JP2956098B2 - Television tuner - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television tuner used for a television receiver, a home VTR, and the like.

2. Description of the Related Art Hereinafter, a conventional technique will be described with reference to the drawings. FIG. 2A is a circuit diagram of an input circuit of a conventional television tuner.

In FIG. 2 (a), 1 is an input terminal from the antenna, 2 is an IF filter, 3, 9, 11, 14, 21 are DC blocking capacitors, 4 is a low band matching coil, and 5 is a high band. The matching coils 6, 7, 12, 22, and 23 are switching diode bias resistors. 8 is a tuning coil for low band, 10 is a tuning coil for high band, 13 and 24 are switching diodes, and 15 is a varicap diode for tuning. 16 is a varicap diode bias resistor, and 17 is an RF signal amplifier circuit. Reference numeral 18 denotes a low-band reception voltage application terminal, 10 denotes a high-band reception voltage application terminal, and 20 denotes a varicap diode voltage application terminal.

The television tuner configured as described above will be described below.

A television signal (hereinafter abbreviated as an RF signal) input to an input terminal 1 from an antenna is attenuated in an intermediate frequency band by an IF filter 2 and input to a high-band matching coil 5 and subsequently to a low-band matching coil 4. Is done. The RF signal output from these is the next stage tuning coil
RF signal amplifying circuit after selecting RF signal of desired channel which is input to 8, 10 and tuning varicap diode 15
The signal is amplified by 17 and transmitted to the next stage. Then, it is converted to an intermediate frequency by mixing with local oscillation and output from the television tuner. Next, a method for switching between low band and high band will be described.

FIG. 2 (b) is an equivalent circuit of the portion A in FIG. 2 (a) at the time of low band reception, and FIG. 2 (c) is an equivalent circuit of the portion A of FIG. 2 (a) at the time of high band reception. ). In FIG. 2 (b), 7A is a combined resistance of the switching diode bias resistors 6 and 7 in FIG. 2 (a),
In FIG. 2 (c), 10A is the combined inductance of the low band tuning coil 8 and the high band tuning coil 10 in FIG. 2 (a), and 22A is the switching diode bias resistor 6 in FIG. 2 (a). 7 and 22 and the combined resistance.

In part A of FIG. 2A, at the time of low band reception, a voltage is applied to the low band reception voltage application terminal 18 and the high band voltage application terminal 19 is set to zero potential or open, thereby via the switching diode bias resistor 7. The cathode potential of the switching diode 13 rises, the switching diode 13 is turned off, and the matching coil for low band reception is formed by connecting the low band matching coil 4 and the high band matching coil 5 in series to obtain low band matching. Similarly, when the switching diode 24 is turned off, the tuning coil 10 for high band is opened, and tuning for low band is performed by the tuning coil 8 for low band. At the time of high-band reception, the low-band reception voltage application terminal 18 is set to 0 potential or open, and a voltage is applied to the high-band voltage application terminal 19, so that a current flows through the switching diode 13 via the switching diode bias resistor 22 and the switching diode 13 is turned on. By doing so, the low-band matching coil 4 is short-circuited, and high-band matching is obtained.
Similarly, when the switching diode 24 is turned on, the tuning coil 10 for high band is grounded and connected in parallel with the tuning coil 8 for low band. Since the high-band tuning coil 10 is sufficiently smaller than the low-band tuning coil 8, the inductance at the time of high-band reception is substantially determined by the high-band tuning coil 10. Thereby, high band reception becomes possible.

Problems to be Solved by the Invention However, in such a configuration, two band switching switching diodes must be used, and there is a problem that the number of components is large and miniaturization is difficult.

In addition, the bias resistors 6, 7, and 22 for the switching diode are connected to the tuning coil 10 for the high band when receiving the hi-band on the circuit.
Are connected in parallel. The combined resistance 22A of the switching diode bias resistors 6, 7, and 22 is 400Ω when the power supply voltage is 5V and the diode current is 2mA, and is a parallel connection of a varicap diode 15 having an impedance of usually about 10KΩ and a tuning coil 10 for high band. There is a problem that it acts as a damping for the tuned circuit to be configured and deteriorates the NF and selectivity of the circuit.

