JPH0622281A - Muse signal processing circuit - Google Patents

Abstract

PURPOSE:To provide a MUSE signal processing circuit in which a signal input level to a MUSE decoder is adjusted automatically to a certain value in spite of the transmission mode. CONSTITUTION:The circuit is a MUSE signal processing circuit in which a MUSE signal in the FM mode or the AM mode is demodulated by a detection circuit 2, the demodulation signal is processed by a MUSE decoder 7 and outputted to a display device 8, and provided with a transmission control signal decode circuit 6 discriminating whether the transmission mode of the MUSE signal is the FM mode or the AM mode based on the transmission control signal included in the MUSE signal and with a signal level converter 5 applying prescribed level conversion to the demodulated signal in response to the discrimination result and outputting the result to the MUSE decoder 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing circuit in the MUSE system proposed as a transmission system for high-definition broadcast signals.

[0002]

2. Description of the Related Art Conventionally, M has been used as a high-definition television system.
A USE (Multiple Sub-Nyquist Sampling Encoding) method has been proposed and is being put to practical use (eg, NHK).
Technical Research 1987 Vol. 39, No. 2, 172, 18 (76) -53 (1
See section 11)).

The MUSE signal is generally transmitted in the FM mode in satellite broadcasting, but is generally transmitted in the AM mode in CATV and the like. Here, the reference level of the demodulated MUSE signal is 0.4 Vp-p in the FM mode, based on the difference in the modulation or demodulation method.
In the AM mode, it is regulated to 0.8 (or 0.7) Vp-p.

[0004]

As described above, since the reference level of the MUSE signal differs depending on the transmission mode, when a common MUSE decoder is used to construct a receiver, the input level of the MUSE decoder is adjusted according to the transmission mode. There is a need to. Also, when a plurality of input systems having different transmission modes are connected, it is necessary to adjust the signal level every time the input signal is switched.

In this case, if the signal level conversion is performed by manual adjustment, not only the operation becomes complicated, but also accurate adjustment is difficult.

An object of the present invention is to provide a MUSE signal processing circuit in which the signal input level to the MUSE decoder is automatically adjusted to a constant value regardless of the transmission mode.

[0007]

Therefore, in the present invention, the 20th bit of the transmission control signal included in the MUSE signal includes a signal for identifying whether the transmission mode is FM or AM. Attention is paid to the automatic adjustment of the signal level based on the detection of the identification signal.

The MUSE signal processing circuit according to the present invention is
Means for determining whether the transmission mode of the MUSE signal is the FM mode or the AM mode based on the transmission control signal included in the USE signal, and a predetermined level conversion for the demodulated signal according to the determination result. Give M
A signal level converting means for outputting to the USE decoder (7) is provided, and a signal of a constant reference level is supplied to the MUSE decoder (7) regardless of the transmission mode of the MUSE signal.

Here, the signal level converting means includes an FIR digital filter which constitutes a waveform equalizer, and a coefficient setting circuit (9) which sets a plurality of tap coefficients of the digital filter according to the transmission mode of the MUSE signal. Can be composed of

The signal level conversion can be performed by switching the tap coefficient at the final stage of the FIR digital filter.

[0011]

The MUSE signal is demodulated by the detection circuit (2) and then supplied to the signal level converting means. At this time, the transmission mode is detected based on the identification signal of the 20th bit of the demodulated transmission control signal, and the gain of the signal level converting means is adjusted according to the detection result. As a result, a signal of a constant reference level is supplied to the MUSE decoder (7) regardless of the MUSE signal transmission mode.

[0012]

According to the MUSE signal processing circuit of the present invention, the signal input level to the MUSE decoder is always automatically adjusted to be constant regardless of whether the transmission mode of the MUSE signal is FM / AM. As a result, accurate decoding can be performed on the MUSE signal.

If the signal level converting means is composed of an FIR digital filter and a coefficient setting circuit and the signal level conversion is performed by switching the tap coefficient at the final stage of the FIR digital filter, the circuit structure is simplified. Can be planned.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. In the MUSE signal processing circuit according to the present invention, the MU received by the tuner (1) as shown in FIG.
The SE signal is demodulated by the detection circuit (2), and the demodulated signal is LP
It is supplied to the A / D converter (4) via F (3).

The digital demodulated signal obtained from the A / D converter (4) is input to the signal level converter (5) and is also supplied to the transmission control signal decoding circuit (6), which in turn is supplied to the decoding circuit (6). The gain control signal corresponding to the AM / FM discrimination signal detected as described above is output to the level converter (5) to adjust the gain of the signal level converter (5).

As is well known, the MUSE signal for one frame period includes transmission control signals indicating various states in the 559th to 563th lines and the 1121st to 1125th lines, and the 20th bit thereof. An identification signal indicating whether the transmission mode is FM or AM is described, and the identification signal is detected by the transmission control signal decoding circuit (6).

The signal level converter (5) sets the gain to 1 in the FM mode based on the detection of the identification signal. On the other hand, in the AM mode, the reference signal level is 0.
At 8V, the gain is halved and the reference signal level is 0.1.
When it is 7V, the gain is set to 4/7.

Here, the signal level converter (5) can have various configurations, and a digital multiplier, an arithmetic circuit including a memory table, etc. can be adopted. When the reference level in the AM mode is 0.8V, it has a doubling relationship with the reference level in the FM mode, which is 0.4V. Therefore, it can be configured with a simple digital circuit that simply performs bit shift.

