JP3413665B2 - D / A converter IC - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a D / A converter IC for switching audio output and D / A conversion of a MUSE decoder or the like.

[0002]

2. Description of the Related Art FIG. 7 is a conventional MUSE in the case of using serial data after selection outputted from a voice output processing IC.
It is a block diagram of a 3-2 system audio | voice output, a MUSE2-2 system audio | voice output, and a BS audio | voice output switching circuit.

In the figure, 1 is an audio output processing IC, 2 is a digital filter (DF), 3 is a D / A (digital / analog) converter (DAC), and 4 is a low-pass filter (LPF). In case of MUSE3-2 system, 1c
h, 2ch, 3ch, 4ch × 2 digital signals are processed to obtain L-ch, R-ch, C-ch, S1-ch, S
It is designed to be converted into five 2-ch signals. 1ch is MUSE L channel audio input, 2ch is MUSE R channel audio input, 3ch
Is MUSE C channel audio input, 4ch is MUSE
S-channel audio inputs are shown respectively.

In the case of 2-2 system stereo and BS audio output, digital signals of 1ch, 2ch, 3ch, and 4ch are processed, and L-ch, R-ch, L'-ch (rear channel), R '. -Ch (rear channel) converted into four signals and converted to MUSE3-2 system audio L-
It is output to the output terminals of ch, R-ch, S1-ch, and S2-ch, respectively. In case of BS voice output, 1c
h is L channel audio input for TV of BS, 2ch is BS
R channel audio input for TV, 3ch for BS ADD
For L channel audio input, and 4ch for BS ADD R channel audio input, respectively.

FIG. 8 shows a conventional MUSE3-2 system audio output and MUSE2- when using the pre-selection serial data.
It is a block diagram of a 2 system audio | voice output and BS audio | voice output switching circuit.

In this circuit, if the conversion is performed as it is, the MUS
E3-2 system, 1ch, 2ch, 3ch, 4ch
Of the digital signal of L-ch, R-ch, C-
ch, S-ch (the same as S1 and S2) are converted into four signals by analog conversion. In case of MUSE2-2 system and BS mode, 1ch, 2ch, 3ch, 4
ch is the same as in FIG. 7 and is D / A converted to L-ch, R-
ch, L'-ch, R'-ch.

[0007]

In the conventional example shown in FIG. 7, the voice output is selected and switched by the voice output processing IC1 before the D / A conversion, and the MUSE voice and the BS are output at the same output terminal. When outputting voice, M
Since the USE3-2 system outputs 5 channels, the D / A converter 3 also requires 5 channels when D / A converting these.

In the conventional example shown in FIG. 8, L'-c
The h and R'-ch are output to the C-ch and S-ch, respectively, and are divided into the front C and the rear L. In order to make it compatible with 5-channel output, it is necessary to switch by the analog switch after passing through the low-pass filter 4, but since it is a voice signal, crosstalk increases with the analog switch, and at least 80 dB or more. However, there is a problem that a very strict circuit design is required because it is necessary to secure the dynamic range of.

An object of the present invention is to provide a D / A converter IC which solves the above-mentioned drawbacks of the prior art and enables switching of signal output while suppressing crosstalk between adjacent channels.

[0010]

To achieve the above object, a D / A converter IC to which the present invention is applied has a plurality of input terminals to which digital audio signals of a plurality of channels are respectively supplied, and the plurality of inputs. A plurality of conversion circuits, which are provided corresponding to the respective terminals, convert the digital audio signal supplied to the input terminal into a 1-bit output signal having a PWM waveform, and are supplied from the plurality of conversion circuits. It is provided between a plurality of output terminals that output the output signal to an externally provided low-pass filter, and between the plurality of conversion circuits and the plurality of output terminals. By controlling the passage,
And a switching circuit for switching connection relations between the plurality of conversion circuits and the plurality of output terminals.

According to a second aspect of the present invention, in the D / A converter IC according to the first aspect, the input terminal is
4 channels of digital audio signals are supplied respectively,
The switching circuit switches the 4-channel output signal supplied from the conversion circuit to a 5-channel output signal, and the output terminal outputs the supplied 5-channel output signal to the low-pass filter. Is characterized by. According to a third aspect of the present invention, in the D / A converter IC according to the second aspect, the switching circuit is composed of a selector or a 3-state buffer.

[0012]

In the present invention, the digital audio signal supplied to the plurality of input terminals is converted into a 1-bit output signal having a PWM waveform by the plurality of conversion circuits, and is externally provided via the plurality of output terminals. Output to the low pass filter. When switching the connection relationship between the plurality of conversion circuits and the plurality of output terminals, passage or non-passage of a 1-bit output signal is controlled. Further, in the low pass filter, a 1-bit output signal having a PWM waveform is converted into an analog audio signal. That is, the digital audio signal is D / A converted into an analog audio signal.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a D / A converter IC according to the first embodiment.
It is a block diagram of. In this embodiment, D of each channel
The Δ-Σ converter 5 is provided in the subsequent stage of F2, the waveform shaping buffer 6 is provided in the preceding stage of the low-pass filter 4, and the selectors 7a and 7b are provided in the preceding stage of the waveform shaping buffer 6 in 3ch and 4ch. Filter 2, Δ-Σ converter 5, waveform shaping buffer 6, selector 7 (7a, 7b)
The D / A converter IC 8 is composed of

The selection combinations of the selectors 7a and 7b are (7a, 7b) = (D2, D2) in the case of MUSE3-2, and (7a, 7b) = (D1) in the case of MUSE2-2 stereo and BS mode. , D1), the output system can be made the same as the output system obtained by D / A converting 5 channels of serial data after selection.

