JPH1093987A - Secam decoding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a precise SECAM decoding filter which does not need adjustment at a rate in which a center frequency is fixed to a clock frequency by providing a switched capacitor crochet filter which filter-processes an SECAM signal at a fixed sampling frequency that is the specified fold of the crochet frequency and supplies a signal which is crochet filter-procesed. SOLUTION: An SECCAMCVBS input signal is supplied to a switched capacitor crochet band-pass filter BPF through continuous time pre-filter CPF and an automatic color control circuit ACCs. The output signal of the filter BPF is supplied to a first mixer M1 multiplying a sine function given by a coefficient 11-1-1 and a second timer M2 multiplying a cosine function given by the coefficient 11-1-1. The input signal is mixed with the frequency which is 1.5 times as much as the crochet frequency and the SECAM signal which is filter- processed is converted into a frequency which is 0.5 times as much as the crochet frequency. The output signals of the mixers 1 and 2 are supplied to an ACC circuit ACCF.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a SECAM decoding filter, and a SECAM including the SECAM decoding filter.
The present invention relates to a decoding method and apparatus, and a SECAM television receiver including such a SECAM decoding apparatus.

[0002]

BACKGROUND OF THE INVENTION A method and apparatus for adjusting a resonant circuit coupled to a frequency discriminator is disclosed in U.S. Pat. No. 4,929,300 (PH).
F-87,571). For example, the resonant circuit is, for example, a "crochet" circuit of a SECAM decoder unit. Known crochet filters are analog circuits comprising resistors, coils and capacitors (capacitors).
The crochet filter comprises capacitors that are switched by integrated interrupters, which deactivate or activate the capacitors to adjust the total capacitance. The result of the measuring operation is supplied to an element for adjusting the resonance circuit.

[0003]

It is an object of the present invention to provide an accurate SECAM decoding filter in which the center frequency has a fixed ratio to the clock frequency, and thus does not need to be adjusted.

[0004]

SUMMARY OF THE INVENTION A SECAM decoding filter according to the present invention filters a SECAM signal at a fixed sampling frequency six times the cloche frequency (Fcloche) and supplies a crochet-filtered signal. (BPF).

[0005] A SECAM decoding apparatus according to the present invention includes a switched capacitor crochet filter (BPF) for filtering a SECAM signal at a fixed sampling frequency six times the cloche frequency (Fcloche) and supplying a crochet-filtered signal. The crochet-filtered signal is mixed with a frequency 1.5 times the cloche frequency (Fcloche), and the crochet-filtered signal is mixed with the cloche frequency (Fcloche) of 0.5.
Means (M1, M2) for converting to a double frequency to form a converted SECAM signal;
Means for limiting the signal to form a limited SECAM signal (ACCf); and means for demodulating the limited SECAM signal to obtain a chrominance signal (BY, RY) (FMD). It is characterized by

In another example of the SECAM decoding apparatus according to the present invention, the mixing means (M1, M2) and the limiting means (A
CCf) and a low-pass filter means (LPF) for suppressing harmonics of the converted SECAM signal.
1, LPF2).

Further, the SECAM decoding method of the present invention comprises the steps of: filtering (SEF) the SECAM signal at a fixed sampling frequency six times the cloche frequency (Fcloche) to supply a signal subjected to crochet filtering; The processed signal is mixed with a frequency 1.5 times the cloche frequency (Fcloche) (M1, M2), and the signal subjected to the crochet filter processing is converted to a frequency 0.5 times the cloche frequency (Fcloche). Forming a converted SECAM signal, and limiting (ACCAC) the converted SECAM signal.
f) forming a restricted SECAM signal; and demodulating (FMD) the restricted SECAM signal.
And supplying a chrominance signal (BY, RY).

Further, the SECAM television receiver according to the present invention generates a chrominance signal (BY, RY) and the SECAM decoding device according to claim 2, and the chrominance signal (BY, RY). ) And the luminance signal (Y) into a matrix to form color signals (B, R, G).
Means (MX) for obtaining the color signals (B, R, G)
(D) for displaying

[0009]

In accordance with the present invention, the SECAM decoding filter (ie, the crochet filter) is a switched capacitor filter operating at a fixed sampling frequency of 6 * Fcloche. This means that the center frequency of the filter has a fixed relationship to the clock frequency. The switched-capacitor filter according to the invention is more complex than a conventional filter, but has the advantage that a fully integrated and accurate filter is obtained, whereby cumbersome adjustments are no longer required.

