JPS6112116A - Auto tuning device - Google Patents

Abstract

PURPOSE:To apply accurate tuning operation without increasing the frequency of a basic clock by providing an automatic minute adjustment signal to an electronic tuner together with a tuning voltage. CONSTITUTION:A frequency detection circuit 26 discriminates an intermediate frequency signal D from a television linear circuit 23, outputs an automatic minute adjuting signal VAFT to a tuner 22 and outputs two kinds of H.L pulse signals. A tuner tuning voltage control circuit 29 forms a tuning signal Vt based on two kinds of pulse signals and output it to the tuner 22. Then the tuner 22 changes its local oscillating frequency in response to the given signals VAFT and Vt, and the local oscillating frequency is adjusted minutely near the tuning of the reception signal. Thus, the tuning is executed accurately witout improving the frequency of the basic clock.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an auto-tuning device for a television receiver or the like.

[Prior art and its problems]

In recent years, small television receivers that use liquid crystal display panels in their display sections have been put into practical use. Conventional small-sized television receivers of this type are generally equipped with an auto-tuning device, so that a tuning operation is automatically performed by operating a tuning amplifier key or down key. In the auto-tuning device described above, in order to perform the tuning operation accurately, tb, in order to reduce the deviation of the frequency at which the channel search operation ends from the ideal frequency (optimal tuning state) K, K is set by the tuner' It is necessary to increase the resolution of the switching voltage/A converter. In order to increase the resolution of this D/A converter, if the channel search speed is held constant, the frequency of the basic clock must be increased. However, increasing the frequency of the basic tarock as described above requires circuit elements with fast response speeds and increases power consumption, which is undesirable.

Furthermore, in order to increase the dividing power of the D/A converter by keeping the frequency of the basic clock constant, the channel search speed must be slowed down, which is impractical.

[Purpose of the invention]

The present invention has been made in view of the above points, and an object of the present invention is to provide an auto-tuning device that can accurately perform tuning operations without increasing the frequency of the basic clock.

[Key points of the invention]

In the present invention, the output of the frequency discrimination circuit is applied to the tuner together with the auto-tuning voltage to perform fine frequency adjustment.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. First, the external configuration of the present invention will be explained with reference to FIG. In FIG. 1, numeral 1 indicates a case, on the front of which a video display section 12, a channel display section 13, and a volume display section 14 are provided. The above video display section 12, channel display section 1
3. The volume display section 14 is configured, for example, integrally on one display panel 15, but is configured to be displayed separately by display windows formed on the front surface of the case 11. In the channel display section 13, numerical values indicating VHF and UHF channels are displayed on both sides of the case 11 by printing or the like. Further, on the front surface of the case 11, an up key 16a and a down key 16b for tuning are provided, and an up key 17& and a down key 17b for volume adjustment are provided. Furthermore, K-x i I K It'! , an auto/manual changeover switch 18 , a VHF/1JHF changeover switch 19 , and a power switch 20 , and a rod antenna 2 is provided at the top of the case 11 .

Next, the configuration of the electronic circuit provided in the case 11 will be explained with reference to FIG. 2. Radio waves received by the antenna 21 are supplied to an electronic tuner 227/C. The electronic tuner 22 selects a desired radio wave from among the received radio waves, converts it into an intermediate frequency A, and outputs it to the television linear circuit 23. This television linear circuit 23 includes an intermediate frequency amplification circuit, a video detection circuit, a synchronous separation circuit, etc., and outputs an audio signal to an audio circuit (not shown).
A video signal B, an intermediate frequency signal D1 and a synchronization signal E are output.

The video signal B output from the television linear circuit 23 is sent to a conversion circuit 24. The Φ conversion circuit 24 converts the video signal B from the television linear circuit 23 into a 4-bit digital signal C, sends it to the liquid crystal drive circuit 25, and drives the video display section 12 on the liquid crystal display panel 15 for display. Further, the intermediate frequency signal outputted from the television linear circuit 23 is sent to a frequency detection circuit 26, and the synchronization signal E is sent to a control circuit 27. The frequency detection circuit 26
discriminates the intermediate frequency signal input from the TV linear circuit 23, outputs the automatic fine adjustment signal VAFT to the tuner 22, and outputs H (Hlgh) and L (Low).
) are output to the control circuit 27. Further, to this control circuit 27, a 4-bit digital signal C is inputted from the above-mentioned key conversion circuit 24, and key data is inputted from the key input section 28. This key human power department 28
is the up key 1 for tuning in Figure 1 above.
6a, down key 16b.

