JPH06177677A - Analog signal processing circuit - Google Patents

Abstract

PURPOSE:To provide an analog signal input-output circuit in which the S/N is not deteriorated in the digital processing even when a signal source different from a 0dB output voltage is connected the circuit. CONSTITUTION:A selector switch 26 selecting any of amplifiers 251, 252 and 253 and any of sound sources 11, 12 and 13 corresponding to the sound sources 11, 12 and 13 is installed to a pre-stage of an A/D converter 23 of the analog signal processing circuit 20 and a programmable attenuator 28 is installed to a post-stage of a D/A converter 24. The gain of the amplifiers is set so that a 0dB voltage of the sound sources is a permissible maximum voltage of the A/D converter 23 and the gain of the programmable attenuator is set to be a reciprocal of the gain of the amplifiers. Thus, in the case of digital signal processing, the range of the digital signal processing level is used maximizingly and the deterioration in the S/N is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an analog signal processing circuit, and more particularly to an analog signal processing circuit which does not deteriorate the processing accuracy of analog signals.

[0002]

2. Description of the Related Art In recent years, the number of devices for digitally processing various analog signals by a microcomputer or the like has increased due to the development of electronic technology. For example, in a sound field control device used in an audio system in recent years, an analog audio signal output from a sound source is digitized by an A / D converter, and a DSP (Digital Signal Prosesso).
After the reverberation sound and the like are added in r), the analog audio signal is restored by the D / A converter, the power is amplified, and the voice is output from the speaker.

[0003]

However, there are many types of sound sources such as FM tuners, cassette tape recorders, and CD players, and even if the same music information is used, it is caused by the difference in the recording level or the output level of the sound source. If the sound source is switched by using the so-called S / N of the output signal
The ratio may change.

For example, when the output signal is not attenuated by the attenuator, that is, in the so-called 0 dB state, the voltage is FM.
5V for tuner, 2.5 for cassette tape recorder
V and 1.25V for a CD player, and the maximum allowable voltage of the input signal of the sound field control device is 5V.
If the A / D converter is 16 bits, an S / N ratio of 98 dB can be obtained when a 5 V signal is applied. That is FM
When 0 dB voltage is output from the tuner, the S / N ratio can be 98 dB from the A / D converter.

However, when the sound source is switched to the cassette tape recorder, the signal level of the cassette tape recorder is -6 dB, so the S / N ratio is 92 dB at maximum.
I can only take it. Furthermore, since the signal level of a CD player is -12 dB, the maximum S / N ratio can only be 86 dB.

Therefore, when the CD player is selected, the sound field control device uses only the signal level of 86 dB, and the noise level peculiar to the sound field control device does not vary depending on the sound source, so that the S / N ratio is Getting worse. The present invention has been made in view of the above problems, and provides an analog signal input / output circuit in which the S / N ratio does not deteriorate during digital processing even when signal sources having different 0 dB voltages are connected. The purpose is to

[0007]

In the analog signal processing circuit according to the present invention, a selection section for selecting and outputting one analog signal from the analog signals output from at least two signal sources is selected by the selection section. A / D converter for converting the converted analog signal into a digital signal, a digital signal processing section for processing the digital signal converted by the A / D converter, and a D for converting the digital signal processed by the digital signal processing section into an analog signal An analog signal processing circuit including an A / A converter,
And at least two input gain adjusting circuits each having a gain such that the maximum output voltage of each of the analog signals output from the at least two signal sources is the maximum allowable voltage of the A / D converter in the analog signal processing circuit in the preceding stage of the selection unit. , D /
At least two output gain adjusting circuits each having a gain that is the reciprocal of the gain of the at least two input gain adjusting circuits, and a switch for switching between at least two output gain adjusting circuits corresponding to the selection in the selection unit And a section.

[0008]

In the analog signal processing circuit according to the present invention, the 0 dB signal output from two or more sound sources is A / D.
It is adjusted to the maximum allowable voltage of the A / D converter before it is input to the converter. The digitally processed output is converted into an analog signal by a D / A converter, and then attenuated and adjusted to the signal level of the sound source.

