JP3533686B2 - Receiver - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving apparatus having a diversity function applied to an in-vehicle liquid crystal television apparatus and the like. 2. Description of the Related Art In a receiving apparatus such as an in-vehicle liquid crystal television apparatus whose receiving state changes every moment, a diversity function for automatically switching and selecting the best receiving state from among a plurality of antennas at any time is provided. By mounting it, more stable reception can be made possible. In general, in the diversity function, a plurality of antennas are sequentially switched and selected arbitrarily within a sufficiently short time within a vertical blanking period of a received signal, for example, about 10 to 20 [μsec], and the carrier wave input is changed. The detection output when input to the tuner circuit is compared in level, and an operation is performed so as to select the antenna input having the maximum level. However, in a normal tuner circuit, an AGC (automatic gain control) that controls the gain of an amplifier circuit so that a stable detection output can be obtained even if there is a slight change in the input electric field level. Gain control) circuit, but this AGC circuit may not be able to follow a sudden and large level fluctuation of the input electric field. Therefore, in the above-described receiving apparatus having the diversity function, when one antenna is switched to another antenna, and a large difference in the input electric field level occurs there, in the initial stage immediately after that. Matching with the gain state on the tuner circuit side could not be performed, resulting in distortion in the detection waveform, which caused problems such as loss of synchronization. SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and has as its object the object of the present invention when a plurality of antennas are switched and used as in a diversity function. It is an object of the present invention to provide a receiving apparatus that can always maintain an accurate and stable receiving state even if the receiving level greatly fluctuates. That is, according to the present invention, a switching selection means for switching and selecting a plurality of antennas is compared with a reception level of each antenna selected by the switching selection means.
Compensation signal generating means for providing information indicating a relative reception level difference
Level comparing means for outputting to the comparator, a compensating signal generating means for generating a compensating signal for automatic gain control based on information indicating a difference between relative reception levels outputted by the level comparing means, and the compensating signal generating means The compensation signal generated by
Supplied to the dynamic gain control means, and
Automatic gain control means for performing automatic gain control so as to correspond to the reception level . With the above configuration, even if the reception level changes significantly before and after switching from one antenna to the other antenna, the gain control on the receiving circuit side can be quickly performed. It is possible to prevent a phenomenon such as distortion of a detection waveform due to an antenna switching operation, and to always maintain an accurate and stable reception state. An embodiment in which the present invention is applied to an in-vehicle liquid crystal television having a diversity function will be described below with reference to the drawings. FIG. 1 shows the entire basic circuit configuration. An antenna group 11 composed of a plurality of antennas is connected to a diversity circuit 12. The diversity circuit 12 supplies the tuner 13 with the television wave received by the antenna selected by switching and selecting the antenna group 11 and the AGC voltage a for compensation accompanying the selecting operation. The tuner 13 selects a specified channel according to a tuning signal from the tuning control circuit 14 and converts the selected channel into an intermediate frequency signal. The intermediate frequency signal output from the tuner 13 is sent to the TV linear circuit 15. The TV linear circuit 15 includes an intermediate frequency amplifier, a SAW filter, a video detector, a video amplifier, an AFT detector, and the like. The TV linear circuit 15 amplifies the intermediate frequency signal from the tuner 13 and detects the video. I do. Then, the obtained audio signal is output to the audio circuit 16. The audio circuit 16 comprises an audio detection circuit and an audio amplification circuit. The audio signal from the TV linear circuit 15 is detected and converted into a low-frequency signal. I do. The output signal of the video detection circuit in the TV linear circuit 15 is sent to the diversity circuit 12, the chroma circuit 18 and the synchronization separation circuit 19 after being amplified by the video amplification circuit. This sync separation circuit 19 separates the horizontal and vertical sync signals included in the video signal and outputs a composite sync signal CS.
YNC is output to the tuning control circuit 14, and the horizontal synchronization signal H-SYNC and the vertical synchronization signal V-SYNC are output to the timing control circuit 20, respectively. Further, the TV linear circuit 34 outputs an SFT-shaped AFT signal obtained by AFT detection of the intermediate frequency signal to the tuning control circuit 14. The tuning control circuit 14 receives key input such as tuning setting data and tuning up / down instructions from a key input unit 21. The tuning control circuit 14
A tuning signal having a voltage value corresponding to a designated channel is created based on the operation of a tuning up / down key in the key input unit 21 and an AFT signal from the TV linear circuit 15 and the like, and is output to the tuner 13. The control circuit 14 outputs a timing signal for antenna switching and reception level detection to the diversity circuit 12 as appropriate within the vertical blanking period. The timing control circuit 20 generates a sampling pulse φs based on the horizontal synchronizing signal H-SYNC and the vertical synchronizing signal V-SYNC sent from the sync separation circuit 19 and outputs the sampling pulse φs to the A / D conversion circuit 22. I do. The chroma circuit 18 performs a chroma process on the video signal supplied from the TV linear circuit 15 to perform R, G, B
A chroma signal composed of the three primary color signals is obtained, and the obtained chroma signal is output to the A / D conversion circuit 22. The A / D conversion circuit 22 converts the chroma signal output from the chroma circuit 18 into the sampling pulse φs
, And converts it into digital video data of 3 to 4 bits per pixel to convert the digital video data into a segment drive circuit 23.
