JPS595730A - Stop signal generating circuit for searching broadcasting station - Google Patents

Abstract

PURPOSE:To prevent the generation of a wrong stop signal, by lowering the level of the control signal of a stop signal generating circuit for searching broadcasting station and the level of a reference comparison voltage when noises in a spurious disturbing wave, etc., increase. CONSTITUTION:A signal of intermediate frequency from a front end part 1 is reduced in band through a band-pass filter 2 and then inputted to a level detector 4 through an amplifier 3 to supply a control signal corresponding to the intensity of an input electric field to a voltage comparator 6. The output of the front end part 1 is inputted to a wide-band filter 9 simultaneously to detect a disturbing signal and a wide-band noise, which are amplified by a noise amplifier 10 to output a variable DC control voltage from a noise level detector 11. A voltage comparator 5 generates a stop signal for searching broadcasting station at the point where the control signal C and variable DC voltage cross each other and output no stop signal when the disturbing wave or noise component level is high.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a stop signal for broadcasting station search that can eliminate misstops caused by interference waves (including broadband noise) particularly outside the intermediate frequency band in an automatic tuning radio receiver. This relates to the generation circuit.

FIG. 1 is a block diagram showing a conventional broadcast station search stop signal generation circuit. In the figure, (1) is a U front-end section, (2) is a bandpass filter that narrows the intermediate frequency from this front-end section (1), and (3) is a bandpass filter that amplifies the output of this bandpass filter (2). An intermediate frequency amplifier, (4) a level detector that outputs a control signal C (see Figure 2) according to the output level from the intermediate frequency amplifier (3), and (5) a level detector that outputs an arbitrary voltage, for example, as shown in Figure 2. A comparison reference voltage source (6) is a comparison reference voltage source (6) that sets the comparison reference voltage VC shown in FIG.
(7) a voltage comparator that compares the comparison reference voltage Vc set in (5) with the comparison reference voltage Vc and outputs a stop signal SP (see Figure 2);
is an output terminal, and (8) is an antenna.

In Fig. 2, the horizontal axis represents the input electric field strength E ('/m).

It is a diagram showing the stop signal generation state when the vertical axis is the voltage V, and the cross point between the control signal C and the comparison reference voltage Vc gives the stop input sensitivity Vi.

Further, the bandpass filter (2) is inserted to narrow the intermediate frequency band, and suppresses interference waves other than the F signal. Also, Fig. 3(a) and Fig. 3(b)
tj: A diagram showing a state in which a miss-stop signal is generated, CNI is a control signal when there is no interference signal, CN2 is a control signal when there is an interference signal, SPt and SPz are miss-stop signals, T is a desired signal, B is a bandpass filter (
In the band 2), A1 and A2 are adjacent channels, Nl is spurious interference, and N2 is broadband noise.

Next, the operation of the broadcast station search stop signal generation circuit having the above configuration will be explained. First, the comparison reference voltage source (5
), the comparison reference voltage Vc is adjusted to a preset stop input sensitivity.

The signal received by the antenna (8) then enters the level detector (4) via the front end section (1), the bandpass filter (2) and the intermediate frequency amplifier (3).

Therefore, the level detector (4) outputs a control signal C according to the input electric field strength. Then, the voltage comparator (6
) operates at the point where the control signal C of the level detector (5) and the comparison reference voltage Vc set in the comparison reference voltage source (5) cross as shown in FIG. 2, and a stop signal Sp is output. .

However, as shown in Fig. 30) and Fig. 3(b), the conventional stop signal generation circuit for broadcasting station search has a problem with the interference signal that cannot be suppressed by the bandpass filter (2), that is, the input electric field strength of the broadcast wave. When becomes excessive, is there a spurious interference wave? 'b and the broadband noise N1 outside the passband width of the bandpass filter (2) can be detected as a signal, and the control signal CM2 crosses the comparison reference voltage Vc, so that a miss-stop signal 8p1 is output. For this reason, there was a drawback that a misstop occurred at a frequency other than the desired reception frequency.

Therefore, the object of this invention is to stop input sensitivity (vi
) is kept constant, and a stop signal generating circuit for broadcasting station search is provided, which prevents a signal from stopping at a frequency other than a desired frequency signal.

