JPS59219013A - Search stop circuit - Google Patents

Abstract

PURPOSE:To attain search stop as desired and to prevent malfunction by using a signal in response to an electric field strength of a receiving signal and an intermediate frequency signal at a prescribed level counted accurately so as to generate a search stop signal. CONSTITUTION:When a detected output signal is applied to an input terminal 16, a control signal in response to the electric field strength is generated at an output of a control signal generating circuit 17. An input transistor (TR)18 is turned on in case of a broadcast station having a large electric field strength, an output signal of a limiter amplifier circuit 14 is applied to a stop signal generating circuit 15 only during the period when a bypass TR19 is turned off and the frequency is counted. On the other hand, in case of a broadcast station having a small electric field, the TR18 is turned off and the TR19 is turned on. Then, an output signal of the circuit 14 is bypassed by the TR19 and not applied to the circuit 15. Thus, no search stop signal is generated from the circuit 15 and the automatic searching is not stopped in the broadcast station having the small electric field strength and the automatic searching is conducted succeedingly.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a search stop circuit in a cheese having an auto-search function.

(b) Prior Art There is a known team which has an auto-search function that automatically changes the oscillation frequency of a local oscillation circuit to perform reception.

Figure 1 shows an example of an AM team having such an auto-search function.The RF (high frequency) signal received by the antenna fil is amplified by the RF amplifier circuit (2), and then sent to the mixing circuit. (3), it is mixed with the output signal of the local oscillator circuit (4), converted into an IF multiplied signal, amplified by the IF amplifier circuit (5), detected by the AM detection circuit (6), and output at the output terminal (
7) A detection output signal is obtained. At this time, since the programmable frequency divider (8), reference oscillator (9) and phase comparator QCII are connected to the local oscillation circuit (4), a PLL loop is formed as a whole. Further, the programmable frequency divider (8) is configured to receive a signal from the search circuit 0D that adjusts the frequency division ratio, and the signal is successively changed by the action of the search circuit 0υ. Furthermore, a search stop circuit az is connected to the search circuit Uυ, and when a broadcast station is received, a stop signal is generated from the search stop circuit (12+), which is applied to the search circuit αD to perform an auto search. stops.

Now, if the glogram pull frequency divider (8) is set to a predetermined state by the output signal of the search circuit (11), the output signal of the local oscillator circuit (4) is set to a predetermined state by the programmable frequency divider (8). The frequency is divided and applied to the phase comparator OQ. Since the output signal of the reference oscillator (9) is applied to the phase comparator (1o), the phase comparator (10)
At the output end of the circuit, a signal corresponding to the phase difference between the two applied signals is obtained, and this signal is applied to the local oscillation circuit (4) to change its oscillation frequency, and eventually the phase difference becomes zero. Through such control, the oscillation frequency of the local oscillation circuit (4) becomes a value corresponding to the frequency division ratio of the programmable frequency divider (8).

As the signal applied from the search circuit (11) to the programmable frequency divider (8) is changed, the oscillation frequency of the local oscillation circuit (4) changes, so that automatic search can be performed. In addition, if a broadcast station is received while auto-search is in progress, the search strike circuit (12
) is activated, a stop signal is generated, and auto search is stopped.

Conventionally, there are two types of search and offset circuits: one that detects the electric field strength of a received signal and one that counts the frequency of an IP signal. In the search stop circuit that detects the electric field strength, a signal corresponding to the electric field strength as shown in Fig. 2 is detected from a signal meter circuit, etc., and the level is compared with a reference level (V,) to generate a search stop signal. However, when a broadcast station with a high field strength was received, a search stop signal was generated at a point far from the center (fo) of the broadcast station, and a broadcast station with a low field strength was received. In some cases, there is a risk that the search stop signal will not be generated, and the problem is that it is difficult to set the reference level (VQ). On the other hand, even in a search strategy circuit that counts the frequency of an IP signal,
There was a risk of a counting error occurring depending on the signal level, and this also made it difficult to set the stop sensitivity and was unsatisfactory.

(c) Purpose of the Invention The present invention has been made in view of the above points, and it is an object of the present invention to provide a search stop circuit that can accurately generate a search stop signal.

B) Structure of the Invention The search stop circuit according to the present invention has an IF of a predetermined level.
a limiter that generates a multiplied signal; a control signal generation circuit that generates a control signal according to the electric field strength of a received signal; and a stop that generates a search stop signal when the frequency of the IF multiplied signal supplied from the limiter reaches a predetermined value. The control signal generation circuit includes a signal generation circuit and a bypass circuit that bypasses the output signal of the limiter when the output signal level of the control signal generation circuit is below a predetermined value.

