JP2578803Y2 - D / A conversion circuit - Google Patents

Description

[Detailed description of the invention] (Industrial application field) The invention relates to a D / A conversion circuit, and more particularly to a D / A conversion circuit that achieves a faithful conversion function even for a minute level signal.

(Prior Art) A D / A conversion circuit in a digital audio device is required to have a conversion characteristic faithful to a wide range of input levels from a high level to a low level.

Conventionally, for example, in a resistance ladder type D / A conversion circuit, the MSB is inverted when the signal crosses the O level, and a maximum current (a weighted maximum current) flows, which is called zero cross distortion as shown in FIG. Distortion occurs. Also, similarly, 2S
Distortion also occurs at the crossing points of the changing point of B (when the 2SB is inverted) and the changing point of the 3SB (when the 3SB is inverted). These distortions are dominant in the distortion of the D / A conversion circuit, and particularly have a great influence on minute level reproduction.

In recent years, D / A that divides input digital data into two systems and shifts by applying a digital bias in the + and-directions near the zero-cross point to remove the zero-cross distortion in principle
Conversion circuits have been proposed. According to this circuit, when the digital data is smaller than the shift amount, there is no value that crosses the original zero-cross point, so that zero-cross distortion does not occur. When the two shifted data are D / A converted and then added, the DC component is removed. These two data have no MSB inversion, and no zero-cross distortion occurs in the composite waveform.

(Problem to be Solved by the Invention) As described above, the conventional D / A conversion circuit focuses only on zero-cross distortion due to inversion of the MSB.

However, not only the MSB but also the distortion caused by 2SB cannot be ignored as the distortion component. The distortion due to the 2SB appears more remarkably in the minute level reproduction, and there is a problem that a highly accurate D / A conversion function cannot be achieved.

Therefore, an object of the present invention is to provide a D / A conversion circuit capable of performing a high-precision conversion function even at a minute level reproduction.

(Means for Solving the Problems) In order to solve the above problems, a D / A conversion circuit according to the present invention includes: a memory for storing input data; a level detecting means for detecting a level value of the input data; When the level value detected by the level detection means is -6 dB or more, the shift amount is set to 0. When the level value is smaller than -6 x NdB (N is a positive integer greater than 1), the absolute value is increased each time the N value increases. Level shift means for shifting the input data level stored in the memory in a DC manner to a positive-side and negative-side change point of a bit representing a lower level by one to generate a two-system output; And D / A conversion means for D / A-converting the outputs of the two systems, respectively, and adder means for adding the outputs of the two D / A conversion means.

(Operation) In the A / D conversion circuit according to the present invention, when the input data level value detected by the level detection means is -6 dB or more, the shift amount is set to 0, and -6 * NdB (N is a positive integer greater than 1) ), The absolute value becomes 1 each time the N value increases.
DC at the + and − transition points of the bit representing the next lower level
The input data level stored in the memory is shifted and output as two-system outputs, and these two-system outputs are D / A-converted and then added to obtain a distortion caused by 2SB other than the MSB. Is eliminated, and a high-precision conversion function is enabled even at the minute level reproduction.

(Example) Next, this invention is demonstrated, referring drawings.

FIG. 1 is a block diagram showing an embodiment of a D / A conversion circuit according to the present invention.

The level of the input data is detected and determined by the level detection circuit 1, and the level information is sent to the level shift circuit 3. On the other hand, input data is stored in the memory 2.

The level shift circuit 3 performs a level shift process on input data stored in the memory 2 in accordance with the value of the detection level detected by the level detection circuit 1. D / A shift output
It is sent to the conversion circuits 4 and 5.

The outputs of the two D / A conversion circuits 4 and 5 are added by an addition circuit 6 and output as conversion outputs.

The operation of this embodiment will be described more specifically. The level detection circuit 1 detects a peak value in a certain section of the input data stored in the memory 2. Detected peak value range is -6dB or more; less than -6dB, -12dB or more; less than -12dB,
When it is -18 dB or more, the following processing is performed for each.

For example, if the peak value of the input data in this section is -6 dB or more, the input data stored in the memory 2 is sent to the D / A conversion circuits 4 and 5 with the shift amount set to 0. Also,
When the peak value in the next section is less than -6 dB and more than -12 dB, the input data of the memory 2 is changed by the level shift circuit 3 to the change point of the 2SB on the + side and the- D / A as DC shifted data to 2SB transition point
It is sent to the conversion circuits 4 and 5. Further, the level detection circuit 1
When the peak value detected in step (1) is less than -12 dB and not less than -18 dB, similarly, as shown in FIG.
Are output to the D / A conversion circuits 4 and 5 as data shifted to the change point of the 3SB and the change point of 3SB on one side.

As described above, the level shift circuit 3 dynamically shifts the data stored in the memory 2 sequentially to the + side and the-side according to the peak value of the input data and outputs the data.

These outputs are D / A converted by D / A conversion circuits 4 and 5, added by an adder 6, and output. Since this shift level has the same absolute amount on the + and-sides, the shift amount is canceled at the output of the adder, and the AC level is doubled and output.

(Effects of the Invention) As described above, the D / A conversion circuit according to the invention shifts the input data level by a predetermined amount in accordance with the input data level, so that distortion caused by 2SB other than the MSB is also reduced. For example, during waveform reproduction of -91 dB, the bit inversion becomes only the LSB inversion, and no more bit inversion is performed with weight. As a result, according to the present invention, high fidelity D / A conversion can be performed even at the time of minute level reproduction.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a D / A conversion circuit according to the present invention, FIGS. 2 and 3 are diagrams for explaining the operation of the embodiment of the present invention, and FIG. FIG. 4 is a diagram for explaining the operation of the D / A conversion circuit of FIG. 1 ... level detection circuit, 2 ... memory, 3 ... level shift circuit, 4,5 ... D / A conversion circuit, 6 ... addition circuit.

Claims (1)

(57) [Scope of request for utility model registration] A memory for storing input data; a level detecting means for detecting a level value of the input data; and a shift amount of 0 when the level value detected by the level detecting means is -6 dB or more. , −6 × NdB (N is a positive integer greater than 1), the plus side and the minus side of the bit representing the level whose absolute value is lower by one as the N value increases.
Level shift means for shifting the input data level stored in the memory to the side change point in a DC manner and generating two-system outputs; and D / A conversion of the two-system outputs shifted by the level shift means, respectively. A D / A conversion circuit, comprising: two D / A conversion units; and an addition unit that adds outputs of the two D / A conversion units.