JPH05115048A - Tuner circuit - Google Patents

Abstract

PURPOSE:To form a frequency characteristic of an obtained intermediate frequency signal to be stable from each channel in a system where a band characteristic of a dual tuning filter and a local oscillation frequency of a local oscillator are varied by a same control voltage. CONSTITUTION:An IF filter 22 whose frequency characteristic is compensated is provided on an output section of an IF signal at the output side of a mixer circuit 13. An output level of a video carrier signal being an output of the filter and an output level of an audio carrier signal are detected by detectors 24, 25. Detection output level information is stored in a memory 23 as level information of a video carrier signal and an audio carrier signal at each channel. A microcomputer 18 for each channel during reception uses the information of the memory 23 so as to uniformize the video carrier signal and the audio carrier signal thereby varying an audio carrier signal level and a video carrier signal level of the IF filter 22.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tuner circuit for controlling an oscillation frequency of a local oscillator by a PLL loop separately from tuning.

[0002]

2. Description of the Related Art FIG. 2 shows a block diagram of a tuner circuit of a conventional television receiver. Reference numeral 10 denotes an antenna section as a tuner input section.
The input high-frequency signal is a band-pass double tuning filter 1 whose pass band follows the band of the received frequency.
Input to 1. That is, in the double-tuned filter 11, the frequency of the pass band changes according to the control voltage V1 from the phase locked loop (PLL) circuit 17. The PLL circuit 17 is
By the control signal D1 from the microcomputer 18,
The control voltage applied to the local oscillator (voltage-controlled oscillator) 14 can be varied to vary the output frequency (local oscillation) of the local oscillator 14. The output of the local oscillator 14 is input to the phase comparator of the PLL circuit 17 and is compared in phase with the signal of the reference frequency, and the error is fed back to the control terminal of the local oscillator 14. As a result, the local oscillator 14 can stably maintain its output oscillation frequency at the desired frequency designated by the microcomputer 18.

The output of the local oscillator 14 is the mixer circuit 1
It is entered in 3. The high frequency signal from the double tuning filter 11 is input to the mixer circuit 13 via the high frequency amplifier 12. Therefore, from the mixer circuit 13, an intermediate frequency signal which is a difference signal between the high frequency signal and the local oscillation signal is derived.

Therefore, the output control voltage V1 of the PLL circuit 17 is changed by changing the frequency division ratio of the local oscillation signal by the control signal D1 from the microcomputer 18, and the oscillation frequency of the local oscillator 14 is also determined by this.
The reception frequency can be determined. Since the control voltage V1 at this time also indicates the reception frequency band, this is also used for controlling the pass band of the double tuning filter 11.

The intermediate frequency (IF) signal output from the mixer circuit 13 is output to the output terminal 20 via the IF filter 16 set in the band of the intermediate frequency signal via the intermediate frequency amplifier 15. Further, this intermediate frequency signal is input to the video detection circuit and the audio detection circuit in the subsequent stage and demodulated.

In the tuner circuit having such a configuration, the double tuning filter 11 and the local oscillator 13 are generally divided for each reception band, and the frequency bandwidth can be switched by a diode switch or the like. Therefore, the double-tuned filter 11 and the local oscillator 13 are continuously variable when the channel is switched within a certain band.

However, even if the same control voltage V1 is applied to the double tuning filter 11 and the local oscillator 13, the frequency change in the pass band of the double tuning filter 11 and the local oscillator 1 are caused.
The frequency change of 3 does not necessarily change exactly the same.

As a result, the frequency characteristics of the IF signal are affected, and the demodulated video signal and audio signal are deteriorated. For example, when the same control voltage V1 is applied to the double tuning filter 11 and the local oscillator 13 and the frequency change of the double tuning filter 11 is faster than that of the local oscillator 13, (a), (b) or () of FIG. As shown in c).

That is, in the case where the IF output signal is adjusted to be flat in the channel centered on the frequency within the band in which the frequency is continuously changed, FIG.
As shown in (b), the output levels of the video signal P and the audio signal S are almost the same, and a uniform signal level can be obtained within the band. However, in the low frequency channel, the result becomes as shown in FIG. 3A, and the level of the video signal P becomes higher than that of the audio signal S. Then, since the levels are not uniform in the pass band, the high frequency component of the video signal is deteriorated. Moreover, in the high frequency channel, it becomes like (c) of FIG. 3,
The level of the video signal P becomes lower than that of the audio signal S. In this case, since the levels are uneven in the pass band, the low frequency components of the video signal are deteriorated. Similarly, when the frequency change of the double-tuned filter circuit is slower than that of the local oscillator 13, (d) of FIG.
As shown in (e) or (f).

That is, when the IF output signal is adjusted to be flat in the channel whose frequency is the center in the continuously variable band, the video signal is adjusted as shown in FIG. The output levels of P and the audio signal S are substantially the same, and a uniform signal level can be obtained within the band. However, in the low frequency channel, it becomes as shown in FIG.
Is lower than the audio signal S. Then, since the levels are not uniform in the pass band, the low frequency components of the video signal are deteriorated. Further, in the high frequency channel, it becomes as shown in (f) of FIG. 3, and the level of the video signal P becomes higher than that of the audio signal S. In this case, since the levels are not uniform in the pass band, the high frequency component of the video signal is deteriorated.