FIG. 2 is a block diagram of a D / A converter IC according to the second embodiment. In this embodiment, the 3-state buffer 9 is provided at the subsequent stage of the 3ch and 4ch Δ-Σ converters 5, and the pre-selection serial data is used as in the case of the first embodiment. When the 3-state buffer 9 is numbered [(1), (2), (3), (4)] as shown in the figure, when the 3-state buffer 9 is enabled as follows, the selected serial data 5 It is the same as the output system obtained by D / A converting the channel.

In the case of MUSE3-2 stereo, [(1), (2), (3), (4)] = [L, H, L,
L] In case of MUSE2-2 stereo and BS mode, [(1), (2), (3), (4)] = [H, L, H,
L].

FIG. 3 is a block diagram of a D / A converter IC according to the third embodiment. In this embodiment, a changeover switch 12 is provided between the output terminal 10 side of the D / A converter 3 and the IC output terminal 11. After the audio signal is D / A converted, the changeover switch 12 is used to select an arbitrary output terminal.

FIG. 4 is a block diagram of a D / A converter IC according to the fourth embodiment. In this embodiment, a disable switch 13 capable of disabling the output of the D / A converter 3 is provided in the subsequent stage of the D / A converter 3, and the signals after the D / A conversion are branched and branched. The output is switched so that it can be disabled.

FIG. 5 is a block diagram of a D / A converter IC according to the fifth embodiment. In this embodiment, 1 bit D
The selector 7 is provided in the / A converter IC 8. Before passing through the waveform shaping buffer 6, the PWM waveform after ΔΣ conversion is selected using the selector 7 or the like. As a result, the output system is switched.

FIG. 6 is a block diagram of a D / A converter IC according to the sixth embodiment. In this embodiment, 1 bit D
The 3-state buffer 9 is provided in the / A converter IC 8. The signals output from the Δ-Σ converter 5 are controlled by using the 3-state buffer 9 for switching the output system.

[0021]

According to the present invention, the D / A converter IC
Since a switching circuit that can switch the connection relationship between the plurality of conversion circuits and the plurality of output terminals by controlling passage or non-passage of the 1-bit output signal is provided in the Signal, that is "1", "0"
It is possible to switch the connection relationship while suppressing the influence of crosstalk between adjacent channels only by processing the signal of. As a result, even if the switching circuit is provided in the D / A converter IC, the reliability of the output signal for each channel can be ensured, and further, the signal switching and D / A conversion can be performed by one IC. Therefore, an inexpensive and simple system configuration can be achieved.

[Brief description of drawings]

FIG. 1 is a block diagram of a D / A converter IC according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a D / A converter IC according to a second embodiment of the present invention.

FIG. 3 is a block diagram of a D / A converter IC according to a third embodiment of the present invention.

FIG. 4 is a block diagram of a D / A converter IC according to a fourth embodiment of the present invention.

FIG. 5 is a block diagram of a D / A converter IC according to a fifth embodiment of the present invention.

FIG. 6 is a block diagram of a D / A converter IC according to a sixth embodiment of the present invention.

FIG. 7 is a block diagram of a conventional audio output switching and D / A conversion circuit.

FIG. 8 is a block diagram of another conventional audio output switching and D / A conversion circuit.

[Explanation of symbols]

2 Digital filter 3 D / A converter 5 Δ-Σ converter 6 waveform shaping buffer 7 selector 9 3-State buffer 12 changeover switch 13 Disable switch

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-3-66234 (JP, A) JP-A-3-66236 (JP, A) JP-A-3-80639 (JP, A) JP-A-5- 260599 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04H 5/00 H04N 7/015 H04N 11/04 H03M 3/02

Claims (3)

(57) [Claims] 1. A plurality of input terminals to which digital audio signals of a plurality of channels are respectively supplied, and a plurality of input terminals are provided corresponding to each of the plurality of input terminals,
A plurality of conversion circuits that convert the digital audio signal supplied to the input terminal into a 1-bit output signal having a PWM waveform, and output signals supplied from the plurality of conversion circuits to a low-pass filter provided outside. A plurality of output terminals that respectively output, and a plurality of conversion circuits that are provided between the plurality of conversion circuits and the plurality of output terminals and control passage or non-passage of a 1-bit output signal. And a switching circuit for switching the connection relationship between the output terminals and the plurality of output terminals. 2. The input terminals are respectively supplied with 4-channel digital audio signals, and the switching circuit switches the 4-channel output signals supplied from the conversion circuit to 5-channel output signals. The D / A converter IC according to claim 1, wherein the output terminal outputs the supplied output signals of the five channels to the low-pass filter, respectively. 3. The D / A converter IC according to claim 2, wherein the switching circuit comprises a selector or a 3-state buffer.