included.

  On the receiving side, a digital signal having an 11-bit configuration by broken line coding is received and converted into a digital signal having a 15-bit configuration by a code converter 114. In this case, the 15th bit is set to 0.5. Then, the signal conversion unit 113 adds 9 bits of all “0” to the lower 15 bits to form a 24-bit configuration, which is input to the D / A converter 112 and converted into an analog signal. Therefore, since the 15th bit from the upper part of the 24-bit configuration is 0.5, and the polarity bit of the most significant bit is a polarity bit at the time of transmission, the polarity of the signal at the minimum level by the least significant bit of the 24-bit configuration There is a problem that the change is amplified to the change in the signal level of the 15th bit from the upper level, and the analog signal converted by the D / A converter 112 includes noise.

  The present invention solves the above-mentioned conventional problems, and provides a converter capable of converting between an analog signal and a digital signal with high accuracy and reducing unnecessary signal components such as noise components. It is.

The converter according to the present invention is an A / D converter for converting an analog signal into a digital signal of a linear code in a converter for converting any one of an analog signal and a digital signal having a plurality of bits into the other, and the A / D converter. and a noise component insertion unit for inserting a digital noise signal in a single or multiple bit positions of lower digital signals converted by D converter, the following position inserting the digital noise signal to the digital signal by the noise component insertion section And a code conversion unit that converts a linear code into a broken line code by deleting the lower bits of the.

  In addition, a noise component insertion unit for generating and inserting an analog noise signal is provided before the analog signal is converted into a digital signal. Alternatively, a noise component insertion unit for generating and inserting a digital noise signal into the digital signal is provided.

  A converter that converts an analog signal into a digital signal or a digital signal into an analog signal, an A / D converter that converts the analog signal into a digital signal of a linear code, and a digital signal converted by the A / D converter. A noise component insertion unit that inserts a digital noise signal into a lower single or multiple bit position, and the noise component insertion unit deletes bits below the position at which the digital noise signal was inserted into the digital signal and And a code conversion unit for converting into a line code.

  When noise components such as white noise and random noise are inserted on the side where analog signals are converted into digital signals and transmitted, the noise components included in the analog signals converted from the received digital signals are dispersed. It will be negligible. Also, when a digital signal with no noise component inserted is received and converted to an analog signal, the noise component is also dispersed and ignored even if the noise component is inserted into the digital signal and converted to an analog signal. It will be as much as possible.

  The converter of the present invention will be described with reference to FIG. 1. In the converter for converting an analog signal into a digital signal by the A / D converter 2 or converting the digital signal into an analog signal by the D / A converter 12, the analog signal is converted into an analog signal. Or it has the structure which provided either of the noise component insertion parts 5a-5c and 15a-15c which insert a noise component into a digital signal.

  FIG. 1 is an explanatory diagram of Embodiment 1 of the present invention, where 1 is an LPF (low-pass filter), 2 is an A / D converter, 3 is a signal converter, 4 is a code converter, 5a, 5b, and 5c are noises. A component insertion unit, 11 is an LPF (low-pass filter), 12 is a D / A converter, 13 is a signal conversion unit, 14 is a code conversion unit, and 15a, 15b, and 15c are noise component insertion units. Each of the noise component insertion units 5a, 5b, 5c, 15a, 15b, and 15c is provided with any one of them, and the noise component insertion unit 5a in the previous stage of the A / D converter 2 is an analog signal. A noise component is output, and a noise component such as white noise is inserted into the analog signal processing portion on the input side of the A / D converter 2. The other noise component insertion units 5b, 5c, 15a, 15b, and 15c are configured to insert single or multiple bits as noise components at bit positions corresponding to predetermined signal levels in the digital signal processing portion. For example, a pseudo random code generator can be used. Alternatively, a table storing pseudo random patterns may be read at a predetermined cycle and inserted as a noise component. Alternatively, a configuration may be adopted in which a lower bit corresponding to a low signal level position in the output bits of the A / D converter 2 is regarded as a random noise bit and inserted into a predetermined bit position.

  For example, as shown in FIG. 2, the noise component insertion unit 5a that generates a noise component as an analog signal includes a resistor 6, a Zener diode 7, and a capacitor 8. The Zener diode 7 is connected to a power source via the resistor 6. A voltage higher than the Zener voltage can be applied, and the white noise component generated by the Zener diode 7 can be input to the A / D converter 2 shown in FIG. For example, when a Zener diode 7 having a Zener voltage 3V is used, a white noise component can be generated by setting the power supply voltage to + 5V. In this case, the noise component insertion unit 5a has an advantage of a simple configuration. In addition, when it is necessary to control a noise component level, the structure which adjusts the noise component level input into the A / D converter 2 via the capacitor | condenser 8 with a variable resistor etc. is added.