In another example of the SECAM decoder of the present invention,
The SECAM signal is filtered at a fixed sampling frequency of six times the cloche frequency Fcloche to provide a crochet filtered signal, and the crochet filtered signal is mixed with a frequency 1.5 times the cloche frequency Fcloche. Then, the signal subjected to the crochet filter processing is converted to a frequency 0.5 times the cloche frequency Fcloche to form a converted SECAM signal, and the converted SECAM signal is restricted to limit SE.
A CAM signal is formed, and the limited SECAM signal is demodulated to obtain a chrominance signal. Therefore, the crochet filter is provided before the discrete time decoder. The input signal is 1.5 times of the cloche frequency Fcloche.
Crochet-filtered S mixed with double frequency
The ECAM signal is converted to a frequency 0.5 times the cloche frequency Fcloche. Any distortion generated in this way is not reflected in the signal band.

[0011]

FIG. 1 shows a SE comprising a sampled data SECAM decoder including a switched capacitor crochet filter at six times the cloche frequency Fcloche.
1 shows an example of a CAM television receiver. SECAM
The CVBA input signal is supplied to a low-speed automatic color control circuit ACCs through a continuous time pre-filter CPF. In FIG. 2, curve a shows the frequency spectrum of the input signal having distortion, and curve b shows the transfer characteristics of the low-pass prefilter CPF. The output signal of the automatic color control circuit ACCs is supplied to a switched capacitor crochet band pass filter BPF to which a 6 * Fcloche switching signal is supplied. In FIG. 2, a curve c indicates a transfer characteristic of the discrete-time crochet filter BPF, and a curve d indicates a frequency spectrum of an output signal of the crochet filter BPF. An output signal of the filter BPF is a first mixer M1 for multiplying a sine function given by a coefficient 11-1-1 and a coefficient 1-1-1.
Is supplied to a second mixer M2 that multiplies the cosine function given by 1. The input signal has the cloche frequency Fcloche 1.
The SECAM signal mixed with the five times frequency (see the arrow in FIG. 2E) and subjected to the filter processing is converted to the cloche frequency Fcl.
Converted to 0.5 times the frequency of oche. In FIG.
Fig. 2 shows the frequency spectrum of the converted SECAM signal.
(F). The output signals of the mixers M1 and M2 are supplied via separate low-pass filters LPF1 and LPF2 to the respective inputs of the high-speed ACC circuit ACCf, which also receive the 6 * Fcloche switching signal.
In FIG. 2, a curve g is a low-pass filter LPF suppressed at a frequency 2.5 times the cloche frequency Fcloche.
1 shows the transfer curves of LPF2 and LPF2, and curve h shows the frequency spectrum of the output signals of the low-pass filters LPF1 and LPF2.

The high-speed ACC circuit ACCf is set to a standard continuous time S
Used as a substitute for the limiter of the ECAM decoder. This is based on the realization that, in the time-discrete example, a simple clipping action results in significant phase errors. However, very good ACC circuits also cause some distortion and for this reason the input signal is not converted to DC, so any resulting distortion moves around 0 Hz and Fcloche without being reflected in the signal band Become like This means that the input signal is 1.5 * Fcloche
Therefore, the filtered SECAM signal is converted to a frequency of 0.5 * Fcloche. The harmonics of the SECAM signal converted to the frequency of 0.5 * Fcloche by the low-pass filters LPF1 and LPF2 are removed. Input signal and 1.
When it is determined that the frequency is mixed with the frequency of 5 * Fcloche, the crochet filter BP before the mixers M1 and M2 is used.
F is a frequency that delays the entire clock cycle as an even multiple of the cloche frequency Fcloche, and 1.5 * Fcloche
Several (ie, 2) as an integral multiple of the mixed frequency of
Need to be clocked at a frequency that achieves the mixer with only a few simple factors (ie, -1 and +1). From these considerations, the crochet filter BPF is 6 *
It must be operated at the frequency of Fcloche.

