JPH0581091B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is an analog signal converter for converting an analog signal such as an audio signal into a digital signal by superimposing (adding) and calculating a dither signal. This invention relates to a digital conversion device.

[Conventional technology]

In PCM recording and reproduction of audio signals, quantization noise (the difference between the quantized output and the input sample value) becomes a problem. Particularly when the input signal level is low and the number of quantization steps is small, quantization noise has a strong correlation with the input and becomes a type of distortion (higher harmonics) of the input signal rather than noise. Furthermore, even if the input signal level is high, unpleasant noise will occur every time the quantization step changes for a signal that changes very slowly. Furthermore, there are variations in the quantization step of the A/D converter itself, which causes nonlinear distortion during A/D conversion. In order to solve the above-mentioned problems, it is already known to add white noise called dither to the input signal and perform A/D conversion, or to add dither, perform A/D conversion, and then subtract the dither. Are known.

[Problem that the invention seeks to solve]

By the way, if the maximum allowable input level of the A/D converter is kept constant and a dither signal is added to the analog signal, the dynamic range will be narrowed by the amount of the dither signal. Of course, if the maximum allowable input level of the A/D converter is increased, the dynamic range can be increased, but this inevitably increases the cost of the device.

In order to solve this kind of problem, it is possible to reduce the level of the analog dither when the level of the input signal becomes high, and to gradually reduce this level via an integrating circuit instead of reducing it suddenly. 57
- It is known from the publication No. 202123. However, it is not known to change the analog dither continuously or in multiple stages. Furthermore, it is difficult to change the analog dither continuously or in multiple stages.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an analog-to-digital converter that can easily and automatically adjust the level of an analog dither continuously or in multiple stages.

[Means for Solving the Problems] To achieve the above object, the present invention provides an analog information signal input line, a digital dither generator that generates digital dither in parallel bit format, and a digital dither generator that generates digital dither in parallel bit format. a digital-to-analog converter for converting digital dither generated from the generator into analog dither; and a multi-bit dither transmission line between the digital dither generator and the digital-to-analog converter. a plurality of switches, an adder for adding the analog information signal on the input line and the analog dither output from the digital-to-analog converter, and an adder for adding the analog dither addition information signal obtained from the adder and the analog-to-digital conversion means for converting the analog dither obtained from the digital-to-analog converter into a digital dither addition information signal and digital dither, respectively; and the digital dither addition obtained from the analog-to-digital conversion means. a subtracter that subtracts the digital dither from the information signal; a plurality of reference voltage sources that provide a plurality of reference voltages having different levels; one input terminal of each is connected to the input line; terminals are respectively connected to the plurality of reference voltage sources, respective output terminals are respectively connected to the control terminals of the plurality of switches, and when the analog information signal becomes higher than the reference voltage, the digital dither and a plurality of comparators whose output terminals correspond to the switches so as to cut off the transmission of the upper bits of the digital dither obtained from the generator before cutting off the transmission of the lower bits. -Related to digital conversion devices.

To explain the correspondence between the present invention and the embodiments, the analog-to-digital conversion means may be two A/D converters 11 and 12 in FIG. 1 or one A/D converter 11 in FIG. Yes, switch is S ₁ to _{S 12}
, and the comparators are C ₁ to C ₁₂ .

[Action and effect] The present invention has the following effects.

(b) Instead of controlling the analog dither with a variable resistor, etc., we installed a switch in the multi-bit transmission line of the digital dither and controlled it with a comparator, so the output of the adder Excessive size can be automatically prevented with a simple configuration.

(b) The dither level can be corrected in multiple stages on a bit-by-bit basis.

〔Example〕

Next, examples of the present invention will be described.

(First Embodiment) A device for converting an information analog signal corresponding to an audio signal into a digital signal according to the first embodiment shown in FIG. has an input line 1, which is connected to an analog adder 2. Digital dither generator 3a and D/
A digital dither level control circuit 9 is connected between the dither generator 3a and the D/A converter 3b.

The digital dither generator 3a is composed of a known M-sequence pseudo-random pulse generation circuit. The 12-bit digital dither obtained from this is converted into analog dither by the D/A converter 3b. The level control circuit 9 consists of 12 switches _S1 to _S12 connected in series to the 12 lines transmitting 12-bit dither, and operates to reduce the level of the dither signal when the level of the analog information signal is high. do.

The level determination circuit 10 for controlling the switches _S1 to _S12 has 12 comparators _C1 to _C12 , one input terminal of which is connected to the analog information signal line 1, respectively.
The other input terminal is connected to a source of reference voltages V _R1 to V _R12 having 12 different levels, and the output terminal is connected to switches S ₁ to S ₁₂ . Each comparator C ₁ ~
The reference voltages V _R1 , V _R2 ... V _R12 of V ₁₂ are the maximum allowable input level of the A/D converter 11 as ±V _M , and the maximum level of the analog dither signal obtained from the dither generator 3 as V _D. Then, V _R1 = +V _M −V _D V _R2 = +V _M −V _D /2 V _R3 = +V _M −V _D /4 〓 V _R12 = +V _M −V _D /2048 There is.

The output of dither generator 3 is coupled to the input of analog adder 2. Therefore, the adder 2 outputs an output resulting from analog addition of the analog information signal and the minute level dither signal.

A first A/D converter 11 converts the output of the adder 2 into a 16-bit digital signal. 12 is a second A/D converter, which converts the dither signal obtained from the dither generator 3 into a digital signal, and generates a random digital signal (dither digital signal) corresponding to the dither signal (white noise). Output.

