KR970004655Y1 - Intermediate frequency stabilization circuit of tuner - Google Patents

Abstract

None.

Description

Tuner Intermediate Frequency Stabilization Circuit

1 is a block diagram of an intermediate frequency stabilization circuit of a conventional tuner

2 is a block diagram of an intermediate frequency stabilization circuit of the inventive tuner

* Explanation of symbols for main parts of the drawings

1 filter unit 2 amplification unit

3: tuning unit 4: mixing unit

5: crystal oscillator 6: image frequency amplifier

7: Image detector 8: Microcomputer

9: intermediate frequency amplifier 10: first divider

11: phase comparator 12: second divider

13 charge pump 14 low pass filter

15: phase synchronizer 16: oscillator

The present invention relates to a tuner (intermediate frequency stabilization circuit). The signal amplified by the antenna is tuned and amplified, and then converted to an intermediate frequency so that the signal can be supplied at the correct intermediate frequency when the signal is supplied to the demodulator.

As shown in FIG. 1, the intermediate frequency stabilization circuit of the conventional tuner includes a filter unit 21 for filtering only a high frequency signal RF induced by an antenna and passing only a desired signal, and in the filter unit 21. An amplifier 22 for amplifying the filtered signal and outputting the amplified signal to the tuner 23, a tuner 23 for receiving a signal output from the amplifier 22 and prepolarizing a frequency of a desired channel, and an oscillation frequency. The crystal oscillator 25 for outputting the mixing unit 24 for mixing the signal tuned by the tuning unit 23 and the oscillation frequency output from the crystal oscillator 25 to convert to the intermediate frequency and the mixing unit ( 24, an image intermediate frequency amplifier 26 for amplifying the intermediate frequency output from the image frequency detector 26, and an image detector for outputting an image signal and an audio signal by detecting the intermediate frequency amplified by the image intermediate frequency amplifier 26; 27) and applied to the image detector 27 When the call is not applied to the correct intermediate frequency, the AFT (Automatic Fine Tuning) circuit unit 28 generates a difference voltage from the intermediate frequency and applies it to the microcomputer 29, and the oscillation frequency of the channel to be viewed is binary code (Code Value is converted and outputted from the lower data bit of the oscillation frequency of the desired channel by the difference voltage output from the AFT circuit section 28, and is output to the phase synchronizing section (PLL) 30 as a binary code value. A microcomputer 29 and a phase synchronization unit 30 for reducing and outputting the data value output from the microcomputer 29 to a voltage.

The intermediate frequency stabilization circuit of the conventional tuner configured as described above filters the high frequency signal RF received from the antenna by the filter unit 21 and passes only the desired signal to be amplified by the amplifier 22 to the tuner 23. When the tuner 23 outputs the signal amplified by the amplifier 22 to the mixer 24 by tuning the frequency of a desired channel, the mixer 24 outputs the crystal oscillator 25. Mixed with the oscillation frequency and the channel frequency output from the tuning unit 23 is converted to the intermediate frequency (IF: 45.75MHz) and output to the image intermediate frequency amplifier 26 and amplified, and then the image detector 27 The intermediate frequency amplifier 26 detects the intermediate frequency amplified and output and outputs the video signal to the monitor and the audio signal to the speaker so that the user can watch.

In this case, the AFT circuit unit 28 does not input the purified intermediate frequency by checking whether the signal input to the image detector 27 is the correct intermediate frequency, and the frequency inputted to the image detector 27 does not correspond to the intermediate frequency. The difference voltage is generated and output, and the microcomputer 29 increases and decreases the data from the lower data bits of the desired channel oscillation frequency and outputs it to the phase synchronizer 30 so that the correct intermediate frequency is input to the image detector 27.

In addition, when the viewer selects a channel to be watched by the viewer, the oscillation frequency of the tuned channel stored in the microcomputer 29 is converted into a binary code value and output to the phase synchronizer 30 to output the phase. The synchronization unit 30 reduces the binary dada value output from the microcomputer 29 to a voltage and outputs it to the crystal oscillator 25 to output the oscillation frequency of the channel tuned by the crystal oscillator 25 and the crystal oscillator. An output of 25 is also applied to the phase synchronizer 30 so that the crystal oscillator 25 outputs an accurate oscillation frequency.

Such an intermediate frequency stabilization circuit of the conventional tuner detects whether the signal input to the image detector 27 is correct and applies it to the microcomputer 29 to change the oscillation frequency oscillated by the crystal oscillator 25, thereby always providing an accurate intermediate frequency. Since a lot of intermediate frequencies are duplexed, a lot of time (1 second to 2 seconds) is required because the loop must be repeated several times for accurate tuning, and the intermediate frequency of the AFT circuit unit 28 is Channel skipping occurs due to mismatching between the differential voltage detection speed and the speed at which the microcomputer 29 controls the phase synchronization unit 30 to change the oscillation frequency of the crystal oscillator 25. There was this.

The present invention changes the frequency of oscillation in the crystal oscillator by always comparing the phase with the output of the oscillator which outputs the oscillation frequency of 45.75 MHz, which is output from the mixing section, to solve the conventional problems. When the input to the image detector to explain the configuration and effect by the accompanying drawings as follows.

