JPH01302913A - Electronic channel selection device - Google Patents

Abstract

PURPOSE:To prevent the malfunction of channel selection and to obtain a device which is superior in operability and advantageous in terms of cost by deciding whether an automatic fine adjustment (AFT) has pull-in a sound carrier or a color sub carrier and detecting the pull-in into a video carrier by means of a micro processor (MPU). CONSTITUTION:Fs and the inverse of Fc in the MPU5 of the electronic channel selection device of a frequency synthesizer system, which has an AFT loop, generate of a prescribed frequency which is increased from the value of fOSC at that time for searching again a carrier P at the time of detecting a carrier S-1 and a carrier C. When the carriers S-1 and C are detected, a switch circuit 31 switches Fs and the inverse of Fc and supplies the prescribed frequency Fs or the inverse of Fc to one of an adder 32. The value of fOSC set in a fOSC memory 33 at that time is supplied to the other input of the adder 32. AFT detects the pull-in of the sound carrier or the color sub carrier to the video carrier by using a frequency difference between the video carrier and the sound carrier of lower side adjacent channel, and between the video carrier and the color sub carrier.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a frequency synthesizer type electronic tuning device used in CATV receivers and the like.

(Prior Art) In general, CATV is becoming multi-channel with the aim of diversifying television services.

Multi-channel CATV transmission systems in the United States include STD, HRC, and IRC. Here, STD is 5 standard frequencies
.

1-I RC is H'armonic Re1ated
Carriers, IRC Incrementa
It is an abbreviation of 1Related Carriers.

These 11 channel arrays change the frequency assignment for each channel to prevent interference, and are based on EIA
(Electronic Industry Federation of America) l5-6 (CP>), STD is the same as the frequency allocation for terrestrial broadcasting (hereinafter referred to as
This video carrier frequency is called fstd, and HRC
Then 5 channels, 6 channels only f std +
Allotted to 0.75MHz±0.3MIIz, fstd -1,25Hz±0.3 for other channels
It is assigned to HH2. Also, in JRC, only 5 channels and 6 channels are fstd+20Hz±0.3M.
Hz, and f st for other channels.
It is assigned to d±0.3MHz. However, ±0.38H
2 indicates a frequency offset.

Also, the frequency interval between channels is 6.0±0.12
The frequency is 5MHz.

As mentioned above, there is a frequency offset in each transmission system, so conventional frequency synthesizer type electronic tuning equipment uses automatic fine adjustment (hereinafter referred to as △F T (Au
It is necessary to apply a method called matic Fine Tuning).

FIG. 4 shows a conventional electronic tuning system using a frequency synthesizer having an FT loop. Voltage controlled oscillator (VCO)2. band pass filter (BPF)
3 constitutes a frequency converter, and by adding and mixing the signal from VCO 2 and the RF signal multiplier 1, R
Frequency conversion is performed on the F-fold signal and the IF-fold signal (referred to as heterodyne detection). The IF multiplied signal from the BPF 3 is input to the ΔFT detector 4, and the AFT detection output voltage (hereinafter referred to as AFT
VAFT (referred to as a voltage) is obtained, and this voltage is supplied to a central processing unit (MPU) 5. The AFT detector 4 is designed to enable the EL to obtain a TF output (that is, obtain a predetermined 1F frequency) even when the RF frequency is offset from a predetermined value as in the CATV system described above. By telling the MPU 5 whether the input IF frequency is higher or lower than a predetermined value, A
This forms an FT loop. The MPU5 generates digital data V2 corresponding to the local oscillation frequency f O3C.
(fO3c ”) is sent and input to the multiplier 6.V
The signal ■1 (fO8C) from CO2 is also input to the multiplier 6. The multiplier 6 and the low-pass filter (LPF) 7 constitute a phase detector, and together with the VCO 2 they form a phase-locked loop (hereinafter referred to as PLL), and the local oscillation frequency fO3C matches fO3C''. It works as expected.

fO3c" is a value (usually digital data) sent by the MPU 5 expressed in local oscillation frequency. Therefore, if the MPU 5 sends fO3c", the VCO2
It becomes possible to set the oscillation frequency (that is, the local oscillation frequency) of the oscillation frequency to a desired value (referred to as a frequency synthesizer). Identification of the broadcast signal channel is based on the local oscillation frequency f
This can be done by detecting a change in the AFT voltage V AFT, which indicates the deviation of the IF frequency from the specified frequency, when O3C is swept in a predetermined direction.

