JP3378844B2 - A / D conversion circuit and audio signal recording device including the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an A / D conversion circuit for converting an analog signal into a digital signal, and an audio signal recording device equipped with the A / D conversion circuit.

[0002]

2. Description of the Related Art In recent years, an IC recorder capable of compressing and recording an audio signal in a memory card has been developed using a memory card having a built-in IC as a signal recording medium. In such an IC recorder, an analog audio signal input from a microphone is supplied to an A / D converter to convert the analog audio signal into a digital audio signal, and the resulting digital audio signal is compressed to a memory card. To record.

Generally, an A / D converter receives three clocks having different frequencies, that is, a master clock MCK, an audio serial data clock SCLK, and an input / output channel clock LRCK when the power is turned on,
First, the calibration for canceling the DC offset is executed. FIGS. 4A, 4B, and 4C show these three types of clocks. In the illustrated example, the master clock MCK is 2,048 MHz, the audio serial data clock SCLK is 512 KHz, and the input / output channel clock LRCK is 8 KHz. Is. As shown in the figure, the calibration is completed by inputting, for example, only 8,224 pulses of the input / output channel clock LRCK, and then the data sampling which is the original operation of the A / D converter is started. A / like this
As the D converter, for example, "AK451 manufactured by Asahi Kasei Co., Ltd.
8 ”is known.

[0004]

By the way, in a magneto-optical disc player, such as a magneto-optical disc player, various servo operations, TOC reading, and the like are performed when a signal is recorded or reproduced on a recording medium. A certain waiting time is required from the beginning to the actual recording operation, but since the user is aware of the need for this waiting time, some delay in the start of recording is a major operational problem. There is no such thing.

However, it is generally recognized that in an audio signal recording device such as an IC recorder which is not equipped with a mechanical mechanism (pickup device) for recording a signal, the recording operation can be performed immediately by turning on the power. However, in spite of that, a waiting time from the power-on to the start of recording due to the above-mentioned calibration has been a serious problem in operation feeling. For example, when the sampling frequency of the A / D converter, that is, the frequency of the input / output channel clock LRCK is 8 KHz, it takes more than 1 second to calibrate as shown in FIG. 4, which is fatal in the IC recorder. Problem.

An object of the present invention is to provide an A / D conversion circuit capable of shortening the waiting time due to calibration without shortening the recordable time on a recording medium, and an audio signal recording device having the same. That is.

[0007]

In order to shorten the above-mentioned calibration period in the A / D conversion circuit, the sampling frequency may be raised, which improves the sound quality. However, since the recordable time of the IC memory card is shortened due to the increase of the bit rate, it is difficult to carry out with an IC recorder used for recording a conference or the like. Therefore, the present invention solves the above-mentioned problems by increasing the sampling frequency at the time of calibration to shorten the calibration period and returning the sampling frequency to the original proper value in the subsequent data sampling.

That is, the A / D conversion circuit according to the present invention is supplied with a control clock of a predetermined frequency for data sampling, and an A / D converter for converting an analog signal into a digital signal, and the control clock. Generate and A /
And a control circuit for supplying the D converter, wherein the control circuit sets the frequency of the control clock higher than the predetermined frequency in the calibration for canceling the offset of the A / D converter, and ends the calibration. In the subsequent data sampling, the frequency of the control clock is set to the predetermined frequency.

The audio signal recording apparatus according to the present invention comprises the above A / D conversion circuit of the present invention.
The audio signal obtained from the / D conversion circuit is recorded on the recording medium.

In the above A / D conversion circuit and audio signal recording apparatus of the present invention, since the frequency of the control clock and the calibration period are inversely proportional, the frequency of the control clock is set higher than the predetermined frequency in the calibration. By doing so, the calibration period is shortened as compared with the conventional case. Further, in the subsequent data sampling, the frequency of the control clock is set to the same predetermined frequency as the conventional one, so that the recordable time for a recording medium such as an IC memory card is not shortened, and for example, for recording a conference, etc. It can be implemented in the IC recorder used.

[0011]

According to the A / D conversion circuit and the audio signal recording apparatus including the same according to the present invention, it is possible to shorten the waiting time due to the calibration without shortening the recordable time on the recording medium. Therefore, a good operation feeling can be obtained.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an embodiment in which the present invention is applied to an IC recorder will be specifically described with reference to the drawings. FIG. 1 shows the main configuration of an IC recorder according to the present invention, in which a memory card (8) as a recording medium can be loaded. The analog audio signal input from the microphone (6) is amplified by the amplifier AMP (5) and then A /
It is converted into a digital audio signal through the D converter (4). The digital audio signal obtained from the A / D converter (4) is supplied to the digital signal processing circuit DSP (3) and subjected to signal processing such as compression, and then the memory card controller (7) performs the memory card (8). Written in.

