JPH0666704B2 - 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 V, U, SHF band television receiver, a communication device, or the like. In particular, the present invention relates to an electronic tuning type receiver using a varactor diode as a tuning element, and its purpose is to detect a frequency characteristic within a reception band and correct it to an optimum frequency characteristic to enable stable reception.

Conventional technology In recent years, not only conventional video and audio,
Digital signals have come to be transmitted as represented by teletext broadcasting. With conventional receivers, the frequency characteristics within the reception band change depending on the desired reception frequency, and also due to the AGC operation of the high-frequency amplifier that suppresses fluctuations in the received electric field strength, causing deterioration of the demodulated image, voice, and data. In order to improve this, the varactor diodes constituting each tuning circuit are selected to suppress the tuning error and the characteristics are made uniform, but the fluctuation of the frequency characteristics for each reception frequency cannot be sufficiently suppressed.

However, future broadcast formats will require further improvements in performance.

Hereinafter, the above-described conventional receiving device will be described with reference to the drawings. FIG. 4 is a circuit block diagram of a conventional receiving device, in which a high frequency signal is supplied to a high frequency signal input terminal 8, selected by an input tuning circuit 2, enters a high frequency amplifier 3, and after being amplified, interstage tuning is performed. It enters the circuit 4 and suppresses signals other than the desired signal, for example, image signals, and enters the mixer 5. The mixer 5 mixes with the local oscillation signal injected from the local oscillator 7 to generate an intermediate frequency signal. This intermediate frequency signal is output to the intermediate frequency signal output terminal 9 via the output tuning circuit 6.
Will be output.

All tuning voltages of each tuning circuit including the local oscillator are selected.
The same voltage is supplied from the tuning voltage generation circuit 17. Therefore,
It is necessary to maintain this optimum characteristic because each tuning circuit cannot always have the optimum characteristic for the desired signal when the desired signal is received, and the frequency characteristic in the reception band changes depending on the reception frequency. This technique, which is represented by a single super reception system, is a basic technique for reception such as a television broadcast signal, and no particularly appropriate document such as literature is mentioned.

Problems to be Solved by the Invention However, in the above configuration, since a common tuning voltage is supplied to the varactor diodes of each tuning stage,
We have attempted to equalize the frequency characteristics within the reception band by suppressing the error of the varactor diode, which is one of the tuning elements, during manufacturing, but it is possible to completely eliminate the error of the varactor diode at each tuning stage. However, the error causes the tuning error of the tuning circuit as it is, and further considering the error of the coil and the capacitor that configure the tuning circuit, suppressing the tuning error causes the circuit configuration to become complicated and the cost to rise. , It was also very difficult to integrate.

The present invention has been made in view of the above-mentioned problems, and detects a change between a desired signal frequency and a change due to gain control of a reception band frequency characteristic of a reception device, and an optimum reception band frequency characteristic for desired signal reception. Therefore, it is an object of the present invention to provide a receiving device with improved performance and productivity without the need to severely suppress the errors of the varactor diode, the coil, and the capacitor that are tuning elements.

Means for Solving the Problems In order to solve the above problems, the receiving apparatus of the present invention supplies a sweep signal for frequency sweeping in a desired reception frequency band to the input end of each tuning stage whose frequency characteristic is to be detected. It is taken out from the output terminal, usually input to a mixer for frequency conversion for reception, frequency converted to an intermediate frequency band, converted to a DC voltage according to the signal level by a signal level detection circuit, and stored in advance. Compared with the optimum frequency characteristics within the reception band, determine the error, connect a tuning control circuit that corrects the tuning voltage, and analyze the effect of the difference between the desired signal frequencies, the change during gain control, and the error of the tuning element. It is equipped with a configuration that suppresses it.