FIG. 5 shows the configuration of the above-mentioned AFT detector, in which the IF multiplier signal limiter 11 limits the amplitude and removes the AM component.
A carrier wave (hereinafter referred to as carrier) is extracted using BPFl 2 tuned to the frequency. Then, one of the carriers is π/
2 phase shifter 13 to obtain two signals having a phase shift difference of π/2, and these signals are input to analog multiplier 14. When the multiplication output is passed through LPFl 5 to remove high frequency components, a phase detection output V DET is obtained. When this output V DET is amplitude limited by a limiter 16, a three-value output of -1, 0, and 1 is obtained. O is the output when detuned. Comparator 17 outputs these three values.

is compared with the reference value V REF and changed to a binary output of 0.1, and it is detected that the llt tone has been adjusted.

FIG. 6 shows a circuit around the comparator 17 of the AFT detector. A DC bias voltage is set at the upper terminal of the comparator 17 by dividing the DC power supply VCC by resistors R1 and R2, and a reference voltage VREF is applied to one terminal. A capacitor C1 is connected between the upper terminal and the reference potential point to remove ripples in the VAFT caused by low frequency components of the video signal. A limiter output current i is supplied to the upper terminal of the comparator 17 from current sources 10+i and 10-i ([0 is the bias voltage L of the limiter 16 and 1 is the output current of the limiter 16].

Figures 7(a) and (b) explain the operation of the △FT detector shown in Figure 5, and the horizontal axis shows fO as frequency data.
3c'', (a) shows the ternary output VAFT' input to the comparator 17, and (b) shows the binary output VAFT' output from the comparator 17.

However, FIG. 7 shows the characteristics when the RF frequency is a fixed sine wave.

The AFT detection output VAFT is then supplied to the MPU 5, and the MPU 5 controls fO3c* to search for a frequency fO at which the ΔFT voltage V AFT changes from 1 to 0 when fO3c* is increased. If fo is found, then AF
Separate the T loop and set fO3c* to fO.

In addition, in VAFT' in Fig. 7(a), the -1 section is +1
The reason why the area is narrower than that is because the characteristics of the BPF 3 are asymmetrical in positive and negative directions with respect to the video carrier P as shown in FIG. 8(b).

Note that this characteristic of the BPF 3 is due to the fact that the M-NTSC system is a vestigial sideband system.

In FIG. 8, (a) shows the spectrum of the carrier input to the BPF 3 in FIG. 4, P is the video carrier, S is the audio carrier, C is the color subcarrier,
3-1. C-1 is the audio carrier of the lower adjacent channel;
Each color subcarrier is shown. (b) is B
It does not show the band characteristics of PF3, and the horizontal axis shows the frequency based on the video carrier.

By the way, the characteristics of the AFT detector shown in Figure 7 are for the case of only the RF multiplied signal video carrier (i.e., sine wave input), but the characteristics of the AFT detector for actual television signal input are shown in Figure 9. It becomes as shown in . However, the reason why the spectrum arrangement is reversed between FIG. 9 and FIG. 8 is because the local oscillation frequency is set higher than the R[frequency.

Figure 9 shows ΔF with respect to changes in fO3c* when a large RF input and an M-NTSC television signal are input.
It shows the change in FT to T voltage voltage, and P, C, and S show the AFT pull-in position by the video carrier, color subchirelia, and audio carrier of the desired station, respectively.
-1. C-1 indicates the lead-in position by the audio carrier and color subcarrier of the lower adjacent channel. Here, if the value of fO3c* corresponding to the video carrier P is fO, then Δfuse''=fO8C*-To.

