JPS615632A - Television tuner - Google Patents

Abstract

PURPOSE:To simplify the constitution and reduce the cost by utilizing the UHF television frequency range for a cable television receiver in use. CONSTITUTION:The television tuner consists of independent blocks which convert television signals of the VHF band and UHF band into intermediate frequency signals respectively and a distributor 13 which distributes television signals inputted to one common input terminal A to the VHF and UHF conversion blocks. The conversion blocks expand a reception frequency range so that a cable channel is receivable in addition to antenna transmitted television signals. The distributor 13 uses a low-pass filter and a high-pass filter to separate frequency components of the VHF and UHF bands and also cuts off one signal while receiving the other, so all cable channel signals of the VHF and UHF bands, not to mention antenna television signals, are received.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a television tuner used in a television receiver.

(Conventional configuration and its problems) Television tuners generally have VHFHF signals and HFHF signals with different frequencies as television conversion high-frequency signals, and in order to convert these into intermediate frequency signals, VHF and UHF are each independent. It has a frequency conversion circuit.

FIG. 1 shows a typical conventional example. The VHFHF signal (for example, US channel numbers 2 to 6, 7 to 13) input from input terminal A passes through input tuning circuit 1, RF amplifier 2, and RF tuning circuit 3, and is then sent to local oscillation circuit 5 and mixing circuit 4 to receive the desired signal. The channel is converted into an intermediate frequency signal component, which is outputted to an intermediate frequency signal output terminal C via an intermediate frequency tuning circuit 6. On the other hand, if the UHFHF signal is input from input terminal B, the US channel number 14~
83), the desired reception channel is converted into an intermediate frequency component by the local oscillation circuit 11 and mixing circuit 10 via the input tuning circuit 7, RF amplifier 8, and RF tuning circuit 9, and then via the φ opening wave number combining circuit 12, Intermediate frequency amplification circuit 4 (
During UHF operation, mixer 4 operates as an intermediate frequency amplifier. ) and the intermediate frequency tuning circuit 6 before being outputted to the intermediate frequency signal output terminal C.

In recent years, television receivers that can receive not only antenna-transmitted television signals (for example, U.S. 2-6.7-13.14-83) but also cable channels (CATV) have become rapidly popular, especially in the United States, and the number of cable channels will increase in the future. The number of receiving channels tends to increase. For example, in the United States, not only the V) (F band signal area) but also the U
There is a movement to use cable television signals up to the HF band frequency range, and there is a need for television tuners capable of receiving multiple channels.

In a television tuner capable of receiving cable television channels in addition to conventional antenna-transmitted television signal channel reception, input tuning circuit 1, RF tuning circuit 3. and a local oscillation circuit 5 is configured as shown in FIG. 2, and serves as a tuning circuit and an oscillation circuit that divides the receiving frequency band and sets switch control voltages according to the divided bands as shown in Table 1 for high frequency switching. Diode - Table 1 Apply voltage to dDM, tDs□, and change the variable capacitance diode D? □
The receiving tuning frequency or oscillation frequency was determined by parallel resonance between the inductive reactance Lzeta and the inductive reactance Lzeta. However, in such a reception system, it is difficult to increase the number of channels in the future due to the limitations of the capacitance change of the variable capacitance diode and the characteristics including the RF amplifier and local oscillation circuit. As seen in the tuning frequency curve of an electronic television tuner for channels, areas where reception is not possible will occur.

OBJECTS OF THE INVENTION The present invention attempts to solve such problems and provide a multi-channel television tuner that can be used in future cable television receivers using the UHF television frequency range.

(Structure of the Invention) In order to achieve the above object, an independent conversion block that converts television signals of VHF band and UHF band into intermediate frequency signals, respectively, and a television signal inputted to one common input terminal, Each conversion block expands the receiving frequency range so that cable channels can be received in addition to antenna-transmitted television signals, and the distributor includes a low-pass filter and a distributor. VH by bypass filter
It is configured to separate the frequency components of the F band and UHF band, and when one of them is being received, the other is cut off. With this configuration, it is possible to receive not only antenna-transmitted television signals but also all cable channel signals in the VHF and UHF bands. This is what is shown. UHF and VHF television signals, including cable television signals, are applied from input terminal A. VHF,
A conversion block (in FIG. 4, a VHF tuner section and a UHF tuner section) for converting a UHF television signal into an intermediate frequency signal is provided, and frequency components corresponding to the conversion block operating frequency are supplied to each conversion block. For example, as shown in FIG. 5, a VHF block has the characteristics shown by the solid line, and the U
In the HF block, a distributor is provided which has the characteristics indicated by the dashed line. The signal input from input terminal A passes through distributor 13, and in the VHF block, input tuning circuit 1, R
F amplifier 2. The signal passes through the RF tuning circuit 3, is converted into an intermediate frequency signal of the desired reception channel by the local oscillation circuit 5 and the mixer 4, and is outputted to the intermediate frequency signal output terminal C via the intermediate frequency tuning circuit 6. On the other hand, in the UHF block,
After passing through the input tuning circuit 7, RF amplifier 8, and RF tuning circuit 9, the signal is converted into an intermediate frequency signal according to the desired reception channel by the local oscillation circuit 11 and mixer 10, and then sent to the intermediate frequency coupling circuit 12, the intermediate frequency amplifier 4, and the intermediate frequency signal. The signal is outputted to the output terminal C via the tuning circuit 6.

