JPS6341471B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an analog-to-digital conversion method for digitally converting a television signal and other information signals such as audio signals. It is intended to perform digital conversion using a digital converter (A/D converter).

Video signal as an analog signal (video signal)
It is well known that when converting an audio signal into a digital signal, the conversion is generally performed under the following conditions.

Analog-to-digital conversion of video signals (A/
In general, the carrier color signal _C
( _C = 3.579545MHz in NTSC mode), the sampling frequency is three times higher than that of C = 3.579545MHz.
The input video signal is sampled at _S and quantized to 8 or 9 bits.

On the other hand, audio signals are sampled at a sampling frequency (30KHz or higher) that is more than twice the audio signal band (approximately 15KHz), and the number of quantization bits is at least 8 bits or more, and about 12 bits for high-quality music signals. is assigned.

Conventionally, A/D conversion of video signals and A/D conversion of audio signals have been performed under completely different conditions as described above.

The present invention combines a video signal and, for example, an audio signal A/D.
When converting, the present invention provides a method of A/D converting both a video signal and an audio signal using one A/D converter.

First, let's discuss A/D conversion of audio signals in a little more detail.

In the case of audio signals, there are sounds ranging from very low levels to very loud levels, and it is said that a quantization level of 12 bits or more is required to transmit almost completely within the human audible range. . However, usually we use a television receiver,
When listening to sound using a radio receiver or the like, a standard audio level is set and the noise is not a problem as long as the S/N is about 45 dB or more with respect to this standard level. In addition, in the case of audio signals, the level may instantaneously reach a high level, but in order to ensure that distortion does not become a problem even at this instantaneous high level, the signal must be three times the standard level. It is said that there is usually no problem if a margin of about (+10 dB) is allowed.

Now, if the audio signal is quantized with 8 bits, the dynamic range will be approximately 48 dB, which is 10 dB.
If the standard audio level is set with a margin of , the quantization noise N _Q for the standard audio level S is
The ratio of S/N _Q is approximately 38 dB, and when quantized with 9 bits, the dynamic range is approximately 54 dB, and the ratio of quantization noise to the standard audio level is S/N _Q.
is approximately 44dB. Therefore, in the case of 9-bit quantization, the level S/
It can be seen that an S/N _Q almost close to N45 dB can be obtained. In addition, in the case of 8-bit quantization, the S/N _Q with respect to the standard audio level is 38 dB, which means that the quantization noise exceeds the permissible level. However, even in the case of 8-bit quantization, when the audio level is high, the quantization noise is masked by the signal and causes almost no problem, and only when the audio level is low, the quantization noise exceeds the allowable level. Therefore, there is a well-known method that emphasizes the level of a low-level audio signal before quantization, and suppresses the low-level signal when converting the quantized signal back to an analog signal (D/A conversion). If the noise suppression method described above is used, the quantization noise is suppressed, so even for low-level audio signals, the quantization noise can be sufficiently suppressed to below the allowable level. (The quantization noise for the level signal can be easily suppressed by 10 dB or more.) Practically sufficient A/D conversion can be performed even with 8-bit quantization.

On the other hand, regarding the sample frequency of the audio signal,
Since the audio signal band only needs to be 15KHz, it is sufficient to sample at a frequency that is more than twice that (30KHz or more). Horizontal synchronization signal of television signal
_H is 15.75KHz, and is sampled twice in one horizontal scanning period of the television signal (sampling frequency is approximately
31.5KHz), audio signal transmission up to 15KHz is possible. By sampling three times in one horizontal scanning period, it is possible to transmit audio signals up to approximately 23KHz.

Next, let's discuss A/D conversion of video signals in more detail. A composite video signal consists of a synchronization signal and a video signal, and the A/D of the video signal
During conversion, synchronization signals are generally not directly A/D converted (except for color synchronization signals), but a special code (for example, the well-known Barker code) is transmitted at the start timing of the synchronization signal, and color synchronization A method is adopted in which only the video period including the signal is directly A/D converted. The synchronization signal after D/A conversion is created from the synchronization signal timing transmitted as a special code, and is combined with the D/A converted video signal to form a composite video signal. Therefore, the A/D converter does not need to operate during the synchronization signal period.

According to the present invention, when a video signal is A/D converted, an audio signal is A/D converted using the same A/D converter during a period when the A/D converter is not required to operate as described above.

A concrete example of a circuit block diagram of the present invention will be explained in detail with reference to FIG. 1 and a waveform diagram in FIG.

