JPH067645B2 - Receiver - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving device that can be used in a television receiver for receiving terrestrial broadcasting including VTV and UHF band CATV. In particular, the present invention relates to an electronic tuning type receiver using a varactor diode as a tuning element, and its object is to detect frequency characteristics within a reception band and adjust optimum frequency characteristics to enable stable reception. .

2. Description of the Related Art In recent years, television broadcasting has come to transmit not only conventional video and audio but also digital signals as represented by character multiplex broadcasting. In the conventional receiving device, the frequency characteristic within the receiving band changes depending on the channel and by the AGC operation of the high frequency amplifier which suppresses the fluctuation of the received electric field strength, which causes deterioration of demodulated image, voice and data. In order to improve this, we have selected varactor diodes that make up each tuning circuit to suppress tuning errors and make the characteristics uniform, but future broadcast formats will require further improvements in performance. It

Hereinafter, the above-described conventional receiving device will be described with reference to the drawings. FIG. 6 is a circuit block diagram of a conventional receiving device, in which a VHF band signal is a high frequency signal input terminal 1.
Input to the input tuning circuit 4, enters the high frequency amplifier 5, is amplified, then enters the interstage tuning circuit 6, suppresses signals other than the desired signal, enters the mixer 7, and outputs an intermediate frequency signal. The converted signal is output from the intermediate frequency signal output terminal 20.

On the other hand, the UHF band signal is input to the high frequency signal input terminal 2, and the input tuning circuit 8 is input as in the case of receiving the VHF band signal.
, The high frequency amplifier 9 enters and is amplified, enters the interstage tuning circuit 10, is converted into an intermediate frequency signal by the mixer 11, and the mixer 7 operates as an intermediate frequency amplifier and after amplification, an intermediate frequency signal output terminal 20 Is output from. The local oscillator 13 operates during reception in the VHF band, and the local oscillator 12 operates during reception in the UHF band to perform tuning and frequency conversion. Since the same voltage is supplied to each tuning circuit from the tuning voltage generator, each tuning circuit does not always have the optimum characteristics for the desired channel frequency when the desired channel is received. Since the frequency characteristic is changing, it was necessary to maintain this optimum characteristic. This technology is VHF
It is a basic technique for receiving television broadcast signals in the band and the UHF band, and documents such as documents relating thereto are not particularly mentioned.

Problems to be Solved by the Invention However, in the above-described structure, the error in the varactor diode, which is one of the tuning elements, is suppressed at the time of manufacturing, so that the frequency characteristics in the reception band are made uniform. Since a common tuning voltage is supplied to the varactor diodes of each tuning stage, the error of each varactor diode produces the tuning error of the tuning circuit as it is, and further the error of the coil and the capacitor that configures the tuning circuit. Considering also, it is difficult to suppress the tuning error because the circuit configuration becomes complicated and the cost increases, and it is very difficult to integrate the circuits.

The present invention has been made in view of the above problems, and detects a change in gain characteristic of a receiving band frequency characteristic of a receiving device and a change between channels to detect a frequency characteristic in a receiving band optimum for receiving a television broadcast signal. It is an object of the present invention to provide a receiving device which is improved in performance and productivity without being required to severely suppress errors of the varactor diode, the coil, and the capacitor, which are the tuning elements.

Means for Solving the Problems In order to solve the above problems, the receiving device of the present invention mixes a part of an oscillation signal of a local oscillator for reception tuning with an oscillation signal of another local oscillator by a mixer. , Generate a signal that sweeps in the same frequency band as the high frequency input signal, input it from the high frequency signal input terminal, change the frequency, and then supply it to the intermediate frequency signal level detection circuit from the intermediate frequency signal output terminal. The converted signal is extracted by extracting the specific frequency with a filter, converted into a DC voltage according to the signal level by the detector, and compared with the optimum reception band frequency characteristic stored in advance. A tuning voltage control circuit that adjusts the tuning voltage at each stage is connected and connected to each other to suppress the influence of the difference between channels, the change during gain control, and the error of the tuning element.

Effect The present invention can suppress the deterioration of the frequency characteristic in the reception band due to the influence of the error of the tuning element, the change at the time of gain control, and the error between channels by the above-mentioned configuration.

