JPH027605A - Electric volume circuit - Google Patents

Abstract

PURPOSE:To reduce click noise caused in the case of switching a digital control input by inserting a low pass filter between a D/A converter and a voltage controlled amplifier(VCA) so as to vary an output voltage of the D/A converter with a time constant. CONSTITUTION:An output voltage of the D/A converter 5 is varied with a time constant by using a low pass filter 7. That is, an output waveform of the D/A converter 5 shown in figure iv-b is a stepwise voltage in response to the combination of an n-bit data of a digital control input 6. Then a high frequency pulse is generated at its switching point and the low pass filter 7 eliminates the high frequency pulse and smooths the voltage as shown in waveform of iv-a. Thus, the amplitude of an output 3 of a VCA 2 is changed smoothly as shown in waveform iii. Thus, the click noise generated at the analog signal output of the VCA is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electronic volume circuit whose gain or attenuation is changed by a digital control input.

[Conventional technology]

Electronic volume circuits that can set gain or attenuation using digital control inputs (consisting of n-bit data, usually n = 4 to 6) have VCA and D/A conversion as shown in Figure 3. This can be achieved by using a device.

FIG. 3 is a configuration diagram showing a conventional electronic volume circuit. In the figure, 1 is an analog signal input, 2 is a VCA, and 3
is analog signal output, 4 is control voltage, 5 is D/
A converter, 6 is a digital control input.

Next, the operation will be explained.

The VCA 2 is an amplifier whose attenuation varies depending on the control voltage 4. A commonly used VCA is manufactured by Mitsubishi Electric, product model number M5222L/M5222.
There is a popular VCA represented by P. M5222
The attenuation characteristic with respect to the control voltage of L/M5222P is expressed by the following formula (Reference material: Mitsubishi general-purpose linear ICM
522XX Series User's Manual 2nd Edition 2-
page 47).

Here, Vc is a control voltage, and q/kT is a reciprocal of a so-called thermal voltage.

The D/A converter 5 converts the n-bit data of the digital control manual 6 into 2'' analog voltages, and the VCA 2
is applied as a control voltage 4. Therefore, V.C.
The attenuation amount of A2 can be set in 2'' ways by the n-bit digital control manual 6, and an electronic volume can be realized.

[Problem to be solved by the invention]

Conventional electronic volume circuits are configured as described above, and when the attenuation amount of the VCA is changed by switching the n-bit data of the digital control input, a click noise occurs when switching to the analog signal output, causing auditory sensitivity. There were cases where this was a problem.

The main cause of click noise is D/
There are cases where whisker pulses are generated in the output of the A converter during data switching, or cases where the DC offset voltage of the VCA differs depending on the amount of attenuation.

This invention was made to solve the above-mentioned problems, and an object of the present invention is to obtain an electronic volume circuit that can prevent click noise that occurs in the analog signal output when switching n-bit data of the digital control input. .

[Means to solve the problem]

The electronic volume circuit according to the present invention has a low-pass filter inserted between the D/A converter and the VCA, and changes the output voltage of the D/A converter with a certain time constant. .

[Effect]

In this invention, since the output voltage of the D/A converter is changed with a certain time constant using a low-pass filter, it is possible to remove whisker pulses that occur in the D/A converter when switching digital control inputs, and also to
It is possible to gently change the amount of attenuation of the VCA, thereby reducing click noise generated in the analog signal output of the VCA, and eliminating an audible sense of discomfort.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an electronic volume circuit according to an embodiment of the present invention. In the figure, the same reference numerals as in FIG. 3 indicate the same or corresponding parts. Also, 7 is a low-pass filter, 4
a is the output of the low-pass filter. Also, 4b is D/
This is the output of the A converter 5.

Furthermore, FIG. 2 is a waveform diagram showing the waveforms of each part of the device in FIG. 1, and in the figure, i, if, iva, iv
b is the analog signal human power 1 in FIG. 1, respectively. Analog signal output 3. These are the waveforms of the low-pass filter output 4a and the D/A converter output 4b. Note that in order to simplify the diagram, the analog signal input 1 is a continuous waveform with a constant amplitude, but in reality, an audio signal or the like is input.

Next, the operation will be explained.

The output waveform ivb of the D/A converter 5 becomes a stepped voltage according to the combination of n-bit data of the digital control manual 6, and at the switching point, a whisker pulse as shown in FIG. 2 is generated. In this embodiment, this whisker pulse is removed by the low-pass filter 7, and the voltage is changed smoothly as shown by the waveform of iv a in FIG. 2, so the waveform of the output 3 of the VCA 2 is ! As shown in Ii, the amplitude changes gradually. Therefore, even if the speaker is driven by the output 3 of the VCA 2 directly or via an amplifier having an appropriate gain, click noise generated at the switching point of the digital control manual 6 can be prevented.

In this way, in this embodiment, a low-pass filter is inserted between the D/A converter and the VCA, and the output voltage of the D/A converter is changed with a certain time constant, so that the D/A converter can be changed at the time of digital control manual switching. Since whisker pulses generated in the A converter are removed and the amount of attenuation of the VCA is changed gradually, click noise generated in the analog signal output of the VCA can be reduced, and an audible discomfort can be eliminated.

It should be noted that in the above embodiment, explanation was given focusing only on the removal of whisker pulses generated in the output of the D/A converter 2.
Needless to say, the same effect can be achieved with respect to click noise caused by the DC offset output voltage that varies depending on the amount of attenuation of the VCA 2.

〔Effect of the invention〕

As described above, according to the present invention, in the electronic volume circuit, a low-pass filter is inserted between the D/A converter and the VCA, and the output voltage of the D/A converter is changed with a certain time constant. With this configuration, it is possible to reduce click noise when switching digital control inputs, and there is an effect that it is possible to eliminate audible discomfort. Also, V.C.
Since the DC offset voltage of A may vary greatly depending on the amount of attenuation, there is an effect that the VCA can be simplified.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an electronic volume circuit according to an embodiment of the present invention, FIG. 2 is a waveform diagram showing waveforms of each part of the circuit in FIG. 1, and FIG. 3 is a configuration diagram showing a conventional electronic volume circuit. It is. 1 is an analog signal input, 2 is a VCA, 3 is an analog signal output, 4a is a D/A converter output, 4b is a low-pass filter output, 5 is a D/A converter, 6 is a digital control input,
7 is a low pass filter. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] (1) A D/A converter that converts digital control input into a control voltage and outputs it, a low-pass filter that changes the output voltage of the D/A converter with a certain time constant, and an output of the low-pass filter. VCA (Voltage Control) whose gain or attenuation changes depending on the voltage
1. An electronic volume circuit comprising: a rolled Amplifier;