  Further, as described above, the noise component insertion units 5b, 5c, 15a to 15c have a configuration for generating a digital noise signal. For example, the noise component insertion unit 5b is a linear component converted by the A / D converter 2. For example, a digital noise signal is inserted into a lower single or multiple bit position of a 24-bit digital signal. The most significant bit of the 24-bit digital signal is a sign bit indicating polarity. Then, the signal conversion unit 3 deletes the lower 9 bits of the 24-bit digital signal to form a 15-bit configuration, which is input to the code conversion unit 4. Rather than adding the digital noise signal in this case to the least significant bit position of the 15-bit configuration including the sign bit, any one bit position or a plurality of bit positions from the most significant bit position before deletion to the 15th to 18th bits Append to bit position. That is, a noise component is inserted at a minute signal level position. For example, when a noise component is inserted at the 16th bit from the most significant bit before the lower 9 bits are deleted, if the signal component at the 16th bit is “1”, a carry is generated at the 15th bit. When it is 0 ″, there is no carry. In this way, when the lower bit is discarded, the noise component is added to the bit position where the lower bit is discarded, so that the lower bit can be reflected.

  FIG. 3 is an explanatory diagram of input / output gain characteristics, showing an example of characteristics of input gain [dBm] and output gain [dBm] when a 1 kHz sine wave signal is input, and no noise component insertion unit is provided. The case of no noise (dotted line) and noise insertion (solid line) in which a noise component is inserted and a noise component is inserted as in the embodiment of the present invention are shown. As for the input signal level, (a) is -60 dBm, (b) is -68 dBm, (c) is -70 dBm, and (d) is -82 dBm. That is, when the input signal level is −68 dBm or less, the output signal level is almost constant in both cases of no noise and noise insertion. However, in the case of noise insertion, the output signal level is lower than that in the case of no noise. It becomes constant. This indicates that the linearity is improved.

  4 to 7 show spectrum measurement results in the frequency range of 0 to 15000 Hz corresponding to the input signal levels (a), (b), (c) and (d) in FIG. 3, respectively. Yes, (A) in each figure shows no noise, and (B) shows the case of noise insertion. In the case of −60 dBm input, as shown in FIG. 4, the harmonic components are substantially similar both in the case of no noise and in the case of noise insertion. However, in the case of −68 dBm input shown in FIG. In the case of 70 dBm input and in the case of −82 dBm shown in FIG. 7, it can be seen that the harmonic component is reduced by noise insertion as shown in FIG.

It is explanatory drawing of Example 1 of this invention. It is explanatory drawing of the noise component insertion part of Example 1 of this invention. It is input / output gain characteristic explanatory drawing of Example 1 of this invention. It is spectrum explanatory drawing of Example 1 of this invention. It is spectrum explanatory drawing of Example 1 of this invention. It is spectrum explanatory drawing of Example 1 of this invention. It is spectrum explanatory drawing of Example 1 of this invention. It is explanatory drawing of a prior art example.

Explanation of symbols

1 LPF (low pass filter)
2 A / D converter 3 Signal conversion unit 4 Code conversion unit 5a, 5b, 5c Noise component insertion unit 11 LPF (low pass filter)
12 D / A converter 13 Signal conversion unit 14 Code conversion unit 15a, 15b, 15c Noise component insertion unit

Claims (2)

In a converter for converting an analog signal and a digital signal having a multi-bit configuration from one to the other ,
An A / D converter for converting the analog signal into a digital signal of a linear code;
A noise component insertion unit that inserts a digital noise signal into a lower single or multiple bit position of the digital signal converted by the A / D converter ;
A code conversion unit for converting the linear code into a broken line code by deleting lower bits below the position where the digital noise signal is inserted into the digital signal by the noise component insertion unit;
Converter comprising the. In a converter for converting an analog signal and a digital signal having a multi-bit configuration from one to the other ,
Before converting the analog signal into a digital signal of a linear code, a noise component insertion unit that generates an analog noise signal and adds the analog noise signal ;
An A / D converter that adds the analog noise signal to the analog signal and converts it into a digital signal by the noise component insertion unit;
A code converter that deletes a predetermined number of lower bits of the digital signal converted by the A / D converter and converts the linear code into a broken line code;
Converter comprising the.

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