JP2584612Y2 - Television tuner - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a television tuner suitable for use in an in-vehicle television receiver or the like. [Related Art] Generally, a television tuner used for a television receiver or the like is required to have strong interference resistance to a signal outside a reception channel, and regulations regarding the interference resistance are set. For example, in the IS-31 regulation in the United States, TV broadcasting (low band represented by channel 6)
Interference immunity to FM broadcasting is specified. In particular, in the case of in-vehicle TV receivers, where the market is expanding in recent years,
Since the reception conditions such as the electric field strength change rapidly with the movement of the automobile, it is essential to further enhance the interference resistance to FM broadcasting. In addition, since the in-vehicle antenna must be small, the sensitivity characteristics thereof are not sufficient, and particularly the sensitivity characteristics in the low band are poor. Therefore, it is inevitably required to increase the gain and the noise of the tuner. That is, the television tuner of the in-vehicle television receiver is required to enhance both the performances of the high sensitivity reception characteristic and the high interference resistance against the FM broadcast. FIG. 7 shows a configuration example of a conventional television tuner, and a conventional example will be described with respect to a television channel and an FM broadcast area using frequencies used in the United States as an example. In FIG. 7, a signal received by the antenna ANT is input to the antenna filter 1. The antenna filter 1 includes a low-pass filter 21, an intermediate frequency trap 22 for attenuating a signal having the same frequency as an intermediate frequency signal (described later), and an FM trap 11 for attenuating a signal in an FM broadcast area.
Are connected in series. The FM trap 11 is composed of a fixed trap based on parallel resonance composed of the coil 7 and the capacitor 8, and a fixed trap based on series resonance composed of the capacitor 9 and the coil 10. As shown in FIG. The values of the coils 7, 10 and the capacitances 8, 9 are determined so as to attenuate the FM broadcast signal between the band and the low band. The reception signal that has passed through the antenna filter 1 is input to the antenna tuning circuit 2, and the signal outside the reception channel is further attenuated. Then, the output signal of the antenna tuning circuit 2 is amplified by the high-frequency amplifier circuit 3 and then input to the mixing circuit 5 via the interstage double tuning circuit 4 and supplied from the local oscillation circuit 6 at a frequency corresponding to the reception channel. Mixed with the local oscillation signal. Then, an intermediate frequency signal having a frequency corresponding to the difference between the frequency of the reception channel and the frequency of the local oscillation signal is output from the mixing circuit 5 and sent to a subsequent intermediate frequency amplification stage (not shown). [Problem to be Solved by the Invention] In the configuration shown in FIG. 7, the FM broadcast signal received by the antenna ANT is an obstacle to receiving the TV broadcast, and is attenuated by the FM trap 11. After being further attenuated by the antenna tuning circuit 2, the signal is input to the high frequency amplifier circuit 3. When a television broadcast in a high band is received, the second harmonic generated by the amplifying operation of the high frequency amplifier circuit 3 is input to the mixing circuit 5 via the interstage double tuning circuit 4,
A beat occurs. Note that this interference mode is hereinafter referred to as 2
Called double mode disturbance. In this case, since the frequency of the receiving channel and the frequency of the FM broadcast are sufficiently separated, the FM broadcast signal is sufficiently attenuated by the FM trap 11 and the antenna tuning circuit 2, and the level of the beat generated in the mixing circuit 5 is reduced. Since it is sufficiently small, there is no problem in practical use. However, when receiving a television broadcast in the low band, the frequency of the reception channel and the frequency of the FM broadcast are close to each other, and there is a problem of interference due to the adjacent mode. Here, the frequency of the receiving channel is fr, the local oscillation frequency is fL, F
If the frequency of the M broadcast is fFM, a beat having a beat frequency fb given by the following equation (1) is generated in the mixing circuit 5. fb = fr + fFM-fL (1) For example, in the case of the United States, when receiving the sixth channel television broadcast having the frequency fr = 83.25 MHz, the frequency fFM = 90 MHz
Disturbed by FM broadcast. In this case, the local oscillation frequency fL
Is 129 MHz, and the frequency fb = 44.2 according to the above equation (1).
