JPS6145431B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a television ghost signal canceling device that can effectively cancel ghost signals caused by multiple reflections in a television receiver. Radio waves arriving at the receiving antenna of a television receiver include not only direct waves but also reflected waves that are reflected by buildings, mountains, etc. and have different propagation paths. The reflected waves cause a so-called ghost image in the displayed image, leading to image deterioration. In order to remove this ghost image, various measures have been taken in the past, such as using a variable delay element or a variable directional antenna. However, the time lag and intensity of the reflected waves generally vary over time, and each channel has a different value. For this reason, the adjustment for ghost elimination is complicated, and it has not been widely used in general home television receivers. Nowadays, one of the methods for erasing ghost images is "Nikkei Electronics. 1977/2/7, P29"
proposed by. FIG. 1 is a schematic diagram showing a modification of the device shown in the above-mentioned document. In the figure, 1 is a transversal filter that applies tap gain weight to the input (television demodulation) signal and performs delay addition, 1a is a charge transfer shift register (such as a CCD) with an addition function, and 1b is a tap gain filter. 1c is an adder. Of the output of this filter 1, the portion corresponding to a specific waveform within the vertical retrace period, specifically the step waveform when moving from the third line to the fourth line, is controlled by the time reference setting circuit 2. The tap gain correction value is then input to the difference circuit 3 and a tap gain correction value is calculated. The tap gain correction value is stored in a register 4 and input to an integrator 5 to determine the tap gain. The integrator 5 provides a tap gain to each of the multipliers 1b. However, such conventional devices have a problem in that it takes a long time for the tap gain to converge when the receiving channel of television broadcasting is switched. In other words, even though the situation in which ghost signals occur usually differs depending on the channel, in conventional devices, when the channel is switched, the tap gain continues to be corrected in the same state, resulting in wasted tap gain. A correction operation is performed, and it takes a long time to finally converge to a tap gain suitable for the receiving channel. SUMMARY OF THE INVENTION An object of the present invention is to provide a television ghost signal canceling device that can shorten the tap gain convergence time when switching channels. In order to achieve the above object, the present invention includes a ghost signal canceling circuit including a transversal filter having a plurality of taps with variable tap gains, a nonvolatile memory storing tap gains corresponding to each channel of television broadcasting, and means for reading out a tap gain corresponding to a selected channel from a nonvolatile memory; and sequentially correcting the tap gain of the transversal filter using the tap gain read by the means as an initial value; and means for updating the tap gain to the corrected tap gain. Generally, the situation in which ghost signals occur differs considerably between different types of channels, but there is little change over time in the same channel. Therefore, according to the present invention, when switching channels, it is only necessary to modify the tap gain by a relatively small amount of change from the final tap gain when the same channel was previously received, which greatly reduces the time required for tap gain convergence. can be shortened to Embodiments of the apparatus of the present invention will be described below with reference to the drawings. FIG. 2 is a schematic configuration diagram. 11 in the figure is a CCD (charge transfer type shift register).
(coupled device), and each element of this CCD 11, that is, the tap input, has a multiplier 12.
Television demodulated signals are input through the . The multiplier 12 multiplies the television demodulated signal by a tap gain, which will be described later, to weight the television demodulated signal. These multipliers 12 and CCD 11 constitute a transversal filter. The signal input to this transversal filter and the signal output via the transversal filter are sent to first and second shift registers (CCD) 15, 1 via analog switches 13, 14, respectively.
6 and stored and held. The analog
The switches 13 and 14 are controlled to open and close by a time reference setting circuit 17, which will be described later. Note that the signal writing to each of the shift registers 15 and 16 is based on the television color subcarrier frequency.
This is done by, for example, 3 times _C (10.7MHz).
