JPS603223A - Automatic channel selecting device - Google Patents

Abstract

PURPOSE:To narrower a tuning band and to reduce the effect of drift of the circuit by providing two detuning discriminating circuits having different threshold values so as to select the detuning discriminating circuits having the large and small threshold values depending on sweeping and non-sweeping state. CONSTITUTION:While a tuning frequency is swept during the automatic channel selection, a signal from a controller 8 changes over a switch circuit 9 to the position of the detuning discriminating circuit 10a. The threshold value of the circuit 10a is smaller than the threshold value of the detuning discriminating circuit 10b and the tuning band is narrowed. A sweeping frequency is increased or decreased at each DELTAf of one channel, larger than the threshold value of the level discriminating circuit l5 at a tuning frequency f0 and smaller than the threshold value of the circuit 10a, then it is discriminated as tuning, an output of an AND circuit 7 transmits a signal of sweep stop to the controller 8 and the sweeping is stopped. Then the control signal from the controller 8 to the circuit 9 is stopped, the circuit 9 is changed over to the circuit 10b, thereby widening the tuning band.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an automatic tuning device for a radio receiver or the like.

Conventional configuration and its problems A conventional automatic channel selection device has a configuration shown in FIG.

That is, the received frequency is swept by the control device 8, and the output of the detuning determination circuit 6 is inputted to the AND circuit 7 based on the output of the received signal level determination circuit 5 and the figure 8 characteristic output of the detection circuit 4, and the output is tuned. .

The signal is non-tuned, and in the case of tuning, the control device 8 stops the frequency sweep. The figure 8 characteristic of the output of detection output 4 is shown in Figure 2 (,
), and when the value is above the threshold value (1) or less, the detuning determination circuit 5 outputs an output above the threshold value Vs as shown in FIG. 2(b). In Figure 2, 'l)z 1+'l) 12
is the tuner input level, and the higher the input level, the wider the band. The outputs of the above two determination circuits are input to the AND circuit 7, and if the signal level is equal to or higher than Vs, it is determined that the tuning is within Δf1 from the tuning point fO. However, since the reception frequency sweep is performed every △f, if △f x △f1fx, then
If the tuner input level is large, it is considered to be tuned at f to fO±, and the tuning point fo and fo one channel below fO
−△f and 1 channel” to fO+ of the 21st rule f and three frequencies are considered to be tuned, and when automatic tuning is performed, fo+△
Sweeping is stopped at f or fO-△f.

In order to solve the above problem, conventionally, the gain of the detection circuit 4 is increased so that Δf> becomes 11, and the slope of the figure-8 characteristic is increased. However, when △f1 is made small, the intermediate frequency increases r
Tuning point f due to temperature drift of lJ circuit 3 and detection circuit 4
If it deviates from o, the output of the AND circuit 7 is input to the control device 8 as a sweep stop signal, and is also used for a muting signal, etc., so there is an inconvenience that muting may occur due to temperature changes during broadcast reception. .

Purpose of the Invention The present invention provides an automatic channel selection device that eliminates the above-mentioned disadvantages.According to the present invention, even when the broadcast frequency interval Δf becomes small, the above-mentioned disadvantages do not occur. Stable reception is possible.

Structure of the Invention The present invention includes a control device that automatically sweeps the tuned frequency and generates a signal indicating that the frequency is being swept, a circuit that determines the received signal level, and two DG discrimination circuits that have different threshold values. , an automatic tuning device equipped with a switch circuit that selects input of the output of the detection circuit to one of two detuning determination circuits, and an AND circuit that receives the outputs of the level determination circuit and the detuning determination circuit as inputs. By using the signal from the sweep control device, a circuit with a low threshold value of the detuning discrimination circuit is selected, and the tuning band for automatic tuning is narrowed, thereby allowing accurate automatic tuning 4\.