In the figure, downward and upward arrows indicate the direction of change in VAFT when fO3c* is increased. Within the area (hatched) surrounded by upward arrows to the right of each carrier position, the VAF
T changes upward. That is, it shows that the rising position varies approximately within the range of this diagonal line. The only thing that changes downward is the position where each carrier is, and the AFT will retract at this position.

Note that the fall of V AFT at the S-1 position is due to S-1.
When the level ratio S-1/P between 1 carrier and P carrier is large (usually 3 dB or more), V AFT falls at the position of color subcarrier C.
This is only true when the level ratio C/S between C/S and S is large (usually 2 dB or more). Therefore, it is when the level of the lower adjacent channel is large that it is pulled into S-1.
Dropping into C occurs when you select a channel when the S level is low and a dark color is being broadcast.

As a result of the above, conventionally, for example, when channel 6 of IRC is selected, the audio carrier 5-1 of the lower adjacent channel
(In other words, there was a problem that it was drawn into the 5-channel audio carrier S).

This is because the conventional API system does not have a means to distinguish between the video carrier P of the desired wave and the audio carrier S-1 of the lower adjacent channel.

To solve this problem, conventionally, STD, 1-IRC,
A changeover switch was provided to switch between each IRC transmission system, and the receiving frequency band in the MPU in the channel selection device was switched for each transmission system, so that the video carrier of the desired channel could be received.

FIG. 10 shows the configuration of a conventional MPU in which the frequency band of the MPU in FIG. 4 is changed by a changeover switch for each transmission system, and 21 is a manual switch for switching the CATV system; By switching each transmission system STD, HRC, IR
2-bit signals (0, 1), (0, 0) (
1, O) is input to the MPU 5. Inside the MPU5, S
Local oscillation data (expected frequency) corresponding to the video gear of the desired channel of each TD, HRC, and IRC system
Means FSTD for generating f 03C (EXPE).

Fl+RC, FIRC (physically, this data is R
(defined in the OM) are provided, and these data are selectively switched for each transmission system by a switch circuit 22 using a signal from the changeover switch 21. Note that channel switching in each transmission system can be performed using a keyboard (not shown) connected to the MPU. f03C(EXPE) corresponding to the video carrier of the desired channel of the target system from the switch circuit 22 is supplied to one input terminal of the adder 24 through the fO3c'' memory 23.On the other hand,
AFT voltage (binary output) from FT detector 4 VAF■
is input to the AFT controller 27 and used to switch the switch circuit 25. When V AFT is II 1 II, the AFT controller 27 changes the frequency in constant steps nF 5T.
In order to increase the EP, switch circuit 25 is switched to the data memory nFsTEP side, and V AFT is N O
At the time of II, in order to decrease the frequency by a constant step nFsTEP, the switch circuit 25 is connected to the data memory -nF
ST[Switch to P side. The output from the switch circuit 25 is supplied to the other input terminal of the tightener 24, and the added output is stored in the fO3c* memory 23, and the digital data from this memory is converted into analog data V2 ( fO8c *) and output it.

If the configuration is such that the frequency band of the MPU is switched by the changeover switch as described above, normal reception is possible without being drawn into the audio carrier of the lower adjacent channel by the AFT operation when selecting a channel.

However, in the above configuration, STD, I-IRC.

There was an inconvenience in that the user had to switch manually according to each IRC CATV system.

(Problems to be Solved by the Invention) As described above, in the conventional channel selection system, the AFT may be drawn into the audio carrier of the lower adjacent channel, making it impossible to receive the audio normally. In order to solve this problem, in the past, users had to use a changeover switch to switch the reception depending on the broadcasting system such as HRC or IRC, which caused the problem of not only requiring a switching operation but also being disadvantageous in terms of cost. there were.

