JP2720261B2 - Digital cassette tape player - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital cassette tape reproducing apparatus, and more particularly, to a digital signal reproducing function for reproducing an audio signal recorded on a magnetic tape digitally, and an audio signal recorded as an analog signal as in the prior art. A digital compact cassette tape reproducing apparatus having a reproducing function for reproducing a signal, and a digital cassette reproducing apparatus such as a digital compact cassette tape recorder also having a recording function in addition to the above, and a reproduction audio signal of a digital signal reproducing system. The present invention relates to an improvement of a reproducing apparatus capable of improving the sound quality of a reproduction device.

[0002]

2. Description of the Related Art In the field of music records, compact disks (CDs) having a size of 12 cm have appeared as recording disks for reproducing digitally recorded audio signals, and are now widely used in place of records. . With its spread, so-called CD radio cassette recorders, component stereo devices, and various car audio devices are equipped with digital cassette tape reproducing devices for reproducing CDs.

On the other hand, in the field of cassette tapes,
A so-called DAT standard for recording an audio signal digitally on a magnetic tape and reproducing it has been proposed and put to practical use. It was thought that DAT recording / reproducing devices would soon spread from analog to digital even on DAT magnetic tapes like CDs. However, it has not yet reached a full-fledged diffusion period.

[0004] Separately, a so-called digital compact cassette tape recorder for performing digital recording on a conventional cassette tape for analog recording has been proposed.
A playback device that plays back an audio signal digitally recorded on a cassette tape, that is, a digital cassette tape playback device (hereinafter, referred to as a DCC player) reads a digital recording signal recorded on a cassette tape and plays it back as an audio signal. At the same time, it reads an analog recording signal recorded according to the conventional standard and reproduces it as an audio signal. In other words, the DCC player has both a digital recording signal reproducing function and an analog recording signal reproducing function. This has the advantage that the high performance and high functionality of the device by digital recording and the use of vast existing software by analog recording can be realized by one device.

FIG. 4 is a block diagram of a conventional portable DCC player which uses a headphone speaker connected thereto. 1 is a head unit, 2 is an analog recording signal reproducing circuit, 3 is a digital recording signal reproducing circuit, 5 is a switch, 6
Is a drive circuit, 8 is a headphone jack, and 9 is a headphone speaker that is inserted into the DCC player when used. The head unit 1 includes a magnetic head 1a for reproducing digital signals and a magnetic head 1b for reproducing analog signals.
Consists of The head 1a reads a recording signal of usually 8 to 10 bits digitally recorded on a cassette tape (not shown) and outputs a digital recording signal D as a digitally recorded audio signal. The head 1b reads a conventional audio recording signal recorded on a cassette tape in an analog manner and outputs the analog recording signal H.

The analog recording signal reproducing circuit 2 is provided with an equalizer circuit (composed of an amplifier 2a, a feedback circuit EQ, and the like) for correcting signal distortion caused by the magnetization characteristics of the recording medium and the like. Receiving the recording signal H, the signal H is corrected, an analog reproduction signal I is generated, and output to the switch 5.

The digital recording signal reproducing circuit 3 includes a head 1
a digital signal processing circuit 3b for receiving the digital recording signal D from the digital signal E and generating a digital signal E from the digital signal E; a D / A converter for generating an analog digital reproduction signal F from the digital signal E; And an attenuator 4 for generating a digital reproduction signal G having an analog value from F. The digital processing circuit 3b normally receives the digital recording signal D, demodulates it to the original digital value before recording, performs error correction processing and the like by digital processing, and generates a digital signal E. The D / A converter unit 3a receives the digital signal E, performs digital / analog conversion, removes a noise component due to quantization by a low-pass filter, and generates a reproduced signal F having an analog value. The attenuator 4 attenuates the amplitude level of the reproduction signal F to reduce the reproduction signal G
Is generated by converting the amplitude level of the output signal G of the digital recording signal reproduction circuit 3 into the amplitude level of the reproduction signal I output from the analog recording signal reproduction circuit, and further, the input signal J from the tuner or the like. This is for adjusting to correspond to the amplitude level.

The switch 5 is a slide type in this example, but may be another switch circuit. This means that the reproduced signals G, I and other input signals, for example, three signals G,
One of them is selected from I and J and output to the drive circuit 6 as a reproduction signal K. The drive circuit 6 power-amplifies the reproduced signal K by the power amplifier 6a, converts the amplified signal M into an AC drive signal N via the coupling capacitor 6c, and outputs the AC drive signal N to the headphone jack 8. Thus, the headphone speaker 9 connected to the headphone jack 8 is driven by the drive signal N.

