JP3376576B2 - Signal conversion circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal conversion circuit used for a DVD player or the like. 2. Description of the Related Art FIG. 4 shows a block diagram of a conventional DVD player. As shown in this figure, the conventional DVD player
NTS including disk reading unit 11, signal processing unit 12, MPEG video decoder 13, video D / A converter
C / PAL encoder 14, L channel, R channel, C (center) channel, rear L channel, rear R channel, SW (super woofer) channel Dolby digital decoder 15 having each output, each channel of this Dolby digital decoder 15 It consists audio D / a converter _{161-164 6} and the system controller 17 connected to the output. That is, the data is read from the disk by the disk reading unit 11, the data is demodulated by the signal processing unit 12, and the MPEG video decoder 13
Decodes the video stream signal with NTSC / PA
An analog video signal is output from the L encoder 14.
On the other hand, the audio stream signal separated by the MPEG video decoder 13 is output to the Dolby digital decoder 15.
Is input L channel, R channel, C channel, rear L channel, rear R channel, after being decoded as respective digital signals SW channel, each channel by the audio D / A converter 16 ₁ ~16 ₆ (ch) And output to an output terminal. The system control unit 17 controls the DV
The operation of the D player is controlled. The above-mentioned DVD player corresponds to Dolby 5.1ch and has a 6-channel analog audio signal output terminal. Therefore, the audio D / A converter is also denoted by reference numerals 16 _{1 to} 16. _Six are provided as indicated by 6. However, despite the provision of six audio D / A converters, the six audio D / A converters may not be effectively used. For example, CD disk, video C
D playback, Dolby Digital downmix playback of a DVD disc, and the like. Therefore, in such a case, it is desired to effectively use all the audio D / A converters to improve the performance of the audio unit. According to the present invention, in order to solve the above-mentioned problems, digital signals of a plurality of channels are D / A converted by a plurality of D / A converters provided corresponding to each channel. The signal conversion circuit includes switching means for switching a circuit so that a D / A converter of another channel operates in parallel with a D / A converter of a specific channel, and the switching means includes two switching means. D
Switch circuit that connects the inputs of the A / A converter in parallel
And two switches whose inputs are connected in parallel by this switch circuit.
An adder for adding the outputs of the two D / A converters;
A gain adjustment circuit added to the output of the adder, and an output terminal
Output from each D / A converter
The output of the adder is switched to the output of the gain adjustment circuit.
And a switching circuit.
When the D / A converters operate in parallel, each D / A converter
A latch circuit is inserted at the input of the inverter, and these two
The latch circuit is fs / 2 (where fs is the sampling
Two clock pulses 180 ° out of phase with each other
And a signal conversion circuit that operates in synchronization with one of the two. Next, an embodiment of a signal conversion circuit according to the present invention will be described in detail with reference to the accompanying drawings. FIG.