At this time, in the UHF variable block, for example, reception restrictions are imposed on channels 69 to 83 of the UHF band television channels in the United States and Canada, so the UHF reception frequency range becomes narrow. Therefore, the variable range margin of the fourth variable capacitance die for electronic tuners used in conventional tuners has been expanded, and as shown in the receiving channel tuning curve shown in Figure 6, the UHF conversion block of conventional tuners has been expanded. It becomes possible to receive channels with frequencies lower than the channels that were being received, especially channels with frequencies lower than the lower limit channel of antenna television (channel 14 in the United States), and it is possible to receive channels with frequencies as low as possible.

On the other hand, in the VHF block, as shown in the conventional example,
Since it is not possible to greatly expand the reception channels to the UHF region, including the variable range and overall characteristics of variable capacitance diodes used in electronic television tuners, the upper limit of the reception channels is set at typical channels as shown in FIG. At this time, if the UHF conversion block channel lower limit and the VHF reception channel upper limit match or cross over, the VHF
You can receive all television signals from to UHF, including cable television channels. Further, operation switching between these conversion blocks and reception channels can be easily performed by a channel selection circuit using a microcomputer.

If an input distributor as shown in FIG. 7 is used as the distributor 13, it becomes possible to ideally distribute signals to each conversion block as shown in FIG. A television signal, including a cable television signal, is applied to input terminal A and is input via DC blocking capacitor C4. A low-pass filter is formed for the VHF conversion block operation channel signal by inductances L, LS and capacitor C5.

At this time, diode D. A control voltage is applied from the DC control terminal H through resistors R4 and R5 so that the diode DI4 is turned on and the diode DI4 is turned off.

At the same time, a diode D is connected to the reference voltage terminal J. .

Ds, a control voltage is supplied via resistor R4.

On the other hand, a bypass filter for UHF conversion block operation is formed by capacitors C, , C, and inductance LG, but diode D85 is off and diode D8
6 is connected to the control terminals H and I and the reference voltage source J so as to be in the on state.
from resistors R,,R,.

A control voltage is applied via Rg. Therefore V
C,,C, when receiving the HF conversion block signal.

The bypass filter consisting of L is a diode Dss.

Since it is cut off by D86, it is only necessary to consider the characteristics of the low-pass filter for the VHF conversion block, and the selectivity of the attenuation range can be idealized as shown by the solid line in Figure 5 without deteriorating the insertion loss of the passband. characteristics can be ensured.

The same idea can be applied when receiving a UHF conversion block signal, turning on diodes D and 5 and turning on diode D.
Apply a control voltage to turn off □, CG, C,
, L6, and on the other hand, since the diode Ds2 is turned off and the diode Ds4 is turned on, the low-pass filter is cut off, and the bypass filter characteristics shown by the broken line in FIG. 5 can be secured.

In FIG. 7, capacitors C, , C1° are high frequency signal bypass capacitors, and capacitor C7 is a DC blocking capacitor. Table 2 shows an example of the mode of the control voltage for driving the high frequency switching circuit by the high frequency switching diode shown in FIG.゛Table 2 (Effects of the Invention) As described above, according to the present invention, the multi-channelization of cable television signals, which will further increase in the future, and even UH
A television receiver capable of supporting cable television signal transmission using an F-band television channel frequency can be constructed relatively easily and at low cost. In particular, it has the great effect of being able to receive channels that could not be received using conventional reception methods, and making it possible to receive all VHF and UHF television channel signals, including cable television signals.

[Brief explanation of drawings]

Figure 1 is a block diagram of a conventional television tuner.
FIG. 2 is a circuit diagram showing the basic configuration of a conventional tuning circuit and oscillation circuit for receiving cable television signals, and FIG.
FIG. 4 is a block diagram of an embodiment of the present invention; FIG. 5 is a characteristic diagram of an input signal divider of the same embodiment; FIG. 6 is a voltage characteristic diagram of the variable capacitance diode for reception tuning for the television channel of the same embodiment, and FIG. 7 is a specific circuit diagram of the input signal distributor of the same embodiment. 1.7...Input tuning circuit, 2,8...RF amplifier/amplifier, 3,9...RF tuning circuit, 4. lO...
Mixer, 5, 11...Local oscillation circuit, 6...
intermediate frequency tuning circuit, 12... intermediate frequency coupling circuit,
13...Distributor, A...Input terminal. Patent applicant: Matsushita Electric Industrial Co., Ltd. Figures 1 and 2 Figure 3 Wandering Kill ♂%? , μm) Fig. 4 Fig. 5 Liquid & (MHz) Fig. 6

Claims (2)

[Claims] (1) In a television tuner that converts a television modulated high frequency signal into an intermediate frequency signal, the VHF and UHF television modulated high frequency signals input to one common input terminal through one television signal cable are
The UHF signal conversion block is equipped with a divider that divides into HF and UHF frequency components, and an independent conversion block that converts each divided high frequency signal into an intermediate frequency signal. The reception frequency range is expanded so that cable channels (CATV) having lower frequency components than channel numbers 14 to 83) can be received, and the VHF signal conversion block expands the reception frequency range so that it can receive cable channels (CATV) having lower frequency components than the antenna transmission television signals (for example, US channel numbers 2 to 6). , 7 to 13) so as to be able to receive cable channels (CATV), and for the lower receivable channel number N of the UHF signal block, the upper receivable upper channel number of the VHF signal conversion block. 1. A television tuner having a number set to N-1 and capable of receiving antenna-transmitted television signals and cable channel signals included in VHF and UHF bands. (2) The distributor includes a low-pass filter that is connected to the VHF signal conversion block and passes the VHF signal and blocks the UHF signal, and a bypass filter that is connected to the UHF signal conversion block and passes the UHF signal and blocks the VHF signal. The television according to claim (1), further comprising a changeover switch circuit that cuts off either a VHF signal or a UHF signal when the other is being received. tuner.