In the high-speed ACC circuit ACCf, the signal from the low-pass filter LPF1 is supplied to the controllable amplifier A1, and the output signal forms the output signal of the circuit ACCf. The output signal of the amplifier A1 is also supplied to the quadrature circuit Q1. Further, the signal from the low-pass filter LPF2 is supplied to the controllable amplifier A2, and the output signal forms the output signal of the circuit ACCf. Amplifier A
2 is also supplied to the quadrature circuit Q2. Adder AD
Add the output signals of the quadrature circuits Q1 and Q2,
The sum signal is supplied to the inverting input terminal of the comparator C1, and the reference signal Vref is supplied to the non-inverting input terminal of the comparator. The output signal of the comparator C1 is supplied to control input terminals of the controllable amplifiers A1 and A2 and also to a low-speed ACC loop filter LF. The output signal of the loop filter LF is supplied to the inverting input terminal of the comparator C2, and the reference signal Vref is supplied to the non-inverting input terminal of the comparator C2. The output signal of the comparator C2 is supplied to the control input terminal of the low speed automatic color control circuit ACCs. An amplitude control exhibiting substantially the same characteristics as the high-speed ACC circuit ACCf is described in German patent application DE-A-31.19.448. In FIG. 2, the curve i represents the second harmonic distortion 2nd Har Dist and the third harmonic distortion.
High-speed ACC circuit AC with harmonic distortion 3rd Har Dist
4 shows a frequency spectrum of an output signal of Cf.

Controllable amplifier A of high-speed ACC circuit ACCf
The output signals of A1 and A2 are chrominance signals BY and R.
−Y is supplied to each input terminal of the FM demodulator FMD. In FIG. 2, a curve j indicates the FM-AM conversion WO.
These chrominance signals BY and RY are CVBS
The signals are supplied to a matrix circuit MX that generates color signals B, R and G together with the luminance signal Y extracted from the input signal. These color signals B, R and G are supplied to a delay unit D via output amplifiers OA1, OA2 and OA3, respectively.

FIG. 3 shows an example of a continuous-time SECAM decoding device including a switched capacitor crochet filter having a frequency of 6 * Fcloche according to the present invention. SECAM C
The VBS input signal is a continuous time pre-filter CPF, a low speed ACC circuit ACCs, a switched capacitor crochet bandpass filter BPF operating at 6 * Fcloche frequency.
And continuous time SE through continuous time post filter CF
This is supplied to the CAM decoder SD. This SECAM decoder S
D generates chrominance signals BY and RY which can be further processed as shown in FIG. In this example, the pre-filter CPF and the post-filter CF do not have to be as high demanding by using a switched capacitor crochet filter operating at a 6 * Fcloche frequency.

FIGS. 4 and 5 show a recursive filter of the SECAM decoding filter of the present invention. The decoding filter is a charge redistribution quasi-differential switched capacitor crochet filter. According to the invention, the sampling frequency is 6 * Fcloche frequency. In the example of FIGS. 4 and 5, each set of switched capacitors comprises four capacitors such that the switch is operated in each of the four different switching phases within each set. Therefore, the outputs of the differential amplifier OTA are the first switches S1.11, S1.12, S1.13 and S1.1.
14, capacitors C11, C12, C13 and C
14. The input signal Vin is supplied to the second switches S2.11, S2.12, S2.13 and S2.14, respectively.
Through capacitors C11, C12, C13 and C14
To supply. Third switch S3.11, S3.12, S
Capacitors C11, C12, C13 and C14 are respectively connected to differential amplifier OT by means of 3.13 and S3.14.
Connect to A's inverting input terminal (-). 4th switch S
The capacitors C11, C12, C13 and C14 are grounded by 4.11, S4.12, S4.13 and S4.14, respectively.

Also, the filter of this embodiment has first switches S1.21, S1.22, S1.23 and S1.2, respectively.
Four other capacitors C21, C22, C2 having four
3 and C24 and second switch S2.2 respectively.
1, S2.22, S2.23 and S2.24,
These switches enable other capacitors C21 and C2
2, ground the left side of C23 and C24. Third switches S3.21, S3.22, S3.23 and S3.2
4, capacitors C21, C22, and C23, respectively.
And the right side of C24 are grounded. Fourth switch S4.2
1, S4.22, S4.23 and S4.24 respectively provide capacitors C21, C22, C23 and C2.
4 is connected to the non-inverting input terminal (+) of the differential amplifier OTA.

In addition, the recursive filter has a similar number of feedback paths. In particular, in addition to each directly switched capacitor arrangement (capacitors and associated switches) provided between the feedback input terminal Vin and the inverting input terminal (-) of the differential amplifier OTA, the output terminal of the differential amplifier OTA and A feedback switched capacitor arrangement is provided between each input terminal. The switches of these feedback switched capacitors operate in the same switching phase as the associated switches of the directly switched capacitor arrangement. Therefore,
In FIGS. 4 and 5, the same reference numerals are used for the direct switched capacitor arrangement and the feedback switched capacitor arrangement, whereby the feedback elements are designated with "f". The second switch of the capacitor provided between the output terminal and the inverting input terminal of the differential amplifier OTA is grounded without being connected to the input terminal Vin. The first of the capacitors connected to the inverting input terminal of the differential amplifier OTA
The switch is connected to the output terminal of the differential amplifier OTA without grounding.