A 5MHz beat occurs. Since the frequency fr of the receiving channel and the frequency fFM of the FM broadcast are close to each other, the FM broadcast signal cannot be sufficiently attenuated by the FM trap 11 and the antenna tuning circuit 2, and the beat level is large, which is a hindrance. Occurs. Therefore, as a countermeasure for suppressing the beat level in the mixing circuit 5, it is conceivable to increase the attenuation of the FM trap 11. However, in such a case, the signal of the television broadcast to be received is also attenuated, and the noise figure deteriorates. In addition, since the antenna tuning circuit 2 has a low impedance of 75Ω, if the frequency of the receiving channel is close to the trap frequency, the receiving characteristics, particularly the matching characteristics with the antenna ANT, are adversely affected, and the frequency characteristics are disturbed. As a result, the pass band of the antenna tuning circuit 2 becomes narrow, the loss increases, and the gain decreases. As described above, the conventional television tuner has a problem that it is difficult to enhance resistance to interference from an adjacent frequency region without deteriorating reception sensitivity. If a tuner for receiving not only the AIR band but also the CATV (cable television) band is to be realized, as is clear from FIG.
As a result, a part of the signal of the CATV band is attenuated, and there is a problem that the reception of the CATV broadcast in the area becomes impossible. The present invention has been made in view of the above-described circumstances, and has as its object to provide a television tuner with enhanced interference resistance to adjacent frequency bands without sacrificing reception sensitivity. [Means for Solving the Problems] The television tuner according to the first invention has a wide range.
A first FM trap for attenuating signals in the FM broadcast area;
A high-frequency amplifier circuit for amplifying a signal that has passed through an FM trap, and a signal amplified by the high-frequency amplifier circuit, and a signal in a narrow-range FM broadcast area adjacent to a television channel is input to the first FM trap. A second FM trap that attenuates more than the attenuation degree and a frequency conversion circuit that frequency-converts a signal passing through the second FM trap are sequentially connected. Further, the television tuner according to the second invention is characterized in that, in the configuration of the first invention, the first FM trap is enabled only when a high-band television broadcast is received. Further, in the television tuner according to the third invention, in the configuration of the first invention or the second invention, the second FM trap includes a series resonance trap capable of changing a trap frequency and a series resonance trap adjacent to an FM broadcast area. A parallel resonance trap that is enabled only when receiving a broadcast of a television channel to be configured, and when receiving the broadcast, configures a trap having a bipolar characteristic by changing the trap frequency of the series resonance trap and the parallel resonance trap. It is characterized by doing. Item 1
Or the television tuner according to claim 2. [Operation] According to the first invention, first, the first FM trap attenuates signals in a wide range of FM broadcast areas. Then, the high-frequency amplifier circuit amplifies the signal that has passed through the first FM trap. Thereafter, the second FM trap receives the signal amplified by the high-frequency amplifier circuit, and attenuates a signal in a narrow FM broadcast area adjacent to the television channel more greatly than the first FM trap. Further, according to the second invention, the first FM trap is enabled only when receiving a television broadcast in a high band,
The FM broadcast signal is attenuated. Further, according to the third invention, a trap having a bipolar characteristic is constituted by the series resonance trap and the parallel resonance trap only when receiving a broadcast of a television channel adjacent to the FM broadcast area. [Embodiment] An embodiment of the present invention will be described below with reference to the drawings based on frequencies used in the United States for television channels and FM broadcast areas.

FIG. 1 shows a configuration of a television tuner according to a first embodiment of the present invention. This television tuner differs from the configuration shown in FIG. 7 in that a second FM trap 16 is interposed between the interstage double tuning circuit 4 and the mixing circuit 5.
The FM trap 16 is the FM trap 11 in the antenna filter 1.
It is the same configuration as. However, while the FM trap 11 is designed to moderately attenuate the frequency range between the high band and the low band over a wide range as shown by the solid line in FIG. As shown by the broken line in FIG. 2, the coils 12, 15 and the capacitors 13, 14 are determined to have appropriate values so that the trap frequency is greatly attenuated in a narrow frequency range close to the sixth channel (first channel in Japan). Have been. When a television broadcast in the high band is received, the FM broadcast received by the antenna ANT together with the television broadcast is sufficiently attenuated by the FM trap 11 and the antenna tuning circuit 2 as in the circuit of the configuration of FIG. The beat level at is kept small. In the case of receiving a television broadcast in the low band, the FM broadcast that has not been sufficiently attenuated by the FM trap 11, the antenna tuning circuit 2, and the interstage double tuning circuit 4 is sufficiently attenuated by the second FM trap 16. Is done. Therefore, even in the case of receiving a low band, occurrence of a beat due to the FM interference signal can be suppressed. FIGS. 3A to 3C show performance comparison data depending on the presence or absence of the second FM trap 16. As shown in FIG. 3 (a), the insertion in the FM trap 16 slightly lowers the gain in the low band. However, the high frequency amplifier circuit 3
Thereafter, since the signal level is sufficiently large, even if the received signal is slightly attenuated, as shown in FIG. 3 (b), it does not contribute much to the deterioration of the noise figure. Therefore, the values of the coil and the capacitance of the FM trap 16 can be determined so that the FM broadcast signal in the frequency band close to the low band can be sufficiently attenuated. As shown in FIG. Signal rejection ability can be increased. Here, since the impedance of the interstage tuning circuit 4 and the mixing circuit 5 is a high impedance of several tens of kilohms, even if the trap frequency of the FM trap 16 is close to the low band frequency, the influence of the FM trap 16 on the low band frequency characteristics is obtained. Less is.

