JPS639218A - Channel selection device - Google Patents

Abstract

PURPOSE:To set an optimum receiving point by detecting a tuning voltage giving two points at point symmetry clipping the center of an S-shaped discrimi nation characteristic from an output of a frequency discrimination circuit and supplying the mean value as an optimum tuning voltage to a channel selection circuit. CONSTITUTION:A window comparator circuit 13 detects two points giving a maximum point and a minimum point at a discrimination output of a frequency discrimination circuit 6. A discrimination output at each point is fetched in a channel selection control circuit 12 via the circuit 13. The midpoint of a blank formed between the maximum and minimum point detection outputs among outputs of the circuit 13 is used as an optimum reception point and the tuning voltage at both ends of the blank is stored in a storage circuit 12a synchronously with the trailing of the maximum detection output and the leading of the minimum point detection output. The stored value is read and averaged by an arithmetic circuit 12b to obtain an optimum tuning voltage, which is fed to a channel selection circuit 3 thereby applying optimum tuning station selection.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a channel selection device that always enables optimum tuning regardless of the band to which a selected channel belongs.

[Prior Art] Tuning devices built into television receivers, video tape recorders, etc. use a voltage sensor system that applies tuning commands as a tuning voltage, or a voltage sensor system that applies tuning commands as a tuning voltage, or a system that uses accurate frequency control that is obtained from a phase-locked loop circuit. P to select stations based on
The LL frequency synthesizer method is known.

Since the voltage sensor type channel selection device does not require high-speed devices and has a relatively simple circuit configuration, most popular machines use this method. The conventional tuning device 1 shown in FIG. The RF multiplied signal tuning of the desired channel is performed according to the voltage. The RF multiplied signal sent from the receiving antenna 2 to the tuning circuit 3 is amplified by the high frequency amplification circuit 3a, mixed with the output of the local oscillation circuit 3c by the mixing circuit 3b, and made into an intermediate frequency, which is then used for tuning. The signal is supplied to a video intermediate frequency amplification circuit 5 connected to the circuit 3. A frequency discrimination circuit 6 is connected to the video intermediate frequency amplification circuit 5, and the signal tuned by the frequency selection circuit 3 is an S
Discrimination is performed according to the character-shaped discrimination characteristic, and the discrimination output is supplied to the channel selection control circuit 4.

[Problems to be Solved by the Invention] In the conventional channel selection device 1 described above, when a desired channel is designated to the channel selection control circuit 4, the channel selection control circuit 4 starts auto-scanning and performs the necessary channel selection. Gradually change the tuning voltage. As the tuning voltage changes, the oscillation frequency of the local oscillation circuit 3c in the tuning circuit 3 changes, and the frequency discrimination circuit 6
The tuning point approaches the center frequency of the figure-8 characteristic. At this time, the discrimination output of the frequency discrimination circuit 6 changes beyond the optimum voltage corresponding to the center frequency, and once reaches the voltage that provides the minimum point of the S-shape. For this reason, the conventional tuning control circuit 4 has 8
When the minimum point of the character is reached, the tuning voltage obtained by subtracting a predetermined fixed offset voltage from the tuning voltage at that time is supplied to the tuning circuit 3 as the optimum tuning voltage. However, the discrimination characteristic of the frequency discrimination circuit 6 is that the shape of the figure 8 is different depending on the band to which the desired channel belongs, and therefore, optimal tuning cannot be expected with the method of subtracting a constant offset voltage regardless of the band. First, there were problems such as poor tuning depending on the channel.

[Means for Solving Problem 1] This invention solves the above problems) and provides a tuning method for tuning the signal of a desired channel using a local oscillation frequency according to a tuning voltage applied from the outside. A circuit, a frequency discrimination circuit for frequency discriminating the signal tuned by this tuning circuit, and detecting a tuning voltage that gives two points located at symmetrical positions across the center frequency of the discrimination output of this frequency discrimination circuit, The present invention is characterized by comprising a tuning control means for calculating a tuning voltage giving the center frequency as an average value of these tuning voltages and supplying the calculated tuning voltage to the tuning circuit.

1. This invention provides a tuning voltage that provides two points located point-symmetrically across the center frequency of the S-shaped discrimination characteristic from the discrimination output of a frequency discrimination circuit that discriminates the frequency of a signal tuned by the tuning circuit. is detected, and the voltage obtained as the average value of these tuning voltages is supplied to the tuning circuit as the optimum tuning voltage.

[Example] Hereinafter, an example of the present invention will be described with reference to FIG. 1.2. FIG. 1 is a circuit configuration diagram showing an embodiment of the channel selection device of the present invention, and FIG. 2 is a signal waveform diagram of each part of the circuit shown in FIG.