A conventional DCC player having such a configuration includes an analog recording signal reproducing circuit 2 to reproduce an existing analog recorded audio signal, and a digital recording signal reproducing circuit 3 to provide a high sound quality. It also plays digitally recorded audio signals. When one of these reproduction outputs is selected by the switch 5, the final signal output to the speaker becomes either an analog recording audio signal or a digital recording audio signal. .

[0010]

By the way, the conventional DC
In the C player, an attenuator 4 is provided in the digital recording signal reproduction circuit 3 to attenuate the amplitude level of the reproduction signal F. This is provided in order to match the amplitude level of the reproduction signal G from the digital recording signal reproduction circuit 3 with the reproduction signal I from the conventional analog recording signal reproduction circuit 2 and the amplitude level of an input signal of a tuner or the like. I have.
Therefore, this will be described in detail. Since the amplitude level of the digital reproduction signal F is usually about 17 dB larger than the amplitude level of the analog reproduction signal I, the attenuator 4
The reproduction signal F is attenuated by 17 dB to obtain the reproduction signal G. By doing so, the portion after the drive circuit 6 can be used as a common portion, and the device can be downsized.

However, attenuating the reproduction signal F by 17 dB means that a part of the signal component is lost. In other words, even if a digitally recorded audio signal is reproduced and a high-quality audio signal is obtained, the S / N ratio is degraded. Therefore, there is a disadvantage that the original characteristics of the digital recording system cannot be sufficiently exhibited because the miniaturization of the apparatus is prioritized.

SUMMARY OF THE INVENTION An object of the present invention is to provide a DCC player capable of hardly lowering the original high sound quality performance of digitally recorded audio signals. It is another object of the present invention to provide a portable DCC player which can hardly reduce the original high sound quality performance of an audio signal recorded digitally. Still another object of the present invention is to provide a small-sized audio circuit that can amplify an audio signal without lowering the S / N ratio of the digital reproduction system in an audio circuit having two signal reproduction systems, a digital reproduction system and an analog reproduction system. DC
C player is to be provided.

[0013]

A feature of the DCC player of the present invention is that a gain of a power amplifier circuit is set so as to correspond to an amplitude level of an audio signal received from an analog signal reproducing system, and a digital signal reproducing system is set. Is selected, the signal of the digital signal reproduction system is input to the power amplifier circuit without attenuating. At this time, the output level of the power amplifier circuit is increased by increasing the amount of feedback that feeds back the output signal of the power amplifier circuit to the input side. To improve the S / N ratio in accordance with the output level of As a result, the high sound quality of the digital source is maintained. In this case, the input stage of the power amplifier circuit or the input stage of the preamplifier that receives an input signal from the digital reproduction system or the analog reproduction system has a dynamic range that does not cause distortion even when directly receiving the input signal of the digital reproduction system. It is assumed that it is constituted by a differential amplifier or the like.

A specific configuration thereof includes an analog recording signal reproducing circuit, a digital recording signal reproducing circuit, a switch circuit, and a drive circuit, wherein the analog recording signal reproducing circuit is a cassette tape on which analog recording is performed. , And amplifies and equalizes this signal to output an analog first reproduction signal. The digital recording signal reproducing circuit receives the recording signal of the audio signal from the cassette tape which has been digitally recorded, demodulates it to a digital value before recording, further performs digital / analog conversion, and removes a noise component by a filter. , And outputs a second reproduced signal. The switch circuit includes a switch and a circuit that outputs a selection signal in conjunction with the switch. The switch circuit receives a first reproduction signal and a second reproduction signal, and selectively switches the selected reproduction signal by the switch. And a selection signal indicating that one of the reproduction signals is selected in response to the selection. The drive circuit includes a power amplifier, and receives the selected reproduction signal and the selection signal, and lowers an amplification factor of the second reproduction signal with respect to the first reproduction signal when the selection signal is received. Thus, the output level is adjusted regardless of the amplitude level of these reproduced signals. As a result, a drive signal is output with an amplification factor that cancels out the level difference between these reproduction signals. The speaker is driven by this drive signal to output an audio signal to the outside.

Further, as another specific example of the present invention, an amplifier of the analog recording signal reproducing circuit, a power amplifier of the drive circuit, and a semiconductor element constituting a filter in the digital recording signal reproducing circuit are provided. One IC for both
It is the one that is accumulated inside.

