JPH10271400A - Television tuner and television receiver provided with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the degradation of S/N and to eliminate the need for the expansion of the dynamic range of a high-frequency amplifier circuit by increasing the gain of an intermediate frequency(IF) amplifier circuit at the reception time of specified channel, when the gain of a tuner part is decreased in comparison with the reception time of the other channel. SOLUTION: The band data of tuning data DA are set to an idle terminal Te among the band switching voltage terminals of a PLL 17, as well so as to have the same voltage appear as respective band-switching voltage terminals Tvl, Tvh and Tu. For example, when reducing the gain of the tuner part 1 because of a channel W of the UHF band, the same voltage is respectively generated at band-switching voltage terminals Tu and Te of the PLL 17 by combining the tuning data and channel data. Then, the voltage from the voltage terminal Te is impressed through a resistor 25 to a transistor 24 and the gain of the IF amplifier circuit 21 is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television tuner in which gain differences due to differences in reception channels are eliminated and gains of all reception channels are leveled, and a television receiver provided with the television tuner. About the machine.

[0002]

2. Description of the Related Art A conventional television tuner will be described with reference to a block diagram shown in FIG. 4 and a gain characteristic diagram shown in FIG.

As shown in FIG. 4, a recent television tuner converts the frequency of a received television signal into a tuner 31 mainly for converting a received television signal into an intermediate frequency. The television signal is amplified by giving a predetermined selectivity characteristic to the television signal, and is integrated into a television receiver as an integrated unit of an intermediate frequency section circuit 32 for video detection.

[0004] The tuner section 31 is composed of a VHF section 33 and a UHF section.
The VHF section 33 has a high-frequency amplifier circuit 35 and a mixing circuit 36, while the UHF section 34 also has a high-frequency amplifier circuit 37 and a mixing circuit 38. The tuner section 31 also includes an intermediate frequency amplifier circuit 3 for amplifying the television signal frequency-converted by the mixing circuit 36 of the VHF section 33 and the television signal frequency-converted by the mixing circuit 38 of the UHF section 34.
9 and a PLL circuit 40 for selecting a TV channel in the VHF band or the UHF band. Further, although not shown, the tuner section 31 includes a tuning circuit before and after the high-frequency amplifier circuits 35 and 37, and a mixing circuit 36,
38 are provided with two local oscillation circuits respectively connected.

The PLL circuit 40 receives tuning data DA and the like from a tuning means (not shown) of a television receiver, and for example, sets low-band switching voltages Vlo and VHF high for selecting a low band of VHF. It outputs control voltages such as a high band switching voltage Vhi for selecting a band, a UHF band switching voltage Vu for selecting a UHF band, and a tuning voltage Vt corresponding to a selected channel, and outputs these control voltages to the VHF unit 33, It is supplied to a tuning circuit (not shown) of the UHF section 34. Further, the oscillation signal Fo is taken into the PLL circuit 40 from a local oscillation circuit (not shown).

On the other hand, the intermediate frequency circuit section 32 includes an intermediate frequency amplifier circuit 41 serving as a preamplifier circuit, a SAW filter 42,
A video detecting circuit 43 is provided. The intermediate frequency amplifying circuit 41 is composed of a transistor 44 to which a fixed bias voltage is applied to a base. Supplements. The output of the intermediate frequency amplifying circuit 41 is given a predetermined selectivity characteristic to the transmission of the intermediate frequency band by the SAW filter 42, and is then detected by the video detecting circuit 43, thereby obtaining the video signal V.
And an audio signal S. An AGC voltage is supplied from the video detection circuit 43 to the high-frequency amplification circuits 35 and 37 via an AGC circuit (not shown) to change the degree of amplification, and input to the video detection circuit 43 regardless of the strength of the received television signal. The television signal in the intermediate frequency band is set to a constant level.

As described above, in the conventional television tuner, the VHF band television signal and the UHF band television signal frequency-converted to the intermediate frequency by the mixing circuits 36 and 38 are:
Common intermediate frequency amplifier circuits 39 and 41, SAW filter 4
2, and is detected by the video detection circuit 43. Therefore, the gain of the intermediate frequency circuit 32 is constant irrespective of the receiving channel, but the gain of the tuner 31 varies depending on the receiving channel or receiving band.