In order to eliminate the above-mentioned phenomenon, these double tuning filters 11 are used when manufacturing the tuner set.
Although the local oscillator 14 is adjusted, it is not always possible to obtain an IF output signal in a flat frequency band in all channels in the band due to a wide band, variations in components, and the like.

[0012]

As described above, in the conventional tuner receiving circuit, the frequency shift between the double tuning filter 11 and the local oscillator 14 is received by the same control voltage from the PLL circuit 17 in all frequency bands. The frequency characteristics of the IF output signal do not necessarily match with each other depending on the channel, and the demodulated video signal and audio signal are adversely affected.

Therefore, the present invention provides a tuner circuit in which a frequency characteristic of an intermediate frequency signal obtained is stable in a system in which the local oscillation of a local oscillator and the band characteristic of a double tuning filter are varied by the same control voltage. The purpose is to provide.

[0014]

According to the present invention, an intermediate frequency filter capable of compensating for frequency characteristics is provided at an output part of an intermediate frequency (IF) signal, and the output level of a video carrier signal which is the filter output and an audio carrier signal. Is provided with a detecting means for detecting the output level of the video carrier signal, and a memory means for storing level information of the video carrier signal and the audio carrier signal in each channel from the detected output level of the detecting means is provided. Control means is provided for controlling the characteristics of the intermediate frequency filter by using the level information of the memory means so that the signal and the voice carrier signal become uniform.

[0015]

By the above means, information for making the levels of the video carrier signal and the audio carrier signal of the IF signal uniform for each channel is obtained from the memory means, and the level is made uniform in the IF filter, so that it is stable. The obtained IF signal can be obtained, and the deterioration of the quality of the video and audio signals can be prevented.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention, and the same parts as those of the circuit shown in FIG.

Reference numeral 10 denotes an antenna section of the tuner input terminal, and the high frequency (R
F) The signal is introduced into a band-pass double-tuned filter 11 whose pass band follows the band of the received frequency. That is, in the double-tuned filter 11, the frequency of the pass band changes according to the control voltage V1 from the phase locked loop (PLL) circuit 17. The PLL circuit 17 is the microcomputer 1
A control signal applied to the local oscillator (voltage-controlled oscillator) 14 is changed by a control signal D1 from the local oscillator 1.
The output frequency of 4 (local oscillation) can be changed. The output of the local oscillator 14 is input to the phase comparator of the PLL circuit 17 and is compared in phase with the signal of the reference frequency, and the error is fed back to the control terminal of the local oscillator 14. As a result, the local oscillator 14 can stably maintain its output oscillation frequency at the desired frequency designated by the microcomputer 18.

The output of the local oscillator 14 is the mixer circuit 1
It is entered in 3. The high frequency signal from the double tuning filter 11 is input to the mixer circuit 13 via the high frequency amplifier 12. Therefore, from the mixer circuit 13, an intermediate frequency signal which is a difference signal between the high frequency signal and the local oscillation signal is derived.

Therefore, the output control voltage V1 of the PLL circuit 17 is changed by changing the frequency division ratio of the local oscillation signal by the control signal D1 from the microcomputer 18, and the oscillation frequency of the local oscillator 14 is also determined by this.
The reception frequency can be determined. Since the control voltage V1 at this time also indicates the reception frequency band, this is also used for controlling the pass band of the double tuning filter 11. The microcomputer 18 is also connected to a memory 23 that can store the information described below for each channel.

The intermediate frequency (IF) signal output from the mixer circuit 13 is an intermediate frequency (I) signal which is a band pass filter capable of compensating for frequency characteristics via the intermediate frequency amplifier 15.
F) Input to the filter 22. This IF filter 22
The operation of will be described later.

The IF signal obtained from the IF filter 22 is output to the output terminal 20. Further, this intermediate frequency signal is input to the video detection circuit and the audio detection circuit in the subsequent stage and demodulated. The output of the IF filter 22 is input to the video carrier signal (P) detector 24 and the audio carrier signal (S) detector 25. These wave detectors are configured so that the wave detection output can be output as digital data. The video carrier signal detector 24 uses an IF
The level of the video carrier signal included in the signal is detected, and the audio carrier signal detector 15 detects the level of the video carrier signal included in the IF signal and supplies the level information to the microcomputer 18.

The above-mentioned IF filter 22 is constructed so that the output levels of the video carrier signal P and the audio carrier signal S can be varied independently by a control signal from the microcomputer 18. Here, the microcomputer 18 is programmed to store the level detection output of the video carrier signal and the level detection output information of the audio carrier signal as a pair in the memory 23 for each channel. And using these information,
It is set so that the output level of the video carrier signal and the audio carrier signal of the IF filter 22 can be controlled for each channel.