[0016]

According to the DCC player of the present invention having the above-described configuration, when the first reproduced signal from the analog recording signal reproducing circuit, which is the same as the conventional one, is selected by the switch circuit, it is determined according to the value of the selected signal. As a result, the drive circuit amplifies the first reproduction signal with the same amplification factor as the conventional one and outputs it as a drive signal, so that it is compatible with the conventional audio signal analog reproduction apparatus.

On the other hand, when the second reproduction signal from the digital recording signal reproduction circuit is selected by the switch circuit, this second reproduction signal is not attenuated unlike the one shown in FIG. However, since the drive circuit cancels and amplifies the increase in the amplitude level, a drive signal in which the signal level difference between the first and second reproduced signals is canceled is output. Moreover, in the performance, the second reproduction signal is not undesirably attenuated on the way, and the amplification factor is reduced by feedback in the power amplification stage, so that the high sound quality of the digital recording system is not impaired. It is possible to maintain until the end. As a result, the influence caused by the coexistence of the circuits of the analog recording system is eliminated, and the high performance of the digital recording system can be sufficiently maintained and exhibited.

[0018]

FIG. 1 is a block diagram of a portable DCC player having only a reproduction circuit according to an embodiment to which the DCC player of the present invention is applied, and FIG. 2 is a drive circuit of another embodiment of the DCC player of the present invention. FIG. 3 is a block diagram mainly showing a drive circuit of another configuration in another embodiment of the DCC player of the present invention. The difference between the DDC player shown in FIG. 1 and the DDC player shown in FIG. 4 is that a switch circuit 50 is provided instead of the switch circuit 5 and a drive circuit 7 is provided instead of the drive circuit 6. Also,. Although a digital recording signal reproducing circuit 30 is provided instead of the digital recording signal reproducing circuit 3, the difference between them is that the latter is not provided with the former attenuator 4. Other components are the same as those in FIG. 4, and similar components are denoted by the same reference numerals. Therefore, their explanation is omitted.

The D / A converter section 3a of the digital recording signal reproducing circuit 30 has a digital processing circuit 3 as in FIG.
Receiving the digital signal E from b, digital / analog conversion is performed by a D / A converter 3c, and a noise component caused by quantization is removed by a low-pass filter 3d to generate a reproduced signal F having an analog value. Since the attenuator 4 existing in the conventional circuit has been removed, the reproduced signal F is output to the switch circuit 50 as it is or via a coupling circuit or the like.
The reproduction signal F may reach the switch circuit 50 via a circuit including a capacitor, a fixed resistor, a variable resistor, or the like for coupling or protection and adjustment.

Similarly, the output of the analog recording signal reproducing circuit 2 is output to the switch circuit 50. Note that this output may also be passed through a capacitor or a resistor for coupling or protection before the reproduction signal I reaches the switch circuit 50, as described above. The switch circuit 50 includes, for example, a slide-type switch 50a and an output circuit 50b that outputs a switching signal P for switching the amplification factor of a subsequent-stage amplifier in conjunction with the switch 50a. The switch circuit 50 receives the reproduced signals F and I and other input signals, for example, three signals F, I and J of J. And the switch 50
One is selected by a, and the selected one is output as a reproduction signal K. At the same time, as the switching signal P having a predetermined value corresponding to this selection, for example, one of a HIGH level signal and a LOW level signal is output from the output circuit 50b.

The drive circuit 7 includes a switch circuit 71,
The input stage comprises a power amplifier 7a composed of an operational amplifier of a differential amplifier circuit. The amplifier 7a power-amplifies the reproduction signal K, and the amplified signal M is coupled to a coupling capacitor 7c.
Through the headphone jack 8
To the headphone speaker 9 connected to the speaker. However, at this time, depending on whether the reproduction signal F side or the reproduction signal I side is selected as the reproduction signal K, the amplitude level of the reproduction signal K which is the input signal of the power amplifier 7a becomes
When a recorded signal for a standard amplitude audio signal is reproduced, the difference is almost 17 dB. Here, it is assumed that the amplification factor of the power amplifier 7a is set so as to generate a standard output when the reproduction signal I receives a signal of the standard level amplitude. If the reproduced signal F can be amplified as it is when received, the output signal will increase by 17 dB because the input signal has increased by 17 dB, an imbalance will occur in the output, and the output must be adjusted. If the amplifier does not have the ability to amplify as it is, the output will be distorted. The first stage of the power amplifier 7a is
As described above, the differential amplifier circuit has a high input impedance and a large dynamic range.
Even if the input signals differ by 17 dB, there is almost no distortion at the input stage. Conversely, the power amplifier 7a is selected such that the input stage is an amplifier having such characteristics.

