KR960002666B1 - Double converter tuner - Google Patents

Abstract

The circuit for compensating mutual frequency deviation between first and second local oscillators with one PLL circuit to get stable second intermediate frequency includes a first mixer mixing high frequency signal received from antenna and a first local oscillated signal to provide a first intermediate signal, a second mixer mixing the first intermediate frequency signal and a second local oscillated signal to provide a second intermediate signal, a third mixer mixing the first oscillated signal and a second oscillated signal to provide a third intermediate signal, and a PLL circuit converting the third intermediate signal to corresponding voltage and supplying it to the first local oscillator.

Description

Frequency tuning device of double conversion tuner

1 is a block diagram of a conventional double-conversion tuner.

2 is a block diagram of a double conversion tuner according to the present invention.

* Explanation of symbols for main parts of the drawings

10: antenna 20: band pass filter

30: high frequency amplifier 40: the first mixing unit

50: first local oscillator 60: first intermediate frequency band pass filter

70: first intermediate frequency amplifier 80: second mixing unit

90: second local oscillation unit 100: phase locked loop

110: dispenser 120: third mixing unit

The present invention relates to a frequency tuning device of a double-conversion tuner, and in particular, a second intermediate that is always stable by correcting the mutual frequency skew of the first local oscillator and the second local oscillator using only one phase looked loop. A frequency tuning device of a double conversion tuner capable of obtaining a frequency (IF) signal.

Referring to the prior art with the accompanying drawings as follows.

In the related art, a high frequency (RF) signal received by the antenna 10 is removed from an unnecessary signal by the band pass filter 20 and then amplified by the high frequency amplifier 30 and supplied to the first mixing unit 40.

The high frequency signal supplied to the first mixing unit 40 is mixed with the first local oscillation signal supplied from the first local wave signal 50 and converted into a first intermediate frequency signal lower than the high frequency signal. After the first intermediate frequency signal is removed from the first intermediate frequency signal band by the first intermediate frequency band bandpass filter 60 and then amplified by the intermediate frequency amplifier 70, the second mixing unit 80 is used. Supplied to. The second mixing unit 80 is mixed with the second local oscillation signal supplied from the second local oscillator 90 to output a second intermediate frequency signal.

On the other hand, since the frequency band of the first local oscillator 50 is mainly 1 to 2 GHZ band, the frequency is polarized by being supplied to the phase synchronization loop 100 after being divided at a low frequency from the divider 110. Since the local oscillator 90 is a fixed oscillation, when the oscillation frequency is distorted, it severely affects the screen of the SET, and thus a stable frequency is secured by using an automatic frequency control circuit or a separate phase synchronization loop on the set side. .

The second intermediate frequency signal is the same frequency band as the single-conversion tuner currently used mainly in television sets, and in the United States, becomes the 45 MHZ band and is output to the image intermediate frequency portion on the set side.

As can be seen from the above description, there are the following problems.

Since the first local oscillator 50 has to oscillate a wide band of about 800 MHz in a frequency band higher than a high frequency signal, a phase-locked loop is used as a frequency tuning device, and the second local oscillator 90 is a fixed oscillation but extremely stable. Since a frequency must be secured, a set of automatic frequency tuning (AFT) circuits or separate phase-locked loops should be used.

In the case of the phase-locked loop 100 for tuning the first local oscillation signal, since the tunable frequency band is mainly less than 1.3 GHZ, the first local oscillation frequency, which is 1 to 2 GHZ band, is divided into low frequencies by using a divider. Because you have to give, the price is quite high.

In the case of the second local oscillation signal, when the frequency correction is performed by using the automatic frequency control circuit on the set side, the automatic frequency control circuit must be built in the tuner side. Some sets do not have a frequency control function, which makes it difficult to correct the second local oscillation signal. When using a separate phase-locked loop, the circuit becomes complicated and the cost increases.

The present invention is to solve the above problems, the phase difference between the two signals generated in the second mixing unit 120 for mixing the oscillation signal of the first local oscillator 50 and the second local oscillator 90 By transmitting to the synchronization loop 130 for tuning, the frequency of the double condenser tuner can always obtain a stable second intermediate frequency signal even if the first local oscillation signal or the second local oscillation signal is changed due to a change in temperature or power. The purpose is to provide a tuning device.

In order to achieve the above object, there is provided a third mixing unit for mixing the first local oscillation signal generated in the first local oscillator and the second local oscillation signal generated in the second local oscillator, the error generated through the third mixing unit By converting the signal into an error voltage corresponding to the error signal through the phase-locked loop, the signal is transmitted to the first local oscillator, thereby always obtaining a stable second intermediate frequency.