Along with an up key 17a and a down key 17b for volume adjustment, an auto/manual changeover switch 18, a power changeover switch 19, and a power switch 20 are provided. , Up key 1 for tuning from key human power section 28
6m and the down key 16b, a tuning control signal is output to the tuner tuning voltage control circuit 29. This tuner tuning voltage control circuit 29 is equipped with a D/A converter for generating a tuner voltage, and converts the tuning control signal from the control circuit 27 into a D/A in synchronization with a predetermined clock pulse as a tuning signal V4. Electronic tuning tuner 22
Output to. In this case, the control circuit 27 outputs a mute signal to the audio circuit to inhibit audio output while the tuning operation is being performed and until the next station is selected. Further, the control circuit 27 outputs a volume adjustment signal to the audio circuit in accordance with the operation of the volume adjustment up key 17& and down key 17b from the key input unit 28. Furthermore, the control circuit 27 outputs a volume display signal and a channel display signal F to the liquid crystal drive circuit 25 in accordance with each key operation in the key manual section 28, and also outputs a volume display signal and a channel display signal F to the liquid crystal drive circuit 25 in accordance with a synchronization signal E from the television linear circuit 23. Outputs the display timing signal to.

The liquid crystal drive circuit 25 controls the video display section 12, channel display section 13, and volume display section 1 on the liquid crystal display panel 15 according to signals from the conversion circuit 24 and the control circuit 27.
・Display drive each of 4.

Next, details of each part in FIG. 2 will be explained.

FIG. 3 shows details of the electronic tuning tuner 22, which includes an antenna coupling circuit 221, a high frequency coupling circuit 222, a mixing circuit 223, and a local oscillation circuit 224. The received signal from the antenna 21 is input to the antenna coupling circuit 221, and the tuning signal vt from the tuner tuning voltage control circuit 29 is input to the local oscillation circuit 224. The local oscillation frequency of the local oscillation circuit 224 changes according to the tuning signal VT from the tuner tuning voltage control circuit 29 and the automatic fine adjustment signal VFT from the frequency detection circuit 26. According to this change in the local oscillation frequency, an intermediate frequency signal A between the mixing circuit 223 and the receiving station is outputted and sent to the television linear circuit 23.

The local oscillation circuit 224 is configured as shown in FIGS. 4(a) and 4(b), for example.
It consists of the following. In FIG. 4, Tr is an oscillation transistor, and a parallel resonant circuit X1 consisting of an oscillation coil L and a capacitor C is connected between the pace of this transistor Tr and ground. Further, a series circuit of the parallel resonant circuit XILK capacitor C1 and a variable capacitance diode DI, and a series circuit of a content capacitor C and a variable capacitance diode Ds are connected in parallel. A tuning signal vt from the tuner tuning voltage control circuit 29 is applied to the connection point between the capacitor cl and the variable capacitance diode D1.
is input via the resistor r1'. Further, an automatic fine adjustment signal V from the frequency detection circuit 26 is connected to the connection point between the content capacitance C2 and the variable capacitance diode D2. is input via resistor r2. The local oscillation circuit 224 configured as described above changes the capacitance of the variable capacitance diode D1 according to the tuning signal vt, and
Variable capacitance diode D according to automatic fine adjustment signal VAFT
2 changes, which changes the local oscillation frequency. ' ・Also, in the example shown in FIG. 4(b), a series circuit α of a capacitor C1 and a variable capacitance diode Dl is added to the parallel resonant circuit Xa.
Connect only. Then, the connection point between the capacitor C1 and the variable capacitance diode D is connected to a signal input terminal t'' via a resistor r, and the tuning signal V! is connected to the input terminal t. and automatic fine adjustment signal 4VAy"r are inputted through resistors R1lR, respectively.
), the local oscillation frequency is changed in the local oscillation circuit 224 by a composite signal of the tuning signal VT and the automatic fine adjustment signal VAFτ.