Output to Further, the timing control circuit 20 creates a timing signal for display control based on the horizontal synchronizing signal H-SYNC and the vertical synchronizing signal V-SYNC supplied from the synchronization separating circuit 19, and generates a segment driving circuit 23 and a common driving circuit. 24 operations are controlled. The common drive circuit 24 generates a scanning signal in accordance with a timing signal from the timing control circuit 20, and sequentially drives the common electrodes of the LCD panel 25. The segment driving circuit 23 sequentially reads 3 to 4 bits of video data supplied from the A / D conversion circuit 22 according to a timing signal from the timing control circuit 20, reads one line of video data, and then reads the video data. A gradation signal is generated according to the signal, and the segment electrodes of the LCD panel 25 are driven for display. Next, mainly the diversity circuit 12
The detailed circuit configuration around the device and its surroundings will be described with reference to FIG. As shown in the figure, the diversity circuit 12 includes an antenna switching circuit 12a, a level comparison circuit 12b, a sample and hold circuit 12c, and a compensation AGC voltage generation circuit 12d. The antenna switching circuit 12a sequentially switches and selects individual antennas constituting the antenna group 11 in a short time according to the timing signal from the tuning control circuit 14, and sequentially transmits the television wave received by the selected antenna to the tuner 13a. Supply to When the tuner 13 selects a designated channel, converts it to an intermediate frequency signal, and sends it to the TV linear circuit 15, the TV linear circuit 15 performs various processes as described above, and the final stage video amplifying circuit 15a To the sample and hold circuit 12c of the diversity circuit 12. The sample and hold circuit 12c samples and holds the video signal supplied from the video amplification circuit 15a in the TV linear circuit 15 by the timing signal from the tuning control circuit 14, and stores the held value in the level comparison circuit 12c.
Output to b. The level comparing circuit 12b sequentially compares the levels of the video signals input from the sample and hold circuit 12c and outputs the result of the comparison to the antenna switching circuit 12a.
The antenna switching circuit 12a switches and selects the antenna having the highest reception level based on the comparison result of the level comparison circuit 12b, and transmits the received television wave to the tuner 13 to perform the receiving operation. The level comparison circuit 12b outputs the comparison result to the antenna switching circuit 12a, and outputs information indicating the level difference to the compensation AGC voltage generation circuit 12d. The compensating AGC voltage generating circuit 12d generates a compensating AGC voltage based on the information of the reception level difference from the level comparing circuit 12b, and supplies this to the AGC circuit 13a for controlling the gain in the tuner 13. In the above configuration, the timing signal from the tuning control circuit 14 is, for example, 10 to 20 [μsec] for a short time during the vertical blanking period of the video signal.
c], the antenna switching circuit 12a sequentially switches and selects the individual antennas constituting the antenna group 11 in accordance with the timing signal. The television wave received by each antenna of the antenna group 11 thus selected is sequentially supplied to the tuner 13, converted into an intermediate frequency signal, and output from the video amplifier circuit 15a by the TV linear circuit 15. The video signal output from the image amplifying circuit 15a is also transmitted to the diversity circuit 12a.
Of the tuning control circuit 14
, Sequentially sampled and held by the timing signal from the controller, and outputs the held value to the level comparator 12b. The level comparing circuit 12b compares the levels of the video signals sequentially inputted, and outputs the comparison result to the antenna switching circuit 12a to output the antenna having the highest receiving level for the next specific period, for example, for one field. And the information indicating the relative level difference between the reception level of the antenna selected up to the previous timing and the reception level of the antenna selected by the antenna switching circuit 12a. Output to 12d. A compensating AGC voltage generating circuit 12d generates a compensating AGC voltage based on the information of the reception level difference, and supplies the compensating AGC voltage to an AGC circuit 13a for controlling a gain in the tuner 13. Then, it is possible to quickly respond to a gain according to the reception level of the antenna selected next. Therefore, even if the level changes suddenly and largely due to the switching selection of the antenna in the diversity circuit 12, the AGC circuit 13a quickly follows the level change without causing any distortion or the like in the detection waveform. It is possible to prevent phenomena such as loss of synchronization and to maintain an accurate and stable reception state at all times. As described above, according to the present invention, when a plurality of antennas are switched and selected as in the case of the diversity function, the reception level fluctuates greatly before and after the antenna switching is selected. However, it is possible to provide a receiving apparatus that can always maintain an accurate and stable receiving state.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an overall circuit configuration according to an embodiment of the present invention. FIG. 2 is a block diagram showing a detailed circuit configuration of the diversity circuit of FIG. 1 and its periphery. [Description of Signs] 11 ... Antenna group, 12 ... Diversity circuit, 12a ... Antenna switching circuit, 12b ... Level comparison circuit, 12c ... Sample hold circuit, 12d ... Compensation AGC voltage generation circuit, 13 ... Tuner, 13a ... AGC circuit , 14: Tuning control circuit, 15: TV linear circuit, 15a: Video amplification circuit, 16: Audio circuit, 17: Speaker, 18: Chroma circuit, 19: Synchronization separation circuit, 20: Timing control circuit, 21: Key input unit ,twenty two…
A / D conversion circuit, 23: segment drive circuit, 24: common drive circuit, 25: LCD panel.

Claims (1)

(57) [Claims 1] Switching selection means for switching and selecting a plurality of antennas, and comparing the reception levels of the respective antennas selected by the switching selection means, and comparing the relative reception levels. The information indicating the compensation signal
No. a level comparing means for outputting to the generator, and the compensation signal generating means for generating a compensation signal for automatic gain control based on the information indicating the difference of the output relative reception level by the level comparing means, said compensating The compensation signal generated by the signal generation means is automatically gain controlled.
Receiving level of the antenna that is supplied to the
An automatic gain control means for performing automatic gain control so as to correspond to the signal.