JPH01293081A - Demodulator for television audio multiplex signal - Google Patents

Abstract

PURPOSE:To realize cost down by simplifying constitution by performing the switching control of the frequency characteristic of a low-pass filter by interlocking with the switching selection operation of a change-over switch. CONSTITUTION:The switching control of the change-over switch 18 is performed by supplying a reception switching signal to receive either a second voice signal or a third voice signal selectively via a terminal 15, and is switched and connected to a terminal (a) side to be selected at the time of receiving the second voice signal, and to a terminal (b) side to be selected at the time of receiving the third voice signal, respectively. The characteristic change-over switch 18 of the low-pass filter LPF17 is also switched simultaneously by the reception switching signal from the terminal 15 by interlocking with the above operation, and the frequency characteristic fitting in the reception of each voice signal can be selected. In such a way, it is possible to share the low-pass filter by switching the characteristic of the low-pass filter LPF17 so as to fit in the optimum characteristic for each voice signal system by interlocking with the reception switching of the second and third voice signals.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a demodulator for television audio multiplexed signals. The present invention relates to a demodulation device that demodulates a television audio multiplex signal in which signals are multiplexed.

[815 of the Invention] The present invention provides a demodulation device for demodulating a television audio multiplexed signal in which second and third audio signals are frequency multiplexed on the higher frequency side than the first television audio signal band. 2
The output from the selector switch that selects and takes out either the detected output of the audio signal or the detected output of the third audio signal is sent to a low-pass filter with variable frequency characteristics, and the frequency characteristics of this low-pass filter are changed by the selector switch. By controlling the switching in conjunction with
, and the third audio signal processing, thereby simplifying the configuration and reducing costs.

[Conventional technology]

For example, in television audio multiplex broadcasting in the United States, the frequency spectrum of the audio signal after FM demodulation is as shown in Figure 6, and as is clear from Figure 6, the frequency spectrum corresponding to the main audio A second multiplexed audio signal S2 corresponding to a stereo difference signal, etc., and a third multiplexed audio signal S, corresponding to a foreign language audio signal, etc. are provided on the higher frequency side than the frequency band of the first audio signal S1. It is arranged. The first audio signal S is disposed on the lower frequency side than f, which is the horizontal scanning frequency of the television signal, and the presence or absence of the second audio signal is identified at the position of frequency f. A pilot signal SPL is arranged for this purpose. The second multiplexed audio signal S2 has a second frequency 2fH
The carrier wave signal of the second audio signal is the stereo difference signal (
L-R), for example, 21 to 4
It has a frequency band of 1kllz. The third multiplexed audio signal S is a carrier wave signal of a third frequency 5f, which is a third audio signal, for example, a foreign language (so-called bilingual)
This is an FM modulated audio signal. Furthermore, on the high range side,
A telemetry signal StL with a center frequency of 6.5 f may also be provided. An example of a television audio transmission system that multiplexes three or more audio signals is disclosed in US Pat. No. 4,405,944 and the like.

As a demodulation device for demodulating such a television audio multiplexed signal, for example, the one shown in FIG. 7 is conventionally known. In this Fig. 7, the input terminal l
A television audio multiplexed signal having a frequency spectrum as shown in FIG. 6, which has been separated from the television video signal and FM demodulated, is supplied to the television receiver. This human signal has a frequency band of 2, which is the frequency band of the second multiplexed audio signal S2.
The first audio signal SI and the second multiplexed audio signal S are sent to an LPF (low-pass filter) 2 having a cutoff frequency sufficiently higher than ~41 kHz, for example, 50 kHz, and are taken out and subjected to first audio signal processing. The signal is sent to the circuit 4 and the second audio signal detection circuit 5, respectively. The output from the first audio signal processing circuit 4 is sent to the LPF 6.
Only the audio signal Sl is taken out, and this first audio signal S1
is sent to the matrix circuit 7. In the second audio signal detection circuit 5, the second multiplexed audio signal S2 is subjected to low frequency conversion by, for example, synchronous detection, and is disposed on the lower frequency side than, for example, f and I. Only the audio signal component is extracted and sent to one selected terminal a of the changeover switch 9. Further, the signal from the input terminal 1 is sent to a BPF (band pass filter) 10 with a passing center frequency of 5f++, where the third multiplexed audio signal S is extracted, and the third audio signal detection circuit 11 performs FM detection. After that, only the third audio signal component is extracted by the LPF 12. The output from this LPF 12 is the changeover switch 9
is sent to the other selected terminal. The output from the changeover switch 58 is sent to a noise reduction circuit 13 such as a so-called DBX (registered trademark) decoder, subjected to noise reduction processing, and sent to the matrix circuit 7. For example, stereo left and right channel audio signals are taken out from the matrix circuit 7.