Further, the present invention provides a control device that automatically sweeps the tuning frequency and generates a signal indicating that the frequency is being swept, a circuit that determines the reception level, a detuning determination circuit, and a detection circuit that can vary the gain using a control signal. This is an automatic tuning device equipped with an AND circuit that takes the outputs of the level judgment circuit and the detuning judgment circuit as inputs.By increasing the gain of the detection circuit with the signal from the control device during sweep, the detuning judgment circuit is equivalently Explanation of Embodiment 11 FIG. 3 shows a first embodiment of the present invention. In FIG. 3, 1 is an antenna, 2 is a tuner, 3 is an intermediate frequency increase rlJ circuit, 4 is a detection circuit, 5 is a level judgment circuit, 7 is an AND circuit, and 8 is a control device, which have the same configuration as the conventional example. It's the same. 9 is a switch circuit, and 61 is an out-of-tuning discrimination circuit, which is composed of two out-of-tuning discrimination circuits having different threshold values, 1oa and 10b.

The operation of this embodiment configured as described above will be explained. First, assuming that automatic tuning is in progress by sweeping the tuning frequency, the switch circuit 9 is switched to the detuning discrimination circuit (a) 10d side by the signal indicating that the tuning frequency is being swept. do. The threshold value of the detuning discrimination circuit (a) 10a is smaller than that of the detuning discrimination circuit (b) 1ob, and the tuning band is narrower. The sweep frequency increases or decreases every f to one channel, and if the tuning frequency fO is larger than the threshold value Vs of the level judgment circuit 6 and smaller than the threshold value of the detuning judgment circuit 10a, it is judged that the tuning is achieved. , the output of the AND circuit 7 sends a sweep stop signal to the control device 8, and the sweep is stopped. From the control device 8 to the switch circuit 9
Since the control signal to is also cut off, the switch circuit 9 switches to the detuning discrimination circuit (b) 1o b side, and the tuning band becomes wider.

FIG. 4 shows a second embodiment of the invention. Fourth
In the figure, numerals 1 to 8 are parts having the same functions as those in FIG. 3. Further, 41 is a detection circuit whose gain is increased by a signal from a control device.

The operation of the embodiment with the above configuration will be explained. If automatic tuning is in progress by sweeping the tuning frequency, the signal indicating that the frequency is being swept is input from the control device 8 to the detection circuit 4°, so the gain of the detection circuit 41 increases, and its output is The slope of the figure 8 characteristic is larger than that during frequency sweep,
Even if the threshold value of the detuning discrimination circuit 6 does not change, it equivalently becomes smaller during the frequency sweep, and the tuning band becomes narrower. Therefore, this embodiment can obtain the same effects as the first embodiment, and is also suitable for IC implementation as a method of varying the gain of the detection circuit by eliminating the current source that affects the gain of the detection circuit.

Effects of the Invention As explained in detail above, according to the present invention, when automatically tuning by sweeping the frequency, the tuning band can be narrowed to achieve accurate tuning, and after tuning, the tuning band can be widened to improve the circuit. Since the influence of drift can be reduced, it has great practical value.

[Brief explanation of drawings]

Figure 1 is a block diagram of a conventional automatic channel selection device, and Figure 2 (
) is an S-shaped characteristic diagram of the automatic tuning device shown in FIG. 1, FIG. 2(b) is a same-level output characteristic diagram, FIG. 3 is a block diagram showing the first embodiment of the present invention, and FIG. FIG. 2 is a block diagram showing a second embodiment of the present invention. 4.4'...Detection circuit, 5...Level judgment circuit, 6.6°...Detuning judgment circuit, 7...
...And circuit, 8...Cross plane circuit.

Claims (2)

[Claims] (1) The first case with different threshold values. a second detuning determination circuit;
The first control signal is controlled by the control signal. a switch circuit for selecting one of the second detuning determination circuits; a received signal level determination circuit; an output of the level determination circuit;
．． An AND circuit which receives the output of the second detuning discrimination circuit as an input, and an output device that automatically sweeps the tuning frequency by using the output of the AND circuit as a sweep stop signal. An automatic tuning device characterized by variable tuning band. (2) a detuning determination circuit, a level determination circuit that determines the reception level, a detection circuit whose gain can be varied by a control wholesale signal, and an AND circuit that manually outputs the outputs of the detuning determination circuit and the level determination circuit; An automatic tuning device comprising a control circuit that automatically sweeps the tuning frequency using the output of the AND circuit as a sweep stop signal, and varying the tuning band between when sweeping and when stopping the sweep.