JPH05344085A - Stereo receiver and its stereo demodulator - Google Patents

Abstract

PURPOSE:To provide a stereo demodulation circuit compatible with a digital signal with low distortion. CONSTITUTION:This receiver is provided with 1st and 2nd A/D converters 14L, 14R to be fed with a stereo multiplex signal SST, a clock pulse forming circuit 17 forming 1st and 2nd clock pulses PCL, PCR whose frequency is a subcarrier frequency and whose phases differ from each other. The 1st and 2nd clock pulses PCL, PCR are fed to the 1st and 2nd A/D converters 14L, 14R as their clock pulses respectively. A left channel digital audio signal L and a right channel digital audio signal R are obtained from the 1st and 2nd A/D converters 14L, 14R. Moreover, an FM tuner circuit having the demodulation circuit and a tuner circuit for DAB broadcast are integrated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stereo receiver such as an FM receiver and a stereo demodulation circuit thereof.

[0002]

2. Description of the Related Art In the current FM stereo broadcasting, as shown in FIG. 4, SST = (L + R) + (LR) cos (2πfsct) + SPL (1) L: left of stereo Channel audio signal R: Stereo right channel audio signal SPL: Pilot signal. SPL = pcos (πfsct) fsc: Subcarrier frequency. The stereo multiplexed signal SST indicated by fsc = 38 kHz p = 10% is transmitted.

That is, the sum signal (L + R) of the signals L and R
Is the main channel signal, and the difference signal (L-
The signal obtained by balance-modulating the subcarrier signal by R) is used as the subchannel signal, and these signals are pilot signals SSP.
At the same time, they are multiplexed and transmitted.

Therefore, there are a switching system and a matrix system as a method of demodulating the signals L and R from the stereo multiplexed signal SST. However, the switching system is generally used because of its simple structure. A stereo demodulation circuit is used.

FIG. 5 shows the switching type stereo demodulation circuit. That is, the stereo multiplexed signal SST
Is supplied to the switching circuit 2 through the terminal 1 and is also supplied to the switching signal forming circuit 6 to form a pulse PSW synchronized with the pilot signal SSP at the frequency fsc (= 38 kHz). To the switching circuit 2 according to the pulse PSW.

In this case, in order to simplify the equation (1), if the pilot signal SSP is ignored, the equation (1) becomes: SST = (L + R) + (LR) cos (2πfsct). ·············································································· (3) is SST = (L + R) + (LR) × 1 = It becomes 2L.

In the equation (2), when cos (2πfsct) =-1 (4), SST = (L + R) + (LR) × (-1) = 2R Becomes

Therefore, when the switching circuit 2 is switched by the pulse PSW, the signal L is taken out from one output terminal of the switching circuit 2 each time the equation (3) is satisfied, and the other output terminal is The signal R is taken out every time the equation (4) is satisfied. That is, the audio signals L and R are demodulated and extracted from the switching circuit 2.

In this case, however, the actual switching circuit 2 is constituted by a double-balance type multiplying circuit as shown in FIG. 6, for example, to facilitate signal processing and IC integration. Then, the balanced stereo multiplexed signal SST is supplied to the transistors Q1 and Q2, and the balanced pulse PSW is supplied to the transistors Q3 to Q6 to extract the signals L and R.

Therefore, the switching pulse PSW at this time has a duty ratio of 50% as shown in FIG. When the stereo multiplexed signal SST is switched by such a pulse PSW, (3)
At the time other than the time when the formula or the formula (4) is obtained, the signal SST
Is taken out as a demodulation output, the demodulated signals L and R include crosstalk components ΔR and ΔL.

Therefore, the signals L and R including the crosstalk components ΔR and ΔL from the switching circuit 2 are supplied to the crosstalk cancel circuits 3L and 3R, and the signals L and R are supplied.
The crosstalk components ΔR and ΔL included in are removed.