Second Embodiment FIG. 4 shows a configuration of a television tuner according to a second embodiment of the present invention. The television tuner according to the first embodiment described above is suitable for receiving only the AIR band and not suitable for receiving the CATV band. However, according to the television tuner according to the second embodiment described below, It is possible to receive not only bands but also CATV bands. This television tuner differs from the configuration of the first embodiment in that FM traps 11a and 16a are inserted instead of FM traps 11 and 16. First, the configuration of the FM trap 11a will be described. In the parallel resonance trap including the coil 7 and the capacitor 8, the connection terminal on the intermediate frequency trap 22 side is connected to one electrode of the capacitor 17, and the connection terminal on the antenna tuning circuit 2 side is connected to the anode of the switch diode 18. . The other electrode of the capacitor 17 and the cathode of the switch diode 18 are commonly connected, grounded via a resistor 28, and connected to a high band selection terminal H via a resistor 20. The anode of the switch diode 18 is connected to an anode bias terminal B via a resistor 19, and a positive anode bias voltage is applied. Next, the FM trap 16a will be described. The parallel resonance trap is formed by connecting the coil 12 in parallel with the capacitor 13 via the capacitor 26. Switch diode 29
In the parallel resonance trap, an anode is connected to a connection terminal on the interstage double tuning circuit 4 side, and a cathode is connected to a connection terminal on the mixing circuit 5 side. The series resonance trap inserted between the input terminal of the mixing circuit 5 and the ground line includes a capacitor 14 and a coil.
The connection point 15 is connected to the anode of the switch diode 27. The cathodes of the switch diodes 29 and 27 are commonly connected, grounded via a resistor 25, and connected to a sixth channel selection terminal B6 via a resistor 24. The anode of the switch diode 29 is connected to the resistor 23.
Is connected to the anode bias terminal B via Hereinafter, the operation of the television tuner will be described.
When receiving a television broadcast in the high band, a positive voltage higher than the anode bias voltage applied to the anode bias terminal B is applied to the high band selection terminal H, and the sixth channel selection terminal B6 is opened. As a result, the switching diodes 18 and 27 are turned off, and the switching diode 29 is turned on. The equivalent circuit of this television tuner is as shown in FIG. The FM trap 11a equivalently operates as a parallel resonance trap composed of the coil 7 and the capacitor 8, as shown in FIG. Then, as shown by the solid line in FIG. 6A, the signal in the FM broadcast area is attenuated by the FM trap 11a. Further, FM trap 16a operates as the combined capacitance and series resonant trap including coil 15 and the junction capacitance C ₂₇ of the capacitor 14 and the diode 27. Here, the switch diode 27 is applied with a voltage obtained by dividing the voltage applied to the anode bias terminal B by the resistors 23 and 25 to the cathode, is in a non-conductive state, and has a junction capacitance C ₂₇ of several pF.
Is the capacitance value. Then, as indicated by a broken line in FIG. 6A, a signal near the upper limit frequency of the low band is selectively attenuated by the FM trap 16a. When receiving a television broadcast in a low band other than the sixth channel, the high band selection terminal H is opened and the sixth channel selection terminal B6 is opened. As a result, the switching diodes 18 and 29 become conductive and the switching diode 27
Is turned off, and the equivalent circuit of this television tuner is as shown in FIG. 5 (b). When the switch diode 18 is turned on, the FM trap 11a is disabled, and the output signal of the intermediate frequency trap 22 passes through the capacitor 17 without being attenuated.