By the way, in order to avoid the above-mentioned problem, the switch 71 is turned on / off according to the value of the switching signal P.
FF "changes the value of the resistor circuit that determines the amplification factor. In this way, the amplification factor in the power amplifier 7a is increased or decreased by an amount corresponding to the difference between the amplitude levels. That is, the power amplifier 7a composed of an operational amplifier Feedback resistors Rf1 and Rf connected in parallel to determine the amplification factor
A switch 71 is inserted in series with the resistor Rf2 among the resistor Rf2 and the resistor Rs on the reference side, and when the reproduction signal F is selected as the input signal, the switch 71 is turned "ON" by the switching signal.
The amount of feedback increases, and the amplification factor decreases by 17 dB. When any other input signal or reproduction signal is selected, the switch 71 is turned "OFF".
As a result, when the reproduction signal F is received, the amplification factor is reduced by about 17 dB, and the reproduction signal K is amplified. Since the reduction of the amplification factor is performed by increasing the amount of feedback, the S / N ratio of the signal of the high-quality digital signal reproduction system is improved as compared to the state before the amplification factor was reduced.

In this way, a drive signal in which the signal level difference between the reproduction signals F and I has been canceled is output, and the output level is substantially maintained regardless of which reproduction signal is selected. . In this type of portable player, the adjustment of the sound volume may be performed by providing a variable resistor for adjusting the sound volume on the output side. May be provided with a variable resistor to adjust the volume.

FIG. 1 shows an example of a configuration for changing the amplification factor of the power amplifier 7a of the drive circuit 7 by switching the resistance value of the resistance circuit by the switch 71 for ease of explanation. FIG. 2 is a block diagram showing a drive circuit having another configuration for switching the amplification factor of the power amplifier and its peripheral circuits. In FIG. 2, reference numeral 60 denotes a variable resistor (VR), and reference numeral 72 denotes a drive circuit. In this example, the variable resistor 60 is for setting the output volume of the speaker. This variable resistor 6
The amplitude level of the reproduction signal K is changed according to 0 and output to the drive circuit 72 as a signal L. In the drive circuit 72, a switch circuit 72b for switching the amplification factor is configured by a transistor or the like, and is incorporated in a power amplifier 72a configured by an operational amplifier. In this example, the switch circuit 72b is inserted before the inverting input terminal of the differential amplifier circuit at the input stage. The amplification factor is determined by the bias circuit A of the amplification factor determination resistors Rfa and Rsa and the bias circuit B of the amplification factor determination resistors Rfb and Rsb, respectively. This is a selection circuit for selecting a circuit. For example, when the reproduction signal I is selected, the bias circuit A is selected and the amplifier 72a is selected.
Is set to a high amplification factor to generate an appropriate output. When the reproduction signal F is selected, the bias circuit B
Is selected and the amplifier 72a is set to a low amplification factor to generate an appropriate output. By doing so, the drive circuit 72 can be easily integrated, which is effective for downsizing the device.

The position of the variable resistor 60, that is, by the time the reproduced signal K is input to the drive circuits 7 and 72,
In addition to the variable resistor, a preamplifier, a graphic equalizer, a heavy bass emphasis circuit, or the like may be inserted. further,
The variable resistor 60 may be an electronic volume circuit. Further, a preamplifier may be inserted at the position of the variable resistor 60 instead of or together with the variable resistor 60. When a preamplifier is inserted at this position, the input stage of the power amplifier may be configured with any circuit as long as the input stage is a differential amplifier circuit having a large dynamic range.

FIG. 3 shows a drive circuit 7 of still another configuration.
3 shows an example. This is to provide a power amplifier that outputs a drive signal M to the power amplifier 72a of the drive circuit 72 having the configuration of FIG. 2 and provide a power amplifier 73a and a power amplifier 73e to receive and output a stereo signal. . That is, in addition to the reproduction signal K as the left and right stereo demodulated signals, a reproduction signal K 'is input, and a drive signal M' corresponding to the reproduction signal K 'is output.