The crosstalk components ΔR and ΔL
The signals L and R from which the noises have been removed are supplied to the filters 4L and 4R, the signal components of the pulse PSW are removed, and de-emphasis is performed to obtain the original audio signals L and R. R is taken out to the terminals 5L and 5R.

[0013]

By the way, in general, a transistor cannot operate as a complete switching element and exhibits a non-linear characteristic. Therefore, the above-mentioned switching circuit 2 also exhibits non-linear characteristics with respect to the stereo multiplexed signal SST, and the demodulated signals L and R have various distortions due to the non-linear characteristics.

Further, the filters 4L and 4R are required to remove the signal component of the pulse PSW, etc. If the filters 4L and 4R are provided, the signals L and R are deteriorated in phase and frequency characteristics. Will end up.

The present invention intends to solve the above problems and further provide a stereo demodulation circuit compatible with the digitization of audio equipment.

[0016]

Therefore, in the present invention, when the reference numerals of the respective parts correspond to the embodiments described later, the sum signal (L + R) of the left and right channel audio signals L and R is the main channel. In the stereo demodulation circuit of the receiver for receiving the stereo multiplexed signal SST, which is a signal, and which is a signal obtained by balance-modulating the subcarrier signal by the difference signal (LR) of the audio signals L and R, is received in the stereo demodulation circuit of the receiver. A clock for forming first and second A / D converters 14L, 14R to which the multiplexed signal SST is supplied and first and second clock pulses PCL, PCR having different phases at the frequency fsc of the subcarrier signal. A pulse forming circuit 17 is provided to supply the first and second clock pulses PCL and PCR to the first and second A / D converters 14.
L and 14R are supplied as their clock pulses respectively, and the first and second A / D converters 14L and 14L are supplied.
The digital audio signal L of the left channel and the digital audio signal R of the right channel are obtained from R.

[0017]

In the A / D converters 14L and 14R, the audio signals L and R are stereo demodulated from the stereo multiplexed signal SST and at the same time A / D converted to output digital audio signals L and R.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, 11 to 13 are FM tuner circuits, 11 is an FM front end circuit, 12 is an FM intermediate frequency amplifier, 13 is an FM demodulation circuit, and the above-mentioned stereo multiplexing from the demodulation circuit 13 is carried out. The signal SST is output.

Then, this stereo multiplexed signal SST is
The clock pulses are supplied to the A / D converters 14L and 14R, and are also supplied to the clock pulse forming circuit 17 constituted by a PLL, for example, to form clock pulses PCL and PCR as shown in FIG. That is, these clock pulses PCL and PCR have a frequency fsc (= 38 kHz), are synchronized with the pilot signal SSP, and have sufficiently narrow pulse widths. If the phases of the pulse PCL and the pulse PCR are different from each other by 180 °. Has been done. That is, the pulse PCL is
A pulse P is formed every time the above equation (3) is satisfied.
CR is formed every time the equation (4) is satisfied.

Then, the clock pulses PCL and PCR are supplied to the A / D converters 14L and 14R as clocks for sampling and holding and A / D conversion.

Therefore, in the A / D converter 14L, the signal SST is sampled and held by the clock pulse PCL and is A / D converted every time the equation (3) is satisfied. From the D converter 14L, the A / D converted digital audio signal L is output.

In the A / D converter 14R, the signal SST is sampled and held by the clock pulse PCR and is A / D converted at each time when the equation (4) is satisfied. D converter 1
Digital audio signal R that has been A / D converted from 4R
Is output.

That is, the A / D converters 14L, 14
At R, the audio signals L and R are demodulated from the stereo multiplexed signal SST, and the signals L and R are A /
It will be D-converted.

Thus, the A / D converters 14L, 14
From R, for example, 16-bit / 1-sample digital audio signals L and R are extracted at a sampling rate of a frequency of 38 kHz (= fsc).