[0008]

However, in the above-mentioned conventional television tuner, a specific channel, for example, FIG.
When the gain is reduced in the channel W located in the middle of the UHF band as shown in FIG. 5, the channel with the higher gain, for example, the channel in the low band of the VHF low band and the channel with the lower gain, for example, the channel in the UHF band A large gain deviation G occurs with the channel W. Therefore, in a region where a television signal has a weak electric field, S / N is deteriorated in a channel W having a low gain, and image quality is deteriorated.

Further, in a television tuner having a large gain deviation G, the dynamic range of the high-frequency amplifier circuits 35 and 37 for performing the AGC operation must be increased, which makes the design thereof difficult. Therefore, the present invention solves such a problem with a simple configuration, reduces the deterioration of S / N even if the gain is reduced in a specific channel, and increases the dynamic range of the high frequency amplifier circuits 35 and 37. The goal is to avoid having to do it.

[0010]

In order to solve the above-mentioned problems, a television tuner according to the present invention comprises a tuner section and an intermediate frequency circuit section having an intermediate frequency amplifying circuit. The gain of the amplifier circuit is increased at the time of reception of a specific channel where the gain of the tuner section is lower than at the time of reception of another channel.

Further, in the television tuner of the present invention, the intermediate frequency amplifying circuit includes an amplifying transistor, and a gain of the intermediate frequency amplifying circuit is increased by changing a base bias voltage of the transistor.

Further, the television tuner of the present invention is provided with a PLL circuit for selecting a channel for generating a first voltage for switching a plurality of bands in the tuner section, and for selecting the specific channel. Based on the tuning data to be selected.
A second voltage is generated from the LL circuit when the specific channel is selected, and the second voltage is also applied to the base of the transistor as the base bias voltage when receiving the specific channel.

Further, a television receiver according to the present invention includes a television tuner according to claim 3, and supplies tuning data corresponding to the specific channel to the PLL circuit.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. Here, FIG. 1 is a block diagram of a television tuner of the present invention, FIG. 2 is a format of channel selection data supplied to the television tuner of the present invention, and FIG. 3 is a television of the present invention. It is a gain characteristic diagram of a tuner.

A television tuner 1 mainly converts a received television signal into an intermediate frequency.
In addition, an intermediate frequency circuit section 2 for amplifying the television signal converted in frequency by the tuner section 1 with a predetermined selectivity characteristic and performing video detection is combined and incorporated into a television receiver as a so-called tuner unit. It is.

The tuner section 1 comprises a VHF section 3 and a UHF section 4
The VHF unit 3 includes an antenna tuning circuit 5, a high-frequency amplification circuit 6, an interstage tuning circuit 7, a mixing circuit 8, and a local oscillation circuit 9. Similarly, the UHF unit 4 also includes an antenna tuning circuit 10, a high-frequency amplifier circuit 11, an interstage tuning circuit 1
2, a mixing circuit 13 and a local oscillation circuit 14. The tuner unit 1 further performs intermediate frequency tuning for transmitting the television signal frequency-converted by the mixing circuit 8 of the VHF unit 3 and the television signal frequency-converted by the mixing circuit 13 of the UHF unit 4 at a predetermined selectivity. A circuit 15, an intermediate frequency amplifying circuit 16 for amplifying the television signal, and a PLL circuit 17 for selecting a television channel in the VHF band or the UHF band are provided.

The intermediate frequency circuit section 2 includes an intermediate frequency amplifier circuit 21, which is a preamplifier circuit, a SAW filter 22, and a video detection circuit 23. The output of the intermediate frequency amplifier circuit 21 is applied to the intermediate frequency band by the SAW filter 22. A predetermined selectivity characteristic is given to the transmission, and the video signal V and the audio signal S are obtained by detecting the signal with the video detection circuit 23 thereafter. Note that the video detection circuit 24 supplies A to the high frequency amplification circuits 5 and 10 via an AGC circuit (not shown).
The GC voltage is supplied to change the degree of amplification, and the intermediate frequency television signal input to the video detection circuit 23 is kept at a constant level regardless of the strength of the received television signal. The intermediate frequency amplifying circuit 21 has an amplifying transistor 24, to which a base bias voltage is applied from the outside via a resistor 25.