In order to achieve such an object, the present invention includes a bandpass filter that limits the passband width of a signal received by an antenna and then input through a front end section, an intermediate frequency amplifier that amplifies the output of this bandpass filter, a level detector that receives the output signal of the intermediate frequency amplifier and outputs a control signal according to the input electric field strength; and a wideband filter that detects band components other than the passband width of the signal input from the front end section. , a noise amplifier that amplifies the noise output output from this wideband filter, a noise level detector that receives the noise output of this noise amplifier as input and outputs a variable DC control voltage that is a reference voltage for comparison, and an output from the level detector. The noise level detector includes a voltage comparator that compares a control signal output from the noise level detector with a variable DC control voltage outputted from the noise level detector, and will be described in detail below using an embodiment.

FIG. 4 is a block diagram showing an embodiment of the broadcast station search stop signal generating circuit according to the present invention. In the figure, (9) is a wideband filter that detects band components other than the passband width limited by the bandpass filter (2);
(10) is a noise amplifier that amplifies the noise output level output from this wideband filter (9), and (11) is a variable DC
This is a noise level detector that outputs a control voltage.

The variable DC control voltage output from this noise level detector (11) becomes the comparison reference voltage of the voltage comparator (6), but if there is no interference wave or noise component, it becomes the initially set comparison reference voltage Vc. When the interference signal arrives, the comparison reference voltage Vc is lowered to prevent the control signal C and the variable DC control voltage from crossing.

Next, the operation of the broadcast station search stop signal generation circuit having the above configuration will be explained. First, the signal received by the antenna (8) is input to the level detector (4) via the front end section (1), the bandpass filter (2) and the intermediate frequency amplifier (3). For this reason, a level detector (
4) outputs a control signal C according to the input electric field strength.

On the other hand, since the output signal of the front end section (1) is input to a wideband filter (9), this wideband filter (
9) detects and outputs interference signals or broadband noise. This detected interference signal or broadband noise is amplified by a noise amplifier (10) and then a noise level detector (11).
). Therefore, this noise level detector (1
1) outputs a variable DC control voltage according to the level of the interference signal or broadband noise. Therefore, the voltage comparator (
In 5), since the control signal C and this variable DC control voltage are input, a stop signal is output at the point where this control signal and the variable DC control voltage cross.

Note that when the spurious interference wave Nl or the noise component level is large, the stop signal may not be output from the voltage comparator (5).

As explained in detail above, according to the stop signal generation circuit for broadcasting station search according to the present invention, when spurious interference waves and broadband noise increase, the control signal drops due to the spurious interference waves and broadband noise. Since the level of the comparison reference voltage is lowered, the control signal and the comparison reference voltage will not cross each other, so even when spurious interference waves or broadband noise arrive, a stop signal with a full v4 will not occur and a stable signal will be maintained. This has the effect of performing a broadcast station search operation.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing a conventional stop signal generation circuit for broadcasting station search, Figure 2 is a diagram showing a stop signal generation state, and Figures 3 (a) and 3 (b) are diagrams showing when a miss stop signal occurs. FIG. 4 is a block diagram showing an embodiment of the broadcast station search stop signal generating circuit according to the present invention. (1)...Front end section, (2)...Band filter, (3)...Intermediate frequency amplifier, (4)...
... Level detector, (5) ... Comparison reference voltage source, (
6)... Voltage comparator, (7)... Output terminal, (
8)... Antenna, (9)... Wideband filter, (10)... Noise amplifier, (11)... Noise level detector. In addition, in the figures, the same reference numerals indicate the same or corresponding parts. Agent Makoto Kuzuno - Figure 1 Figure 2 Figure 4

Claims (1)

[Claims] A bandpass filter that limits the passband width of the signal received by the antenna and input via the front end section, an intermediate frequency amplifier that amplifies the output of this bandpass filter, and the output signal of this intermediate frequency amplifier is input, A level detector that outputs a control signal according to the input electric field strength, a wideband filter that detects band components other than the passband width of the signal input from the front end section, and a noise output from the wideband filter. A noise amplifier for amplification, a noise level detector that receives the noise output of this noise amplifier as input and outputs a variable DC control voltage that is a reference voltage for comparison, and a control signal output from the level detector and from this noise level detector. 1. A stop signal generation circuit for broadcasting station search, comprising a voltage comparator for comparing an output variable DC control voltage.