JPH0134443Y2 - - Google Patents

Description

[Detailed description of the invention] (1) Technical field of the invention This invention relates to a tuner circuit for a television receiver that can receive radio waves in the VHF band and UHF band with a single receiving device. This invention relates to a local oscillation output transmission circuit that has a simplified configuration by sharing as many common parts of a UHF circuit as possible.

Since radio frequencies have a very wide range, in order to receive them, a circuit element structure corresponding to each frequency band is required. Television receiving equipment is a familiar example in which tuners having different element structures and receiving radio waves in different reception bands are incorporated into one device. As is well known, the number of television radio waves in the UHF band has increased in addition to the VHF band, and they are present all over the country, especially in the United States, where UHF band broadcasting has become mainstream.
The receiver receives radio waves in the VHF and UHF bands and converts them into signals using a tuner circuit called an all-channel tuner.

(2) Prior art This tuner circuit is mainly based on an electronic tuning circuit that uses a voltage-to-capacitance conversion element, such as a voltage variable capacitance diode, in the tuning circuit, and also allows the VHF circuit and UHF circuit to be integrally formed. began to occupy Furthermore, this electronic tuning tuner is roughly divided into three tuning methods. In the first method, the tuning voltage is preset for each channel by a potentiometer, and selected by a tuning switch. The second method generates a tuning voltage in the form of a pulse train, generates a tuning voltage corresponding to the pulse, and controls tuning without using a potentiometer by using pulses set for each channel. The third method divides the local oscillation frequency, compares the phase with a reference oscillator, and controls the local oscillation circuit of the electronically tuned tuner using the error output.

Figure 1 shows a conventional electronically tuned tuner based on the third method above, in particular a VHF local oscillation circuit and a UHF
The circuit diagram of the transmission part which guides the frequency output of a local oscillation circuit to a prescaler is shown.

The configuration of FIG. 1 will be explained. The VHF local oscillation circuit (hereinafter referred to as VHF local oscillation circuit) is indicated by the reference numeral 1, and is composed of a resonant circuit section (RSO) and a transistor (TR ₁ ). The output terminal P ₁ of this VHF local oscillator circuit 1 is connected to capacitors C ₁ , C ₂ and resistors.
It is connected to a VHF extraction terminal _P2 provided along the tuner housing via a first low-pass filter 2 configured by _R1 . This lead-out terminal _P2 is connected to a lead-in terminal _P3 on the receiver main body side via a signal conductor _LD1 .

On the other hand, the UHF local oscillation circuit (hereinafter referred to as UHF local oscillation circuit) 3 has resonant lines L ₁ , which are inductively coupled to each other.
It consists of L ₂ , transistor TR ₂ , voltage variable capacitance diode CD ₁ , etc. resonant line
One end of _L2 is grounded via a resistor _R2 , and the other end is connected to the UHF extraction terminal _P4 of the tuner housing. This UHF lead-out terminal _P4 is connected to a lead-in terminal _P5 on the receiver main body side via a signal conductor _LD2 .

Of the signal conductors LD ₁ and LD ₂ drawn into the receiver body side in this way, the VHF lead-in terminal P ₃ is connected to the T-shaped second low frequency band which is grounded from the connection intersection of the inductances L ₃ and L ₄ via the capacitor C ₃ . Via the pass filter 4, the connection point _P6 is connected to the UHF inlet terminal _P5 . The UHF lead-in terminal _P5 is a T-type filter with characteristics opposite to those of the low-pass T-type filter 4,
The connection intersection of capacitors C ₄ and C ₅ is connected to the connection point P ₆ via a high-pass filter 5 with an inductance L ₅ grounded. This coupling point P ₆ is connected to the output terminal P ₇ via a DC blocking capacitor C ₆ . This output terminal _P7 is connected to the input part of a prescaler (not shown), which is a type of frequency divider, and outputs a frequency obtained by lowering the local oscillation frequency to a phase comparator that compares it with a reference frequency.

The conventional circuit is configured as above, but VHF
The second low-pass filter 4 on the circuit side and the high-pass filter 5 on the UHF circuit side prevent the frequencies of both circuits from interfering with each other. In other words, the prescaler divides the tuner's local oscillation output within the operating frequency range of the programmable frequency divider.When the UHF circuit is operating, the UHF signal is sent to the VHF circuit, and when the VHF circuit is operating, the VHF signal is sent to the UHF circuit.
They are separated so that they are not transmitted to the circuit side.

Therefore, before the high-frequency signal is input to the prescaler, a second low-pass filter 4 is required to cut out the harmonics when receiving the VHF band, and a second low-pass filter 4 is required to cut out the harmonics when receiving the UHF band. A high-pass filter 5 was required to cut out the components.

(3) Problems with the conventional technology In this way, the so-called
In the PLL synthesizer tuning device, two signal conductors LD ₁ , LD ₂ and a second low-pass are used to send the VHF local output and UHF local output from the tuner section to the prescaler provided on the receiver body side. Each of the filter 4 and the high-pass filter 5 has become indispensable. Therefore, the circuit configuration has become complicated.