Means for Solving the Problems In order to solve this problem, the present invention connects both ends of a low-band matching coil and one end of a high-band matching coil to an input terminal of a television tuner, A low-band tuning coil is connected between one end and the other end of the high-band matching coil, and one end of the high-band tuning coil is connected to a connection point between the high-band matching coil and the low-band tuning coil, The other end of the high band tuning coil is connected to the ground, and a tuning diode is connected in parallel with the low band tuning coil.

Operation According to this configuration, the conventional switching diode 2
A single unit can be used instead of a single unit, and the number of components can be reduced, including reduction of the attached bias resistor and DC blocking capacitor.
Further, since the bias resistor of the switching diode can be placed before the matching coil having a low impedance, deterioration of NF and selectivity due to tuning circuit damping can be prevented.

Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1A is a circuit diagram according to one embodiment of the present invention. 1 (a), 1 (b) and 1 (c), 1 is an input terminal from an antenna, 2 is an IF filter, 3, 9, 11, and 14 are DC blocking capacitors, Is the matching coil for the low band, 5 is the matching coil for the high band, 6, 7, and 12 are the bias resistors for the cowling diode, 8 is the tuning coil for the low band, 10 is the tuning coil for the high band, 13 is the switching diode, and 15 is the switching diode. A tuning varicap diode, 16 is a varicap diode bias resistor, 17 is an RF signal amplifier circuit, and 18 is a low band receiving voltage application terminal. 19 is a high-band receiving voltage application terminal, and 20 is a varicap diode voltage application terminal. 5A is the inductance due to the parallel connection of the low band matching coil 4 and the high band matching coil 5 at the time of high band reception, and 7A is the resistance due to the parallel connection of the switching diode bias resistors 6 and 7. Next, the operation will be described. The RF signal input to the input terminal 1 from the antenna is attenuated in the intermediate frequency band by the IF filter 2 and is input to the connection point between the low-band matching coil 4 and the high-band matching coil 5. The RF signals output from these are input to both ends of the next-stage low-band tuning coil 8 and to one end of the high-band tuning coil 10 and one end of the tuning varicap diode 15. After selecting the RF signal of the desired channel, the RF signal is amplified. Circuit 17
, And is transmitted to the next stage. Thereafter, the signal is converted into an intermediate frequency by mixing with local oscillation, and output from a television tuner.

Next, the operation at the time of switching between the low band and the high band will be described in detail. In part A of FIG. 1 (a), a low-band reception voltage application terminal for low-band reception
A voltage is applied to 18, and the high-band voltage application terminal 19 is set to 0 potential or open, so that the low-band reception voltage application terminal
The voltage applied to the switching diode 13 is divided by the switching diode bias resistor 6 and the switching diode bias resistor 7, and the cathode side of the switching diode 13 via the low band matching coil 4, the high band matching coil 5, and the low band tuning coil 8. Becomes high, and the switching diode 13 is turned off. Since the high-band tuning coil 10 is sufficiently smaller than the high-band matching coil 5 and the low-band tuning coil 8, it can be considered that the short-circuit state is almost a short-circuit at the time of low-band reception. Therefore, FIG. 1 (a) at the time of low band reception
The equivalent circuit of the part A is as shown in FIG. 1 (b). Low band matching is obtained by the matching coil 4. Low band tuning is selected by the low band tuning coil 8 and the varicap diode 15, and the low band channel is selected. Reception becomes possible. When the low-band reception voltage application terminal 18 is set to 0 potential or open for high-band reception and a voltage is applied to the high-band reception voltage application terminal 19, switching is performed via the switching diode bias resistor 12 and the high-band tuning coil 10. A voltage is applied to the anode of the diode 13, the switching diode 13 is turned on, and the tuning coil 8 for low band is short-circuited. Thereby, the matching coil for high band reception is formed by connecting the high band matching coil 5 and the low band matching coil 4 in parallel. Also, since the low-band tuning coil 8 is short-circuited, the tuning coil for high-band reception is formed by the high-band tuning coil 10. Accordingly, FIG.
The equivalent circuit of the unit is as shown in FIG. 1 (c), and it is possible to receive high band channels. As described above, according to this embodiment, one end of the low-band matching coil 4 and one end of the high-band coil 5 are connected together, and one end of the low-band matching coil 4 and the high-band matching coil 5 are connected to the switching diode. Bias resistor 6
And one end of the switching diode bias resistor 7, the other end of the switching diode bias resistor 7 is connected to ground, and the other end of the switching diode bias resistor 6 is connected to the low band receiving voltage application terminal 18 to provide the low band matching. A low-band tuning coil 8 is connected between the other end of the coil 4 and the other end of the high-band matching coil 5, and a DC blocking point is provided at a connection point between the high-band matching coil 5 and the low-band tuning coil 8. Capacitor 9
The other end of the high-band tuning coil 10 is connected to the other end of the low-band tuning coil 10 and the other end of the high-band tuning coil 10 is connected to the ground via a DC blocking capacitor 12. The cathode of the switching diode 13 is connected to the connection point, and the anode of the switching diode 13 is connected to the connection point of the DC blocking capacitor 9 and the tuning coil 10 for high band.
One end of the switching diode bias resistor 12 is connected to the connection point between the high band tuning coil 10 and the DC blocking capacitor 12, and the high band receiving voltage application terminal 19 is connected from the other end of the switching diode bias resistor 12. As a result, one switching diode, one DC blocking capacitor, and two switching diode bias resistors can be reduced, and downsizing can be achieved. Further, as is clear from FIG. 1 (c), the equivalent circuit at the time of high-band reception, the switching diode bias resistors 6 and 7 and the combined resistor 7A have a band reception voltage of 5 V and a switching diode current.
If it is 2 mA, it can be set to about 1 KΩ, which is larger than the conventional example of 400 Ω, and it is connected to the antenna input section (connection point of the low-band matching coil 4 and the high-band matching coil 5) having a low impedance of 75 Ω. The circuit is hardly damped. Therefore
This has an effect that a circuit design that prevents deterioration of NF and selectivity can be performed.