Embodiment Hereinafter, a receiver according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a block diagram of a receiving apparatus according to an embodiment of the present invention. In FIG. 1, a VHF band signal is input from the VHF band input terminal 1, passes through a signal switching circuit 3 that switches between the sweep signal generated from the mixer 18 and the television broadcast signal, and is supplied to the input tuning circuit 4 tuned to the desired channel. After being amplified by the high frequency amplifier 5, it is further selected by the interstage tuning circuit 6. The interstage tuning circuit 6 is generally composed of a double tuning circuit, and in this case, it is composed of two tuning elements. The signal output from the interstage tuning circuit 6 is
It enters the VHF band mixer 7, is mixed with the local oscillation signal injected from the VHF band receiving local oscillator 13, and an intermediate frequency signal appears. This intermediate frequency signal enters the signal switching circuit 14 that switches to supply it to the intermediate frequency signal level detection circuit 15 for detecting the frequency characteristic in the reception band, and the intermediate frequency signal level detection circuit 15 is detected when the frequency characteristic in the reception band is detected. The intermediate frequency signal is supplied from the intermediate frequency signal output terminal 20 by the signal switching circuit 14 when the frequency characteristic within the reception band is set. When detecting the frequency characteristic in the reception band, the AGC voltage of the high frequency amplifier 5 is held, the signal switching circuit 3 is switched to the direction in which the sweep signal is input, and the tuning voltage control circuit 16 further controls the local oscillator 13 and the local oscillator 17. By controlling so that the oscillation frequency can be swept, a part of the oscillation signal of the local oscillator 13 and the local oscillator 17
The local oscillation signal of is injected into the mixer 18 to generate the sweep signal in the same frequency band as the desired channel frequency, and the fluctuation of the sweep signal level due to the deviation of the oscillation output level of the local oscillator and the deviation of the conversion gain of the mixer is suppressed. Through the level control circuit 19 into the input tuning circuit 4 by the signal switching circuit 3 and after high frequency amplification, intermediate frequency conversion is performed and an intermediate frequency signal is sent to the intermediate frequency signal level detection circuit 15 via the signal switching circuit 14. In the intermediate frequency signal level detection circuit 15, a specific frequency in the intermediate frequency band, for example, for a high frequency input signal, a center frequency for detecting flatness in the receiving channel band and a spectrum of the television broadcast signal. The signal level of the video carrier frequency and the audio carrier frequency of the frequency where the Is supplied to the tuning voltage control circuit 16 after changing to a DC voltage corresponding to. The tuning voltage control circuit 16 compares the levels of the frequency characteristics stored in advance, particularly the center frequency of the desired channel, the video carrier frequency, and the audio carrier frequency to determine the quality of the reception band frequency characteristics, If it is good, the signal switching circuit 3,
Switch 14 to the side that can receive TV broadcast signals. On the other hand, in the case of no, the tuning voltage is individually supplied to each tuning circuit to obtain the optimum in-band frequency characteristic. Further, signal reception in the UHF band is input from the UHF band input terminal 2, selected by the input tuning circuit 8, amplified by the high frequency amplifier 9, passed through the interstage tuning circuit 10, and converted into an intermediate frequency signal by the mixer 11. , And is amplified by the mixer 7. The local oscillator is switched to the UHF band receiving local oscillator 12, and the sweep signal is the local oscillator 12 described above.
A part of the oscillating signal and the local oscillating signal of the local oscillator 17 are injected into the mixer 18 and generated. As described above, according to the present embodiment, the AG depending on the electric field strength at the time of receiving the television broadcast signal is
Since the C voltage is held and the level deviations between the specific frequencies are compared with each other, compared to the setting of the tuning circuit that simply finds the maximum point of the intermediate frequency signal output, the reception with improved performance can be performed and each tuning can be performed. The error of the tuning circuit can be suppressed while including the error of the element. Hereinafter, a configuration diagram of the intermediate frequency signal level detection circuit of the receiving device showing the first embodiment of the present invention will be described with reference to FIG. The intermediate frequency signal supplied from the signal switching circuit 14 is a sampling filter
Select only the signal of the specific frequency mentioned above in 22 and
The DC voltage corresponding to the intermediate frequency signal level is generated and supplied to the tuning voltage control circuit 16. The constituent blocks of the sampling filter will be described below with reference to FIGS. 3, 4, and 5. FIG. 3 is a concrete configuration diagram of the intermediate frequency signal level detection circuit of the receiving apparatus showing the first embodiment of the present invention. The sampling filter 22 is a fixed frequency filter whose center frequency is the center frequency corresponding to the desired channel in the above-mentioned intermediate frequency band, video carrier frequency, audio carrier frequency and upper adjacent channel video carrier frequency, lower adjacent channel audio carrier frequency. 24a, 24b, 24c, 24d, 24e are arranged in parallel, the input terminal is switched by the signal switching circuit 14,
The output terminals of the fixed frequency filters 24a, 24b, 24c, 24d, 24e are connected to the detector 23 to generate a DC voltage according to the signal level of the specific frequency. In this configuration, as described with reference to FIG. 1, the tuning voltage control circuit 16 causes the local oscillators 12 and 13 to oscillate fixedly at the local oscillation frequency corresponding to the desired channel, that is, _R is the desired channel frequency and _L is the local oscillation frequency. When the oscillation frequency of the oscillators 12 and 13 is _IF , and _IF is an intermediate frequency, and the reception system is the upper side local oscillation, it is expressed as _L = _R + _IF (1). Here oscillates the local oscillator 17 is at an intermediate frequency band _(IF), maximum, sweep up vertically adjacent channel (± Δ _{L ')} Then, the oscillation frequency of the said local oscillator 17, _IF' ± Δ _L '......... (2) Therefore, when a part of the local oscillation signals of the local oscillators 12 and 13 and the local oscillation signal of the local oscillator 17 are mixed by the mixer 18, from the equations (1) and (2), _L − ( _IF ′ ± _L ′) = _R ± Δ _L ′ (3) The input signal is swept by Δ _L ′ and the local oscillators 12 and 13 oscillate at a fixed frequency.
An intermediate frequency signal (3) and _{(1), L - (R ± Δ L} ') as shown in _{= IF ± L' ............ (4} ) Equation (4), ± the intermediate frequency band Delta] f _L A sweep signal of'appears. In addition, the local oscillator 17 is oscillated at the sum f _S of the desired channel frequency and the oscillation frequencies of the local oscillators 12 and 13, and the maximum and upper and lower adjacent channels are swept (± Δ
f _L ′) Then, the oscillation frequency of the local oscillator 17 is f _S ± Δf _L ′ ……………… (5) ∵ (f _S = f _L + f _R ), so that the local oscillators 12 and 13 have When the local oscillation signal of the part and the local oscillator 17 of the local oscillation signal are mixed in mixer 18, formula from (5) and _{(1), (S ± Δ} L ') - L = S - L ± Δ L _{'= R ± Δ L' ............} (6) to the input is supplied with a signal which is swept by ± delta _{L ',} since the local oscillator 12 and 13 is oscillating at a fixed frequency, wherein
(4) the sweep signal of ± delta _{L 'appears} in middle frequency band as shown by. At this time, by the signal switching circuit 14, the frequency fixed filters 24a, 24b, 24c, 24d, 24e of a specific frequency are sequentially switched, the maximum detection output corresponding to each is obtained from the detector 23, and the tuning voltage control circuit 16 is provided. The voltage is supplied to generate a control voltage to control the tuning circuit. As described above, according to the present embodiment, the center frequency of the frequency fixed filter can be accurately fixed, and the frequency characteristic within the reception band can be known only by obtaining the maximum value of the sampling filter output. There is no need to set the frequency band strictly.