In FIG. 1, the tuning device II includes a tuning control circuit 12 and a window comparator circuit 13 provided between the tuning control circuit 12 and the frequency discrimination circuit 6, which constitute tuning control means. . The window comparator circuit 13 detects the discrimination output of the frequency discrimination circuit 6 at two points: a point giving a maximum point and a point giving a minimum point, and the discrimination output at each point is detected via the window comparator circuit 13. It is taken into the channel selection control circuit 12. The tuning control circuit 12 sets the tuning voltage Va corresponding to the above two points.

A memory circuit 12a that stores Vb, and this memory circuit 12
It has a built-in arithmetic circuit +2b that calculates the average value of the tuning voltages Va and Vb read from a, and this arithmetic circuit +2
Let the output of b be the optimum tuning voltage Vm.

Therefore, if the tuning control circuit 12 gradually increases the tuning voltage in order to tune to the desired channel set,
First, when the tuning range is moderate, the synchronization signal shown in FIG. 2(A) is detected from the output of the video intermediate frequency amplification circuit 5. Then, following the detection of the synchronization signal, Fig. 2 (B
), the discrimination output of the frequency discrimination circuit 6 is also increased □
As a result, the maximum point detection output of the window comparator circuit 13 is obtained as shown in FIG.

Next, when the tuning point reaches the S-shaped characteristic, the frequency discrimination circuit 6
The discrimination output begins to decrease, passing the optimal reception point and reaching the minimum point. The fact that the tuning point has reached the minimum point is shown in Figure 2 (D
) is determined based on the minimum point detection output of the window comparator circuit 13.

Here, the window comparator circuit! Among the outputs of 3, the center point of the blank area formed between the local maximum point detection output and the local minimum point detection output is the optimal reception point, and the tuning voltage Va that gives both ends of this blank area, Vb is
The signal is stored in the storage circuit +2a in synchronization with the fall of the maximum point detection output of the window comparator circuit 13 and the rise of the minimum point detection output. Therefore, by reading out the tuning voltages Va, . The optimal tuning voltage Vm obtained from the arithmetic circuit 12a is immediately supplied to the tuning circuit 3, thereby performing optimal tuning.

In this way, the station selection device 11 is located at a point symmetrical position across the center frequency of the S-shaped discrimination characteristic from the discrimination output of the frequency discrimination circuit 6 that discriminates the frequency of the signal tuned by the channel selection circuit 3. Tuning voltage Va that gives two points (maximum point and minimum point)
, Vb are detected, and the voltage Vm obtained as the average value of these tuning voltages Va and ■b is supplied to the tuning circuit 3 as the optimum tuning voltage. Even if the S-shape of the discrimination characteristic changes, the optimum reception point can always be set at the center of the S-shape of the discrimination characteristic of the frequency discrimination circuit 6, and the predetermined offset voltage can be inserted from the voltage that gives the minimum point. <Unlike the conventional channel selection device 1, it is possible to always achieve the optimum reception state.

[Effects of the Invention] As explained above, the present invention provides point-symmetrical positions across the center frequency of the S-shaped discrimination characteristic from the discrimination output of the frequency discrimination circuit that discriminates the frequency of the signal tuned by the channel selection circuit. The tuning voltage that gives the two points in Even if the S-shape of the characteristic changes, the optimum reception point can always be set at the center of the S-shape of the frequency discrimination circuit's discrimination characteristic, and a predetermined offset voltage can be subtracted from the voltage that gives the minimum point. Unlike conventional channel selection devices, the present invention has excellent effects such as being able to always reliably achieve optimal reception conditions.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram showing an embodiment of the channel selection device of the present invention, FIG. 2 is a signal waveform diagram of each part of the circuit shown in FIG. 1, and FIG. 3 is a diagram of a conventional channel selection device. FIG. 2 is a circuit configuration diagram showing an example. 3190 channel selection circuit, 6. ,,frequency discrimination circuit. 11.0. Channel selection device, +2. ,,Tuning control circuit. 13. Window comparator circuit.

Claims (1)

[Claims] a tuning circuit that tunes and tunes a signal of a desired channel using a local oscillation frequency according to a tuning voltage applied from the outside;
This tuning circuit detects the frequency discrimination circuit that frequency-discriminates the frequency of the signal tuned by this tuning circuit, and the tuning voltage that gives two points located symmetrically across the center frequency of the discrimination output of this frequency discrimination circuit, and these tuning voltages are detected. A tuning device comprising tuning control means for calculating a tuning voltage giving the center frequency as an average voltage value and supplying the calculated tuning voltage to the tuning circuit.