JPH0543543Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial field of application] The present invention relates to a VHF tuner, and more specifically, an electronically tuned VHF tuner that configures a tuning circuit in a single band.
It is about Chiyuna.

[Conventional technology]

Channel allocation for the VHF reception band is divided into low channel and Haiti channel.
In an electronically tuned television tuner that uses a variable capacitance diode as a variable reactance element,
Usually, a two-band system is adopted: a low channel channel and a high channel channel. For example, a conventional VHF tuner is shown below with reference to FIGS. 3 and 4. In the block diagram shown in FIG. 3, 1 is an input circuit;
2 is a high frequency amplification circuit, and 3 is a frequency conversion circuit. The input circuit 1 includes an input filter 4 connected to an input terminal IN, a tuned circuit 5 connected to the output of the input filter 4, and a switch element 6 connected to the tuned circuit 5.
and a tuning circuit 7 which is connected or disconnected by. The high frequency amplifier circuit 2 includes an amplifier circuit 8 connected to the input circuit 1, a tuning circuit 9 connected to the output of the amplifier circuit 8, and a tuning circuit 11 connected to or disconnected from the tuning circuit 9 by a switch element 10.
The frequency conversion circuit 3 includes a mixing circuit 12 and a local oscillation circuit 13, and the mixing circuit 12 includes a tuning circuit 14 connected to the high frequency amplification circuit 2 and a tuning circuit 14.
It consists of a tuning circuit 16 connected or disconnected by a switch element 15, and a mixer 17 connected to the output of the tuning circuit 14. The local oscillation circuit 13 includes an oscillation element 1 whose oscillation output is connected to the input of a mixer 17.
8 and a tuning circuit 1 connected to the input of the oscillation element 18
9, and a tuning circuit 21 connected or disconnected from the tuning circuit 19 by a switch element 20.

In the above configuration, when receiving the VHF low channel, the switch elements 6, 10, 15 in each circuit,
20 and each tuning circuit 5 and 7, 9 and 11,
Connect 14 and 16, and 19 and 21, respectively. Also, when receiving VHF high channel, switch elements 6, 10, 15, 20 in each circuit are switched to the ground side, and each tuning circuit 5, 7, 9, 11,
14 and 16, and 19 and 21 are separated, respectively, and only the tuning circuits 5, 9, 14, and 19 are used.

Next, a general circuit example of the above block diagram will be shown with reference to FIG. First, in the input circuit 1, the input filter 4 consists of a high-pass filter H, and
When receiving the Haiti channel, the input stage tuning circuit 5 applies a voltage of, for example, 12V to the terminal BH and switches the switching diode SD ₁ [corresponding to the switching element 6]
It is formed when a variable capacitance diode is made conductive.
VD ₁ and tuning coil L ₁ , L ₄ and capacitor C ₁ , C ₃ ,
Equipped with C ₄ and C ₅ . In addition, the input stage tuning circuits 5 and 7 during low channel reception are formed when a voltage of, for example, 12V is applied to the terminal BL to cut off the switching diode SD ₁ , and the variable capacitance diode VD ₁ and the tuning coil L ₁ are formed when the switching diode SD 1 is cut off. , L ₂ , L ₃ , L ₄ and capacitors C ₁ , C ₂ , C ₆ , C ₄ , C ₅ , and applies a tuning voltage to the variable capacitance diode VD ₁ from the terminal BT when receiving each channel.

Next, in the high frequency amplifier circuit 2, the amplifier circuit 8 consists of a transistor _Q1 , and is connected to the input circuit 1 via a coupling capacitor _C7 . Furthermore, the tuning circuit 9 of the high frequency amplification stage during high channel reception is formed when a voltage is applied to the terminal BH to make the switching diode SD ₂ [corresponding to the switching element 10] conductive, and is tuned to the variable capacitance diode VD ₂ . It includes a coil _L5 and capacitors _C8 , _C9 , _C10 , and _C11 . Further, the tuning circuits 9 and 10 of the high frequency amplification stage during low channel reception are formed when voltage is applied to the terminal BL to cut off the switching diode SD ₂ , and the tuning circuits 9 and ₁₀ are formed when the switching diode SD ₂ is cut off by applying a voltage to the terminal BL. ₆ , _L9 and capacitors _C8 , _C9 , _C11 , _C12
terminal when receiving each channel.
Apply tuning voltage to variable capacitance diode VD ₂ from BT.

