JPS5829641Y2 - tv jiyeon chiyuna - Google Patents

Description

[Detailed description of the invention] This invention is a television tuner that uses an amplifier converter to group-convert VHF band input signals to UHF band, especially for UHF band input signals.
The present invention relates to coupling a signal subjected to group conversion to a tuner circuit in a television tuner that enables selection of all channels assigned to both the HF band and the VHF band.

By group-converting the received signals in the VHF band to the UHF band, it becomes possible to electronically tune the conventional two-band system in the VHF band to a single band system, and it is also possible to select it when allocating to the entire VHF band such as CATV. There are advantages such as ease of station operation.

Furthermore, it is possible to tune both the vHF band and UHF band channels in a single band using a common tuner circuit.

For example, convert the VHFi received signal to UHF using an amplifier converter.
The signal is group-converted within the band and tuned using a single-handed electronically tuned tuner circuit in the same way as the original UHF band received signal.

In this case, a band selection circuit that switches the received signals of both bands is inserted between the amplifier converter and the tuner circuit, but a switching circuit that uses a switching diode to achieve good separation between the two bands is used to switch the band selection circuit. Ru.

However, a problem with such a method is the leakage of harmonic components from the fixed oscillator of the upconverter that occurs when group converting a VHF band input signal to a UHF band. It is an interference signal to the signal that was received.

In particular, it is desired to effectively eliminate the oscillator signal in order to effectively utilize the oscillation force and to approximately equalize the signal coupled to the tuner circuit via the band selection circuit regardless of the received signal band. Ta.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks, and to provide a television tuner in which local harmonic components of a signal group-converted by an amplifier converter are eliminated and coupled to a tuner circuit.

According to the present invention, in an amplifier converter that group-converts a vHF band input signal to a UHF band, the local signal generated by the local oscillation stage and the VHF band input signal are mixed in a double-balanced mixer stage to convert the frequency. This converted signal is coupled to the tuner circuit via a low-pass filter circuit inserted at the output side of the mixer stage.

A low-pass filter circuit (c) uses a T-type low-pass filter, and its cutoff frequency is the upper limit of the high frequency range of 650-900 MHz, which is obtained by group-converting a VHF band input signal of 50-300 MHz with a local signal of 600 MHz. It is set around 900MHz.

As a result, the leakage of harmonic components of the local signal to the next-stage tuner circuit was suppressed, and the conversion loss in the converter was improved by 3 to 4 dB, and the NF was significantly improved to 2 to 3 dB.

In particular, since a double-balanced mixer circuit is employed in the up-converter of the vHF band input circuit, a specific circuit using an impedance converter on the input/output side is disclosed.

In addition, a UHF band input circuit that supplies a UHF band input signal and a VHF band input circuit that group converts and supplies a VHF band input signal, that is, a band selection switching circuit that improves isolation with the up converter and an input with AGC. A UHF-VHF television tuner including the circuit is also disclosed.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIGS. 1 and 2 are schematic diagrams illustrating the television tuner of the present invention.

With this tuner, UHF imperial channel reception RJH
The F antenna 1 is coupled to a UHF band input circuit 2, and the VHF antenna 3 for receiving VHF band channels is coupled to an amplifier converter 4 of the VHF band input circuit.

This amplifier converter 4 includes an attenuator 5 that applies a VHFAGC signal to a signal of a predetermined level, a wideband amplifier 6 that amplifies the band all at once, a local oscillator 7 that generates a fixed frequency oscillation signal, an amplified input signal and a local oscillation signal. The mixer circuit 8 includes a mixer circuit 8 for mixing the mixer circuit, and a low-pass filter circuit 9 inserted into the output side of the mixer circuit.

Here, the low-pass circuit 9, which is a feature of the present invention, uses a T-type filter, and its cut frequency is selected near the upper limit of the high frequency range of the group transform signal.

Signals from the UHF band and VHF band input circuits are selectively switched by a band selection circuit 17 and coupled to the tuner circuit 10 at the next stage.

The tuner circuit 10 has substantially the same configuration as a normal UHF tuner, and includes a preselector circuit 11, a variable frequency local oscillation circuit 12, a mixing circuit 13, an intermediate frequency tuning circuit 14, and a buffer circuit 15. IF
A signal is derived.

Here, the tuner circuit 10 includes a single-band tuning circuit using a variable capacitance diode, and achieves tuning of a desired channel in each stage by a single-band electronic tuning method.

It should be noted that the pre-selector circuit 11 is provided with an amplification circuit as required to amplify the signal from the input side to a predetermined level.

FIG. 2 shows a partially detailed circuit configuration of FIG. 1, especially the input circuit and its switching band selection circuit 1.
7 and the power supply for tuner operation.