The shift register 15 has a length that can accommodate, for example, the waveform of the main part of the input signal (the part corresponding to the non-zero section of the reference waveform), and the shift register 16 has a length that matches the length of the shift register 15. The length is the sum of the length of the delay line (CCD 11). The signals stored in these shift registers 15 and 16 are read out at a slow speed, for example, at the television horizontal synchronizing signal frequency _H (15.75 kHz). This signal is converted to an analog-to-digital converter (ADC) 18
and are each digitally encoded. The input signal waveform stored in the shift register 15 and encoded by the ADC 18 is once input to the shift register 19 and temporarily stored. The output signal waveform stored in the shift register 16 and encoded by the ADC 18 is sent to the difference circuit 20.
is input. This difference circuit 20 has a memory 21
A coded reference waveform that is a reference written in advance in (for example, composed of ROM) is input,
A difference from the encoded output signal waveform, that is, an error waveform is calculated. This error waveform is input to the shift register 22 and temporarily stored. These registers 19 and 22 are similar to the registers 15 and 16.
The stored signal is input to the arithmetic circuit 23. This arithmetic circuit 23
The tap gain correction value is calculated using a multiplier that multiplies the above-mentioned signals together, an integrator that cumulatively adds the multiplied values, and the like. This tap gain correction value is stored in a tap gain memory device (for example, composed of a RAM) 2 that stores and holds the tap gain.
It is combined with the tap gain from 4 by adder 25. The tap gain is thus modified by the adder 25, and the modified tap gain is supplied to a digital-to-analog converter (DAC) 26 and fed back to the tap gain memory device 24. This tap gain memory device 24 is
Tap gain memory buffer 27, distribution circuit 28,
A plurality of memory elements 29 and the distribution circuit 2
8 and selects a memory element 29. Therefore, each memory element stores and holds a tap gain corresponding to a respective broadcast channel.
Here, the plurality of memory elements 29 are made up of, for example, RAM made up of nonvolatile memory. The signal converted into an analog signal, that is, the corrected tap gain, is then sequentially input to a shift register (CCD) 31 and held there via the DAC 26. The signals stored in this CCD 31 are sent to each holding circuit 33 via an analog switch 32 at an appropriate time at the beginning of the vertical retrace period.
is entered and retained. This holding period, that is, the discharge time constant of the holding circuit 33 is set to a value that is at least sufficiently larger than, for example, the repetition period (17 m Sec) of the vertical retrace period. These holding circuits 33 provide the tap gain of the transversal filter (multiplier 12). Thus, the signal processed by the tap gain is output from the transversal filter as an output signal. At the time when the tap gain converges, the ghost signal is removed from this output signal. Further, the time reference setting circuit 17 extracts and outputs subcarrier synchronization, horizontal synchronization (H), and vertical synchronization from the input signal, and also controls the operation timing of each section described above based on each of the synchronization signals. There is. Furthermore, the ADC 18 first encodes the input waveform (output of the shift register 15), and then encodes the input waveform (output of the shift register 15).
It encodes the output waveform (output of the shift register 16), and operates in a time-division manner here. The operation of the apparatus shown in FIG. 2 will be explained below. Let us now assume that the input television signal is x(t), the output signal is y(t), and the reference signal output from the memory 21 is r(t). It is assumed that r(t) is a periodic waveform that is repeated at a period τ, and the tap gain of the transversal filter is corrected for each period τ. Here, the tap interval, or period, of the transversal filter is T, and
Each of the above signals has sample values x (kT), y (kT), r
(kT) (where k=0, 1, 2, . . . ) will be expressed and explained. Here, if the tap gain of the multiplier 12 is expressed as C ₀ , C ₁ , ~, _Co in order from the left in the figure, then the input waveform {x
_k } and the output waveform {y _k }, the following equation holds. Here, when the difference from the output waveform {r _k } of the memory 21 is calculated, the error waveform {e _k } is shown as follows. In other words, as a quantity to evaluate the magnitude of error {e _k } Considering this, the tap gain {C
_i } control algorithm is generally achieved by using the maximum slope method. In this algorithm, the function of variable X = (x ₁ , x ₂ , ..., x _k )