In this case, the clock pulses PCL, PCL
CR pulse width, that is, A / D converter 14L, 1
Since the time required for sampling and holding the signal SST in 4R can be made sufficiently smaller than the period of the pulses PCL and PCR, the digital audio signals L and R from the A / D converters 14L and 14R can be obtained. Includes almost no crosstalk components ΔR and ΔL, or the crosstalk components ΔR and ΔL are small enough to be ignored even if included.
By the way, when the pulse widths of the pulses PCL and PCR are 1/12 of the cycle, that is, when the pulse width is 30 ° with respect to the cycle of 360 °, the crosstalk becomes −45 dB.

Then, the A / D converters 14L, 1
The digital audio signals L and R from the 4R are supplied to the digital filters 15L and 15R to remove unnecessary signal components, deemphasized, and then taken out to the terminals 16L and 16R.

Although not shown, the digital audio signals L and R taken out to the terminals 16L and 16R, together with digital audio signals from a CD player, DAT, DAB tuner (digital audio broadcasting tuner), etc. The digital audio signal is supplied to the D / A converter device and selected (this selection is made by the user's switching operation), and the selected digital audio signal is D / A.
A converted and taken out. Alternatively, it is supplied to the D / A converter to convert the analog audio signals L and R into D / A.
To be converted.

Thus, according to the present invention, the stereo multiplexed signal SST is supplied to the A / D converters 14L and 14R, and the A / D conversion is performed at the subcarrier frequency fsc of the stereo multiplexed signal SST. Therefore, in the A / D converters 14L and 14R, the signal S
It is possible to demodulate the audio signals L and R from the ST and at the same time obtain the digitized audio signals L and R.

In this case, in particular, according to the present invention, since it is not necessary to perform switching by directly A / D converting the stereo multiplexed signal SST, various distortions caused by the switching may occur. Absent.

Moreover, the digital filters 15L and 15R
Because of the digital processing, since the audio signals L and R are D / A-converted in the subsequent stage, it is possible to obtain characteristics in which the phase around and the frequency characteristics are not deteriorated, and the excellent audio signals L and R can be obtained. Obtainable.

Further, the A / D converters 14L, 14R
The pulse width of the clock pulses PCL and PCR supplied to
Since it can be made sufficiently smaller than the cycles of the pulses PCL and PCR, the digital audio signals L and R from the A / D converters 14L and 14R hardly include crosstalk components ΔR and ΔL. Even if it is included, it becomes negligibly small, and the crosstalk cancel circuit can be omitted.

Since the audio signals L and R from the FM tuner can be obtained in the state of digital signals,
Even in a single D / A converter device that selects a digital audio signal from a CD player, DAT, DAB tuner, etc. and performs D / A conversion to an analog audio signal, the audio signals L, R from the FM tuner are also included.
Can also handle.

In that case, the D / A converter device only needs to select the input digital signal in accordance with the user's operation and then D / A convert and output the selected digital signal. The processing unit can be clearly separated, and an extremely high-quality analog audio signal can be output.

FIG. 3 shows an example of a tuner device in which an FM tuner and a DAB tuner are integrated. DAB
Broadcasting includes BS broadcasting and CS broadcasting carried out in Japan, and DSR broadcasting carried out in Germany. Generally, the modulation format of the main carrier signal by digital audio data is PSK modulation or digital audio data. Sampling frequency is 32k depending on the mode
Hz or 48 kHz. Also, digital audio data may be scrambled for a fee.

In FIG. 3, reference numerals 21 to 24 denote DAB receiving systems thereof, in which a DAB signal from a broadcasting satellite is received by a parabolic antenna and a frequency converter (neither is shown) and a predetermined first signal is received. The signal is down-converted to an intermediate frequency, the down-converted signal is supplied to the front end circuit 21 and frequency-converted into a second intermediate frequency signal, and this signal is supplied to the PSK demodulation circuit 23 through the intermediate frequency amplifier 22 for demodulation. A data string of digital audio data is extracted from the circuit 23.