The band selection circuit 17 is composed of a switching diode 18, whose cathode side is directly grounded, and when a switching voltage is applied to the anode side, it becomes conductive and substantially short-circuits and grounds the upconverter 4 of the VHF band input circuit, thereby switching the UHF band input circuit. A signal from the input circuit 2 is coupled to the pre-selector circuit 11 of the tuner circuit via a coupling capacitor 19.

In addition, the switching diode 1 of the band selection circuit 17
When the upconverter 8 is in the cutoff state, the signal from the upconverter 4 is coupled to the pre-selector circuit 11 of the tuner circuit via the coupling capacitor 20, and the UHF band input circuit 2 is isolated.

The switching voltage to the switching diode 18 is applied via the choke coil 21 to the UHF 1,000 Yuna unit operating voltage U.
It is supplied from the B terminal 30 and enables UHFHF multi-channel communication.

On the other hand, when the band switching voltage is not applied to this diode 18, that is, when the VHF band channel reception is cut off, a part of the local signal of the up converter 4 is used to apply the reverse bias voltage of the diode 18 to the capacitor 23. Generate.

That is, by inserting the rectifier diode 24 between one end of the capacitor 23 and the ground, a potential of the polarity shown in the figure is generated in the capacitor 23, and this is reverse biased to the switching diode 18 via the resistor 25.

Since this reverse bias voltage is actually 2 to 3 volts, it is effective for interrupting the switching diode 18, and its interrupting capacity can be used as the termination capacitance of the pre-selector circuit 11.

The terminal group required to operate the television tuner of the present invention is the UHF terminal connected to the UHF antenna 1.
Input terminal 26, VHF connected to VHF antenna 2
In addition to the input terminal 21 and the IF output terminal 16, various operating power supply terminal groups 28 to 33 are used.

That is, the terminal 28 is a VAGC terminal that provides an AGC signal to the attenuator 5 of the asoph converter 4, and the terminal 29 is a VHF terminal.
The VB terminal and terminal 30 used during band reception are the UH terminals mentioned above.
UB terminal 1 used during F-band reception, terminal 31 is the TU terminal that supplies the tuning voltage of the tuner circuit, and terminal 32 is the U
This is a UAGC terminal that provides an AGC signal to the HF band input circuit 2.

Further, a B for operating the tuner circuit 10 as shown in FIG.
A terminal 33 and an AFT terminal (not shown) are also provided.

FIG. 3 is a circuit diagram specifically showing the input circuit which is the main part of the present invention.

In the figures, the symbols shown in FIGS. 1 and 2 have been explained in the respective figures and will therefore be omitted.

In this specific circuit diagram, the up-converter 4 includes a diode attenuator 5, a transistor broadband amplifier 6, a fixed oscillator 7, an unbalanced-balanced converter 35, a double-balanced mixer circuit 8, a balanced-unbalanced converter 36, and a pair of Koi#
A T-type low-pass filter circuit 9 including two condensers 37 and 38 is provided.

Further, the UHF band input circuit 2 is composed of a diode attenuator including a balanced-unbalanced converter 40.

Further, the tuner circuit 10 is connected to the F after the selector circuit 11.
An amplifier circuit using ET45 is inserted to amplify the signal from the input side.

The tuner circuit 10 is driven by a common power supply from an operating power supply B terminal 33, and channel selection is performed by varying the tuning voltage.

Further, this tuner circuit 10 is automatically fine-tuned by supplying an AFT signal to its local oscillator in the same way as a normal UHF tuner.

Therefore, the output terminal of the tuner circuit has UHF or VHF.
An IF signal for any selected channel of the band is generated and coupled to the next television IF amplification stage.

[Brief explanation of drawings]

1 and 2 are block diagrams showing an outline of a television tuner according to the present invention, and FIG. 3 is a specific circuit diagram of the main part of FIG. 2. 2...UHF band input circuit, 4...Amplifier converter, 8...Mixer circuit (stage), 9...
- Curved low-pass filter circuit, 10... Tuner circuit, 35... Square root balanced-balanced converter, 36...
- Balanced-unbalanced converter.

Claims (3)

[Scope of utility model registration request] (1) In an amplifier converter that group-converts a VHF band input signal into a UHF band at a mixer stage using a signal from a fixed local oscillator, a low-pass filter circuit is interposed on the output side of the mixer stage to pass the group-converted signal. A television tuner characterized in that a tuner circuit is connected to a later-stage tuner circuit. (2) The mixer stage is configured by installing a double balanced mixer circuit, an unbalanced-balanced converter and a balanced-unbalanced converter on the input and output sides thereof, respectively, and the low-pass filter circuit is a T-type low-pass filter usable device. The television tuner according to claim 1, wherein the sonocant frequency is set near the upper limit of the high frequency range of the group-converted signal. (3) The television according to claim 1, wherein the tuner circuit is coupled to the up-converter via a VHF band and UHF band input signal switching circuit and is equipped with a single-band electronic tuning circuit. John tuner.