[0009]

1 is a block diagram of an embodiment of an analog signal processing circuit according to the present invention, which is used as a sound field control device. As the sound source, the FM tuner 11, the cassette tape recorder 12, and the CD player 13 are connected. The 0 dB voltage of the FM tuner 11 is 5
V, 0dB voltage of cassette tape recorder 12 is 2.5
V and the 0 dB voltage of the CD player 13 is assumed to be 1.25V.

The sound field control device 20 includes a control microcomputer 22 centering on a bus 21 and a sound field control D.
It is composed of an SP 22, an A / D converter 23 and a D / A converter 24. If necessary, a memory may be connected. The sound field control device 20 further includes three amplifiers 251, 252 and 253 for amplifying the signal output from the sound source before the A / D converter 23, and these three amplifiers.
A selection switch 26 is provided which selects one signal from the outputs of the two amplifiers 251, 252 and 253 and supplies it to the A / D converter 23.

A buffer 27 and a programmable attenuator 28 are also included in the subsequent stage of the D / A converter 24. The selection switch 26 and the programmable attenuator 28 are the control microcomputer 22.
Interlocked control by. Here, the A / D converter 23
Assuming that the maximum allowable voltage of 5 V is 0 dB, the gains of the three amplifiers 251, 252 and 253 are determined as follows.

That is, the maximum signal level 5 of the FM tuner 11
V is 0 dB, and the voltage of 0 dB and the A / D converter 2
Since the maximum allowable voltages of 3 match, the first amplifier 25
The gain of 1 is set to 0 dB. The maximum signal level −2.5V of the cassette tape recorder 12 corresponds to −6 dB, so the amplification factor of the second amplifier 252 is +6 dB, and the CD
The maximum signal level 1.25V of the player 13 is -12 dB.
The gain of the third amplifier is +12 dB.
Is set to.

By setting in this way, the maximum signal level is processed as 0 dB regardless of which sound source is selected during digital processing, and it is possible to prevent deterioration of the S / N ratio due to digital processing. A sound field signal is added to the signal digitally converted by the A / D converter 23 by the DSP 23, and converted into a processed analog signal by the D / A converter 24.

The processed analog signal is supplied to the programmable attenuator 28 via the buffer 27. The programmable attenuator 28 has a gain of 0 dB when the FM tuner 11 is selected as a sound source by the control microcomputer 22, and a gain of -6 when the cassette tape recorder 12 is selected.
When the CD player 13 is selected to dB, the gain is set to -12 dB.

Therefore, the 0 dB voltage of the processed analog signal becomes equal to the 0 dB voltage of the input analog signal, all bits can be used for digital signal processing, the S / N ratio does not deteriorate, and the 0 dB voltage does not change.

[0016]

In the analog signal processing circuit according to the present invention, the S / N ratio is deteriorated by the digital processing because the 0 dB equivalent voltage is adjusted to the maximum allowable voltage of the A / D converter prior to the digital signal processing. This is prevented, and the 0 dB voltage is readjusted in the subsequent stage of the D / A converter, so that the 0 dB voltage of the analog signal does not change.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment.

[Explanation of symbols]

 11 ... FM tuner 12 ... Cassette tape recorder 13 ... CD player 20 ... Analog signal processing circuit 21 ... CPU 22 ... DSP 23 ... A / D converter 24 ... D / A converter 251, 252, 253 ... Amplifier 26 ... Selection switch 27 ... Buffer 28 ... Programmable attenuator

Claims (1)

[Claims] 1. A selection unit for selecting and outputting one analog signal from analog signals output from at least two signal sources, and an A / D for converting the analog signal selected by the selection unit into a digital signal. Analog signal processing including a converter, a digital signal processing unit that processes the digital signal converted by the A / D converter, and a D / A converter that converts the digital signal processed by the digital signal processing unit into an analog signal In the circuit, in the preceding stage of the selection unit, there is a gain such that the maximum output voltage of each analog signal output from at least two signal sources becomes the maximum allowable voltage of the A / D converter in the analog signal processing circuit. At least two input gain adjusting circuits, and the gains of the respective D / A converters are provided in the subsequent stages. Also including at least two output gain adjustment circuits that are the reciprocals of the gains of the two input gain adjustment circuits, and a switching unit that switches between the at least two output gain adjustment circuits in response to selection by the selection unit. Signal processing circuit.