(4) Purpose of the invention This invention was made in view of the above circumstances.
Provides a local oscillation output transmission circuit that simplifies the circuit configuration by sharing as many parts as possible when inputting VHF local oscillation output and UHF local oscillation output to a prescaler, and that does not cause interference between both outputs. The purpose is to

(5) Summary of the invention This invention connects the output end of a VHF local oscillation circuit via a low-frequency circuit to one end of an output-side resonant line from which the output of the VHF local oscillation circuit is inductively coupled. It is a frequency divider input circuit with the other end connected to the input terminal of the prescaler,
The harmonic components for the VHF band wave in the low frequency circuit, resulting in harmonics of the VHF oscillation output,
In addition, leakage of the UHF oscillation output to the VHF local oscillation circuit is suppressed, and the local high-frequency signal is guided to the prescaler via one signal line connected to the other end of the resonant line.

(6) Example of the invention This invention will be explained in detail below based on the drawings from FIG. 2 onwards. Fig. 2 is a circuit diagram showing an embodiment of this invention, Fig. 4 is a characteristic diagram showing the frequency characteristics of the input impedance of the prescaler, and Fig. 5 is a frequency characteristic diagram showing the minimum input sensitivity of the prescaler. be.

In FIG. 2, the VHF power supply terminal VB is connected to the collector of the oscillation transistor TR ₃ of the VHF local oscillator circuit 21. A resonant circuit RES is connected to the base side of this oscillation transistor TR ₃ so that oscillation occurs at its resonance point. The output terminal 22 of this VHF local oscillator circuit 21 is connected via a low frequency circuit 23 to one end of the output side resonant line L ₆ of the inductive coupler IC.

This low frequency circuit 23 is a DC blocking capacitor.
One end of capacitor _C7 is connected to the output terminal of the VHF local oscillator circuit 21, and the other end of capacitor _C7 is connected to one end of high frequency capacitor _C8 , the other end of which is connected via resistor _R2 . , the resonant line L ₆ is connected from one end of this capacitor C ₈ through a resistor R ₃ of relatively large value.
It consists of a circuit connected to one end, and absorbs harmonics from the VHF local oscillator circuit 21 side and from the resonant line L ₆ side.
UHF frequency, that is, UHF local oscillator circuit 24 described later
It attenuates local leakage from the

The above UHF local oscillator circuit 24 is an oscillation transistor
TR ₄ , the inductive coupler IC, the variable capacitance diode CD ₂ and the like, and the UHF power supply terminal UB is connected to the collector of the oscillation transistor TR ₄ .

Here, a power supply voltage is applied to the VHF power supply terminal VB and the UHF power supply terminal UB individually during VHF reception and UHF reception, respectively. In addition, the inductive coupler IC constitutes a resonant circuit of the oscillation transistor TR ₄ together with the variable capacitance diode CD ₂ , and the oscillation output induced in the input side resonant line L ₇ is guided to the output side resonant line L ₆ and taken out. It's summery.

This oscillation output is transmitted from the other end of the output side resonant line _L6 .
It is designed to be led out to the output terminal 25 of the UHF local oscillator circuit 24. The output terminal 25 of the UHF local oscillator circuit 24 is the only output terminal 25 provided along the tuner housing, and this terminal 25 is connected to a prescaler input terminal 26 via a signal conductor LD ₃ . However, if a PLL circuit system such as a prescaler (not shown) is installed inside the tuner housing,
The signal conductor LD ₃ for external connection is provided within the same housing by using printed wiring technology, etc., and the signal conductor LD 3 for external connection is PLL.
Signal conductor that serves as the circuit output conductor and tuner output
Of course, this is not necessary for LD ₃ .

This idea is structured as described above. Next, the operation of the above-mentioned constituent circuit will be explained. Regarding the output impedance at the extraction terminal 25 of this circuit,
Let Z _OV be the impedance when transmitting a high frequency signal in the VHF band, and let Z _OU be the impedance when transmitting a high frequency signal in the UHF band. Figure 3 is
Output terminal 22 and extraction terminal 2 of VHF local oscillator circuit 21
In Figure 3, Zosc is the output impedance of the VHF local oscillator circuit 21, Zc7 is the impedance of capacitor C7, Zc8 is the impedance of capacitor C8, R2 and R3 are resistors, and ZL6 is the impedance of the resonant line L6, and the output impedance during VHF reception is
Assuming Zov, from the equivalent circuit in Figure 3, Zov=(Zosc+Zc7+R2)×Zc8/(Zosc+Zc7+R2)+
It can be expressed as Zc8 +R3+ZL6...(1).

During VHF reception, Zosc《R2, Zc7《R2, Zc8》R2, ZL6《R3 according to the design constant values. Therefore, equation (1) becomes Zov=R2×Zc8/R2+Zc8+R3=R2/R ₂ /Zc8+1+R3 ≒R2+R3 (Ω) (2).