Therefore, the present invention is intended to solve the above problems.
It is an object of the present invention to provide an electronic channel selection device that prevents channel selection malfunctions, has excellent operability, and is advantageous in terms of cost.

[Configuration of the Invention (Means for Solving the Problems)] In the electronic channel selection device of the present invention, the MPU has frequency deviations between the video carrier and the audio carrier of the lower adjacent channel, and between the video carrier and the color leave carrier. The present invention is configured to include a means for determining whether the AFT has been drawn into the audio carrier or the color subcarrier using the above, and detecting the drawing into the video carrier.

(Function) In the present invention, the AFT detects whether it has fallen into the audio carrier or the color subcarrier, and if it has fallen into these carriers, searches for the video carrier again to detect the video carrier. Try to find a point of agreement. Therefore, even without switching the transmission system using a manual switch, automatic channel selection of television signals is possible without being drawn into the audio carrier or color subcarrier.

(Example) The present invention will be described below based on the example shown in the drawings.

The overall block diagram of a frequency synthesizer type tuning system having an AFT loop according to the present invention is the same as that shown in FIG. 4, and the configuration of the AFT detector 4 is also the same as that shown in FIG. The AFT detector 4 extracts the IF multiplied signal frequency change from the BPF 3 constituting the frequency converter as a DC voltage change, and informs the MPU 5 whether the IF frequency is higher or lower than a predetermined value. That is, AFT detector 4
outputs the AFT voltage VAFT, and the MPL15 controls TfO3C* (MPU (7) transmission through local oscillation frequency expression) based on this voltage VAFT, and when fO3c* is raised, VAFT changes from "1" (5V) to O" In the present invention, in the process of searching, the AF
It detects whether T has been drawn into the target video carrier P, the audio carrier S-1 of the lower adjacent channel, or the color sub-gear C, and the carrier S-
1 or carrier C, the video carrier P is searched again.

FIG. 1 shows MP in an electronic channel selection device according to an embodiment of the present invention.
FIG. 2 is a block diagram showing the configuration of U.

In Fig. 1, FS and -FC are carrier S-
1. Means for generating constant frequency data that increases or decreases from the value of fO3c'' at that time in order to search for carrier P again when carrier C is detected,
Or when the carrier C is detected, the switch circuit 31
S or -FC is switched to supply one input terminal of the adder 32 with a constant frequency FS or -FC. Adder 32
The value f 03C1 of fO3c* set in the fO3c* memory 33 at that time is supplied to the other input terminal of .

= 15 - Here, taking the case of the M-NTSC system as an example, the value of FS is 1,5 MHZ 4-250 k l-I Z
= 1.

It may be about 75 M l-1z. 1.5M above
H2 is the frequency deviation between the video gear '+7 rear P and the audio carrier 3-1 of the lower adjacent channel, which is 1.5MH7-
It is defined as ((channel A/channel exclusive bandwidth 6.0 MHz) - (audio intermediate frequency 4.5 Ml - 1 z)).

Further, the above-mentioned 250 kHz is a value that takes into consideration the above-mentioned inter-channel frequency deviation variation of 125 kHz and the AFT circuit variation. The value of FC may be approximately 3.31M1-1z in the M-NTSC system. Here, 3.31M
t-(z)(color subcarrier frequency 3.57954
5MHz>-250k l-1z.

Based on the input channel switching signal, the control circuit 43
is a fixed frequency cheater f corresponding to the desired channel
O3c (EXPE) Memo 'J 4173" + fO8
Load it into the c8 memory 33. Its frequency data fos
c'' is converted into a voltage value V2 (fO3c'') by the converter 36, and channel switching is performed. AFT detector 4 detects AFT voltage V A according to V2 (fO3c *)
FT is output, and the three AFT controllers activate the ΔT loop to search for fO. When the AFT is pulled in, the AFT controller 39 switches the switch circuit 37 to the b side, and the S-1 carrier pull-in detector 34 and C carrier retraction detector 35
make it work. Whether it is detected by the S-1 carrier pull-in detector 34 or the C carrier pull-in detector 35 is whether the value of fO8c at that time is on the audio carrier S-1 side of the lower adjacent channel of each channel. Or it depends on whether it is on the color subcarrier C side of each channel.