FIG. 4 is a specific configuration diagram of the intermediate frequency signal level detection circuit of the receiving device showing the second embodiment of the present invention. The sampling filter 22 is composed of a frequency variable tuning type filter that can be tuned to any frequency in the intermediate frequency band, and a varactor diode or the like is used as a tuning element. Since the sweep signal generation method is the same as that described with reference to FIG. 3, detailed description thereof will be omitted. In the case of this configuration, the intermediate frequency signal is supplied from the signal switching circuit 14 to the sampling filter as it is, and the switching as described in FIG. 3 is not performed. In the intermediate frequency signal level detection, a sampling filter is set to a specific frequency in the intermediate frequency band, a sweep signal which is a high frequency input signal is input, and the intermediate frequency signal level of each specific frequency is detected. According to the present embodiment, it is possible to set a specific frequency with one sampling filter, and it is also possible to increase the number of the specific frequencies.
It is possible to make a detailed comparison of the frequency characteristics within the reception band. Further, it is not necessary to change the circuit configuration.

FIG. 5 is a concrete configuration diagram of the intermediate frequency signal level detection circuit 15 of the receiving apparatus showing the third embodiment of the present invention. The sampling filter 22 is set to a single frequency in the intermediate frequency band, and its output is supplied to the detector 23.
In this configuration, as described with reference to FIG. 1, the tuning voltage control circuit 16 causes the local oscillators 12 and 13 to sweep and oscillate up and down adjacent channels centering on the local oscillation signal corresponding to the desired channel. _{That, (L ± Δ L) .....................} (7) where _L denotes the oscillation center frequency of the local oscillator 12 and 13, delta _L represents a sweep frequency range. On the other hand, the local oscillator
17 an intermediate frequency _IF 'oscillates with the sweep signal obtained by mixing them local oscillation _{signal, (L ± Δ L) -} IF' = L - IF '± Δ L ... (8) , and the signal switching circuit Supply through 3. High frequency amplification, frequency of the intermediate frequency signal extracted after frequency conversion, from the equation (1) (6), ( L ± Δ L) - (L - IF '± Δ L) = IF' ............... ……… (9), which is a constant frequency regardless of the sweep. This matches the oscillation frequency of the local oscillator 17. Therefore, the error between the center frequency of the sampling filter and the frequency of the intermediate frequency signal can be optimized by finely adjusting the oscillation frequency of the local oscillator 17. According to the present embodiment, the sampling filter can be composed of one frequency fixed filter, and the circuit structure is simple.