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 the desired signal frequencies by the above 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. Here, input tuning circuit 2, high frequency amplifier 3, interstage tuning circuit 4, mixer 5, tuning circuit
6. The operation of the local oscillator 7 is the same as that of the conventional example, and detailed description thereof will be omitted. In FIG. 1, when the desired signal is received, the same tuning voltage is first supplied to each tuning circuit, but since the frequency characteristics within the receiving band are not optimal, the desired signal immediately input from the high frequency signal input terminal 8 is received. The AGC voltage is held and a frequency sweep signal generated by the tuning control circuit 10 that oscillates in the desired signal frequency band and is swept is supplied to the signal switching circuit 11. In order to detect the frequency characteristic within the reception band of the input tuning circuit 2 of each tuning circuit, the tuning control circuit supplies a switching control signal to the switching circuits 21 and 22,
Connect to terminals 13 and 15, respectively. Therefore, the frequency sweep signal output from the switching circuit 21 enters the signal switching circuit 1 from the terminal 13. The signal switching circuit 1 is a circuit for switching between a desired signal and a frequency sweep signal. The frequency sweep signal output from the signal switching circuit 1 is supplied to a high frequency amplifier 3 through an input tuning circuit 2 and its output terminal, that is, interstage. The frequency sweep signal is taken out from the connection point with the tuning circuit 4 and enters the switching circuit 22 from the terminal 15. The frequency sweep signal output from the switching circuit 22 is supplied from the terminal 16 to the input terminal of the mixer 15, and enters the mixer 5. on the other hand,
The local oscillator 7 has an oscillating frequency matched to reception of a desired signal, and this local oscillating signal is injected into the mixer 7, mixed with the frequency sweep signal, and taken out from the output end of the mixer 7,
It is supplied to the signal level detection circuit 12. Signal level detection circuit
At 12, the DC voltage corresponding to the signal level is converted and supplied to the tuning control circuit 10. By detecting the DC voltage corresponding to each frequency by the tuning control circuit 10, the frequency characteristic within the reception band can be known. This is compared with a flat reception band frequency characteristic, and a control voltage according to the error is supplied from the tuning control circuit 10 to the input tuning circuit 2, for example, a tuning circuit including a variable voltage capacitance element and an inductor. The frequency characteristic within the reception band can be made flat by changing the tuning frequency.

Next, in order to detect the frequency characteristic within the reception band of the interstage tuning circuit 4, the tuning control circuit 10 supplies a frequency sweep signal to the signal switching circuit 11, while the tuning control circuit 10 switches the switching circuit.
A switching control signal is supplied to 21, 22, and the switching circuit 21
And the switching circuit 22 is opened. Therefore the switching circuit
The frequency sweep signal output from 19 is the high frequency amplifier 3 from terminal 14.
Enter the input end of. The frequency sweep signal output from the high frequency amplifier 3 passes through the inter-stage tuning circuit 4, further enters the mixer 5, undergoes frequency conversion into the intermediate frequency band, and then enters the signal level detection circuit. The signal level detection circuit 12 converts the DC voltage according to the signal level and supplies the DC voltage to the tuning control circuit 10. By detecting the DC voltage corresponding to each frequency by the tuning control circuit 10, the frequency characteristic within the reception band can be known.
This is compared with a flat reception band frequency characteristic, and a control voltage according to the error is supplied from the tuning control circuit 10 to the interstage tuning circuit 4, for example, a tuning circuit including a variable voltage capacitance element and an inductor. By supplying and changing the tuning frequency, the frequency characteristic within the reception band can be made flat.

As described above, after the frequency characteristics of the input tuning circuit 2 and the interstage tuning circuit 4 are optimized, the switching circuits 21 and 22 are opened to suppress the influence on the receiving circuit section. Further, according to the present embodiment, the switching circuits 21 and 22 are mechanical, but they may be constituted by semiconductor elements as long as they can input and output signals reliably.

FIG. 2 shows the first frequency relation of the receiving apparatus showing the embodiment of the present invention. The tuning control circuit 10 causes the local oscillator 7 used for reception tuning to oscillate fixedly at a local oscillation frequency corresponding to a desired reception frequency. Here, f _R is the desired reception frequency, f _L is the oscillation frequency of the local oscillator 7 used for reception tuning, f1F is the intermediate frequency, and f _L = f _R + f1F ( 1) is represented. Now, when the frequency sweep signal 18 generated from the tuning control circuit 10 is expressed as f _R ± Δf _S (2), the local oscillation signal 19 and the frequency sweep signal 18 of the local oscillator 7 used for reception tuning are Mixed in the mixer 5,
From equations (1) and (2), f _L − (f _R ± Δf _S ) = fIF ± Δf _s (3), and as shown in equation (3), ± Δf _S in the intermediate frequency band.
The sweep signal of appears. This frequency sweep signal is supplied to the signal level detection circuit 12 to obtain a DC voltage corresponding to each input frequency and supplied to the tuning control circuit 10. The tuning control circuit 10 generates a control voltage to control the tuning circuit so that it has a number characteristic.

According to this embodiment, the signal appearing in the signal level detection circuit 12 is always in the intermediate frequency band, the frequency characteristics of the detection circuit can be easily flattened, and the DC voltage corresponding to the input signal frequency can be accurately detected. . If multiple sampling filters are provided in the signal level detection circuit 12 by this method, if the center frequency of the filter is determined in advance, there is no need to set the sweep frequency width of the frequency sweep signal, and each sampling filter extracts samples at a specific frequency. , The frequency characteristic within the reception band can be detected by detecting only the obtained maximum voltage. Regarding the frequency sweep, only the frequency sweep is performed so as to include the necessary range without strictly setting the sweep width and the oscillation frequency. Good.