On the other hand, the PLL circuit 17 takes in the local oscillation signal Fo from the local oscillation circuits 9 and 14, and outputs the clock signal C from a channel selecting means of a television receiver (not shown).
L, receives the tuning data DA together with the enable signal EN, and selects a band to which the selected channel belongs so that the VHF unit 3 or the UHF unit 4 can receive the television signal of the channel to be selected. And a control voltage such as a tuning voltage corresponding to the selected channel. The control voltage is supplied to the VHF unit 3 and the UHF unit 4.

The PLL circuit 17 has four band switching voltage terminals for outputting a band switching voltage so as to be able to switch between four bands in a general IC circuit. In the tuner,
Since the entire reception band is divided into three bands of a low band of the VHF band, a high band of the VHF band, and a UHF band to select a channel, three of the four band switching voltage terminals are switched. Voltage terminals are used.

That is, when the low band of the VHF band is selected, the low band switching voltage Vlo is selected. When the high band of the VHF band is selected, the high band switching voltage Vhi is selected.
When selecting the UHF band, the UHF band switching voltage V
A band switching voltage (first voltage) such as a u-band switching voltage is applied to each band switching voltage terminal Tvl, TVh, T
u, among which VHF low-band switching voltage Vlo and VHF high-band switching voltage Vlo
hi is supplied to the antenna tuning circuit 5, the interstage tuning circuit 7, and the local oscillation circuit 9 of the VHF unit 3, and the UHF band switching voltage Vu is supplied to the UHF unit 4. A tuning voltage V corresponding to a channel in each band is supplied from a tuning voltage terminal.
t is supplied to the antenna tuning circuits 5 and 10 of the VHF section 3 and the UHF section 4, the inter-stage tuning circuits 7 and 12, and the local oscillation circuits 9 and 14, respectively. Therefore, one band switching voltage terminal Te is an empty terminal.

As shown in FIG. 2, the channel selection data DA input to the PLL circuit 17 is, for example, 4-bit band data BD and 15-bit channel data C.
D and is sent serially. When the band data BD is "1, 0, 0, 0", the band switching voltage terminal Tvl outputs the band data BD "0,
1, 0, 0 ", the band switching voltage terminal Tvh
When the band data BD is "0, 0, 1, 0", the band switching voltage is output to the band switching voltage terminal Tu.

Furthermore, the last data of each band data
If the data value (the data value of the fourth bit) is "1", the remaining band switching voltage terminal Te is used as the remaining band switching voltage terminal Te for the channel specified by the subsequent channel data CD. Also each band switching voltage terminal Tvl, Tv
A voltage (second voltage) having the same value as the band switching voltage appearing at h and Tu appears. For example, when the band data BD is "1, 0, 0, 1", the first voltage and the second voltage appear at the band switching voltage terminals Tvl and Te, respectively.

Therefore, in the present invention, the four band switching voltage terminals TV1, Tvh, Tu, T
e, the band switching voltage terminal Te which is an empty terminal
Is connected to the base of the transistor 24 of the intermediate frequency amplifying circuit 21 via a resistor 25. For example, when the gain of the tuner unit 1 decreases in the channel W of the UHF band, the When the channel selection data DA of the UHF band is received, "0, 0, 1,.
The band switching voltage terminal T of the PLL circuit 17 is obtained by combining the band data BD of 1 "and the channel data CD of the channel W which follows.
A second voltage is generated at each of u and Te.
That is, in the UHF band, the first voltage for band switching is generated at the band switching voltage terminals Tu in all the channels, and the band switching terminal Te is set only when the channel W is selected in the UHF band. A second voltage is generated.

Therefore, in the case of the channel W, the voltage from the band switching voltage terminal Te, which is a vacant terminal among the band switching voltage terminals of the PLL circuit 17, is applied to the intermediate frequency circuit 2 provided through the resistor 25 in the intermediate frequency circuit section 2. The voltage applied to the base of the transistor 24 of the circuit 21 increases, and the gain of the intermediate frequency amplifier 21 increases. Accordingly, with respect to the channel W, the total gain of the tuner 1 and the intermediate frequency amplifier 21 without the intermediate frequency circuit 2 can be increased as shown by the dotted line A in FIG. -It is possible to compensate for the decrease in the gain of the corner section 1. As a result, the deterioration of the S / N ratio due to the decrease in the gain of the tuner unit 1 is small, the deviation Ga of the gain in all the receiving channels is small, and the high-frequency amplifier circuits 5 and 10 whose gain is controlled can be easily designed. Become.

