JPH05191738A - Diversity tv receiver - Google Patents

Abstract

PURPOSE:To reduce switching noise at FM demodulation caused at the changeover of antennas. CONSTITUTION:Reception signals from antennas 1-4 are added by adder circuits 6, 20 via electronic switches 5, 19. The signal from the adder circuit 6 is demodulated by an FM demodulation circuit 8 and detected by a video detection circuit 10. The demodulated signal is supplied to a gain control circuit 21 and outputted therefrom. An electronic switch 19 is switched with a pulse outputted from a switching pulse generating circuit 12 based on a vertical synchronizing signal separated from the detected video signal by a synchronizing separator circuit 11. A pulse generating circuit 16 generates antenna selection and decision pulses c, b based on noise resulting from a signal from an adder circuit 20 detected by a noise detection circuit 15 and the switch 5 is switched in response to the pulse (c). The pulse (b) is fed to a control circuit 22, from which a gain control signal (d) is generated and supplied to the gain control circuit 21, from which an audio signal (e) whose noise is reduced is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a TV receiver, and more particularly to an improvement of a diversity TV receiver of a type in which a plurality of receiving antennas are switched based on a comparison result of received electric field strengths in a vertical blanking period.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional diversity TV receiver. In the figure, 1 to 4 are receiving antennas, 5 is an electronic switch, 6 is an adding circuit, 7 is an intermediate frequency (IF) amplifier, 8 is an FM demodulation circuit, 9 is an audio signal output terminal, 10
Is a video detection circuit, 11 is a sync separation circuit, 12 is a switching pulse generation circuit, 13 is an electronic switch gate pulse generation circuit, 14 is a gate circuit, 15 is a noise detection circuit,
Reference numeral 16 is an antenna determination pulse generation circuit, 17 is a hold pulse generation circuit, and 18 is an electronic switch.

Received signals from the receiving antennas 1 to 4 are applied to an electronic switch 5, and output signals thereof are combined by an adder circuit 6, and the combined signal is sent to an FM demodulation circuit 8 and a video detection circuit 10 via an IF amplifier. In addition, the FM demodulation circuit 8
Outputs an audio signal to the output terminal 9.

On the other hand, the video signal output from the video detection circuit 10 is input to the sync separation circuit 11 and the vertical sync signal is extracted and added to the switching pulse generation circuit 12. The switching pulse generating circuit 12 generates a switching pulse of a short period τ (several μs) in the vertical blanking period based on the timing of the vertical synchronizing signal, and is generated by the gate pulse generating circuit 13 in response to the switching pulse. Based on the gate pulse, the electronic switch 5 is turned on / off for each τ period in the order of 5a, 5b, 5c, 5d.

Since there is no signal in the vertical blanking period, if the output of the video detection circuit 10 is gated by the gate circuit 14, only the noise component can be extracted. The output signal of the gate circuit 14 is detected by the noise detection circuit 15, and the detected noise component is the antenna determination pulse generation circuit 1
6 is input. The antenna determination pulse generation circuit 16 is
The noise included in the reception signals of the receiving antennas 1 to 4 is compared, and the antenna with the smallest noise has the highest electric field strength.
A pulse for determining the corresponding antenna is generated based on the comparison result, and the electronic switch 18 is operated by this pulse to select the hold pulse from the hold pulse generation circuit 17 and add it to the switch 13 and add it to the switching pulse. To do.

FIG. 4 shows the timing of the switching pulse, and A to D are switching pulses of a period τ for turning on / off each of the receiving antennas 1 to 4 in the vertical blanking period, for example, of the noise detection circuit 15. Output is antenna 1
Is the highest strength, the switch 5 is the antenna 1 in (A).
Select.

[0007]

As described above, one of the antennas 1 to 4 having the maximum electric field strength is selected, and the switching of the antenna is performed within the vertical blanking period, so that the influence of the switching is affected. Does not appear on the screen.

However, according to the above-mentioned conventional method, when the electric field strength is weak, the antenna selection switch 5 is operated every vertical blanking, that is, every 1/60 sec,
Therefore, as the output of the FM demodulation circuit 8, as shown in FIG. 5, noise n (generally heard as a boon) every 1/60 sec.
Occurs, and there is a drawback that it is offensive to the ears.

It is an object of the present invention to reduce the switching sound caused by antenna switching in a diversity TV receiver to improve the sound quality during TV reception.

[0010]

In order to achieve the above object, a diversity TV receiver of the present invention selects first and second signals for selecting, adding and outputting received signals from a plurality of receiving antennas. Means, FM demodulation means for FM demodulating the received signal output by the first signal selecting means to obtain an audio signal, and video signal for video detection of the received signal output by the first signal selecting means And a vertical synchronizing signal is extracted from the video signal to generate a switching signal of a predetermined cycle during a vertical blanking period based on the signal, and the second signal is generated based on the switching signal. A switching signal generating means for selecting and outputting each reception signal by the selecting means and a noise component of each reception signal from the second signal selecting means are compared, and reception with a small noise component is performed. Noise detecting means for outputting to the first signal selecting means a selection signal for selecting an antenna of No. 1 and a switching noise by the first signal selecting means included in the audio signal based on the selection signal. Gain control means for controlling the gain of the audio signal from the FM demodulation means so as to reduce it.