Here, noise reduction processing such as dbx (registered trademark) is required for each of the second and third audio signals, but providing a noise reduction circuit for each audio signal system requires a large circuit scale. Since the noise reduction circuit 13 is shared by the second and third audio signal systems in popular models, as shown in the configuration shown in FIG. In many cases, a configuration is adopted in which one of the three audio signals can be selected and received.

[Problem to be solved by the invention]

By the way, in the above configuration, LPF 8.12 is provided for each signal system even though either one of the second and third audio signals is selected and received. this is,
Due to the signal passband characteristics of the BPFIO for extracting the third multiplexed audio signal S, the detection characteristics of the detection circuit 11, etc., the frequency characteristics of the detection output decrease in the high range as shown in Figure 8. This is because the frequency characteristics of the LPF 12 are made to have a peak near the cutoff in order to cancel this level drop in the high frequency range. On the other hand, the LPF 8 of the second audio signal system has normal low-pass characteristics without such a peak.

Therefore, LPF 8 with different frequency characteristics
．． 12 cannot be shared even if they are not used at the same time, and the circuit configuration is accordingly complicated.

The present invention has been made in view of the above circumstances, and is designed to select and receive either the second or third audio signal of a television audio multiplex signal in which three or more audio signals are multiplexed. The object of the present invention is to provide a demodulator for television audio multiplexed signals that can simplify the circuit configuration and reduce costs by sharing the low-pass filter used in these audio signal circuit systems.

(Means for Solving the Problems) A demodulating device for television audio multiplexed signals according to the present invention includes:
In order to solve the above-mentioned problems, the second and third television audio signal bands are set higher than the first television audio signal band.
A demodulation device for demodulating a television audio multiplexed signal obtained by modulating and frequency multiplexing a carrier wave signal of a frequency with a second audio signal and a third audio signal, respectively. 3, and a low-pass filter to which the output from the selector switch is supplied and whose frequency characteristics change according to the control signal; The present invention is characterized in that the frequency characteristics of the low-pass filter are switched and controlled in conjunction with the switching selection operation.

[For production]

By switching the characteristics of the low-pass filter to the optimum characteristics for each audio signal system in conjunction with the switching of reception of the second and third audio signals, it is possible to share the low-pass filter.

〔Example〕

FIG. 1 is a block circuit diagram showing a schematic configuration of a television audio multiplexed signal demodulation device according to an embodiment of the present invention.

In FIG. 1, an input terminal 1 is supplied with a television audio multiplexed signal having a frequency spectrum as shown in FIG. 6 above. That is, the second and third frequencies (2fH2) are set higher than the frequency band of the first main television audio signal S1.
Second and third multiplexed audio signals S2 obtained by modulating the carrier wave signal of 5fH) with the second and third audio signals, respectively.
, S3 are superimposed on the television audio multiplexed signal is supplied to the input terminal l. This input signal is sent to an LPF (low pass filter) 2 having a cutoff frequency of, for example, 50 kl (z), which is sufficiently higher than the frequency band of 21 to 41 kHz of the second multiplexed audio signal S2, and then filters the first multiplexed audio signal S2. The audio signal S1 and the second multiplexed audio signal S2 are extracted and sent to the first audio signal processing circuit 4 and the second audio signal detection circuit 5, respectively.First audio signal processing circuit 4
The output from the LPF 6 is sent to the first audio signal Sl.
This first audio signal S1 is sent to the matrix circuit 7. In the second audio signal detection circuit 5, the second multiplexed audio signal S2 is converted to a lower frequency by, for example, synchronous detection, and is placed on the lower frequency side than fII, and is connected to one selected terminal a of the changeover switch 16. Sent. Furthermore, the television audio multiplexed signal from input terminal 1 is filtered through a BPF (band pass filter) with a passing center frequency of 5 fH.
10, the third multiplexed audio signal S3 is taken out, subjected to FM detection in the third audio signal detection circuit 11, and then sent to the other selected terminal of the changeover switch 16. The output signal from this changeover switch 16 is sent to an LPF (low pass filter) 17 whose frequency characteristics are switched and controlled. The changeover switch 16 is controlled by being supplied via the terminal 15 with a reception switching signal for selectively receiving either the second audio signal or the third audio signal. When receiving the audio signal, the selected terminal a
When the third audio signal is received, the selected terminal is connected to the selected terminal. In response to the reception switching signal from the terminal 15, the characteristic selection switch 18 of the LPF 17 is simultaneously switched, so that a frequency characteristic suitable for receiving each audio signal is selected. The output signal from the LPF 17 is sent to the matrix circuit 7 via the noise reduction circuit 13.