Is input to FM trap 16a is similar to the case of receiving a television broadcast in the high-band, operates as a series resonant trap according combined capacity and the coil 15 of the junction capacitance C ₂₇ of the capacitor 14 and the switching diode 27. Then, as indicated by the broken line in FIG. 6 (b), the signal near the upper limit frequency of the low band in the output signal of the interstage double tuning circuit 4 is attenuated by the FM trap 16a. When receiving the television broadcast of the sixth channel in the low band, the high band selection terminal H is opened, and a positive voltage is applied to the sixth channel selection terminal B6. As a result, the switch diode 18 becomes conductive and the switch diode 29
And 27 are non-conductive, and the equivalent circuit of this television tuner is as shown in FIG. 5 (c). That is, the FM trap 11a is invalidated, and the intermediate frequency trap 22
Output signal of the antenna tuning circuit 2 is not attenuated.
Is input to The FM trap 16a has a capacity 13 and a coil 1
A parallel resonant trap according 2, and a series resonant trap is enabled by the combined capacitance and the coil 15 of the junction capacitance C ₂₇ of the capacitor 14 and the switching diode 27. The capacitance value of the junction capacitance C ₂₇ of the switch diode 27 is reduced by the positive voltage applied from the sixth channel selection terminal B6,
The trap frequency of the series resonance trap moves to higher. Then, the series resonance trap and the parallel resonance trap cooperate to constitute a trap having a bipolar characteristic in a frequency region adjacent to the sixth channel as indicated by a broken line in FIG. 6C. Therefore, the FM broadcast signal in this area is sufficiently attenuated. As described above, the trap range is changed depending on the band and channel to be received.
Signals in the TV band are not unnecessarily attenuated. Therefore, it is possible to increase both the reception sensitivity of the AIR band and the resistance to interference with signals outside the reception band without sacrificing the reception of the CATV band. In Japan, since the FM broadcast area is in a lower frequency band than the low band of television broadcasting, it is adjacent to the lower side of the first channel instead of the FM broadcast signal adjacent to the upper side of the sixth channel in the United States. It goes without saying that the trap frequency of the second FM trap is set so as to attenuate the FM broadcast signal. [Effects of the Invention] As described above, according to the first invention, there is an effect that interference resistance to signals outside the reception channel is enhanced without sacrificing the reception sensitivity. Further, according to the second and third inventions, the switching of the trap characteristic is possible, so that the television tuner having the CATV band can perform the FM without reducing the sensitivity and narrowing the reception range.
There is an effect that a fundamental measure is taken against the interference, and a television tuner with high sensitivity and high resistance to interference is realized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a television tuner according to a first embodiment of the present invention, FIG. 2 is a diagram illustrating attenuation characteristics of FM traps 11 and 16 in the embodiment, and FIG.
4A to 4C are diagrams for explaining the effect of the FM trap 16 interposed in the embodiment, FIG. 4 is a block diagram showing the configuration of a television tuner according to a second embodiment of the present invention, and FIG. 6A to 6C are diagrams for explaining an equivalent circuit of the embodiment for each reception band, and FIGS. 6A to 6C are graphs showing attenuation characteristics due to the FM trap in the embodiment for each reception band. FIG. 7 is a block diagram showing a configuration of a conventional television tuner, and FIG. 8 is an FM trap shown in FIG.
FIG. 11 is a diagram illustrating an example of an attenuation characteristic of the eleventh embodiment. 3 ... high frequency amplifier circuit, 5 ... mixed circuit, 6 ... local oscillator circuit, 11, 11a ... first FM trap, 16, 16a ... second
FM trap, 7,12,15 …… coil, 8,13,14 …… capacity,
18,29,27 ... Switch diode. H: High band selection terminal, B6: Sixth channel selection terminal.

Claims (3)

(57) [Scope of request for utility model registration] 1. A first method for attenuating signals in a wide range of FM broadcast areas.
An FM trap, a high-frequency amplifier circuit for amplifying a signal passed through the first FM trap, and a signal amplified by the high-frequency amplifier circuit, and a signal in a narrow-range FM broadcast area adjacent to a television channel is input. A television tuner, characterized in that a second FM trap that attenuates more than the attenuation of the first FM trap and a frequency conversion circuit that converts the frequency of a signal passing through the second FM trap are sequentially connected. 2. The television tuner according to claim 1, wherein the first FM trap is enabled only when receiving a high-band television broadcast. 3. The second FM trap includes a series resonance trap capable of changing a trap frequency, and a parallel resonance trap that is enabled only when receiving a broadcast of a television channel adjacent to an FM broadcast area, 3. The television tuner according to claim 1, wherein when the broadcast is received, a trap having a bipolar characteristic is formed by changing a trap frequency of the series resonance trap and a trap frequency of the parallel resonance trap.