In the above description, the channel whose gain decreases is only the channel W of the UHF band. However, the gain of the tuner unit 1 can be compensated for a plurality of channels. In this case, the channel data CD corresponding to the desired channel is
7 can be input. Similarly, gain compensation is possible in other channels of other bands.

In the present invention, since the gain is increased in the intermediate frequency amplifier circuit 21 after frequency conversion at the time of receiving a specific channel having a low gain of the tuner section 1, the selectivity characteristic of the intermediate frequency band is changed. And the gain of all channels can be leveled. Further, the gain can be easily increased only by changing the base bias voltage of the transistor 24 of the intermediate frequency amplifier circuit 21. Further, it is possible to easily increase the gain of the intermediate frequency amplifying circuit 21 only by using the band switching voltage of the PLL circuit 17. Further, the PLL circuit 1
The gain can be increased simply by inputting specific channel data to the channel 7.

[0027]

As described above, the television tuner according to the present invention includes a tuner section and an intermediate frequency circuit section having an intermediate frequency amplifier circuit.
Since the gain of the tuner section is increased at the time of receiving a specific channel, the deterioration of the S / N due to the decrease of the gain of the tuner section is small, and the deviation of the gain in all the receiving channels is reduced. This also facilitates the design of a high frequency amplifier circuit.

In the television tuner of the present invention, the intermediate frequency amplifying circuit is provided with an amplifying transistor, and the gain of the intermediate frequency amplifying circuit is increased by changing the base bias voltage of the transistor. The gain can be increased in a later intermediate frequency amplifier circuit, and the gain of all channels can be equalized without changing the selectivity characteristics of the intermediate frequency band.

Further, the television tuner of the present invention comprises a tuner.
The channel section includes a PLL circuit for selecting a channel for generating a first voltage for switching a plurality of bands, and a P for selecting a channel based on channel selection data for selecting a specific channel having a low gain.
The second voltage is generated from the LL circuit when this specific channel is selected, and the second voltage is applied to the base of the transistor as the base bias voltage when the specific channel is received. It is possible to easily increase the gain of the intermediate frequency amplifying circuit only by inputting channel selection data for specifying a specific channel having a low frequency.

Further, the television receiver of the present invention has a PLL
Since the tuning data corresponding to a specific channel is supplied to the circuit, the gain can be increased only by inputting the tuning data.

[Brief description of the drawings]

FIG. 1 is a block diagram of a television tuner of the present invention.

FIG. 2 shows channel selection data supplied to the television tuner of the present invention.
Format.

FIG. 3 is a characteristic diagram of a gain of the television tuner of the present invention.

FIG. 4 is a block diagram of a conventional television tuner.

FIG. 5 is a characteristic diagram of a gain of a conventional television tuner.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Tuner part 2 Intermediate frequency circuit part 3 VHF part 4 UHF part 5.10 Antenna tuning circuit 6.11 High frequency amplifier circuit 7.12 Interstage tuning circuit 8.13 Mixing circuit 9.14 Local oscillation circuit 15 Intermediate frequency tuning Circuit 16.21 Intermediate frequency amplification circuit 17 PLL circuit 22 SAW filter 23 Video detection circuit 24 Resistance 25 Transistor

Claims (4)

[Claims] A tuner section; and an intermediate frequency circuit section having an intermediate frequency amplifier circuit, wherein the gain of the intermediate frequency amplifier circuit is compared with the gain of the tuner section when receiving another channel. A television tuner characterized by being raised when receiving a specific channel which is lowered. 2. The television according to claim 1, wherein the intermediate frequency amplifier circuit includes an amplifying transistor, and a gain of the intermediate frequency amplifier circuit is increased by changing a base bias voltage of the transistor. Chu
Na. 3. The tuner section further comprises a tuning PLL circuit for generating a first voltage for switching a plurality of bands, based on tuning data for tuning the specific channel. A second voltage is generated from the PLL circuit for tuning when the specific channel is selected, and the second voltage is also applied to the base of the transistor as the base bias voltage when receiving the specific channel. The television tuner according to claim 2, wherein: 4. A television tuner according to claim 3, further comprising:
A television receiver characterized in that tuning data corresponding to the specific channel is supplied to the PLL circuit.