The power amplifier 73a receives the reproduction signal K and generates and outputs a drive signal M. Power amplifier 73e receives reproduction signal K ', generates and outputs drive signal M'. The amplifier 73b receives a constant bias voltage Q, amplifies the power, and outputs the amplified voltage to the feedback signal line 73d of the drive signal M. As a result, a predetermined constant voltage is supplied to the signal line fed back from the speaker as the operating point voltage of the drive signal M.
As a result, since the speaker can be directly driven, the coupling capacitor 7c used in the drive circuit 7 in the configuration of FIG. 1 becomes unnecessary. In this case, the amplifier 73b for applying the operating point voltage is also used for the drive signals M and M '. This can operate even if only one of the circuits is used.

Although not shown, the amplifier 2a of the analog recording signal reproduction circuit 2 and the amplifier 7a (or 72a, 73a, 7a) of the drive circuit 7 (or 72, 73) are used.
3b) are integrated in one IC, and furthermore, the amplifier 2a of the analog recording signal reproducing circuit 2 and the amplifier 7a (or 72) of the drive circuit 7 (or 72, 73).
a, 73a, 73b) and the semiconductor element of the filter 3d of the digital recording signal reproducing circuit 3 are integrated in one IC, so that the device can be downsized.

It should be noted that the speaker in the embodiment is not limited to the headphone speaker. Further, an amplifier for equalizing the analog recording signal reproduction circuit in the embodiment, a power amplifier of the drive circuit,
By integrating the semiconductor element of the filter of the digital recording signal reproduction circuit together with the semiconductor element in one IC, it is possible to realize a compact device more suitable for a portable DCC.

[0030]

As can be understood from the above description, in the present invention, the attenuator for lowering the signal level is removed from the digital recording signal reproducing circuit, and the amplification factor of the drive circuit is changed according to the reproducing signal level. Change
By adopting a configuration that maintains the compatibility of the sound output level when reproducing digital recording and when reproducing analog recording, the excellent S / N ratio of the digital recording system can be output without deteriorating to the end. Can be played. Therefore, when the digital recording signal reproduction is selected, the original performance of the digital recording system is sufficiently exhibited without being affected by the coexisting analog recording system, and the noise based on the reproduction circuit itself is hardly audible. Is suppressed until. Furthermore, by adopting a configuration in which the number of external components is reduced, the integration rate can be increased, and the device can be made smaller. As a result, a compact and high-performance DCC player can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram of a portable DCC player having only a reproducing circuit according to an embodiment to which a DCC player of the present invention is applied.

FIG. 2 is a block diagram focusing on a drive circuit in another embodiment of the DCC player of the present invention.

FIG. 3 is a block diagram mainly showing a drive circuit of another configuration in another embodiment of the DCC player of the present invention.

FIG. 4 is a block diagram of a portable DCC player having only a reproducing circuit, which is one of the conventional DCC players.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Head 2 ... Analog recording signal reproduction circuit 3 ... Digital recording signal reproduction circuit 4 ... Attenuator 5 ... Switch 7 ... Drive circuit 8 ... Headphone jack 9 ... Headphone speaker 50 ... Switch circuit 60 ... Variable resistance circuit 70 ... Drive circuit 71 ... Switch 72: Drive circuit 73: Drive circuit

Claims (2)

(57) [Claims] An analog recording signal reproducing circuit that receives the analog recording signal and outputs a first audio reproduction signal when an analog recording signal is read from a cassette tape; and reads a digital recording signal from the cassette tape. A digital recording signal reproducing circuit that receives the digital recording signal, demodulates the digital recording signal into a digital value at the time of recording, performs digital / analog conversion and outputs a second audio reproduction signal, and an output of the analog recording signal reproduction circuit. And a switch circuit that receives and outputs an output from the digital recording signal reproducing circuit, selects and outputs one of them, and outputs a signal indicating that one of the outputs is selected in response to the selection; and the switch circuit. And when the output of the digital recording signal reproducing circuit is selected, the feedback of the amplifier A drive circuit that outputs a drive signal to a speaker by decreasing the amplification factor by increasing the amount of distortion, wherein the drive circuit amplifies the output signal from the digital recording signal reproduction circuit without substantially distorting it. A digital cassette tape reproducing device, characterized in that: 2. A signal indicating that either one of the outputs is selected is a switching signal for switching an amplification factor of the amplifier, and the drive circuit includes a reproduction signal selected by the switch circuit and the switching signal. And a first amplifier for amplifying the reproduction signal selected by the switch circuit and outputting a drive signal at an amplification factor according to the value of the switching signal, and receiving a constant bias voltage and amplifying the same. A second operating point voltage for outputting a constant operating point voltage to the feedback signal line of the drive signal;
2. The digital cassette tape reproducing apparatus according to claim 1, further comprising an amplifier.