The present invention provides an antenna (ANT) 10 for receiving a high frequency signal of the VHF / UHF and a band pass filter (BPF) 30 for passing a predetermined band signal such as a high frequency signal received by the antenna and supplying it to the high frequency amplifier. A first mixing unit 40 for mixing the local oscillating signal of the first local oscillator 50 and outputting a first intermediate frequency, and receiving the signal from the first mixing unit 40 and the first intermediate frequency amplifier 70. A first intermediate frequency band pass filter 60 which sends a signal to the first intermediate frequency band pass filter 60, a signal from the second local oscillator 90, and a signal from the first intermediate frequency band pass filter 60 are mixed to output a second intermediate frequency. The third mixing unit 120, the third mixing unit 120 and the third mixing unit 120 to mix the oscillation signal of the first local oscillator 50 and the second local oscillator 90 Phase synchronization loop 130 for tuning the intermediate frequency output.

The present invention configured as described above is described in detail with the accompanying drawings.

Referring to FIG. 2, in a polarity device for tuning a local oscillation signal of a desired channel, a first local oscillation signal generated by the first local oscillator 50 and a second local oscillator 90 generated by the second local oscillator 90 are shown. The local oscillation signal is mixed by the third mixing unit 120 and supplied to the phase synchronization loop 130 to tune.

Referring to the frequency tuning operation of the present invention in more detail, the first local oscillation signal and the second local oscillation signal are mixed in the third mixing unit 12 to supply the frequency of the difference between the two signals to the phase synchronization loop 130. The phase locked loop 130 performs tuning based on the frequency of the difference between the two local oscillation signals. Therefore, when the first local oscillation frequency is changed by a change in temperature or power, the frequency of the difference between the two local oscillation signals, which is the output of the third mixing unit 120, is shifted, so that the phase synchronization loop 130 corresponds to the frequency shift. By generating an error voltage and supplying it to the first local oscillator 50 to correct the first local oscillation frequency, the second intermediate frequency signal supplied to the set side is always constant, and the second local oscillation frequency is shifted. In this case as well, since the third mixing unit 120 is distorted, a phase oscillation voltage 130 generates an error voltage corresponding to the frequency disparity and supplies it to the first local oscillator 50 to correct the first local oscillation frequency. This results in the same correction of the second local oscillation frequency so that the second intermediate frequency signal can be kept constant at all times.

As can be seen from the above description, the frequency tuning apparatus of the present invention can accurately correct the misalignment of the local oscillation frequency of FIG. Regardless of the model, only the phase-locked loop data can be supplied from the set side and stabilized by the tuner alone, so that stable image quality can be obtained at all times, and the circuit configuration can be simplified and the cost can be lowered.

In addition, since the operating frequency of the phase-locked loop is lowered and becomes the same frequency band as the single-conversion tuner currently used, there is no need to use a separate divider. There is also a significant drop in price.

Claims (5)

First mixing means for mixing the high frequency signal received through the aerial line ANT and the first local oscillation signal generated by the first local oscillation unit to output a first intermediate frequency signal lower than the high frequency signal; A double conversion tuner having a second mixing means for outputting a second intermediate frequency signal by mixing a first intermediate frequency signal generated by a second local oscillation signal generated by a second local oscillator. Third mixing means for mixing a local oscillation signal and the second local oscillation signal to output a third intermediate frequency signal, and receiving a third intermediate frequency signal from the third mixing means at a voltage corresponding to the third intermediate frequency signal. And a phase synchronizing circuit section for converting and feeding the first local oscillator. The double conversion tuner according to claim 1, wherein the high frequency signal received through the aerial line ANT further includes means for allowing a high frequency of a predetermined band network to pass through a band pass filter connected to the aerial line. Tuning device. 2. The apparatus of claim 1, wherein the first intermediate frequency generated by the first mixing means passes through the first intermediate frequency band pass filter connected to the first mixing unit. Double tuner tuner tuning device characterized in that provided with. 3. The high frequency signal passing through the band pass filter further comprises an amplifying means for amplifying a high frequency of a predetermined size by a high frequency amplifying stage connected between the band pass filter and the first mixing unit. Double-conversion tuner tuner. 4. The frequency converter of claim 3, wherein the first intermediate frequency passing through the first intermediate frequency band pass filter is a constant frequency by a first intermediate frequency amplifying stage connected between the first intermediate frequency band pass filter and the second mixing unit. Double tuner tuner tuning device characterized in that it further comprises an amplification means for amplifying.