EFFECTS OF THE INVENTION As is clear from the above description, the present invention detects the frequency characteristic within the reception band in the electric field enhancement at the time of receiving the desired channel, and tunes each tuning circuit so that the frequency characteristic is suitable for receiving the television broadcast signal. By individually controlling, supplying and setting the voltage, it is not necessary to severely suppress the error of each tuning element, and it is possible to suppress the error of the tuning circuit as a whole, which is difficult for the conventional receiving device. It is possible to provide a receiving device capable of improving performance and productivity while suppressing deterioration of frequency characteristics in the reception band due to changes in gain control and the influence of differences between channels.

[Brief description of drawings]

1 is a block diagram of a receiver of the present invention, FIG. 2 is a block diagram of an intermediate frequency signal level detection circuit of the receiver of the present invention, and FIG. 3 is a receiver of the first embodiment of the present invention. FIG. 4 is a block diagram showing a concrete configuration of the intermediate frequency signal level detecting circuit, FIG. 4 is a block diagram showing a concrete configuration of the intermediate frequency signal level detecting circuit of the receiving device according to the second embodiment of the present invention, and FIG. FIG. 6 is a block diagram of a concrete configuration of an intermediate frequency signal level detection circuit of a receiver in the third embodiment of the present invention, and FIG. 3 ... Signal switching circuit, 4 ... Input tuning circuit, 5 ... High frequency amplifier, 6 ... Interstage tuning circuit, 7, 11 ... Mixer, 8
...... Input tuning circuit, 9 …… High frequency amplifier, 10 …… Interstage tuning circuit, 12,13 …… Local oscillator, 14 …… Signal switching circuit, 1
5 ... Intermediate frequency signal level detection circuit, 16 ... Tuning voltage control circuit, 17 ... Local oscillator, 18 ... Mixer, 19 ... Level control circuit.

Claims (9)

[Claims] 1. A first local oscillator for VHF reception which operates during VHF reception, and a second local oscillator for UHF reception which operates during UHF reception, wherein the oscillation frequencies of the first and second local oscillators There is a third local oscillator that oscillates in a frequency relationship in which the difference matches the desired channel frequency, and mixes a part of the local oscillation signal of the first or second local oscillator with the local oscillation signal of the third local oscillator. Then, a mixer is connected so as to generate a signal of the same frequency as the desired channel, and the generated desired channel same frequency signal is supplied to the broadcast signal input terminal through an automatic level control circuit that keeps the signal level constant. It is connected to a first signal switching circuit, the oscillation frequencies of the first and second or third local oscillators are swept, and the frequency swept signal is input to the broadcast signal input terminal to output the intermediate frequency signal. An intermediate frequency signal level detection circuit composed of a second signal switching circuit for extracting a signal of a specific frequency from the frequency sweep signal appearing at the output terminal, a sampling filter, and a detector for converting to a DC value is connected to form an intermediate frequency signal. The level at the specific frequency of is detected, and the frequency characteristic of each stage becomes the optimum frequency characteristic for receiving the TV broadcast signal,
Compare the detected frequency characteristics with the frequency characteristics stored in advance and correct the error in the frequency characteristics.
A receiving device, to which a tuning voltage control circuit for adjusting the tuning voltage of each stage is connected. 2. The receiving apparatus according to claim 1, wherein the third local oscillator sets an oscillation frequency to an intermediate frequency band. 3. The third local oscillator according to claim 1, wherein the oscillation frequency is the sum of the oscillation frequency of the first or second local oscillator and the desired channel frequency. Receiver. 4. Sweeping of a desired channel frequency is performed by sweeping only a third local oscillator, and a swept signal appears in an intermediate frequency band. The receiving device according to item 3. 5. The desired channel frequency is swept by sweeping only the first or second local oscillator, and signals of the same frequency always appear in the intermediate frequency band. The receiving device according to item 2, item 2 or item 3. 6. A sampling filter, wherein different center frequencies are set so as to individually extract a plurality of signals of different frequencies in the intermediate frequency band, and the sampling filters are characterized in that: The receiver according to item 4. 7. A sampling filter, wherein a single center frequency is set so as to sample a signal of a single frequency in an intermediate frequency band. The receiver described. 8. The receiving apparatus according to claim 6, wherein the sampling filter is composed of a plurality of frequency fixed filters for sampling signals of a plurality of different frequencies. 9. The receiving apparatus according to claim 6, wherein the sampling filter is a frequency tunable filter for sampling signals of a plurality of different frequencies.