In FIGS. 1 and 2, a video signal A is input to an input terminal 1 and guided to a switch circuit 8, and a horizontal synchronizing signal _H is separated in a horizontal synchronizing signal separating circuit 2. A sample pulse ( _2H ) like the one shown in FIG. A sample-and-hold signal such as E is obtained at the output of this sample-and-hold circuit 5. This sample and hold signal C is sampled and held again by the sample and hold circuit 7.
is sampled and held again using a sample pulse such as F generated by the sample pulse generator 6, and a sample-and-hold signal delayed by approximately one sample time is obtained at the output of 7.

The second sample pulse generates a pulse twice in one horizontal scanning period, and is configured to generate a pulse, for example, between the trailing edge of the horizontal synchronizing signal and the horizontal synchronizing signal, and the second sample pulse corresponds to the timing of the second pulse. It is considered to be a pulse that generates a time slightly ahead of the
The changing point of the sample and hold signal is located during the period of the horizontal synchronization pulse.

The sample hold signal H created in this way is led to the switch circuit 8 mentioned above, and is switched by the video signal A led to the other input terminal of the switch circuit 8 and the pulse of the switching pulse generator 9. A video signal is obtained in which a sampled and held audio signal is inserted into the horizontal synchronizing signal period as shown in FIG.

The output of this switch circuit 8 is led to a sample hold circuit 10, and a sample pulse generator 11
The sample pulse _S (for example, _S = 3 _C = 3/2 × 455 _H , _C : carrier color signal frequency) synchronized with the horizontal synchronization signal created by Quantized in bits.

The output of the A/D converter 12 is led to the processor 13 as a 9-bit parallel signal, for example. A clock synchronized with a frequency nine times the output _S of the sample pulse generator 11 is generated and guided to the processor 13 by a clock generator 14, and a horizontal synchronization timing pulse is also introduced to the processor 13.

Then, at the output 15 of the processor 13, a signal such as, for example, H is obtained.

In this case, quantized video information, is a special synchronization code representing a horizontal synchronization signal, is a cue signal for indicating the information position of the audio signal, and corresponds to the first sample hold value of the horizontal scanning period of the audio signal. The quantization information of one sample is synchronization information inserted between the quantization information of the first sample signal and the second sample signal of the audio signal,
is the quantization information of one sample corresponding to the second sample hold value of the audio signal, and is the cue synchronization signal for the video signal inserted between the audio signal and the next video information.

Here, each piece of information is either a 9-bit parallel signal or a signal obtained by converting this parallel signal into a serial signal.

As mentioned above, one of the synchronization codes is the Barker code, which was created by taking into account the number of bits and the probability of error and calculating a pattern in which the bit arrangement of the information signal is unlikely to occur. An example of a 27-bit Barker code is as follows.

000001001001010111011100111 The insertion position of the Barker code does not necessarily have to be inserted from the falling point of the synchronization signal, it can be inserted at any position of horizontal blanking.
By performing signal processing on the composite side using the position of this Barker code as a reference, an accurate synchronization signal can be restored. Furthermore, when the synchronization code causes an error in the transmission system, the PLL circuit operates to stably restore the synchronization signal.

The audio signal input to terminal 4 in FIG.
When the D converter is 8 bits, if a low-level audio signal is input in an expanded form, A/D conversion with sufficient dynamic range even against quantization noise is possible.

Further, the information to be A/D converted during the horizontal blanking period is not necessarily limited to audio signals, but various information signals similar to audio signals can be processed.

Furthermore, the information signal to be A/Ded during the horizontal blanking period is not limited to one signal, but can be transmitted in the same way as a plurality of signals by time division.

Furthermore, as a method for compressing information of two or more samples within horizontal blanking, the sample-hold method is shown in the above explanation, but it is also possible to use a method of time compression using a memory circuit or the like.

As described above, according to the present invention, a video signal and other information signals (for example, audio signals) can be A/D converted by the same A/D converter using the horizontal blanking period of the video signal. ,
The cost of the entire device can be reduced, transmission can be performed in the same band, and there are various advantages.

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram showing a specific example of the circuit configuration of the present invention, and FIG. 2 is a waveform diagram for explaining the operation of the circuit shown in FIG. 1, 4...Input terminal, 2...Synchronization separation circuit, 3,
6, 11...Sample pulse generation circuit, 5, 7, 1
0...Sample hold circuit, 8...Switch circuit,
9... Switching pulse generator, 12... A/D converter, 13... Processor.

Claims (1)

[Claims] 1 A video signal and other information signals with a band sufficiently narrower than the television video signal band are converted into analog
When performing digital conversion, the other information signal is sampled multiple times during one horizontal scanning period, and the signal sampled multiple times is time-compressed and inserted within the horizontal synchronization signal period of the video signal, and the video signal and the compressed signal are information signal and the same analog signal.
An analog-to-digital conversion method characterized by time-divisional digital conversion using a digital converter.