Then, this data string is supplied to the decoder 24 for error correction and error correction, and in some cases, descramble processing for canceling the scramble processing is performed, and the digital audio data is output from the decoder 24. Are extracted as a serial signal S24 of a predetermined format.

The signal S24 is sent to the switch circuit 31.
And a clock pulse P24 synchronized with the signal S24 from the decoder 24.
24 is supplied to the switch circuit 35. Further, the switch circuits 31 and 35 are connected in the state shown in the figure when receiving a DAB broadcast by the output of the band changeover switch 38.

Thus, when receiving a DAB broadcast, the signal S24 from the decoder 24 is supplied to the digital filter 32 through the switch circuit 31 to remove unnecessary signal components, and then supplied to the D / A converter 33 to provide an analog audio signal. The signals L and R are D / A converted into L and R, and these signals L and R are taken out to terminals 34L and 34R. further,
The signal S24 from the switch circuit 31 is the converter circuit 3
The data string is supplied to 6 and converted into a data string of a predetermined format, and this data string is output to the digital output terminal 37.

At this time, the clock pulse P24 is
The circuit 32, 3 is taken out through the switch circuit 35.
3 and 36 are supplied as their clocks.

Further, the FM receiving systems 11 to 17 are constructed in the same manner as described above, and the digital audio signals L and R are taken out from the A / D converters 14L and 14R, and
These signals L and R are supplied to the synthesizing circuit 18 to generate the signal S24.
Is converted into a serial signal S18 similar to the above, and this signal S18 is supplied to the switch circuit 31.

Further, the clock pulse P from the forming circuit 17
A clock pulse P17 similar to CL and PCR is taken out, and this pulse P17 is supplied to the switch circuit 35. Then, the switch circuits 31 and 35 are connected to the states opposite to those shown in the drawing when receiving the FM broadcast by the output of the band changeover switch 38.

Thus, during reception of FM broadcasting, the signal S18 from the synthesis circuit 18 is supplied to the digital filter 32 through the switch circuit 31 to remove unnecessary signal components, and then supplied to the D / A converter 33 for analog audio. The signals L, R are D / A converted, and these signals L,
R is taken out to the terminals 34L and 34R. Further, the signal S18 from the switch circuit 31 is supplied to the converter circuit 36 and converted into a data string of a predetermined format,
This data string is output to the terminal 37.

At this time, the clock pulse P17 is
The circuit 32, 3 is taken out through the switch circuit 35.
3 and 36 are supplied as their clocks. The clock frequency at the time of FM reception is 38 kHz, which is 32 kHz of the clock frequency at the time of DAB broadcasting.
Since it is in the middle of 48 kHz, the clock frequency at the time of FM reception will not be too high or too low and will not interfere with D / A conversion.

Thus, according to this tuner device, D
Since it is possible to receive both AB broadcasts and FM broadcasts, usability is improved. That is, when the output signal of this tuner device is supplied to the control amplifier in the subsequent stage, it may be either the audio signals L and R of DAB broadcasting which is digital broadcasting or the audio signals L and R of FM broadcasting which is analog broadcasting. , Only one of the terminals 34L and 34R or the terminal 37 is used, and it is not necessary to connect digital signal lines for DAB broadcasting and analog signal lines for FM broadcasting. , Easy to connect. Moreover, there is no possibility that a strange signal loop is formed between the tuner device and the control amplifier in the subsequent stage.

Moreover, at that time, the sound quality of the FM broadcast is free from the distortion caused by switching as described above, and the phase characteristics and frequency characteristics are also good. Furthermore, the digital filter 32, the D / A converter 33, and the converter circuit 36 are connected to the DAB tuner and FM.
Since it can also be used as a tuner, cost increase can be suppressed.

In the above description, the A / D converter 1
Clock pulse PCL, PCR for convenience of 4L, 14R, etc.
If the pulse width of the audio signal cannot be made sufficiently smaller than the period, crosstalk cancellation may be necessary for the audio signals L and R. In that case, for example, the digital filters 15L and 15R are used. In, the crosstalk cancellation can be performed.