The S-1 carrier attraction detector 34 uses its control output to switch the switch circuit 31 to the data generation means FS, and temporarily stores the value of the fO8c* memory 33 at that time into the f'sC1 memory 42.
The value of fO3c* memory 33 is increased by a predetermined frequency FS. Next, measure AFT and VA
Since gear rear P is detected when FT is '0'', the judgment is reversed that it has been pulled into carrier S-1 at f03C1.In this case, this fO3c*Memory 3
If the carrier is searched again from the value of 3, that is, fO8CI+FS, it is possible to pull into the P carrier. That is, the switch circuit 37 is switched to the a side and a search is performed using the FSTEP data. Data memory n FSTEP, -n
The operation of the switch circuit 38 for switching FSTEP is similar to the switch circuit 25 of the conventional example (FIG. 10). Also, VAFT “0” at fO3C1-1-F, S
” is not detected, it is determined that f 03C1 is carrier P, and the value of fO3C1 memory 32 is returned to fO3c* memory 33.

The C carrier pull-in detector 35 uses its control output to switch the switch circuit 31 to the data generation means -FC, and the current f
After moving the value of O3c* memory 33 to f 03C1,
The value of fO8c* is decreased by a predetermined frequency FC. Next, AFT is measured, and when VAFT is 1101+, carrier P is detected, so the value of fO3c* is f 0
At 3C1, it is determined that the carrier C has been retracted. Then, as in the case of S-1, by switching the switch circuit 37 to the a side and searching for carrier P from carrier f 03C1-FC in units of F 5 TIEP, it is possible to pull into carrier P. VAFT in f 08CI-FC C
If “0” is not detected, fosc1 is
Assuming that, fO3c* is returned to f 03CI.

FIG. 2 explains an example of MPU operation according to the present invention. Time is plotted on the horizontal axis and fO8C* is plotted on the vertical axis.
First, carrier C detection is performed by setting the value of fO3c* to f 03CI-FC, and then carrier s-i is detected by setting the (direction of fosc * to f 08C1 + F S. If carrier C or carrier S
Since the value of fosc1 was not pulled down to -1, the value of fosc1 was changed to f
It has been reverted to 03C1.

FIG. 3 explains another example of the MPU operation according to the present invention, and shows a case where only carrier S-1 detection is performed. Set the value of fO3c* to f03CI0FS and key 17
Since the rear 3-1 was detected and correctly drawn into the carrier P at f03C1, the value of fO3c* was changed to fosci.
is returning to .

Next, the effectiveness of the above means will be explained using FIG.

(1) If fosc1 is pulled into P (i.e., f
03CI is the frequency fO corresponding to the key 11 rear P), carrier C detection is ΔfO3c*=-FCy~
Since it is performed at 3.31 MHz, VAFT=5V (ie, logic "1"), and no pull-in is detected. Carrier S-1 detection is ΔfO8c*=Fs = 1.75MHz
Since it is done at this time, V AFT-5V is also obtained.
No retraction is detected. Therefore, the MPU returns fO3c'' to f 03CI (ie, fo) and normally tunes to carrier P.

(2) If it is pulled into carrier S-1, carrier C detection is △fO8c *--1, 5MHZ-3,
It will be performed at 31MHz--4.81MHz.

Although this frequency is not shown, the characteristic of FIG. 9 repeats periodically with an inter-tunnel spacing of 6 M l-1z. For example, ΔfO3c *= 6MHZ-4,81MH
Looking at the VAFT at z=1.19M1-1z, it is 5V, and no pull-in is detected. Carrier S-1 detection is Δf O8C*=-1,5MHz+1
．． 75MHz=0. At 25MHz, VAFT-OV
Therefore, it is determined that the carrier was pulled into carrier S-1. Therefore, since the search is restarted from 0.25 MHz, it is possible to correctly pull into the carrier P.