Next, in the mixing circuit 12 of the frequency conversion circuit 3, the tuning circuit 14 of the mixing stage at the time of high channel reception is formed when the switching diode SD ₂ [corresponding to the switching element 15] is made conductive, and the variable capacitance diode VD ₃ and It includes a tuning coil _L7 and capacitors _C13 , _C14 , _C10 , and _C15 . Also, the tuning circuit 1 of the mixing stage when receiving the low channel
4 and 16 are formed when a voltage is applied to the terminal BL to cut off the switching diode SD ₂ , and the variable capacitance diode VD ₃ and the tuning coils L ₇ , L ₈ , L ₉
and capacitors C ₁₃ , C ₁₄ , C ₁₅ , and C ₁₂ , and a tuning voltage is applied from terminal BT to variable capacitance diodes VD ₂ and VD ₃ during reception of each channel. Further, the mixer 17 consists of a transistor _Q2 , and the outputs of the tuning circuits 14 and 16 are connected to its input via a coupling capacitor _C16 .

Next, in the local oscillation circuit 13 of the frequency conversion circuit 3, the tuning circuit 1 when receiving the Haiti channel
9 is formed when a voltage is applied to the terminal BT to make the switching diode SD ₃ (corresponding to the switching element 20) conductive, and the variable capacitance diode VD ₄ , the tuning coil L ₁₀ , and the capacitors C ₁₇ , C ₁₈ , C ₁₉ , C ₂₃ . It is connected to the base of a transistor Q ₃ as an oscillation element 18 via a coupling capacitor C ₂₂ , and forms a local oscillation circuit with capacitors C ₂₃ , C ₂₄ , C ₂₅ , etc. Further, the tuning circuits 19 and 21 at the time of low channel reception are formed when voltage is applied to the terminal BT to cut off the switching diode SD ₃ , and include the variable capacitance diode VD ₄ , the tuning coils L ₁₀ and L ₁₁ , and the capacitor C. ₁₇ , _C18 , _C19 ,
C ₂₀ and C ₂₁ , and a tuning voltage is applied to the variable capacitance diode VD ₄ from the terminal BT during reception of each channel.

[The problem that the idea aims to solve]

By the way, as mentioned above, VHF tuners are divided into Japan channels, low channels 1 to 3, and Haiti channels 4 to 12, and the tuning circuit is switched between low and high channels, so low Electronic parts for the Haitian channel were required, which increased the number of parts and processing costs, causing an increase in costs.

[Means to solve the problem]

The present invention includes an input circuit and a high frequency amplification circuit.
An RF input stage, a frequency conversion stage including a mixing circuit and a local oscillation circuit are connected in a predetermined order, and each of the circuits is formed of tuning variable capacitance diodes with a tuning section capacitance change ratio of 11 or more, The circuits of the RF input stage and frequency conversion stage are coupled by a coupling variable capacitance diode, and a peaking circuit is connected to the input side of the mixing circuit, and each tuning section in each of the circuits is tuned to the entire VHF band. It is characterized by being formed by a single band that spans the entire range.

[Effect]

According to the above technical means, the tuning of the VHF tuner is formed in a single band over the entire VHF reception band.

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. First, in the block diagram shown in FIG. 1, 22 is an input circuit, 23 is a high frequency amplification circuit, and both circuits constitute an RF input stage.
4 is a frequency conversion stage. The input circuit 22 is
It consists of an input filter 25 connected to the input terminal IN, and a tuning section 26 connected to the output of the input filter 25. The high frequency amplification circuit 23 includes an amplification circuit 27 and a tuning section 28 on its output side. The frequency conversion stage 24 includes a mixing circuit 29 and a local oscillation circuit 30, and the mixing circuit 29 includes a tuning section 31 connected to the high frequency amplification circuit 23 and a mixer 32 connected to the output of the tuning section 31. The local oscillation circuit 30 is
An oscillation element 33 whose oscillation output is connected to the input of the mixer 32, and a tuning section 3 connected to the input of the oscillation element 33.
It consists of 4.