Further, the signal S24 from the decoder 24 is separated into a signal L and a signal R, and these separated signals L and R,
The signals L and R from the A / D converters 14L and 14R can be selected and D / A converted or taken out as an output.

Further, for example, if the output signal (data string) taken out to the terminal 37 is not de-emphasized, an identification code indicating that de-emphasis is necessary is added to the output signal. , This terminal 3
In the D / A converter device connected to 7, the de-emphasis can be performed.

[0049]

According to the present invention, the stereo multiplexed signal SST is supplied to the A / D converters 14L and 14R, and the subcarrier frequency f of the stereo multiplexed signal SST is supplied.
Since A / D conversion is performed by sc, A / D
The converters 14L and 14R can demodulate the audio signals L and R from the signal SST and at the same time obtain the digitized audio signals L and R.

In this case, in particular, according to the present invention, since it is not necessary to perform switching by directly A / D converting the stereo multiplexed signal SST, various distortions caused by the switching may occur. Absent.

Moreover, the digital filters 15L and 15R
Because of the digital processing, since the audio signals L and R are D / A-converted in the subsequent stage, it is possible to obtain characteristics in which the phase around and the frequency characteristics are not deteriorated, and the excellent audio signals L and R can be obtained. Obtainable.

Furthermore, the A / D converters 14L, 14R
The pulse width of the clock pulses PCL and PCR supplied to
Since it can be made sufficiently smaller than the cycles of the pulses PCL and PCR, the digital audio signals L and R from the A / D converters 14L and 14R hardly include crosstalk components ΔR and ΔL. Even if it is included, it becomes negligibly small, and the crosstalk cancel circuit can be omitted.

Since the audio signals L and R from the FM tuner can be obtained in the state of digital signals,
Even in a single D / A converter device that selects a digital audio signal from a CD player, DAT, DAB tuner, etc. and performs D / A conversion to an analog audio signal, the audio signals L, R from the FM tuner are also included.
Can also handle.

In that case, the D / A converter device only needs to select the input digital signal in accordance with the user's operation and then D / A-convert it for output. The processing unit can be clearly separated, and an extremely high-quality analog audio signal can be output.

Further, the DAB tuner and the FM tuner can be integrated so that the DAB broadcast and the FM tuner can be integrated.
Usability is improved because both broadcast and broadcast can be received. That is, when the output signal of this tuner device is supplied to the control amplifier in the subsequent stage, it may be either the audio signals L and R of DAB broadcasting which is digital broadcasting or the audio signals L and R of FM broadcasting which is analog broadcasting. , Only one of the terminals 34L and 34R or the terminal 37 is used, and it is not necessary to connect digital signal lines for DAB broadcasting and analog signal lines for FM broadcasting. , Easy to connect. Moreover, there is no possibility that a strange signal loop is formed between the tuner device and the control amplifier in the subsequent stage.

Further, the digital filter 32, the D / A converter 33, and the converter circuit 36 can be used both as the DAB tuner and the FM tuner, so that the cost increase can be suppressed.

[Brief description of drawings]

FIG. 1 is a system diagram showing an example of the present invention.

FIG. 2 is a waveform chart for explaining the operation of the circuit of FIG.

FIG. 3 is a system diagram showing another example of the present invention.

FIG. 4 is a frequency spectrum diagram of a stereo multiplexed signal.

FIG. 5 is a system diagram for explaining a conventional example.

6 is a connection diagram showing an example of a part of the circuit of FIG.

7 is a waveform chart for explaining the operation of the circuit of FIG.