(3) If it is drawn into carrier C, when carrier C is detected, Δf O3C is 3.58MHz-3,
Since 31MHz=0.27MHz, VAFT=O
V, and it is determined that it was pulled into carrier C.

Then, since the search is restarted from 0.27 MHz, it becomes possible to tune to the carrier P correctly. in this case,
If carrier S-1 is detected first, ΔfO3c
” =3.58MHz+1.75MHz=5.33Mh
lz, and it is unclear whether VAFT is OV or 5V, which is not preferable.

As described above, according to the above embodiment, the video carrier P
The frequency deviation between S-1 and 2 and the frequency deviation between P and 0 are used as a means for identifying the audio carrier S-1 of the lower adjacent channel, the video carrier P, and the color subcarrier C. Therefore, the video carrier P can be identified regardless of the 0ATV transmission system (that is, regardless of the absolute frequency of the video carrier P).

In addition, AFT voltage VAFT, VAFT' (7)
It goes without saying that the ffl property can also be implemented in the opposite manner to that of the above embodiment.

[Effects of the Invention] As described above, according to the present invention, automatic channel selection is possible without causing channel selection malfunctions due to being drawn into the audio carrier of the lower adjacent channel or the color subcarrier of the desired channel. . Therefore, as in the past, HRC and IRC
There is no need for the user to change the operation switch depending on the CATV system such as the above, which improves operability and is advantageous in terms of cost.

[Brief explanation of the drawing]

FIG. 1 shows MP in an electronic channel selection device according to an embodiment of the present invention.
FIG. 2 and FIG. 3 are explanatory diagrams explaining the operation of the MPU shown in FIG. 1. FIG. 4 is a block diagram showing a frequency synthesizer type electronic tuning system with a ΔFT loop. , Fig. 5 is a block diagram showing the configuration of the AFT detector, Fig. 6 is a circuit diagram without showing an example of the surroundings of the comparator of the AFT detector, and Fig. 7 explains the operation of the AFT detector shown in Fig. 5. Figure 8 is an explanatory diagram to explain the input carrier spectrum and BPF characteristics of the BPF in Figure 4, and Figure 9 shows the AFT detection characteristics for the actual television signal input shown in Figure 4. The explanatory diagram, Fig. 10, is the conventional example M.
FIG. 2 is a block diagram showing the configuration of a PU. 1.6... Multiplier, 2... VCO13... BPF
, 4...AFT detector, 5...MPU, 7...L
P.F. 31.37.38...Switch circuit, 32...Adder, 33...fO3c" memory, 34...S-1 carrier attraction detector, 35...C carrier attraction detector, 36. ...Converter 39...AFT controller, 41...fO3c (EXPE) memory, 42...
f 03CI memory. Agent Patent Attorney Susumu Ito - Shichi (〉) I
n.

Claims (1)

[Claims] A frequency converter that converts an RF signal into an IF signal, and an AFT that outputs the deviation of the IF frequency from a specified frequency as an AFT voltage when the local oscillation frequency of the frequency converter is swept in a predetermined direction. Detector and A from this AFT detector
A control means that searches for a change in the FT voltage and outputs data corresponding to the local oscillation frequency at the time of the change, and a PLL that operates to match the local oscillation frequency of the frequency converter with the data corresponding to the local oscillation frequency from the control means. A frequency synthesizer type electronic channel selection device comprising a frequency synthesizer circuit, wherein the control means includes an AFT using frequency deviations between a video carrier wave and an audio carrier wave of a lower adjacent channel, and between a video carrier wave and a color subcarrier wave. An electronic channel selection device characterized by comprising means for determining whether or not the signal is drawn into the audio carrier wave or the color subcarrier, and detects the drawing into the video carrier wave.