13 is a digital subtracter, one input terminal is connected to the output terminal of the first A/D converter 11, the other input terminal is connected to the output terminal of the second A/D converter 12, The digital dither signal obtained from the second A/D converter 12 is subtracted from the digital dither addition information signal obtained from the first A/D converter 11, and the analog information signal is output to the output line 14. Send out information signals.

Next, the operation of the circuit shown in FIG. 1 will be explained.

An analog information signal is input from line 1,
The dither generator 3 outputs a dither signal having a lower level than the analog information signal. Both the analog information signal and the dither signal are input to the adder 2, and a summed output of these is obtained, and this is the A/D signal.
It is converted into a digital signal by a converter 11. on the other hand,
The dither signal is converted into a digital signal by the second A/D converter 12 and sent to the digital subtracter 13 as a random digital dither signal corresponding to white noise. In the subtracter 13, the digital dither signal is subtracted from the digital dither addition information signal, and a digital information signal substantially free of dither is output.

In the apparatus shown in FIG. 1, when the level of the input analog information signal is low, the output of the digital dither generator 3a is directly converted into an analog dither signal by the D/A converter 3b. i.e. 12 reference voltages
When the level V _S of the input analog information signal is lower than the lowest level V _R1 among V _R1 to V _R12 ,
The outputs of all comparators C ₁ to C ₁₂ are at high level,
All switches _S1 to _S12 are kept on. At this time, even if the maximum dither V _D is added to the input analog information signal V _S , the allowable value V _M is not exceeded.

The input analog information signal level V _S is V _R1 and V _R2
When between, only the first comparator C ₁ generates a high level output, only the switch S ₁ of the MSB signal line is controlled off, and the remaining switches S ₂ ~
S ₁₂ is kept on. Therefore, the 11-bit dither is D/A converted and supplied to adder 2 and A/D converter 12.

The input analog information signal level V _S is the reference voltage
If V _R12 is greater than then all comparators C ₁ ~
Since the output of C ₁₂ is at a high level, all switches S ₁ -S ₁₂ are turned off and the dither supply is cut off.

In this method, the effects of dither addition and subtraction can be obtained up to a high level of the input analog signal. When the level of the input analog signal is high, the dither level becomes low, but the characteristics are better than when the dither is cut off.

(Second Embodiment) Next, an A/D converter according to a second embodiment shown in FIG. 2 will be described. However, parts common to those in FIG. 1 are designated by the same reference numerals and their explanations will be omitted. In this device as well, as in the device shown in FIG.
is provided. However, the second
The A/D converter 12 is omitted. Instead of this,
The A/D converter 11 is used in a time-division manner, and the same A/D converter 11 converts both the dither addition information signal and the dither signal into digital signals. In order to perform time division control, the device shown in FIG. 2 includes a gate circuit 15, a memory 16, and a sampling gate circuit 17. Although not shown, a sample-and-hold circuit for information signals and dither signals, and a control circuit for time-division multiplexing control are of course also provided.

In the system shown in FIG. 2, when the information signal is cut off by the gate 15, only the dither signal is input to the adder 2 and output as is. on the other hand,
When the gate 15 is open, both the information signal and the dither signal are input to the adder 2, and a summed output is obtained. As a result, the A/D converter 11
A/D converts the dither addition information signal and the dither signal in a time division manner.

The memory 16 temporarily stores the digital dither signal, and the digital dither addition information signal is sent to the subtracter 13.
A dither signal is output in synchronization with the input period. Sampling gate 17 extracts only information signals. Note that the determination circuit 10 and dither generator 3 are constructed in the same manner as in FIG. 1 and operate in the same manner.

[Modified example]

The present invention is not limited to the above-described embodiments, but can be modified, for example, as follows.

(1) A time division multiplex signal forming circuit may be provided on the output side of the adder 2.

(2) The dither addition information signal may be written into the memory 16.

(3) A gate circuit may be provided to input only the necessary dither addition information signal and dither signal to the subtracter 13.

[Brief explanation of drawings]

FIG. 1 shows an A/D according to a first embodiment of the present invention.
FIG. 2 is a block diagram showing an A/D converter according to a second embodiment. DESCRIPTION OF SYMBOLS 1... Input line, 2... Adder, 3... Dither generator, 9... Level control circuit, 10... Analog information signal level determination circuit, 11... First A/D converter, 12... ...Second A/D converter, 1
3...Subtractor.

Claims (1)

[Scope of Claims] 1. An input line for an analog information signal, a digital dither generator that generates digital dither in parallel bit format, and converting the digital dither generated from the digital dither generator into analog dither. a plurality of switches connected to a multi-bit dither transmission line between the digital dither generator and the digital to analog converter; and an analog information signal on the input line. an adder that adds the analog dither output from the digital-analog converter; and an adder that adds the analog dither output from the digital-to-analog converter; analog-to-digital conversion means for converting the dither addition information signal and digital dither, respectively; and subtracting the digital dither from the digital dither addition information signal obtained from the analog-to-digital conversion means to generate the analog information. a subtracter that sends out a digital information signal corresponding to the signal as an analog-to-digital conversion output; a plurality of reference voltage sources that provide a plurality of reference voltages having different levels; one input terminal of each of which is connected to the input line; , each other input terminal is connected to each of the plurality of reference voltage sources, each output terminal is respectively connected to a control terminal of the plurality of switches, and the analog information signal becomes higher than the reference voltage. In this case, a plurality of comparisons whose output terminals correspond to the switch so that the transmission of the upper bits of the digital dither obtained from the digital dither generator is cut off before the transmission of the lower bits is cut off. Analog-to-digital converter equipped with a device.