As described above, according to the present invention, one end of the low-band matching coil and one end of the high-band coil are both connected to the input terminal of the tuner, and the other end of the low-band matching coil and the high-band matching coil are connected. A low-band tuning coil is connected to the other end, and one end of the high-band tuning coil is connected to a connection point between the high-band matching coil and the low-band tuning coil. Is connected to the ground, and a switching diode is connected in parallel to the tuning coil for low band, thereby realizing a television tuner with a small number of parts, space saving, suitable for miniaturization, and excellent in NF and selectivity.

[Brief description of the drawings]

FIG. 1A is a circuit diagram of an input circuit section of a television tuner according to one embodiment of the present invention, FIG. 1B is an equivalent circuit diagram of section A in FIG. 1A at the time of low band reception, 1 (c) is an equivalent circuit diagram of the portion A in FIG. 1 (a) at the time of high band reception, FIG. 2 (a) is a circuit diagram of an input circuit portion of a conventional television tuner, and FIG. 2B is an equivalent circuit diagram of the portion A in FIG. 2A at the time of low band reception, and FIG. 2C is an equivalent circuit diagram of the portion A of FIG. 2A at the time of high band reception. 1 ... input terminal from antenna 2 ... IF filter,
3, 9, 11, 14… DC blocking capacitor, 4… Low band matching coil, 5… High band matching coil, 6, 7, 12… Switching diode bias resistor, 8… Low band tuning Coil, 10… Tuning coil for high band, 13… Switching diode, 15…
... Varicap diode for tuning, 16 ... Bias resistor for varicap diode, 17 ... RF signal amplifier circuit, 18
... Low-band reception voltage application terminal, 19... High-band reception voltage application terminal, 20... Varicap diode voltage application terminal, 5 A... Low-band matching coil 4 and high-band matching coil 5 for high-band reception , 7A..., The resistance of the switching diode bias resistors 6 and 7 connected in parallel.

Continued on the front page (72) Inventor Akio Iwase 1006 Kadoma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. 56) References JP-A-56-42424 (JP, A) JP-A-3-192914 (JP, A) JP-A-57-131034 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , (DB name) H03J 3/20-3/22 H03J 5/00-5/24 H03J 3/08

Claims (1)

(57) [Claims] An end of a low-band matching coil and one end of a high-band matching coil are both connected to an input terminal of a tuner to which a television signal is input, and the other end of the low-band matching coil is connected to the high-band matching coil. A low-band tuning coil is connected between the other end of the coil, and one end of the high-band tuning coil is connected to a connection point between the high-band matching coil and the low-band tuning coil. A television tuner having the other end connected to ground and a switching diode connected in parallel to the low-band tuning coil.