(E) Embodiment FIG. 3 shows an embodiment of the present invention, in which α3) is connected to the output terminal of the IP amplifier circuit (5) in FIG.
The input terminal α4) to which the signal is applied is connected to the IF signal (4'
55 K11z), and generates a search stop signal, (16)
is a control input terminal connected to the output terminal of the detection circuit (6) in Fig. 1 and to which the detection output signal is applied; 08) is an input transistor that is turned on and off by the output signal of the control signal generation circuit (17); is a bypass transistor driven by K. Note that the control signal generation circuit αη can be replaced with a level make drive circuit attached to a normal AM tuner.

Now, if the search circuit (11) in Fig. 1 is operated to perform an auto search, the frequency division ratio of the programmable frequency divider (8) is set according to the output signal of the search circuit 01), and the PLL loop operates, so the local oscillator circuit (
The oscillation frequency of 4) has a value corresponding to the output signal of the search circuit Ql). Therefore, by varying the output signal of the search circuit 01), the oscillation frequency of the local oscillation circuit (4) is changed, and automatic search can be achieved. value (455
KIIZ), the stop signal generating circuit 05) in FIG. 2 is activated, a stop signal is generated, and the auto search is stopped. At that time, the IP applied to input terminal 03)
Since the double signal and limiter amplification circuit (14) produce a predetermined level, the stop signal generation circuit (05) accurately outputs the I
F-fold signal frequency can be counted and no malfunction will occur.

Further, when a broadcast station is received, a detection output signal is applied to the control input terminal (16), and a control signal corresponding to the electric field strength of the broadcast station is generated at the output terminal of the control signal generation circuit (17). The control signal has the center frequency f of the broadcasting station, as shown in FIG. It has a unimodal characteristic with a maximum level at
As shown in Figure 2 (a) or (b), the level changes depending on the electric field strength. If the field strength is set to ■, then in the case of a dog broadcasting station as shown in Figure 2 (a), the frequency is f2.
Input transistor 0 & turns on in a range smaller than
The bypass transistor (19) is turned off. Therefore, only during the period when the bypass transistor (19) is off, the output signal of the limiter amplifier circuit (141) is applied to the stop signal generation circuit α2, and the frequency is counted. On the other hand, in the case of a broadcasting station where the electric field strength is small as shown in Figure 2 (b), the output signal level of the control signal generation circuit 07) is on level (VO).
, the input transistor (18) is turned off and the bypass transistor fi91 is turned on. Therefore, all the output signals of the limiter amplifier circuit α4) are bypassed by the bypass transistor (l) and are not applied to the stop signal generation circuit u9. Therefore, no search stop signal is generated from the stop signal generation circuit θ5). , the auto search does not stop at the station where the electric field strength is small, and the auto search continues.

The on level of the input transistor 08) is controlled by the variable resistor (4
) can be freely set by adjusting the voltage division ratio for dividing the output signal of the control signal generation circuit αη. If you want to receive broadcasting stations with low field strength and poor quality, you can set the on level (■0) to a low value.

(F) Effects of the Invention According to the present invention, a signal corresponding to the electric field strength of a received signal,
Since the search stop signal is generated using an IF multiplied signal of a predetermined level that can be accurately counted, the search stop signal can be stopped as desired and has the advantage of not causing malfunction.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of a cheese having an auto-search function in which the search stop circuit according to the present invention is used, FIG. 2 is a characteristic diagram for explaining the present invention, and FIG.
The figure is a circuit diagram showing one embodiment of the present invention. Description of main drawing numbers 02...Search stop circuit, α4)...Limiter amplifier circuit, Q51...-Stop signal generation circuit,
(17)... Control signal generation circuit, (1 o... Bypass transistor. 65

Claims (1)

[Claims] (11) An auto search tuner that automatically changes the oscillation frequency of a local oscillation circuit to perform reception includes a limiter that generates an intermediate frequency signal at a predetermined level and a control signal that generates a control signal according to the electric field strength of the received signal. a control signal generation circuit that generates a search stop signal when the frequency of the intermediate frequency signal reaches a predetermined value; and a stop signal generation circuit that generates a search stop signal when the frequency of the intermediate frequency signal reaches a predetermined value; A search stop circuit consisting of a bypass circuit that bypasses the output signal of the limiter.