[0011]

In the diversity TV receiver of the present invention, based on the vertical synchronizing signal extracted from the video signal,
A switching signal of a predetermined cycle is generated during the vertical blanking period, and the second signal selection means selects and outputs the reception signal of each antenna by this switching signal. The noise components of these respective reception signals are compared, and a selection signal for selecting an antenna of the reception signal having a small noise component is output to the first signal selection means. Further, the gain of the FM demodulated audio signal is controlled based on the selection signal, and the switching noise by the first signal selection means is reduced.

[0012]

Embodiments of the present invention shown in the drawings will be described below.
1 shows an embodiment of a diversity TV receiver according to the present invention. The same symbols as those in FIG. 3 represent the same or similar circuits. The difference from FIG. Is performed in the auxiliary circuit system without performing the above step and the gain control of the FM demodulation output when the receiving antenna is switched.

That is, in FIG. 1, the electronic switch 5 and the adder circuit 6 form a first signal selecting means, and the electronic switch 19 and the adder circuit 20 form a second signal selecting means. The FM demodulation circuit 8 corresponds to the FM demodulation means, and
The amplifier 7 and the video detection circuit 10 constitute the video detection means.

The sync separation circuit 11 and the switching pulse generation circuit 12 constitute the switching signal generating means. The noise detection circuit 15 corresponds to the noise detection means, and the pulse generation circuit 16, the gain control circuit 21 and the control circuit 22 constitute the gain control means.

The received signal from each receiving antenna is applied to the electronic switches 5 and 9. The output signals of the electronic switch 5 are combined by the adder circuit 7, and the combined signal is the IF amplifier 7
Is added to the video detection circuit 10 via. The video signal from the video detection circuit 10 is input to the sync separation circuit 11 to extract the vertical sync signal, and the switching pulse generation circuit 1
2 generates a switching pulse having a period τ equal to the vertical blanking period according to the timing of the signal, and the received signal of each antenna is switched by the electronic switch 19 by this switching pulse in the same manner as in FIG. The output signal of the switch is combined by the adder circuit 20, the combined signal is input to the noise detection circuit 15, and the pulse generation circuit 16 generates an antenna selection pulse (FIG. 2C) from the detected waveform. The electronic switch 5 operates in response to
The received signal from each antenna is selected and output.

As described above, the audio signal output from the FM demodulation circuit 8 contains the noise n generated at the timing of t ₂ associated with the antenna switching as shown in FIG. 2 (a).

Therefore, in the present embodiment, the pulse generation circuit 16
2 (b), the control circuit 22 generates the gain control signal of FIG. 2 (d) and supplies it to the gain control circuit 21 to control the gain of the audio signal.

Timing t of the start of the gain control signal (d)
_{Since 1} (the time when the antenna selection is determined) precedes t ₂ (the time when the antenna is actually switched), when the antenna switching is determined at t = t ₁ , it is delayed by τ ₁ and then t ₂
To be set. Since the audio signal is smoothly restored even after t ₂ = t ₁ + τ ₁ t = t _{2, the} gain control signal (d) has a characteristic waveform of a substantially valley curve centered on t ₂ as shown in the figure. The output signal of the gain control circuit 21 has the waveform shown in FIG. 2 (e), and the switching noise is significantly reduced and substantially eliminated.

[0019] In order to prevent feel hearing even lack of hatched portion in FIG. (E) by the time tau _1, tau ₂ such gain control of FIG. 2, for example, τ ₁ ≧ 5ms (τ ₂ is the same). Therefore, the switching frequency of the antenna and the number of operations of the switch 5 are also limited.

[0020]

As described above, according to the present invention, in the diversity TV receiver of the type in which the antenna having the highest electric field strength is selected and the antennas are switched in the vertical blanking period, the electric field strengths of the antennas are compared. Since the auxiliary circuit system different from the main signal circuit system is used, the main signal is not switched every field, and the switching noise contained in the audio signal at the time of FM demodulation is reduced. Further, since the switching noise is aurally reduced by performing gain control of the demodulated audio signal, good sound quality can be reproduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a timing chart for explaining the operation of the above embodiment.

FIG. 3 is a block diagram showing a conventional diversity TV receiver.

FIG. 4 shows switching pulses in the device of FIG.

5 is a diagram showing noise included in an FM demodulated audio signal in the apparatus of FIG.

[Explanation of symbols]

 1-4 reception antenna 5,19 electronic switch 6,10 adder circuit 8 FM demodulator circuit 10 video detection circuit 11 sync separation circuit 12 switching pulse generation circuit 15 noise detection circuit 16 pulse generation circuit 21 gain control circuit 22 control circuit

Claims (1)

[Claims] 1. First and second signal selecting means for selecting, adding and outputting received signals from a plurality of receiving antennas, and receiving signals output by the first signal selecting means by F
FM demodulation means for M-demodulating to obtain an audio signal, video detection means for video-detecting the received signal output by the first signal selecting means to obtain a video signal, and a vertical synchronization signal extracted from the video signal. Switching signal generating means for generating a switching signal of a predetermined cycle during a vertical blanking period based on the signal, and selecting and outputting each reception signal by the second signal selecting means based on the switching signal; Noise detecting means for comparing the noise components of the respective received signals from the second signal selecting means and outputting to the first signal selecting means a selection signal for selecting an antenna of the received signal having a small noise component; Based on the selection signal, the voice signal from the FM demodulating means is reduced so as to reduce switching noise included in the voice signal by the first signal selecting means. And a gain control means for controlling the gain of the signal.