Shows an embodiment of a signal conversion circuit according to the present invention, in which the signal conversion circuit of the present invention is provided in an audio section of a DVD player. In this figure, reference numeral 21 denotes a Dolby digital decoder, which decodes an audio stream signal supplied from an MPEG video decoder (not shown), and outputs digital signals of L channel, R channel, C channel, rear L channel, rear R channel, and SW channel. Is output. This Dolby Digital Decoder 2
The first L channel output is input to the first audio D / A converter 22 ₁ , the R channel output is input to the second audio D / A converter 22 ₂ , and the C channel output is output via the switch element 23 ₁ . 3 audio D /
The input of the A converter 22 _3, rear L channel output to the input of the fourth audio D / A converter 22 ₄ through the switch element 23 _2, the rear R channel output fifth audio through the switching element 23 ₃ D / a converter 22 to the _fifth input, SW channel output sixth audio D / a converter via the switch 23 ₄ 2
Connected to ₂₆ inputs respectively. The L channel output of the Dolby digital decoder 21 is the switch element 2
4 ₁ via the third audio D / A converter 22 ₃
It is connected to the input of which is connected to an input of a fourth audio D / A converter 22 ₄ through the switch element 24 _2, further Dolby Digital decoder 21
The 5 R channel output via the switching element 24 ₃
It is connected to an input of an audio D / A converter 22 ₅ is connected to the input of the sixth audio D / A converter 22 ₆ via the switching element 24 _4. On the other hand, the output of the first audio D / A converter 22 ₁ is in the analog audio signal output terminal of the L channel through the switch element 25 ₁ (Lch), a second audio D / A converter 22 and _second output the analog audio signal output terminal of the R-channel through the switch element 25 _2, the analog audio signal output terminal of the output of the third audio D / a converter 22 ₃ direct C channels, a fourth audio D / a converter 2
2 to ₄ the output of the analog audio signal output terminal of the direct rear L channel, the output of the fifth audio D / A converter 22 ₅ analog audio signal output terminal of the direct rear R channel, a sixth audio D / A converter 22 output ₆ is connected to an analog audio signal output terminal of the direct SW channel. Further, first, third, and fourth audio D / A converters 22 ₁ ,
22 _3, 22 ₄ outputs the first of the first adder 26 _1, the second is connected to the third input, the output of the first adder 26 ₁ is the first gain adjusting circuit 27 ₁ and the switching element 28 ₁ via the series connected to an analog audio signal output terminal of the L channel. Similarly, the second, fifth, and sixth audio D / A converters 22 ₂ , 22 ₅ , 22
The output of the ₆ first second adder 26 _2, the second, is connected to the third input, the second output of the adder 26 ₂ and the second gain adjustment circuit 27 ₂ and the switching element 28 ₂ Are connected in series to an analog audio signal output terminal of the R channel. In such a circuit, a digital signal of each channel is normally output to each output of the L channel, R channel, C channel, rear L channel, rear R channel, and SW channel of the Dolby digital decoder 21. . In this case, the switch element 24 _{1-24 4,} 28 _1, 28 ₂ while being turned off, the switch element 23 ₁ to 23 _4, 25 _1, 25 ₂ is turned on. Therefore, the Dolby Digital decoder 21
The digital signal output from each channel output is D / A converted by _{first to sixth} audio D / A converters 221 to 226 provided corresponding to each channel, and the analog audio signal of each channel is output. Is output to the analog audio signal output terminal of each channel. On the other hand, when playing back a CD disk or the like, digital signals are output to the L channel and R channel outputs of the Dolby digital decoder 21, but other channel outputs, ie, C channel, rear L channel, rear R channel, and SW are output. No digital signal is output to each output of the channel. In this case, the switch element 23 21 _to
34 , 25 ₁ and 25 ₂ are turned off, and the switch elements 24 _{1 to} 24 ₄ , 28 ₁ and 28 ₂ are turned on. Then, the first audio D / A converter 22 ₁ of the L-channel, C channel and the third for the rear L channel, the fourth audio D / A converter 22 _3,
22 ₄ are connected in parallel, Dolby Digital decoder 21
The digital signal of the L channel output of the first, third, fourth
Audio D / A converters 22 ₁ , 22 ₃ , 22 ₄
, And the three analog signals after the conversion are added by the _first adder 26 ₁ ,
Moreover, the level is adjusted by the first gain adjustment circuit 27 ₁ and output to the L-channel analog audio signal output terminal via the switch element 28 ₁ . At the same time, the second audio D / A converter 22 ₂ for the R channel, the fifth for the rear R channel and SW channel,
Sixth audio D / A converters 22 ₅ and 22 ₆ are connected in parallel, and the digital signal of the R channel output of the Dolby digital decoder 21 is converted to _second , _fifth , and sixth audio D / A converters 22 ₂ , 22 ₅ , and 22. D in each of 22 ₆
/ A conversion, and the three analog signals after the conversion are added by the second adder 26 ₂ , and the level is adjusted by the _second gain adjustment circuit 27 ₂ to switch the switch element 28 ₂ . The signal is output to the R channel analog audio signal output terminal via the terminal. As described above, in the above-described circuit, in the two-channel mode of the L channel and the R channel, the two-channel audio D / A converters 22 ₁ and 22 2 are used.