The signal output of the constant reference level from the signal level converter (5) is sent to the MUSE decoder (7) and the MU
After the SE-specific decoding is applied, the display
It is supplied to (8).

FIG. 2 shows an example in which the signal level converter (5) is composed of an FIR digital filter. The tap coefficients of the filter are determined so as to exert the function of the waveform equalizer as described later.

The signal level converter (5) has the number of taps (n).
, A delay element (52) and an adder (53), each of which has a first selector switch (54) at the input end of the final stage multiplier (51). , Final stage adder (53)
The second changeover switch (55) is provided at each input end of
The switches 54 and 55 are switched and controlled by a control signal from the transmission control signal decoding circuit 6.

A transmission control signal decoding circuit
The control signal from (6) is connected to the coefficient setting circuit (9), and the coefficient setting circuit (9) switches and sets tap coefficients (filter coefficients) H _{1 to} H _n for each multiplier (51). .

When the transmission control signal decoding circuit (6) detects the FM mode, the first and second changeover switches (54) and (55) are set to the side a respectively.
At this time, each tap coefficient is set by the coefficient setting circuit (9) and is supplied to each multiplier (51) so as to form a waveform equalizer from the first to n-th taps.

Various well-known methods can be adopted in setting the coefficient for constructing the waveform equalizer by the FIR digital filter (for example, Journal of Television Engineering Vol. 4).
5, No5, pp573-580 (1991)). Each coefficient set by this is registered in the coefficient setting circuit (9).

The digital MUSE signal waveform-equalized by the n-tap FIR digital filter is
The standard input signal level remains 0.4V, and the MUSE
It is sent to the decoder (7).

On the other hand, the transmission control signal decoding circuit
When the AM mode is detected by (6), the first and second changeover switches (54) and (55) are set to the b side respectively. In this case, the 1st excluding the tap of the nth stage (final stage)
To each tap coefficient in the coefficient setting circuit (9) in order to configure the waveform equalizer from the taps of the (n-1) th stage,
It is supplied to each multiplier (51). Also in this case, similarly, a well-known method can be adopted for setting (n-1) coefficients for forming the waveform equalizer, and each coefficient is registered in the coefficient setting circuit (9).

Further, regarding the tap of the nth stage (final stage),
When the reference signal level is 0.8 V, tap coefficient H _{n is set} to 1 /
2. When the reference signal level is 0.7 V, the tap coefficient H _n is set to 4/7.

Accordingly, the FI of the (n-1) taps is
The digital MUSE signal waveform-equalized by the R digital filter is converted to a reference signal level of 0.4 V and then sent to the MUSE decoder (7) in the subsequent stage.

In this case, the taps at the final stage are separated and the number of taps is reduced by 1, but the taps at the final stage are
It is for processing the front ghost included in the video signal, and in general, the front ghost is a minor one,
There is no fear that the waveform equalization function will be significantly impaired by the separation of the taps.

According to the above MUSE signal processing circuit, the digital filter constituting the signal level converter (5) exhibits the signal level converting function at the same time as the function of the waveform equalizer. Therefore, the MUSE decoder ( The input signal level for 7) can be made uniform.

The above description of the embodiments is for explaining the present invention, and should not be construed as limiting the invention described in the claims or limiting the scope. The configuration of each part of the present invention is not limited to the above-mentioned embodiment, and it goes without saying that various modifications can be made within the technical scope described in the claims.

For example, in the signal level converter (5) of FIG. 2, the signal level conversion is performed only by the tap coefficient switching setting at the final stage, but the present invention is not limited to this, and a plurality of other tap coefficients are included. It is also possible. The second changeover switch (55) is moved from the input side to the output side of the final stage adder (53), one input terminal a is connected to the output end of the adder (53), and the other input terminal is connected. It is also possible to connect b to the output terminal of the multiplier (51).

Furthermore, the gain of signal level conversion is not limited to 1/2 and 4/7, but can be changed and set to an arbitrary value according to the definition of the transmission mode.

[Brief description of drawings]

FIG. 1 is a block diagram showing a basic configuration of a MUSE signal processing circuit according to the present invention.

FIG. 2 is a block diagram showing a specific configuration of a signal level converter.

[Explanation of symbols]

 (2) Detection circuit (5) Signal level converter (6) Transmission control signal decoding circuit (7) MUSE decoder

Claims (3)

[Claims] 1. An FM mode or AM mode MUSE signal transmitted by the MUSE system is demodulated by a detection circuit (2), the demodulated signal is processed by a MUSE decoder (7), and a display (8) is displayed. In the MUSE signal processing circuit for outputting to the), a means for determining whether the transmission mode of the MUSE signal is the FM mode or the AM mode based on the transmission control signal included in the MUSE signal, The MUSE decoder (7) is provided with a signal level conversion means for performing a predetermined level conversion according to a mode determination result and outputting the signal to the MUSE decoder (7) regardless of the transmission mode of the MUSE signal.
A MUSE signal processing circuit, characterized in that the signal is supplied to the MUSE signal processing circuit. 2. The signal level converting means comprises a FIR digital filter forming a waveform equalizer and a coefficient setting circuit (9) for setting a plurality of tap coefficients of the digital filter according to a transmission mode of a MUSE signal. The MUSE signal processing circuit according to claim 1, which is configured. 3. The MUSE signal processing circuit according to claim 2, wherein the signal level conversion is performed by switching the tap coefficient at the final stage of the FIR digital filter.