The CPU (1) comprises an oscillator (2), and based on a reference clock of 16.38 MHz obtained from the oscillator (2), a master clock M of 2.048 MHz is provided.
CK, an audio serial data clock SCLK of 512 KHz, and an input / output channel clock LRCK of 8 KHz are generated and supplied to the A / D converter (4).
The A / D converter (4) performs calibration and sampling based on these clocks and converts an analog audio signal into a digital audio signal.

FIGS. 3A, 3B and 3C show the master clock MCK, the audio serial data clock SCLK and the input / output channel clock LRCK in the calibration and sampling. In calibration, the master clock MCK is 12.
288MHz, audio serial data clock SC
LK is 3.072MHz, input / output channel clock L
RCK is set to 48 KHz. Each of these frequencies is a high frequency which is 6 times as high as the frequency of the conventional control clock shown in FIG. 4, whereby the calibration period is ⅙ of the conventional period, that is, from 1.028 seconds to 0.1.
It will be shortened to 713 seconds.

After the calibration is completed, the master clock MCK is set to 2.048 MHz, the audio serial data clock SCLK is set to 512 KHz, and the input / output channel clock LRCK is set to 8 KHz, which are returned to the same low frequencies as in the conventional case. As a result, the same sound quality and recordable time as before can be obtained.

FIG. 2 shows the control clock switching operation by the CPU (1). In step S1, it is determined whether or not the power of the main body is turned on, and if the result is YES, the process proceeds to step S2 and the power of the A / D converter is turned on. Then, in step S3, control clocks (master clock MCK, audio serial data clock SCLK, and input / output channel clock L
RCK) is set to the above high frequency, and A / D
Output to converter (4). In response to this, the A / D converter (4) starts calibration.

Thereafter, in step S4, it is determined whether or not a predetermined time required for executing the calibration has elapsed. If the determination is YES, the process proceeds to step S5, and the control clock (master clock MCK, audio The serial data clock SCLK and the input / output channel clock LRCK) are respectively set to the above low frequencies and output to the A / D converter (4). In response to this, the A / D converter (4) starts sampling and converts the analog audio signal into a digital audio signal.

According to the above-mentioned IC recorder of the present invention, recording is possible after the A / D converter (4) is powered on while maintaining the recordable time for the memory card (8) at the same length as before. It is possible to significantly reduce the waiting time until the start, and it is possible to obtain a good operational feeling.

The constitution of each part of the present invention is not limited to the above-mentioned embodiment, and various modifications can be made within the technical scope described in the claims. For example, the present invention is not limited to the IC recorder and can be implemented in various audio signal recording devices. As the control clock, the master clock MCK and the audio serial data clock SCLK described above are used.
In addition to the input / output channel clock LRCK, any other type of clock may be used as long as it defines the sampling frequency.

[Brief description of drawings]

FIG. 1 is a block diagram showing a main configuration of an IC recorder according to the present invention.

FIG. 2 is a flowchart showing a control clock switching operation of a CPU.

FIG. 3 is a time chart showing a control clock at the time of calibration and sampling.

FIG. 4 is a time chart showing a control clock at the time of conventional calibration and sampling.

[Explanation of symbols]

(1) CPU (2) Oscillator (3) DSP (4) A / D converter (5) Amplifier (6) Microphone (7) Memory card controller (8) Memory card

Continuation of the front page (56) Reference JP-A-7-221645 (JP, A) JP-A-6-90170 (JP, A) JP-A-57-138218 (JP, A) JP-A-9-331258 (JP , A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H03M 1/00-1/88

Claims (2)

(57) [Claims] 1. An A / D converter which receives a control clock having a predetermined frequency for data sampling and converts an analog signal into a digital signal, and a control which generates the control clock and supplies the control clock to the A / D converter. In the A / D conversion circuit including a circuit, the control circuit is
In the calibration for canceling the offset of the D converter, the frequency of the control clock is set higher than the predetermined frequency, and in the data sampling after the end of the calibration, the frequency of the control clock is set to the predetermined frequency. An A / D conversion circuit characterized by: 2. An audio signal recording apparatus capable of recording an audio signal obtained from an internal A / D conversion circuit on a recording medium, wherein the A / D conversion circuit has a control clock of a predetermined frequency for data sampling. Is supplied to the A / D converter for converting an analog signal into a digital signal, and a control circuit for generating the control clock and supplying the control clock to the A / D converter. In the calibration for canceling the offset, the frequency of the control clock is set higher than the predetermined frequency, and in the data sampling after the calibration is completed, the frequency of the control clock is set to the predetermined frequency. Audio signal recording device.