Now 2 ₂ other channels of audio D / A converter with respect to 22 _3, 22 ₄ or 22 _5, 22 ₆ operating in parallel, all the audio D / A converter is effectively used. By performing the parallel operation in this manner, the SNR (S / N ratio), which is the performance of the audio unit, is obtained.
And D-A converters that operate in parallel in the D range and the like can be improved by a factor of 30.5 (in this case, ^30.5 times). [0010] As is clear from the above operation, the switch element 23 ₁ to 23 _4, 24 _{1-24 4,} the first switching circuit 29 for switching the input of the audio D / A converter connected in parallel and individually connected , And the switch elements 25 ₁ , 25 ₂ , 28 ₁ , 28 ₂ are provided with an addition output and a D / A
2nd switching of converter independent output to output terminal
Of the switch circuit 30 of FIG. Further, operation modes such as either 2-channel mode or full channel mode grasps the system controller 17 shown in FIG. 4, the switch element 23 ₁ to 23 _4, 2
4 _{1-24 4,} 25 _1, 25 _2, 28 _1, 28 ₂ ON, OFF is controlled by the system control unit 17. FIG. 2 is a circuit diagram showing another embodiment of the signal conversion circuit of the present invention. In this figure, reference numeral 41 denotes a Dolby digital decoder, which decodes an audio stream signal supplied from an MPEG video decoder (not shown) to perform L channel, R channel, C channel,
It outputs digital signals of the rear L channel, the rear R channel, and the SW channel. L channel output of the Dolby Digital decoder 41 to a first input of an audio D / A converter 43 ₁ through the switch element 42 _1, the second audio D / A converter R-channel output via the switch element 42 ₂ 43 ₂ inputs, C channels output to the input of the third audio D / a converter 43 ₃ through the switching element 42 _3, rear L channel output fourth audio D / a through the switching element 42 ₄ the input of the converter 43 _4, the input of the rear R channel output directly fifth audio D / a converter 43 _5, SW channel output directly sixth audio D of
/ It is connected to the input of the A converter 43 _6. Further, the L channel output Dolby Digital decoder 41 is connected to the input of the latch circuit 44 ₁ and the first audio D / A converter the switch element 45 ₁ via the series 43 _1, the latch circuit 44 ₃ and the switch element 45 ₃ is connected to an input of a third audio D / a converter 43 ₃ through the series, further R-channel output of the Dolby digital decoder 41 via the latch circuit 44 ₂ and switch element 45 ₂ in series the 2
It is connected to an input of an audio D / A converter 43 ₂ of the latch circuit 44 ₄ and the switch element 45
₄ in series via a fourth audio D / A converter 4
3 is connected to a _fourth input. The latch circuits 44 ₁ , 44 ₂ ,
44 _3, as a 44 ₄ specifically D-FF circuit is used. Meanwhile, the output of the first audio D / A converter 43 ₁ is in the analog audio signal output terminal of the L channel through the switch element 46 ₁ (Lch), a second audio D / A converter 43 and _second output the analog audio signal output terminal of the R-channel through the switch element 46 _2, the analog audio signal output terminal of the output of the third audio D / a converter 43 ₃ direct C channels, a fourth audio D / a converter 4
3 the output of the ₄ analog audio signal output terminal of the direct rear L channel, the output of the fifth audio D / A converter 43 ₅ analog audio signal output terminal of the direct rear R channel, a sixth audio D / A converter 43 output ₆ is connected to an analog audio signal output terminal of the direct SW channel. Furthermore, the first and third audio D / A converters 43 ₁ and 43 ₃
The output of the first ₁ first adder 47, is connected to the second input, the output of the first adder 47 ₁ via the first gain control circuit 48 ₁ and the switch element 49 ₁ in series To the L channel analog audio signal output terminal. Similarly, the second, the output of the fourth audio D / A converter 43 _2, 43 ₄ the first of the second adder 47 ₂ is connected to the second input of the second adder 47 ₂ output is connected to an analog audio signal output terminal of the R-channel through the second gain control circuit 48 ₂ and the switching element 49 ₂ in series. In such a circuit, a digital signal of each channel is normally output to each output of the L channel, R channel, C channel, rear L channel, rear R channel, and SW channel of the Dolby digital decoder 41. . In this case, the switch element ₄₅ 1 _{to 45 4,} 49 1, 49 ₂ while being turned off, the switch element ₄₂ 1 _{to 42 4,} 46 1, 46 ₂ is turned on. Therefore, the Dolby Digital decoder 41
The digital signal of each channel output from each channel output of each of the _first to _sixth audio D / A converters 431 to 436 provided corresponding to each channel.