[Explanation of symbols]

 11 Front End Circuit 13 FM Demodulation Circuit 14L, 14R A / D Converter 15L, 15R Digital Filter 17 Clock Pulse Forming Circuit 18 Synthesis Circuit 21 Front End Circuit 23 PSK Demodulation Circuit 24 Decoder 32 Digital Filter 33 D / A Converter 36 Converter Circuit 38 Band switch

Claims (4)

[Claims] 1. A sum signal of left and right channel audio signals L and R is used as a main channel signal, and a signal obtained by balance-modulating a sub carrier signal by a difference signal of the audio signals L and R is used as a sub channel signal. In a stereo demodulation circuit of a receiver for receiving a stereo multiplexed signal, a first and a second A to which the stereo multiplexed signal is supplied.
A D / D converter and a clock pulse forming circuit that forms first and second clock pulses having different phases at the frequency of the subcarrier signal, and the first and second clock pulses are The clock pulses are supplied to the first and second A / D converters, respectively, and the left and right channel digital audio signals L and R are supplied from the first and second A / D converters, respectively. Stereo demodulation circuit to obtain. 2. A sum signal of left and right channel audio signals L and R is a main channel signal, and a signal obtained by balance-modulating a subcarrier signal by the difference signal of the audio signals L and R is a sub channel signal. These signals are multiplexed with the pilot signal SSP, and in the stereo demodulation circuit of the receiver for receiving the stereo multiplexed signal, the first and second A signals to which the stereo multiplexed signal is supplied.
And a D / D converter, and a clock pulse forming circuit that forms first and second clock pulses that are synchronized with the pilot signal and that are 180 ° out of phase with each other at the frequency of the subcarrier signal. The first and second clock pulses are supplied to the first and second A / D converters as their clock pulses, respectively, and A / D converted from the first and second A / D converters. The left channel audio signals L and A / D
A stereo demodulation circuit adapted to obtain the converted right channel audio signal R. 3. A sum signal of left and right channel audio signals L and R is used as a main channel signal, and a signal obtained by balance-modulating a sub carrier signal by the difference signal of the audio signals L and R is used as a sub channel signal. A first receiving circuit for receiving the stereo multiplexed signal, and first and second A to which the stereo multiplexed signal is supplied.
An A / D converter, a clock pulse forming circuit that forms first and second clock pulses having different phases at the frequency of the subcarrier signal, a second receiving circuit that receives digital audio broadcasting, and a second receiving circuit. A decoder for decoding digital audio data from the receiving circuit, a switch circuit for selecting the digital audio data from the decoder and the output signals of the first and second A / D converters, and a switch circuit for selecting D is supplied with the signal
A / A converter, and supplies the first and second clock pulses to the first and second A / D converters as their clock pulses, respectively. The left channel digital audio signal L and the right channel digital audio signal R are obtained from the D converter, and the left channel audio signal L and the right channel audio signal R are obtained from the D / A converter.
And a D / A converted analog signal of the digital audio data, which is selectively obtained according to the selection of the switch circuit. 4. A sum signal of left and right channel audio signals L and R is used as a main channel signal, and a signal obtained by balance-modulating a sub carrier signal with the difference signal of the audio signals L and R is used as a sub channel signal. A first receiving circuit for receiving the stereo multiplexed signal, and first and second A to which the stereo multiplexed signal is supplied.
An A / D converter, a clock pulse forming circuit that forms first and second clock pulses having different phases at the frequency of the subcarrier signal, a second receiving circuit that receives digital audio broadcasting, and a second receiving circuit. A decoder for decoding digital audio data from the receiving circuit, a switch circuit for selecting the digital audio data from the decoder and the output signals of the first and second A / D converters, and a switch circuit for selecting An output terminal for outputting a signal that has been output, and supplies the first and second clock pulses to the first and second A / D converters as the clock pulses, respectively. From the second A / D converter, the left-channel digital audio signal L and the right-channel digital audio signal L are input. The audio signal R is obtained, and the left channel audio signal L is output to the output terminal.
And a stereo receiver adapted to selectively output the right channel audio signal R and the digital audio data according to the selection of the switch circuit.