In the tuner circuit having such a configuration, the RF signal from the antenna 10 is input for each channel during set adjustment, and the video carrier signal level and the audio carrier signal level are respectively output at the output terminal 20 corresponding to the output terminal of the tuner circuit. The video carrier signal detector 24 and the audio carrier signal detector 25 of FIG. The detected digital output is input to the microcomputer 18, and the output level information of the video carrier signal and the audio carrier signal for each channel is stored in the memory 23. At the time of actual reception, the microcomputer 1
The level information of the video carrier signal and the audio carrier signal of the selected channel is read from the memory 23 connected to 8, so that the video signal and the audio signal can be output at the same level to the output terminal 20 from these level information. I
A control voltage for adjusting the video carrier signal level and the audio carrier signal level of the F filter 22 is output from the microcomputer 18.

As a result, the double-tuned filter 11 and the local oscillator 13 are continuously variable within a certain band, and the same control voltage V1 from the PLL circuit 17 for tuning is applied to the double-tuned filter 11 and the local oscillator. In addition to 13, even if the frequency change of the passband of the double tuning filter 11 and the frequency change of the local oscillator 13 do not necessarily change in exactly the same way, the frequency characteristics of the final IF signal are affected and the demodulated image is displayed. Deterioration of signals and audio signals will not occur.

For example, when the same control voltage V1 is applied to the double-tuned filter 11 and the local oscillator 13 and the frequency change of the double-tuned filter 11 is faster than that of the local oscillator 13, conventionally, as shown in FIG. If the IF output signal is adjusted to be flat in the channel whose frequency is the center within the variable band,
As shown in (b), the output levels of the video signal P and the audio signal S are almost the same, and a uniform signal level can be obtained even within the band. However, in the low frequency channel of FIG. As a result, the level of the video signal P becomes higher than that of the audio signal S, and furthermore, the level is not uniform in the pass band, so that the high frequency component of the video signal is deteriorated. Further, in the high frequency channel, as shown in FIG. 7C, the level of the video signal P becomes lower than that of the audio signal S, and further, the level is not uniform in the pass band, so that the low frequency components of the video signal are low. Will be deteriorated. However, in this embodiment, since these characteristics are corrected by the microcomputer 18, signal deterioration does not occur. That is, where the level of the video signal P is higher than that of the audio signal S in the low frequency channel, the microcomputer 18 records the output level of the video carrier signal and the audio carrier output level of the channel selected during the set adjustment. Recalling each level from the memory 18, the video signal level P and the audio signal level S
The IF filter 22 is controlled by the control signal from the microcomputer 18 such that Therefore, the IF output signal becomes flat and the levels are uneven, so that the low frequency components of the video signal are not deteriorated.

Similarly, when the frequency change of the double-tuned filter 11 is slower than that of the local oscillator 13, the IF filter is controlled by the same operation, so that the IF output signals have uneven levels, so that the high frequency of the video signal is high. Deterioration of the components does not occur.

Although not shown, the microcomputer 18 is associated with a tuning device such as a remote control system, and when tuning is designated, tuning data corresponding to the channel is supplied to the PLL circuit 17. At the same time, the data for controlling the characteristics of the IF filter 22 is read from the memory 23 and given to the filter. Although it is time to store the data in the memory 23, it is preferable to input the basic data at the time of factory shipment or at a service center. Further, a function of adding correction data to the basic data may be provided, and the correction data may be operated by operating the correction data creation switch when the user thinks it is necessary.

[0028]

As described above, since the IF output signal is controlled by the control means (microcomputer) so that it is always flat, the signal pass band of the double tuning filter and the acquisition frequency depending on the oscillation frequency of the local oscillator. IF with no signal deterioration even if a gap occurs
The signal output can be obtained on either channel.

[Brief description of drawings]

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

FIG. 2 is a block diagram of a conventional tuner circuit.

FIG. 3 is a characteristic diagram of various frequency bands of an intermediate frequency signal shown for explaining the problems of the conventional tuner circuit.

[Explanation of symbols]

10 ... Antenna, 11 ... Double tuning filter, 12 ... High frequency amplifier, 13 ... Mixer circuit, 14 ... Local oscillator, 15
… Intermediate frequency amplifier, 17… Phase-locked loop circuit, 18…
Microcomputer, 22 ... Intermediate frequency filter, 23
... memory, 24 ... video carrier signal detector, 25 ... audio carrier signal detector.

Claims (1)

[Claims] 1. A detection means for providing an intermediate frequency filter capable of compensating for frequency characteristics at an output part of an intermediate frequency (IF) signal, and further detecting an output level of a video carrier signal and an output level of an audio carrier signal which are outputs of the filter. Is provided
Memory means for storing level information of the video carrier signal and the audio carrier signal in each channel from the detection output level of the detection means is provided so that the video carrier signal and the audio carrier signal become uniform for each channel being received. 2. A tuner circuit, further comprising control means for controlling the characteristics of the intermediate frequency filter using the level information of the memory means.