The analog-to-digital conversion is performed on the analog audio signal output terminal of each channel. On the other hand, when playing back a CD disk or the like, digital signals are output to the L channel and R channel outputs of the Dolby digital decoder 41, but other channel outputs, that is, C channel, rear L channel, rear R channel, and SW are output. No digital signal is output to each output of the channel. In this case, the switch elements 42 ₁ to 4 ₁
2 _4, 46 _1, with 46 ₂ is turned off, the switch element 45 ₁ to 45 _4, 49 _1, 49 ₂ is turned on. Then, L first audio D / A converter 43 ₁ 3 for the C channel relative to the audio D / A converter 43 ₃ for channels are connected in parallel, a digital signal of L channel output Dolby Digital decoder 41 First and third audio D / A converters 43 ₁ , 43
_3, the two analog signals after the conversion are added by the _first adder 471, and the level is adjusted by the _first gain adjustment circuit 481. is output to the L-channel analog audio signal output terminal through the switch element 49 _1. At the same time, R
Second audio D / A converter 43 for channel
For the rear L-channel to _two fourth audio D /
A converter 43 ₄ are connected in parallel, a digital signal of the R channel output Dolby Digital decoder 41 second, fourth audio D / A converter 43 _2, 43 ₄
, And the two analog signals after the conversion are added by the _second adder 47 ₂ ,
Moreover level is adjusted by the second gain adjustment circuit 48 ₂ is output via the switching element 49 ₂ to R-channel analog audio signal output terminal. Thus, the first and third audio D / A
When the converters 43 ₁ , 43 ₃ and the second and fourth audio D / A converters 43 ₂ , 43 ₄ operate in parallel, the audio D / A converters 43 ₁ , 43 ₂ , 43
_3, 43 latch circuit 44 to respective inputs of _{4 1,} 44 _2, 4
4 _3, 44 ₄ is inserted. Here, a latch circuit 44 connected in common to the L channel output Dolby Digital decoder 41 _1, 44 _3, fs / 2 (although, fs is the sampling frequency) 3 with 180 ° out of phase with
It operates in synchronization with one of the clock pulses as shown in (e) and (f). That is, the clock pulse, the latch circuit 44 ₃ in FIG. 3 the latch circuit 44 ₁ (e) is 3
It operates in synchronization with the clock pulse of (f). Therefore, the L-channel output of the Dolby digital decoder 41 has a sampling frequency fs = 96 kHz of FIG.
An L-channel digital signal as shown in FIG. 3C obtained by separating the L-channel data from the digital signal shown in FIG. 3B (FIG. 3A shows a sampling pulse of 96 kHz) is output. Latch circuits 44 ₁ , 4
4 ₃ If is provided, each data diagram of the digital signal in FIG. 3 (c) 3 (g) , are latched alternately by the latch circuits 44 _1, 44 ₃ every other one as shown in (h) Te, two fs / 2 that is, the first as a digital signal of a sampling frequency of 48kHz, supplied to the third audio D / a converter 43 _1, 43 _3. Such an operation is the same on the R channel output side of the Dolby digital decoder 41.