Next, a general circuit example of the above block diagram will be shown with reference to FIG. First, in the input circuit 22, the input filter 25 consists of a high-pass filter H,
The tuning section 26 includes a variable capacitance diode VD ₅ with a capacitance change ratio of 11 or more within the usage range, and tuning coils L ₁₂ , L ₁₃ ,
It includes L ₁₄ and capacitors C ₂₆ and C ₂₇ , and forms a tuning section in a single circuit over the entire VHF reception band.
Next, in the high frequency amplification circuit 23, the amplification circuit 27
consists of a transistor Q ₄ and is connected to the input circuit 22 using a variable capacitance diode VD ₆ and capacitors C ₂₈ and C ₂₉ as coupling capacitors. In other words, if the conventionally fixed coupling capacitor is made variable and the tuning capacitance increases during low channel reception,
As the Q of the tuning section decreases and the loss increases, the coupling capacitance is increased to make it easier for the signal to flow.Also, when receiving the Haiti channel, the coupling capacitance is decreased to minimize the dangling tuning capacitance, which reduces gain and noise. Increase exponential characteristics. In addition, the tuning section 28 of the amplification stage is a variable capacitance diode with a capacitance change ratio of 11 or more within the usage range.
VD ₇ and tuning coil L ₁₅ , L ₁₆ and capacitor C ₃₀ ,
C ₃₁ and C ₃₂ , and is formed by a single circuit covering the entire VHF reception band.

Next, in the mixing circuit 29 of the frequency conversion stage 24, the tuning section 31 includes a variable capacitance diode VD ₈ with a capacitance change ratio of 11 or more within the usage range, a tuning coil L ₁₇ ,
L ₁₆ and capacitors C ₃₃ , C ₃₄ , C ₃₂ ,
It is formed as a single band over the entire VHF reception band, and is inductively coupled to the tuning section 28. The mixer 32 is composed of a transistor _Q5 , and is connected to the peaking circuit 35 formed by a capacitor _C36 , a coil _L18 , a switching diode _SD4 , and a resistor R, and a coupling capacitor _C35 at the front stage of the input side. It is connected to the output of the tuning section 31. That is, since the coupling capacitor C ₃₅ cannot be made too large, a peaking circuit is used to couple the mixer 32 and the tuning section 31 to increase the coupling impedance and facilitate the coupling. Further, in the local oscillation circuit 30, the tuning section 34 includes a variable capacitance diode VD ₉ with a capacitance change ratio of 11 or more within the usage range, a tuning coil L ₁₀ , and a capacitor.
C ₃₇ and C ₃₈ , and is formed in a single band over the entire VHF reception band. Then, it is connected to the oscillation element 33 using the variable capacitance diode VD ₁₀ and the capacitors C ₃₉ and C ₄₀ as a coupling capacitor. That is, like the input circuit 22, the conventionally fixed coupling capacitor is made variable, and when the tuning capacitance increases during low channel reception, the Q of the tuning section decreases and the loss increases, so the coupling capacitance is increased. It makes it easier for signals to flow, and when receiving a Haitian channel, it reduces the coupling capacitance and widens the frequency variable range. Further, an oscillation element 33 connected to the tuning section 34
consists of transistor Q ₆ and capacitor C ₄₂ ,
Form a local oscillation circuit with _C43 etc.

Also, each terminal IN, BU, BT, BV, AGC, BM,
IF is input, UHF power supply, tuning voltage, VHF power supply, AGC voltage, mixed circuit power supply, IF respectively
These are the connection terminals for each output.

[Effect of idea]

According to the present invention, since each tuning section included in the VHF tuner is formed by a single band, the number of parts is reduced and processing costs are also reduced, making it possible to significantly reduce costs.

[Brief explanation of the drawing]

1 and 2 are a block diagram and a circuit diagram showing an embodiment of a VHF tuner according to the present invention, and FIGS. 3 and 4 are a block diagram and a circuit diagram showing a specific example of a conventional VHF tuner. 22...Input circuit, 23...High frequency amplification circuit,
24...Frequency conversion stage, 26, 28, 31, 34
... Tuning section, 29 ... Mixing circuit, 30 ... Local oscillation circuit, VD ₅ , VD ₇ , VD ₈ , VD ₉ ... Tuning variable capacitance diode, VD ₆ , VD ₁₀ ... Coupling variable capacitance diode, 35... Peaking circuit, Q ₆ ...
...Oscillation element.

Claims (1)

[Scope of utility model registration request] an RF input stage including an input circuit and a high frequency amplification circuit;
It consists of a frequency conversion stage including a mixing circuit and a local oscillation circuit, and uses a tuning variable capacitance diode with a capacitance change ratio of 11 or more in the tuning section of each circuit, and a coupling variable capacitance diode coupled between each circuit. A VHF tuner characterized in that a peaking circuit is provided on the input side of a mixing circuit, and each of the tuning sections described above is formed with a single band covering the entire VHF band.