Considering _(x) , the differential coefficient vector of the variable vector X ⁿ when the n-th control is performed can be expressed as follows. ▽ _(x) |x=x ⁿ =(δ/δx ₁ , δ/δx ₂ , ..., δ/δx _k ) | x=x ⁿ ...(4) Then, at the (n+1)th time, α is set to positive The tap gain is corrected by using an infinitesimal constant: X ⁿ⁺¹ =X ⁿ −α▽ _(x) |x=x ⁿ (5). When a minimum point exists in this vicinity, X ⁿ converges to the minimum point as n increases. Therefore, it can be expressed as follows. x _j ⁿ⁺¹ = x _j ⁿ −αδ/δx _j | x _j = x _j ⁿ …(6) Here, the tap gain {C _i } that minimizes the error E based on the above algorithm is C _i ⁿ⁺¹ =C _i ⁿ −αδE/δC _i |c _i =c _i ⁿ …(7), It can be found as Accordingly All you have to do is make a tap gain correction. Furthermore, as the error E

If we consider [formula] All you have to do is make a tap gain correction. Note that sgn(e _k ⁿ ) in the above equation (10') indicates the positive or negative sign of e _k ⁿ . Now, here, let the input signal stored in the register 19 be {x ₀ , x ₁ , x ₂ , ..., x _R-1 }, and let the error signal between the output signal stored in the register 22 and the reference signal be { e ₀ , e ₁ , e ₂ , ..., e _R-1 }. However, the number of stages of registers 19 and 22 is R, respectively. These signals When this is performed by the arithmetic circuit 23, the calculation result corresponds to the second term of equation (10) described above, and the tap gain correction value has been calculated. However, in this calculation, the addition for x is stopped at x ₀ ~ _{x R-1} ,
Although this will cause an error, since it substantially sufficiently covers the non-zero section of the specific scanning line signal within the vertical retrace period of the television signal, it will hardly cause any adverse effects. Therefore, the tap gain stored in the tap gain memory device 24
By adding it to C ₀ , the tap gain is corrected by (C ₀ +ΔC ₀ ). tap gain
When the correction of C ₀ is completed, only one sample is newly read from the output waveform register 16 into the register 22, ΔC ₁ is calculated by the above-mentioned operation, and C ₁ is corrected. Similar operations are repeated up to _Co.
These modified tap gains C ₀ , C ₁ , ..., _Co
are sequentially stored in the CCD 31. This CCD31
The tap gains stored in , for example, are input all at once to the holding circuit 33 and held at the beginning (timing) of the vertical retrace period. Therefore, the television video signal input following the vertical retrace period is
Tap gain weighting is performed based on the retained tap gain, and ghost signals are eliminated. On the other hand, the signal of the specified portion within the vertical retrace period is stored in registers 15 and 16, and the processing period of the television video signal (approximately 17 m Sec) is stored in the registers 15 and 16.
The tap gain correction process is performed slowly over the period. What should be noted here is that in deriving equations (10) and (10)' above, no restrictions were placed on the relative time relationship between x(t) and r(t). be.
That is, although both are defined with respect to the same time axis, for example, the positions of the peaks do not need to have a fixed time relationship. Therefore x(t) and r
(t) is a substantially similar waveform, and r(t) is x(t)
Assuming that there is a delay of approximately lT compared to , the tap gain Cl (main tap) will be approximately 1. The other tap gains take smaller absolute values than Cl. Therefore, if the relative time relationship between x(t) and r(t) deviates, the position of the main tap simply moves, and there is no essential effect on the overall operation. On the other hand, the length of the tapped delay line is finite,
Therefore, it is not preferable that the position of the main tap deviates significantly from the designed position. Therefore, it is clear that the time accuracy required of the time reference setting circuit 17 is on the order of several taps at most, which is much simpler than the conventional device described above (FIG. 1). . Furthermore, this device is a waveform equalizer in a broad sense, and for example, when an impulse is used as the basic waveform, the impulse response of the entire system including the ghost canceling circuit can be made close to the desired response. However, in some cases, waveform equalization in this sense is not necessary, and it is sufficient to eliminate only the temporally distant original ghosts without considering the transient response portion of the impulse. In other words, nearby ghosts within a specific delay time may be ignored. In this case, there is no need to control several taps before and after the main tap, and the tap gain can be fixed. For example, you can set it as follows. C ₀ - C ₁₀ ; Variable C ₁₁ - _{C 15} ; 0 C ₁₀ ; 1 C ₁₇ - _{C 22} ; 0 C ₂₃ - _{C N} ; Variable On the other hand, if the reference waveform is non-zero only in some sections,
In the case of a waveform in which other sections are zero (0), one input to the difference circuit 20 in FIG. 2 becomes "0" except for the non-zero sections. If the tap gain is not controlled for the part corresponding to the non-zero section of the reference waveform, the basic waveform will be all "0" for the part where tap gain control is actually performed.
