JPS59202716A - Sound volume adjusting device - Google Patents

Abstract

PURPOSE:To make a noise caused by switching unaudible by attenuating a noise exceeding an audio frequency contained in an output of a sample holding circuit SH by a low-pass filter LF, and making only an acoustic signal pass through so that an acoustic signal whose noise has been eliminated is generated in an output terminal Vt. CONSTITUTION:A sound volume change instruction is supplied to a terminal (a) of a pulse generating circuit PG by a manual operation as shown in a figure (a), and a sampling pulse and a clock pulse of a frequency exceeding an audio frequency as shown in sigures (b), (c) are generated from terminals (b), (c). A sample holding circuit SH is provided with an analog switch consisting of an MOS. FET and generates a noise as shown in a figure (f) when a state of the analog switch is switched at the time of a rise and a fall of the sampling pulse. In this case, since the sampling pulse is set in advance to a frequency exceeding of an audio frequency of >= about 20kHz, a frequency of the noise exceeds the audio frequency and does not become a trouble in an auditory sense.

Description

[Detailed description of the invention] The present invention relates to a volume adjustment device.

2. Description of the Related Art In recent years, audio equipment has adopted a volume adjustment device called an electronic volume, which uses a semiconductor analog switch. There are various types of semiconductor analog switches used in this electronic volume, but MOS-F
ET (metal oxide semiconductor field effect transistor) is the best.

Examples of analog switches using MOS3-F]lC'l' are shown in FIGS. 1 and 2.

In Fig. 1, the input terminal P1 is supplied with an acoustic signal.
Connect multiple resistors R1 to RN in series between and the ground terminal,
MOS/
Analog switches 80 to SN such as FKT or ``)'' are connected.By turning on any of the analog switches, the amount of attenuation of the acoustic signal is controlled and the volume is adjusted.

Figure 2 uses a DlA conversion circuit (digital/analog conversion circuit) D. An acoustic signal is input to the reference power supply terminal v1, and data specifying the volume is input to the terminals dl-dn.
This is to obtain an attenuated acoustic signal at the output terminal (2).

When MOB-FETs are used as analog switches as described above, there is a problem in that noise is generated as the analog switches open and close.

This noise is the MOB-FET gate source.

This is caused by capacitive coupling between the volume designating data and the analog signal line due to capacitance between the gate and drain, between the gate and the substrate, and occurs when the level of the data changes. This noise contains a large amount of audible frequency components and is therefore undesirable for the auditory sense, leading to a deterioration in the performance of high-performance audio equipment in particular.

Therefore, the present invention provides MOB/FE in the attenuation control circuit.
The present invention provides a volume adjustment device which eliminates noise caused by switching in a switcher circuit and a sample/hold circuit made up of T.

An embodiment of the present invention will be described below based on the drawings. Third
The figure shows a case where the present invention is applied to the one shown in FIG. 2, which uses a D/h conversion circuit as a control circuit.

In the figure, volume designation data inputted through a manual volume adjustment operation is supplied to input terminals t1 to tn of a latch circuit constituting a storage circuit. 8H is MOB
PG is a pulse generation circuit, and LF is a low-pass filter.

In the above configuration, a volume change command is supplied to the terminal α of the pulse generating circuit PG by manual operation as shown in FIG. Generate sampling pulses and clock pulses with a frequency higher than the frequency. The sample-and-hold circuit sH enters the hold mode when the sampling pulse is 1'', enters the sample mode when the sampling pulse is 60#, and repeats the sample-and-hold operation.

On the other hand, in the latch circuit, the above clock pulse is t'11I.
The timing of the clock pulse and the nogle width are set so that this latch operation is always performed when the sample-and-hold circuit SH is in the hold mode.

For example, if the data to the latch circuit changes from Dl to D2 as shown in Figure 4d, data D2 will be latched by the latch circuit with the first clock pulse after this change, and the data to the DlA conversion circuit will be latched by the first clock pulse after this change. changes.

Along with this change, the analog switch in the D/A converter circuit is switched, and the amount of attenuation is switched, and noise is generated as shown in FIG. 4C. However, at this time, the sample
Since the hold circuit 8H is in hold mode,
The above-mentioned noise is blocked and does not interfere with the sense of hearing as in the past.

However, the problem here is that the sample-and-hold circuit SH is equipped with an analog switch made of MOB-PET, and when the state of the analog switch changes at the rising and falling edges of the sampling pulse, as shown in FIG. It is to generate noise like this.

In the present invention, the sampling pulse is approximately 20KHz.
The frequency is set to be higher than the above audible frequency, so that the frequency of the noise is higher than the total audible frequency, so that it does not interfere with the sense of hearing.

In other words, the noise above the audible frequency included in the output of the sample-and-hold circuit 8H is attenuated by the low-pass filter LF, and by passing only the acoustic signal, an acoustic signal from which the noise has been removed is generated at the output terminal Vt. be.

Although the above embodiment describes the case where a D/A conversion circuit is used as the control circuit, the same applies to the one shown in Fig. 1 and other attenuation circuits using analog switches consisting of MOB-FETs. It can be applied to

In addition, the frequency of the sampling pulse is set above the audible frequency, but the audible frequency range varies from person to person.
When setting the above-mentioned frequency, it is sufficient to select a frequency that does not interfere with the auditory sense of the general public, and depending on the type of audio equipment, it may be possible to make the frequency 20 KHz or lower even.

As described above, according to the present invention, it is possible to eliminate the noise associated with switching, which has conventionally been a problem in volume control devices using switching circuits consisting of MOB-FETs, and particularly in high-performance audio devices. The volume can be adjusted without deteriorating performance.

[Brief explanation of the drawing]

Figures 1 and 2 are electric circuit diagrams showing an example of a fidget attenuation control circuit, Figure 3 is a block diagram showing an embodiment of the present invention, and Figure 4 is a time diagram for explaining the operation. It is a chart. D...Control circuit L...Memory circuit PG, °°...Pulse generation circuit and above Applicant Japan Precision Circuits Co., Ltd. Agent Patent attorney Tsutomu Mogami

Claims (1)

[Scope of Claims] It is equipped with a storage circuit that latches data specifying the volume using a clock pulse of a constant frequency, and a switching circuit that is made up of a MOS-F'ET that is switched based on the data in the storage circuit marked with ○. a control circuit that adjusts the amount of attenuation of the acoustic signal supplied to the MOS-FBT;
a sample-and-hold circuit equipped with a switching circuit consisting of; and a pulse generator that generates a sampling pulse with a frequency higher than an audible frequency so that the sample-and-hold circuit is in a hold state at the timing when data is latched in the storage circuit. A volume adjustment device consisting of a circuit.