As shown in FIGS. 3 (i) and 3 (j), each data of the digital signal of FIG. 3 (d) which is separated from the digital signal of FIG. One placed in the latch circuit 44 _2, 44 second as a digital signal of a sampling frequency of ₄ to be latched alternately two kinds of fs / 2 (48kHz), fourth audio D
/ A converter 43 ₂ is supplied to the 43 _4. Therefore, according to the circuit of FIG. 2, the first to fourth audio D / A converter 43 _{1-43 4} becomes capable of operating at 48kHz is fs / 2, inexpensive audio D
A / A converter can be used. This means
The signal reproduced by the DVD player is Dolby 5.1ch
The sampling frequency is usually 48 kHz, but the sampling frequency is 96 kHz
There is a case. At that time, the system controller determines that the sampling frequency is 96 kHz and switches the switch. Also in the circuit of FIG. 2, the audio D / A converters of the other channels operate in parallel in the two-channel mode of the L channel and the R channel, so that the audio D / A converters are effectively used. Of course, the performance of the audio section can be improved by the parallel operation. In FIG. 2, the switching element 42
_{1-42 4} 45 _{1-45 4} constitutes a first switch circuit 50 for switching the audio D / A converter in parallel operation and individual operation, the switch elements 46 _1, 46 _2, 4
9 _1, 49 ₂ constituting the second switch circuit 51 for switching the addition output and the D / A converter alone outputted to the output terminal. Further, in the present embodiment, a latch circuit is used as a circuit for lowering the sampling frequency, but another circuit may be used. In the above, the decoder in the stage preceding the audio D / A converter is a Dolby digital decoder 5.1c.
In the case of h, when the decoder is 7.1ch of an MPEG2 audio decoder, the decoder has eight channels of digital signal outputs and eight D / A converters. D / A
The converters can be operated in parallel. Furthermore, the above description is for the case where the present invention is applied to a DVD player. However, the present invention can be used for other audio devices, and can be widely used for electronic devices other than audio devices. it can. As described in detail above, according to the signal conversion circuit of the present invention, the D / A converter of another channel operates in parallel with the D / A converter of a specific channel. Therefore, the D / A converter can be used effectively, and the performance of the circuit can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing an embodiment of a signal conversion circuit according to the present invention. FIG. 2 is a circuit diagram showing another embodiment of the present invention. FIG. 3 is a waveform chart of each unit according to another embodiment of the present invention. FIG. 4 is a block diagram showing a conventional DVD player. [Description of Reference Numerals] 22 _{1-22 6,} 43 ₁ to 43 ₆ audio D / A converter 26 ₁ of the first to sixth, 26 _2, 47 _1, 47 ₂ first, second adder 27 _1, 27 _2, 48 _1, 48 ₂ first, second gain adjustment circuits 29,50 first switch circuit 30, 51 second switch circuit 44 ₁ to 44 ₄ latch circuit

Claims (1)

(57) [Claim 1] In a signal conversion circuit in which digital signals of a plurality of channels are D / A converted by a plurality of D / A converters provided corresponding to each channel, has a switching means for switching the circuit to the other channels of the D / a converter with respect to D / a converter channels operating in parallel, said switching means connects the inputs of the two D / a converters in parallel Switch
Switch and two switches whose inputs are connected in parallel by this switch circuit.
An adder for adding the output of the D / A converter, a gain adjustment circuit added to the output of the adder, and an output connected to the output terminal for each of the D / A converters
From the output to the gain adjustment circuit output of the adder output.
And a switching circuit for switching two D / A converters in parallel.
When making, the input of each D / A converter is latched
A circuit is inserted, and the two latch circuits are fs / 2
(Where fs is the sampling frequency) 180 ° phase
Operates in synchronization with each of the two clock pulses
A signal conversion circuit.