It can be considered that Now, if the reference output waveform is set as all zeros, it is sufficient to always output information "0" from the memory 21. Then, the error can be calculated by subtracting the information "0" from the output waveform. That is, in this case, it means that the output waveform can be used as it is as the error waveform, and therefore the memory 21 and the difference circuit 20 can be omitted. Therefore, by performing tap gain correction using the specified "0" level signal, the configuration can be greatly simplified. Now, according to the present apparatus, the tap gain is corrected every cycle of the vertical retrace period, so that ghosts in the displayed image are gradually erased. Here, if the tap gain is corrected every time the channel is switched, a considerable amount of adjustment time will be required each time, and the displayed image will be troublesome. Therefore, in this device, in the tap gain memory device 24,
For each channel, the tap gain at the time of completion of ghost erasure for that channel is held. The ghost signal of each channel is determined to some extent by the installation conditions of the antenna and its frequency.
Therefore, by using the tap gains stored and maintained for each channel as initial values,
The tap gain can be converged without requiring much time. Also, in this case, since this tap gain is stored separately for each channel,
There is an advantage that tap gains of other channels are not used in the specified channel, and unnecessary tap gain modification can be prevented. Note that the present invention is not limited to the above embodiments. For example, the tap gain correction period may be set to an integer multiple of the vertical synchronization period, and the writing/reading period of signals to the registers (CCD) 15 and 16 may of course be set according to the specifications. be. Further, the number of stages of the transversal filter may be set as appropriate; for example, tap gain correction may be selectively performed. Furthermore, when modifying the tap gain using the output of the arithmetic circuit 23, it is also possible to vary the proportionality constant α, which is multiplied by the output, depending on the stage of convergence. Additionally, the output value of the arithmetic circuit 23 can be made into a positive or negative value with a constant absolute value. In short, the present invention can be implemented with various modifications without departing from the gist thereof.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a row of conventional devices, and FIG. 2 is a schematic diagram showing an embodiment of the device of the present invention. 11...Charge transfer type shift register (CCD), 1
2... Multiplier (tap gain), 15... First shift register (CCD), 16... Second shift register (CCD), 20... Difference circuit, 21... Memory (reference signal waveform), 23... Arithmetic circuit, 24...Tap gain memory device, 25...Adder, 31...Register (Tap gain register, CCD), 33...Holding circuit (Tap gain holding).

Claims (1)

[Scope of Claims] 1. A ghost signal canceling circuit including a transversal filter having a plurality of taps with variable tap gains, a nonvolatile memory storing tap gains corresponding to each channel of television broadcasting, and this nonvolatile memory. means for reading out a tap gain corresponding to a channel selected from the above, and sequentially modifying the tap gain of the transversal filter using the tap gain read by the means as an initial value, and after modifying the contents of the nonvolatile memory. 1. A television ghost signal canceling device comprising means for updating the tap gain to a tap gain of . 2. The non-volatile memory consists of a plurality of memory elements, each memory element individually stores the tap gain corresponding to each channel of television broadcasting, the tap gain is read out corresponding to the selected channel, and the tap gain is read out corresponding to the selected channel. 2. The television ghost signal canceling device according to claim 1, wherein the tap gain is updated to the corrected tap gain when the gain is corrected.