Here, the LPF 17 is a so-called bicond filter using two integrators 19 and 20 as shown in FIG.
It has a filter configuration. That is, the output signal from the changeover switch 16 is sent to the non-inverting input terminal of the first integrator 19, and the output from the integrator 19 is sent to the second voltage-dividing resistor through the first voltage dividing resistor consisting of resistors 21 and 22. It is sent to the non-inverting input terminal of the integrator 20. This first voltage dividing resistor is turned on and off by the switch 18. The output signal from integrator 20 is fed back to the inverting input terminal of integrator 19 and is also fed back to the inverting input terminal of integrator 20 via a second voltage dividing resistor consisting of resistors 23 and 24. This second voltage dividing resistor is also controlled to be on/off by the switch 18.

The transfer function T (S
) according to the on/off state of the switch 18, we get:
When the resistance values of the resistors 21 to 24 are respectively R1-R4, the switch 18 is turned off (receiving the second audio signal) and the switch 18 is turned on (receiving the third audio signal). This changes from the switch off state where the Q value is 1 to the Q value (R
By switching to the ON state of z+Ra)/Rs, a peak occurs near the cutoff frequency on the frequency characteristics of the LPF 17, and filter characteristics that compensate for the high frequency level reduction characteristics shown in FIG. 8 described above can be obtained. .

A more specific example of the circuit configuration of such LPF 17 is shown in FIG. Each integrator 1 of the LPF 17 shown in FIG.
The configuration of 9.20 itself is common and is not directly related to the gist of the present invention, so a description thereof will be omitted. Also, the third
Regarding the second audio signal detection circuit 5 and the third audio signal detection circuit 10 in the figure, only the output stage multiplier is shown.
The reception selection switch 16° selectively connects a current source to only one of these multipliers, so that the detection circuit 5,
It selects which of the IOs to put into operation. In the specific example of FIG. 3, the output signal from the selected one of the multipliers of the detection circuit 5 and IO is L in the form of current Δi.
The voltage is supplied to the integrator 19 of the PF 17, and output from the integrator 20 in the form of voltage v0. Also, the integrator 1 in Fig. 2
The transfer function T (s) in 9.20 is expressed using l/s, but for the transfer function of the integrator in Fig. 3, the current value ■ in the figure. , T1, and L/jωReCr, which is determined by the resistance value Re and the capacitance value C of the integrating capacitor. Here, LPF for T1m human power Δi
The transfer function T(s) (=v, /Δi) of F17 is calculated according to the on/off state of the switch 18 linked to the reception selection switch 16°. Signal reception) status (1)
@-1l/ ReCI 6 Q=1 ■Shf18 on (third audio signal reception) state ωo'
=(r+/ReCIo)・&R+/(R++Rz)Q'
=(R's + R4)/Ry, and these filter characteristics are as shown by the curves aS and b in FIG. 4. Therefore, by using one LPF 1 7, the filter characteristics required for each audio reception can be switched and realized, and the circuit configuration can be simplified and costs can be reduced.

Regarding the other configurations in FIG. 3, explanations will be omitted by assigning the same reference numerals to the parts corresponding to those in FIG. 2.

Next, FIG. 5 is a block circuit diagram showing another embodiment of the television audio multiplex signal demodulation apparatus according to the present invention.