The construction of the present invention, as shown in FIG. 2, filters the high frequency signal (RF) induced by the antenna to pass only the desired signal, and amplified signal filtered by the filter unit (1) Amplifying section 2 for outputting to the tuning section 3, a tuning section 3 for receiving the output signal from the amplifying section 2 and tuning a frequency of a desired channel, and a crystal oscillating section for outputting an oscillation frequency ( 5), a mixing unit 4 for mixing the signal tuned by the tuning unit 3 and the oscillation frequency output from the crystal oscillating unit 5 and converting the mixed frequency into an intermediate frequency, and an intermediate output from the mixing unit 4. An image intermediate frequency amplifier 6 for amplifying a frequency, an image detector 7 for detecting an intermediate frequency amplified and output from the image intermediate frequency amplifier 6, and outputting a video signal and an audio signal; Phase synchronization by converting the oscillation frequency of the An intermediate frequency amplifier 9 for amplifying the intermediate frequency output from the microcomputer 8 and the mixing unit 4 to the image intermediate frequency amplifier 6, and the intermediate frequency amplifier 9 The first signal 10 divides the digital signal, the oscillator 16 outputs an oscillation frequency of 45.75 MHz, and the oscillation frequency output from the oscillator 16 as a digital signal.

A phase comparator 11 for comparing a phase of a signal output from the second divider 12 and the first divider 10 and the second divider 12 to output a difference voltage, and the phase Charge pump 13 for amplifying the voltage output from the comparator 11 to a predetermined level and converting the signal into an analog signal and outputting an alternating current (AC) component of the signal output from the charge pump 13 The low pass filter 14 outputting only the direct current (DC) voltage to which the phase difference is removed, and the binary data value output from the microcomputer 8 are reduced to a voltage and outputted to the low pass filter 14. The phase output unit 15 outputs the voltage output from the crystal oscillator 5.

The intermediate frequency stabilization circuit of the inventive tuner configured as described above filters the high frequency signal RF received from the antenna by the filter unit 1 and passes only a desired signal to amplify the amplification unit 20 to the tuning unit 3. The tuning section 3 outputs the signal amplified by the amplifying section 2 to the mixing section 4 by tuning the frequency of a desired channel, and the mixing section 4 outputs the crystal oscillating section 5. Mixed with the oscillation frequency and the channel frequency output from the tuning unit 3, converts the frequency into an intermediate frequency, outputs the image to the intermediate frequency amplifier 6, and amplifies it. 6) detects the intermediate frequency amplified output and outputs the video signal to the monitor and the audio signal to the speaker so that the user can watch.

At this time, the intermediate frequency output from the mixing unit 4 to the image intermediate frequency amplifier 6 is amplified by the intermediate frequency amplifier 9 and output to the first divider 10, the first divider 10 When the signal is divided into digital signals and output to the phase comparator 11, the phase comparator 11 compares the phase of the oscillation frequency of 45.75 MHz output from the oscillator 16 with the phase divided by the signal divided by the second divider 12. The difference voltage is generated and output, and the difference voltage output from the phase comparator 11 is amplified to a predetermined level by the charge pump 13, and then converted into an analog signal, and is alternating through the low pass filter 14. Only the voltage of the DC component from which the component is removed is applied to the phase synchronizer 15 so that the phase synchronizer 15 changes the oscillation frequency output from the crystal oscillator 5 so that an accurate intermediate frequency is always obtained. 7) to be applied.

In addition, the microcomputer 8 tunes a channel that the viewer wants to watch, converts the oscillation frequency of the tuned channel stored in the microcomputer 8 into a binary code value, and outputs it to the phase synchronizer 15 to output a phase. The synchronizer 15 reduces the binary data value output from the microcomputer 8 to the crystal oscillator 5 to output the oscillation frequency of the channel tuned by the crystal oscillator 5 and outputs the crystal oscillator ( The output of 5) is also applied to the phase synchronizer 15 so that the crystal oscillator 5 outputs the correct oscillation frequency.

As described above, the intermediate frequency output from the mixing unit 4 is configured to have an exact intermediate frequency so as to compare the phase with the oscillation frequency of 45.75 MHz oscillated by the oscillator 16 and output from the crystal oscillator 5. By changing the oscillation frequency, it is possible to improve the speed for accurate tuning and to improve the channel skip phenomenon.

Claims (1)

A mixing unit 4 for mixing the signal tuned by the tuning unit 3 and the oscillation frequency output from the crystal oscillating unit 5 and converting the oscillation frequency into an intermediate frequency, and the image intermediate frequency amplifying unit 6 in the mixing unit 4. An intermediate frequency amplifier 9 for amplifying the intermediate frequency outputted by the digital signal, an eleventh divider 10 for dividing the signal amplified by the intermediate frequency amplifier 9 into a digital signal, and an oscillation frequency of 45,75 MHz. An oscillator 16 for outputting a signal, a second divider 12 for dividing an oscillation frequency output from the oscillator 16 into a digital signal, the first divider 10 and a second divider 12 A phase comparator 11 for comparing the phases of the signals output from the output phase difference 11 and a charge pump 13 for amplifying the voltage output from the phase comparator 11 to a predetermined level and then converting the signal into an analog signal and outputting the analog signal; And, phase synchronization unit 15 only the DC voltage from which the AC component of the signal output from the charge pump is removed. The charge pump 13 and the low pass filter 14 and the binary data value output from the microcomputer 8 are reduced and outputted as voltages, and the voltage output from the low pass filter 14 is modified into a crystal oscillator ( 5) a tuner intermediate frequency stabilization circuit, characterized in that consisting of a phase synchronization unit 15 for changing the oscillation frequency output from the crystal oscillator (5).