In the example of FIGS. 4 and 5, the capacitance of each of the feedback capacitors is nine times the capacitance of each of the direct capacitors.

The present invention is not limited only to the above-described example, and various modifications and changes can be made without departing from the gist. For example, if the sample frequency 1 / T is equal to the 6 * Fcloche frequency in the example of the present invention, instead of the example of FIGS. 4 and 5, the applicant's European patent application filed on Oct. 20, 1995, The example of FIG. 5 of No. 95202849.6 can also be used. In the embodiment of the present invention, 6 * Fcloche
Although the case where the frequency is used has been described, it goes without saying that a frequency that is an integral multiple of this frequency or a frequency substantially equal to this frequency can be used without departing from the gist of the invention. In addition, symbols and reference numerals in parentheses in the claims do not limit the scope of the claims.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating an example of a SECAM television receiver including a first example of a SECAM decoding device according to the present invention.

FIG. 2 is a frequency spectrum diagram further illustrating the operation of the receiver of FIG. 1;

FIG. 3 is a schematic circuit diagram of a second example of the SECAM decoding apparatus of the present invention.

FIG. 4 is a schematic circuit diagram showing an example of the SECAM decoding filter of the present invention.

FIG. 5 is a schematic circuit diagram showing an example of the SECAM decoding filter of the present invention.

[Explanation of symbols]

 CPF pre-filter ACC Low-speed automatic color control circuit CPF continuous-time pre-filter BPF discrete-time crochet filter M1, M2 mixer LPF1, LPF2 low-pass filter A1, A2 controllable amplifier C1, C2 comparator Q1, Q2 quadratic (right angle) Circuit AD Adder FMD FM Demodulator Har Dist Harmonic Distortion LF Loop Filter MX Matrix Circuit OA1, OA2, OA3 Output Amplifier D Display Unit CF Continuous Time Post Filter SD SECAM Decoder OTA Differential Amplifier C11-C24 Direct Switched Capacitor C11f ~ C24f Feedback switched capacitor S1.11 ~ S4.24 switch S1.11f ~ S4.24f Feedback switch

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Arnoldus Johannes Juliana Baud Dewein The Netherlands 5621 Baer Eindhoven Fen-Frunewawswech 1

Claims (5)

[Claims] 1. A switched capacitor crochet filter (BPF) for filtering a SECAM signal at a fixed sampling frequency six times the cloche frequency (Fcloche) and supplying a crochet-filtered signal. SECAM decoding filter. 2. A switched-capacitor crochet filter (BPF) for filtering the SECAM signal at a fixed sampling frequency six times the cloche frequency (Fcloche) to provide a crochet-filtered signal;
This crochet-filtered signal is mixed with a frequency 1.5 times the cloche frequency (Fcloche) to convert the crochet-filtered signal to a frequency 0.5 times the cloche frequency (Fcloche). Means (M1, M2) for forming a converted SECAM signal;
Means for limiting the converted SECAM signal to form a limited SECAM signal (ACCf), and means for demodulating the limited SECAM signal to obtain a chrominance signal (BY, RY) ( FMD). 3. The converted SE provided between the mixing means (M1, M2) and the limiting means (ACCf).
3. The SECAM decoding device according to claim 2, further comprising low-pass filter means (LPF1, LPF2) for suppressing harmonics of the CAM signal. 4. A step of filtering (SEF) the SECAM signal at a fixed sampling frequency six times the cloche frequency (Fcloche) to supply a crochet-filtered signal; and providing the crochet-filtered signal and the crochet signal. SECAM signal converted by mixing (M1, M2) 1.5 times the frequency (Fcloche) and converting the signal subjected to the crochet filter processing to 0.5 times the cloche frequency (Fcloche) And limiting the converted SECAM signal (ACCf) to form a limited SECAM signal, and demodulating (FMD) the limited SECAM signal to form a chrominance signal (BY). , R-
Supplying Y).
ECAM decoding method. 5. The SECAM decoding device according to claim 2, which generates a chrominance signal (BY, RY), and outputs the chrominance signal (BY, RY) and the luminance signal (Y). The color signals (B,
R, G) and a color signal (B,
(D) for displaying R, G). SECAM television receiver.