FIG. 4 shows a second frequency relationship of the receiving device showing the embodiment of the present invention. The local oscillation signal 19 of the local oscillator 7 used for reception tuning by the tuning control circuit 10 oscillates up and down with the local oscillation frequency corresponding to the desired reception frequency as the center. That is, (f _L ± Δf _S ) ... (4) where f _L is the local oscillator 7 used for the reception tuning.
Represents the oscillation center frequency, and Δf _S represents the sweep frequency width. Now, the frequency sweep signal 18 generated from the tuning control circuit 10
Is expressed as (f _R ± Δf _S ) ... (5), when the local oscillation signal 19 of the local oscillator 7 used for reception tuning and the frequency sweep signal 18 are mixed by the mixer 5, (f _L ± Δf _S ) − (f _R ± Δf _S ) = f1F (5), which is a constant frequency regardless of the sweep. This signal is supplied to the signal level detection circuit 12 to obtain a DC voltage corresponding to each input frequency, and it is supplied to the tuning control circuit 10 to generate a control voltage to control the tuning circuit and signal each tuning circuit. Use in-band frequency characteristics that are optimal for reception. According to the present embodiment, the signal that appears in the signal level detection circuit 12 is always a fixed frequency within the intermediate frequency band, it is easy to flatten the frequency characteristics of the detection circuit, and the DC voltage corresponding to the input signal frequency is accurately detected. can do. If the signal level detection circuit 12 is provided with one sampling filter by this method, if the center frequency of the filter is predetermined, the sweep frequency of the frequency sweep signal and the sweep frequency of the local oscillator used for reception tuning can be determined. When synchronized, the frequency characteristic within the reception band can be detected by synchronously detecting only the DC voltage corresponding to the signal output by the sampling filter.

EFFECTS OF THE INVENTION As is apparent from the above description, the present invention detects the frequency characteristic within the reception band according to the electric field strength at the time of reception, and individually adjusts the tuning voltage of each tuning circuit so that the frequency characteristic is suitable for signal reception. It is not necessary to severely suppress the error of each tuning element by controlling, supplying, and setting to, and it is possible to comprehensively suppress the error of the tuning circuit. Furthermore, the frequency characteristics within the reception band can be detected for each circuit stage without considering the influence of the circuit stages, and the frequency sweep signal is fixed in the intermediate frequency band where signal processing is easy or is taken out as a sweep signal so that it is within the accurate reception band. It is possible to correct the frequency characteristic. Therefore, it is possible to maintain the high performance by detecting the deterioration of the frequency characteristic in the reception band due to the influence of the change in the gain control and the difference between the reception frequencies, which is difficult in the conventional receiving device, for each frequency in the reception band. It is possible to provide a receiving device capable of improving the property.

[Brief description of drawings]

FIG. 1 is a block diagram of a receiver of the present invention, FIG. 2 is a relationship diagram of a first frequency of the receiver in the embodiment of the present invention, and FIG. 3 is a second diagram of the receiver in the embodiment of the present invention. FIG. 4 is a block diagram of a conventional receiving device. 2 ... Input tuning circuit, 3 ... High frequency amplifier, 4 ... Interstage tuning circuit, 5 ... Mixer, 6 ... Tuning circuit, 7 ... Local oscillator, 8 ... High frequency signal input terminal, 10 ... Tuning control circuit, 11 ... signal switching circuit, 13, 15, 16 ... terminals.

Claims (3)

[Claims] 1. A first switching circuit for supplying the frequency sweep signal by selecting either a frequency sweep signal input terminal of a signal switching circuit or an input terminal of a high frequency amplifier, and an input terminal of an interstage tuning circuit. A second switching circuit that opens and closes the output end, and switches the first and second switching circuits to detect the frequency characteristic of the input tuning circuit or the interstage tuning circuit, and outputs a frequency sweep signal. The input tuning circuit or the interstage tuning circuit is supplied to the input tuning circuit or the interstage tuning circuit, and the frequency sweep signal extracted from each of the circuit parts is supplied to the mixer to be converted into an intermediate frequency band signal. It is provided with a tuning control circuit that corrects the tuning voltage of each stage so that the frequency characteristic of each stage becomes a flat frequency characteristic within the reception band. To receive Location. 2. The receiving device according to claim 1, wherein the signal obtained at the output of the mixer is a frequency sweep signal. 3. The signal obtained at the output of the mixer is always a fixed frequency signal.
The receiving device according to the item.