In addition, the output impedance during UHF reception is ZoU
Then, when receiving UHF, the frequency becomes higher, so
Zc8 becomes sufficiently small and becomes Zc8《(Zosc+Zc7+R2), Zc8《R3, ZL6《R3. Therefore, ZoU=(Zosc+Zc7+R2)×Zc8/(Zosc+Zc7+R2)+
R3+ZL6=Zc8+R3+ZL6≒R3(Ω)…(3).

Thus, the output impedance when receiving VHF depends on the value of resistor R2 + R3, and the output impedance when receiving UHF depends on the value of resistor R3.

To give an example of specific circuit constants, Zosc=30Ω,
C7=1000pF, R2=110Ω, C8=5pF, R3=220Ω,
L6=15nH.

When comparing the above matters with the input impedance characteristics of the prescaler shown in FIG. 4, the input impedance on the vertical axis becomes smaller as the frequency becomes higher with respect to the frequency on the horizontal axis. In other words, the output impedance at the extraction terminal 25 is
The characteristics are similar to those when receiving VHF and UHF. This means that the circuit of this invention, so to speak, the local oscillation circuit, can be easily matched with the prescaler.

In addition, the output level of the local oscillation output in the VHF band becomes smaller as the frequency becomes higher due to the lag filter consisting of the resistor R ₂ and the capacitor C ₈ of the low frequency circuit 23. In addition, the local oscillation output in the UHF band is
Due to the filter operation of the capacitor C ₈ and the resonant line L ₆ , the higher the frequency, the lower the output level becomes. This is extremely well suited to the sensitivity characteristics of the prescaler shown in FIG. 5 in terms of the circuit. The vertical axis in FIG. 5 shows the input level of the prescaler, and the horizontal axis shows the frequency. FIG. 5 shows the minimum level at which the prescaler operates normally when the local oscillator output level of a certain frequency input to the prescaler is at the input level shown in this figure. In other words, it is shown that as the frequency increases, the prescaler operates normally even at a small input level.
Therefore, as the local oscillation output of the circuit of this invention increases, it is unlikely that the prescaler will malfunction even if its output level decreases. In this way, the prescaler operates reliably, and its divided output has narrow band characteristics, forming an accurate tuning voltage.

Furthermore, it has been confirmed through experiments that in the circuit according to this invention, there is almost no leakage to other tuners when receiving VHF or UHF.

Note that this invention is not limited to the case where the outputs of the VHF local oscillator circuit 21 and the UHF local oscillator circuit 24 are input to a prescaler, but can also be applied to the case where they are supplied to the mixer stage of a tuner circuit. The point is that the uniqueness lies in the fact that in the configuration of each local oscillator circuit, the shareable parts are shared as much as possible.

(7) Effects of the invention As stated above, according to this invention, the output terminal of the VHF local oscillator circuit is connected to the UHF
Since it is connected to one end of the resonant line on the output side of the local oscillator circuit, individual filter elements are used to remove the harmonics of the VHF local oscillation output when receiving VHF, and the low frequency components of the UHF local oscillation output when receiving UHF. This eliminates the need for one signal conductor when connecting from the tuner housing to the receiver body. In other words, when receiving UHF or VHF, the local output can be transmitted using a single common signal conductor.

Further, it is also possible to include a prescaler and the like in the tuner itself and form it integrally, and based on this, there is an advantage that an electronic tuner including a PLL synthesizer can be provided.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing a conventional example of a circuit that mixes and guides the oscillation outputs of a VHF local oscillation circuit and a UHF local oscillation circuit to a prescaler, and Figure 2 is a circuit diagram showing a transmission circuit for local oscillation outputs according to this invention. , FIG. 3 is an equivalent circuit diagram of the main part of FIG. 2, FIG. 4 is a characteristic diagram showing the frequency characteristics of the input impedance of the prescaler, and FIG. 5 is a characteristic diagram showing the minimum input sensitivity frequency characteristics of the prescaler. 21...VHF local oscillation circuit, 23...Low frequency circuit, 24...UHF local oscillation circuit, 25...
Output terminal, 26...Prescaler input terminal, IC
...Inductive coupler (L ₆ ... Output side resonant line, L ₇
...input side resonant line), _C7 , _C8 ...capacitor,
R ₂ , R ₃ ...resistance.

Claims (1)

[Scope of utility model registration request] The first oscillation frequency is controlled by the tuning voltage.
an oscillation circuit, a second oscillation circuit that oscillates at a higher frequency than the oscillation frequency of the first oscillation circuit, and whose oscillation output is taken out via an inductive coupler;
is provided between the output terminal of the oscillation circuit and one end of the output side inductor of the inductive coupler, and the first
wave means for attenuating harmonics of the oscillation output and leakage components of the second oscillation output to the first oscillation circuit, the output of the first oscillation circuit and the output of the second oscillation circuit being A transmission circuit for local oscillation output, characterized in that the output is taken out from the other end of the output side inductor.