In this FIG. 5, a television audio multiplex signal having a frequency spectrum as shown in FIG. The signal is sent to, for example, a second-order BPF (band pass filter) 41 whose center pass frequency is 5-f. The output signal from this BPF 41 is sent to a subtracter (adder) 42 and a trap filter or trap 43.
The output signal from is sent to trap 44.

4 calculator 42 converts the input signal from L terminal 1 to BPF 41.
These BPF41
The subtracter 42 forms a trap filter or trap that removes the carrier frequency 5f component. The output signal from this subtracter 42 is sent to a pilot signal cancellation (so-called viroft cancellation) circuit 3.

The pilot signal removal circuit 3 is for removing the pilot signal (frequency f) in the input signal, and the adder 51 removes the pilot signal from the signal input to the pilot signal removal circuit 3. The pilot signal is removed or attenuated by adding a signal (pilot cancellation signal) with the opposite phase of the signal. That is, first, the carrier regeneration circuit 52 extracts a signal (pilot signal) of frequency f from the input signal in a phase-synchronized form using a PLL circuit or the like, and converts the pilot signal of frequency f'x to the amplitude of a multiplier or the like. The signal is sent to an adjustment circuit 55 to form a signal (pilot cancellation signal) having an opposite phase and an amplitude proportional to the input pilot signal, and this pilot cancellation signal is sent to an adder 51. The pilot signal detection circuit 53 detects the level of the pilot signal in the input signal by synchronously detecting the signal input to the circuit 3 with a signal (pilot signal) of frequency f obtained from the carrier regeneration circuit 52. and
The obtained detected DC output signal is sent to a coefficient multiplier 62 and a level discriminator (comparator) 63 via a level adjustment circuit 6I. The output from the coefficient multiplier 62 is sent to the amplitude adjustment circuit 55 to adjust the amplitude of the pilot cancellation signal. The level discriminator 63 discriminates the pilot detection DC output signal obtained via the level adjustment circuit 61 based on the reference level from the reference voltage source 64, for example, and determines the presence or absence of the pilot signal. The output for determining the presence or absence of this pilot signal is, for example, output from the matrix circuit 7.
etc., to control switching between stereo playback and monaural playback.

The output signal from the pilot signal removal circuit 3 is sent to a first audio signal processing circuit 4 and a second audio signal detection circuit 5,
The output signal from the first audio signal processing circuit 4 is sent to the matrix circuit 7 via the LPF 6. A so-called synchronous detection circuit is used as the second audio signal detection circuit 5, and the carrier signal to be multiplied by the input signal is a pseudo sine wave signal with a frequency of 2fH from the carrier regeneration circuit 52. is used. This pseudo sine wave signal is, for example, a signal obtained by removing or compressing the 6fH frequency component, which is the third harmonic, from a triangular wave or a staircase wave.The level of this 6fs component is, for example, a fundamental wave (frequency This is a 40 dB decrease from the level of 2fM). Such a pseudo sine wave signal is input to the second audio signal detection circuit 5, that is, the trap consisting of the BPF 41 and the subtracter 42 converts the 5fw carrier wave component of the third multiplexed audio signal S from the television audio multiplexed signal. By multiplying the signal by the signal whose neighboring parts have been suppressed and the f component has been removed by the pilot signal removal circuit 3, the third multiplexed audio signal S is suppressed by the amount converted to the lower frequency side. 2
It becomes possible to perform low frequency conversion and detection of the multiplexed audio signal S2. The output signal from this second audio signal detection circuit 5 is
The signal is sent to one selected terminal a of the changeover switch 16. This changeover switch 16 is controlled in response to a reception changeover signal (switching signal for selecting which of the second audio signal and third audio signal to receive) supplied from the terminal 15,
When receiving the second audio signal, it is switched to the selected terminal a side, and when receiving the third audio signal, it is switched to the selected terminal A side.

Next, the traps 43 and 44 of the third audio signal system are connected to the BPFI of FIG. 1 or 7 together with the BPF 41.
0, each with a trap frequency of 6
For example, a second-order trap circuit of r□ and 4F construction is used. The output signal from the trap 44 is detected by the third audio signal detection circuit 11 and sent to the selected terminal of the changeover switch 16.