FIG. 5 shows details of the television linear circuit 23.
An intermediate frequency signal A is input from the electronic tuning tuner 22 to the intermediate frequency amplifier circuit 231 from the intermediate station wave amplification circuit 231, the detection circuit 232, the signal amplifier circuit 233, and the synchronization separation circuit 234. The intermediate frequency amplification circuit 231 amplifies the input intermediate frequency signal A, outputs it to the audio circuit, and also outputs it to the video amplification circuit "233" via the first detection circuit 232.
Output to. The video signal B output from the video amplification circuit 233 is sent to the cross-conversion circuit 24 and also to the synchronous separation circuit 234. This synchronous separation circuit 2
34 separates a Σ horizontal synchronizing signal φ7 and a vertical synchronizing signal φh included in the video signal from the video amplification circuit 233, and outputs them to the control circuit 27.

FIG. 6 shows details of the frequency detection circuit 26, in which intermediate frequency signals sent from the frequency discriminator 261, comparators 262 and 263, and the TV linear circuit 23 are input to the frequency discriminator 261. Ru. Then, the output of the frequency discriminator 261 is taken out as an automatic fine adjustment signal VAFT, and the output of the comparator 262 is
” terminal and the “-” terminal of the comparator 263. Further, reference power supplies 264 and 26 are connected to the "-" terminal of the comparator 262 and the "+" terminal of the comparator 263.
5 are connected to each other. And comparator 2
62,263 output auto tuning control signal.

It is output as H and sent to the control circuit 27.

As shown in FIG. 7, the frequency discriminator 261 outputs a positive discrimination signal if the input frequency is lower than the set frequency jp, and outputs a negative discrimination signal if it becomes higher. When the discrimination signal becomes higher than the reference voltage Vl, the comparator 262 outputs a signal H, and when the discrimination signal becomes lower than the reference voltage V2, the comparator 263 outputs a signal H. Then, the output signals L and H of the comparators 262 and 263 are sent to the control circuit 27 for auto-tuning processing.

Next, the operation of the above embodiment will be explained. In FIG. 2, a television signal induced in an antenna 21 is tuned and frequency-converted by an electronic tuner 22, band-amplified and image-detected by a television linear circuit 23, and taken out as a video signal B. This video signal is converted into a 4-bit digital signal C in the digital conversion circuit 24, and is sent to the liquid crystal drive circuit 25 and displayed on the video display section 12. Furthermore, an audio signal is output from the television linear circuit 23 and sent to the audio circuit. This audio circuit amplifies the audio signal from the television linear circuit 23 and outputs it to multiple speakers.

Furthermore, the television linear circuit 23 outputs the intermediate frequency signal amplified by the internal intermediate frequency amplification circuit 231 to the frequency detection circuit 26, and also outputs the vertical synchronization signal φ7 and horizontal synchronization signal φh separated by the synchronization separation circuit 234. Output to control circuit 27. The frequency detection circuit 26 inputs the intermediate frequency signal from the TV linear circuit 23 to the frequency discriminator 261, converts the frequency change into a voltage change, and outputs the automatic fine adjustment signal FT to the electronic tuning tuner 222.
It is output to comparators 262 and 263 as well as input to comparators 262 and 263. These comparators 262 and 263 have a reference voltage v
AF for auto tuning by comparison with i+vz
Create T signals H and L. Currently, in Japan, an upper heterodyne system is used in which the local oscillation frequency is higher than that of the received radio wave signal. Therefore, the local oscillation frequency is always higher than the video carrier of the receiving channel by the intermediate frequency. As the tuner tuning voltage increases, the local oscillation frequency also gradually increases. As a result, the intermediate frequency, which is the difference between the local oscillation frequency and the received video frequency, also gradually increases. FIG. 7 shows the change in the output voltage of the frequency discriminator 26 with the intermediate frequency at this time on the horizontal axis. As shown in FIG. 7, the frequency discriminator 261 outputs a positive discrimination signal if the input frequency is lower than the set frequency fp, and outputs a negative discrimination signal if it is higher. Therefore, when the input frequency is much lower than the set frequency F and the frequency discriminator 261 outputs a positive signal whose signal level exceeds the reference voltage 71, the comparator 262 outputs an AFT signal. Further, when the input frequency is higher than the set frequency FP and a negative signal is output from the frequency discriminator 261 and the signal level becomes below the reference voltage V, the comparator 2
AFT signal H is output from 62. If the tuner tuning voltage is fixed when the AFT signals are output in the order of L-H from the frequency detection circuit 26, the intermediate frequency can be correctly set to a predetermined frequency, for example, 58.75 MHz.