The output signal from the changeover switch 16 is sent to an LPF (low pass filter) 17 with variable frequency characteristics.
This LPF 17 controls switching control B to filter characteristics suitable for each audio reception in response to a reception switching signal from the terminal 15.
be done. That is, when receiving the third audio signal, taking into consideration that the frequency characteristics of the output signal from the detection circuit 11 tend to decrease in high frequencies, the filter characteristics are switched to have a peak near the cutoff frequency. The output signal from the LPF 17 is sent to the matrix circuit 7 via the noise reduction circuit 13.

Further, when receiving the third audio signal, the noise that occurs when the RF electric field is weak becomes hysterical noise with many high frequency components due to the characteristics of the LPF 17, but in order to prevent this, the noise detection circuit 25 inputs the noise. The noise level of the signal is detected and sent to the LPF 17 for control so as to reduce the peak near the cutoff of the filter characteristics.

According to the television audio multiplexed signal demodulation device having the configuration shown in FIG. Since it can be shared by each audio signal system, the circuit configuration can be simplified and costs can be reduced. Also, when receiving the third audio signal, RF
When the electric field becomes weak and noise increases, the noise detection circuit 25 detects the noise level and controls the frequency characteristics of the LPF 17 to reduce the high-frequency components of the noise and eliminate auditory discomfort. That's what I do.

Furthermore, the conventional LPF 2 of the 1st and 2nd audio signal system
and BPF 10 of the third audio signal system, a part of the internal circuit configuration is shared and can be configured with three secondary filter circuits, which simplifies the circuit configuration and reduces costs. First, the S/N and separation characteristics can be improved. Further, the output from the pilot signal detection circuit 53 is level-adjusted by a level adjustment circuit 61, and then sent to a coefficient multiplier 62 for setting the level of a pilot cancellation signal and a level discriminator 63 for determining the presence or absence of a pilot signal. Therefore, there are fewer adjustment points, which contributes to simplifying adjustment work and reducing costs.

It should be noted that the carrier frequency, modulation form, etc. of the second and third audio signals in the present invention are not limited to those of the embodiments, and can of course be modified in various ways without departing from the gist of this invention. I'll go.

〔Effect of the invention〕

By switching the frequency characteristics of the shared low-pass filter to the optimum characteristics in conjunction with switching between the reception modes of the second and third audio signals, one low-pass filter can be used for each of these audio signal systems. Therefore, the circuit configuration can be simplified and costs can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram schematically showing an embodiment of a demodulating device for television audio multiplexed signals according to the present invention; FIG. 2 is a block circuit diagram showing the vicinity of the LPF, which is the main part of the embodiment; FIG. 3 is a circuit diagram showing a specific circuit configuration example of the LPF, FIG. 4 is a graph showing the frequency characteristics of the LPF, and FIG. 5 shows another embodiment of the audio multiplex signal demodulation device according to the present invention. A block circuit diagram, FIG. 6 is a graph showing the frequency spectrum of a television audio multiplexed signal used in the present invention, FIG. 7 is a block circuit diagram schematically showing a conventional television audio multiplexed signal demodulation device, and FIG. The figure is a block circuit diagram showing the frequency characteristics of the detected output of the third audio signal. ■...Television audio multiplex signal input terminal 2.6.8.12 Self...LPF (low pass filter) 4...First audio signal processing circuit 5...
. . . Second audio signal detection circuit 7 . . . Matrix circuit 9 . . . Changeover switch 10 . . . BPF (band pass filter) 11
...... Third audio signal detection circuit 13 ... Noise reduction circuit 16 ... Changeover switch 18 ... Switch

Claims (1)

[Claims] Carrier wave signals of second and third frequencies set higher than the first television audio signal band are
, a demodulator for demodulating a television audio multiplexed signal modulated and frequency-multiplexed by a third audio signal, the detection output of the second audio signal and the detection output of the third audio signal. It has a change-over switch that selects and takes out one of the two, and a low-pass filter to which the output from the change-over switch is supplied and whose frequency characteristics change according to the control signal. A demodulator for a television audio multiplex signal, characterized in that the frequency characteristics of a filter are switched and controlled.