Conversely, if you lower the tuner tuning voltage, the intermediate frequency will gradually become lower, so the AFT signal will change from H to L.
If the tuner tuning voltage is fixed when output from the frequency detection circuit 26 in this order, the intermediate frequency can be set correctly as in the above case. Therefore, the AP'T signal output from the frequency detection circuit 26 is sent to the control circuit 27. This control circuit 22 controls the AF
Based on the T signal and the H signal, a control signal is sent to the tuner tuning voltage control circuit 29 to control the tuning frequency of the electronic tuning tuner 22.

A output from the frequency detection circuit 26 as described above
Tuning control is performed based on the FT signal H, and at this time, the signal output from the frequency discriminator 261 is used as the automatic fine adjustment signal VAFT to the electronic tuning tuner 2.
2, where the tuning frequency is finely adjusted.

Now, for example, if the tuning amplifier key 16a is operated in the key manual section 28, a control command is sent from the control circuit 27 to the tuner tuning voltage control circuit 29, which causes the tuner tuning voltage control circuit 29 to tune the electronic tuning tuner 22. A signal vt is applied to increase the local oscillation frequency. When the intermediate frequency for the next channel reaches fl shown in FIG. 7 due to this increase in the local oscillation frequency, the output of the frequency discriminator 261,
The automatic fine adjustment signal VA, , starts to rise from point (7) as shown in FIG. In FIG. 7, the straight line indicated by a dashed line indicates the characteristic of the oscillation frequency change with respect to the voltage change of the electronic tuning tuner. When the automatic fine adjustment signal WAFT begins to rise, the local oscillation frequency of the electronically tuned tuner 22 further increases, thereby accelerating the rise of the automatic fine adjustment signal WAFT.

In this way, the local oscillation frequency rapidly increases and becomes a stable frequency fzK.

When the local oscillation frequency is further increased, the automatic fine adjustment signal V
AFT begins to fall. For this reason, the electronic tuning tuner 22
The local oscillation frequency increases slowly. That is, the local oscillation frequency is 'f1' as shown in FIG.
When it reaches f, it rapidly rises to fco' due to the pull-in phenomenon. FIG. 8 shows the operating characteristics of the local oscillator 224, with the free oscillation frequency plotted on the horizontal axis and the actual oscillation frequency plotted on the vertical axis. Furthermore, the local oscillation frequency f1'# f R' a f 8' + Z 4' in Fig. 8 and the intermediate frequency fx - fa - fs in Fig. M7
The relationship with -fa is, when the received signal frequency is f, f
x' f-value f8 fs' fsfs fs' fsfs f a' f = f 4 . After the local oscillation frequency is pulled in as described above, the frequency □ change becomes gradual K as described above. However, as the local oscillation frequency increases and the wave number of the intermediate station increases, the automatic fine adjustment signal VAF outputted from the frequency discriminator 261 continues to decrease as shown in FIG. When becomes F, the central level reaches the point. Furthermore, as the intermediate frequency increases, the automatic fine adjustment signal Vm? When i changes in the negative direction from the center level and its signal level drops below the reference voltage v2, the AFT signal is output from the converter/4 router 263. When the AFT signals are output in the order of L-H as described above, the control circuit 27 fixes the tuner tuning voltage at that point.

The tuner tuning voltage is controlled as described above, but if the local oscillation frequency is further increased from the above tuning position, the output of the frequency discriminator 261 will change when the intermediate frequency reaches fs in FIG. It starts to rise. For this reason, the pull-in of the local oscillation frequency is lost, and the frequency changes from point fs' at point (9) to f4 at point (9), as shown in Figure 8.
'.

rapidly rises to. Furthermore, if the local oscillation frequency is lowered from this state, the above-mentioned inevitable pull-in phenomenon will occur (at the point where the output of the frequency discriminator 261 occurs, as shown in FIG. 7), and the local oscillation frequency is Fig. 8 VC (to) → (
Changes as shown in e) → (support) → (b). Therefore,
The frequency pull-in range is between (branch) and ■ in Figure 8, and (to) - (
If the frequency range is not within the frequency holding range, the tuning process is performed in the same manner as when the tuning down key 16b is operated in the same manner as when the up key 16m is operated.

As mentioned above, when the received signal is near, the automatic fine adjustment signal VAFT pulls in the local oscillation frequency. It is possible to reduce frequency deviations, bumps, and deviations from the ideal stopping frequency jp when stopped.

〔Effect of the invention〕

As described in detail above, according to the present invention, the automatic fine adjustment signal VAFT is applied to the electronic tuning tuner together with the tuning signal Vt, and when the local oscillation frequency approaches the vicinity of the receiving channel, the tuning voltage is adjusted due to the pull-in phenomenon. The change in local oscillation frequency per step of the A converter can be reduced. Therefore, the frequency error when the search operation stops can be made very small, and the same effect as increasing the resolution of the D/A converter for tuning voltage can be obtained, allowing tuning operation to be performed without increasing the frequency of the basic clock. It can be done accurately.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention; FIG. 1 is an exterior configuration diagram, FIG. 2 is a clock diagram showing the overall configuration of an electronic circuit, and FIG. 3 is a block diagram showing details of an electronic tuning tuner.
Figures 4 (a) and (b) are circuit configuration diagrams showing details of the local oscillator in Figure 3, Figure 5 is a block diagram showing details of the TV linear circuit, and Figure 6 is a block diagram showing details of the frequency detection circuit. 7 is a timing chart for explaining the operation of the frequency detection circuit of FIG. 6, and FIG. 8 is a diagram showing changes in the oscillation frequency of the local oscillator. 11... Case, 12... Video display section, 13...
Channel display section, 14...Volume display section, 15...
Display panel, 16a... Atsuzo key for tuning, 16b... Down key, 17a... Aggressive key for volume adjustment, 17b... Down key, 18... Auto/manual changeover switch, 19... VHF/1J
HF selector switch, 20...Power switch, 21...
・Antenna, 22... Electronic tuning tuner, 23...
TV linear circuit, 24... N-conversion circuit, 25...
・Liquid crystal drive circuit, 26...Frequency detection circuit, 27...
- Control circuit, 28... Key human power section, 29... Tuner tuning voltage control circuit, 221... Antenna coupling circuit,
222... High frequency coupling circuit, 223... Mixing circuit,
224...Local oscillation circuit, 231...Intermediate frequency amplification circuit, 232...Detection circuit, 233...Video amplification circuit, 234...Synchronization separation circuit, 261...Frequency discriminator, 262, 263...Comparator, 264°2
65...Reference power supply. Applicant's representative Patent attorney Takehiko Suzue Figure 1 Figure 5 264-'265. Fig. 7↑1 ηrpT3 f4IF

Claims (1)

[Claims] An electronic tuning tuner, a frequency discriminator that discriminates the frequency received by the electronic tuning tuner and outputs a discrimination signal according to the frequency difference between the input frequency and the set frequency, and a frequency discriminator that detects the output signal of the frequency discriminator. means for generating a tuning signal; means for controlling the local oscillation frequency of the electronic tuning tuner according to the tuning signal obtained by the means; and a means for controlling the electronic tuning by using the discrimination output of the frequency discriminator as an automatic fine adjustment signal. An auto-tuning device comprising means for inputting the signal into a local oscillator of a tuner and slowing down frequency changes in the vicinity of a received signal.