JPH0352320A - electronic tuner - Google Patents

Abstract

PURPOSE:To reduce the number of components by using a surplus circuit of band changeover circuits of a PLL integrated circuit because of 3 band sections for a switching of a trap circuit to constitute the trap circuit at an optional band of the reception band. CONSTITUTION:A PLL(Phase Locked Loop) integrated circuit 18 incorporating 4 band switching circuits or over is provided in the same case for a tuber circuit and a control signal from a microcomputer 20 is inputted so as to select band switching terminals of the PLL integrated circuit 18 to bands 1a, 1b and bands 2, 3 respectively. Moreover, an output of the PLL integrated circuit 18 is inputted to a local oscillation circuit 13 via an active filter 19 and only the output of the switching circuit 16 of the band 1b is fed to a switching diode 6 of the bypass circuit via a bias resistor 8. Thus, the trap circuit is formed to an optional reception band and number of inter-stage tuning circuits and local oscillation circuits at the VHF band is decreased, thereby reducing the number of components.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an electronic tuner used in television receivers, video tape recorders, and the like.

2. Description of the Related Art In conventional electronic tuners, when configuring a trap circuit for the FM band or the like in any reception band, it is difficult to configure it within the same reception band due to the balance with the attenuation band of the trough. 5 [A trap circuit was set in the band outside the band to ensure interference characteristics.

The conventional electronic tuner described above will be explained below based on the drawings.

FIG. 3 is a configuration diagram of a trap circuit and a band switching circuit of a conventional electronic tuner.

The channel signal (RF signal) of the television receiver input from the antenna input terminal l is input to the IF} wrap circuit 2,
The signal passes through the coupling capacitor 3, passes through the FM} wrap circuit consisting of the coil 4 and the capacitor 5, passes through the input tuning circuit 9, and then passes to the subsequent RF amplifier 1l and the interstage tuning circuit 12. FM} A bypass circuit consisting of a switching diode 6 and a coupling capacitor 7 is connected in parallel to the wrap circuit for RF signal bypass, and a switching diode 21 is connected to the switching diode 6 of this bypass circuit.
, when a forward bias voltage is applied via the bias resistor 8, the switching diode 6 becomes conductive,
The RF signal that has passed through the antenna input terminal 1, the F-trap circuit 2, and the coupling capacitor 3 does not pass through the FM wrap circuit, but passes through the switching diode 6 and the coupling capacitor 7, and flows to the input tuning circuit 9 at the subsequent stage. In addition, a control microcomputer (hereinafter referred to as microcomputer) 20 for switching bands is provided, and the selected band signal is
Switching circuit l7 for band 1 and band 2, respectively
The switching diode 21, the input tuning circuit 9,
tJ}iF circuit lO, interstage tuning circuit 12, and local oscillation circuit (VFO) 13 to perform a switching operation.

FIG. 4 shows a band classification diagram for the United States as an example. The problem with the FM broadcast interference regulation (IS31) is that the FM wrap circuit must be operated because there is interference in the FM broadcast shown in Figure 4 when receiving channel 6 of the Pando 1 TV broadcast in both band classifications A and B. When band 2 and band 3 are selected in band division A, the switching circuit 16 for band 2 is switched on as shown in FIG.
Alternatively, the switching circuit 15 for band 3 is operated to bypass the FM trap circuit by applying a forward bias to the switching diode 6 to pass the RF signal component in an alternating current manner and input it to the RF amplifier 1l.

Problems to be Solved by the Invention However, in such a conventional electronic tuner, although it is possible to configure an FM trap circuit in the case of band division A shown in FIG. There is a problem in that three oscillation circuits 13 are required, making the circuit configuration complicated.

In addition, in the case of band classification B, FM within the band 1 band
It is necessary to configure an FM} wrap when receiving band l, and there is a problem in that if the FM} wrap is configured, the band of the CATV channel will also be attenuated, making reception impossible.

The present invention solves the above problems. It is an object of the present invention to provide an electronic tuner in which a trap circuit can be configured in any reception band and the circuit configuration can be reduced.

Means for Solving the Problems In order to solve the above problems, the electronic chainer of the present invention uses a PLL (Phase Lo
cked Loop) integrated circuit is provided in the same housing as the chainer circuit, the band classification of the tuner circuit is three bands or less, and one of the band switching circuits is used as a switching circuit for a specific band trap circuit.

Effect: With the above configuration, by dividing the band into three bands, P
The LL integrated circuit has one or more band switching circuits, and by using this one circuit as a switching circuit for a specific band trap circuit, it is possible to set a trap circuit for any interference wave within the band. Become. Further, by using three bands, that is, band division A to band division B shown in FIG. 4, it is possible to reduce the number of interstage tuning circuits and local oscillation circuits in the VHF band, and the number of parts can be reduced.

EXAMPLE Hereinafter, an example of the present invention will be described based on the drawings. Note that the same components as those in FIG. 3 of the conventional example are given the same reference numerals and explanations are omitted.

FIG. 1 is a configuration diagram of a trap circuit and a band switching circuit of an electronic tuner showing an embodiment of the present invention, and FIG. 2 is a band division diagram of the electronic tuner.

The band of band 1 of band classification B in FIG. The band switching terminals of the integrated circuit l8 are connected to band la, band xb, band 2, and
A control signal is input from the microcomputer 20 so that it can be switched to band 3 for use. Further, the output of the PLL integrated circuit 18 is input to the local oscillation circuit (VCO) 13 via an active filter (LPF) 19. Furthermore, only the output of the switching circuit 16 of band 1b is connected to the switching diode 6 of the bypass circuit via the bias resistor 8.
is applied to.

The operation of the above configuration will be explained.

During band 1a reception, no forward bias is applied to the switching diode 6, and the antenna input terminal l
The signal inputted from
} Passes through the wrap circuit and passes through the input tuning circuit 9 to the subsequent RF
It passes to the amplifier 11 and the interstage tuning circuit l2. Next, when receiving the band peak, the FM consisting of coil 4 and capacitor 5
}A forward bias is applied from the band 1b switching circuit 16 to the switching diode 6 connected in parallel to the wrap circuit, and the switching diode 6 becomes conductive, connecting the antenna input terminal l, the IF trap circuit 2, and the coupling capacitor 3. The passed signal does not pass through the FM trap circuit, but passes through the switching diode 6 and the capacitor 7, and flows to the input tuning circuit 9, which is a subsequent circuit. Furthermore, the switching operations of the input tuning circuit 9, the crotch tuning circuit 12, and the local oscillation circuit 13 are performed in the band LA.
and the switching diode 21 of the outputs of the switching circuits 16 and 17 for band LB.
, when receiving band 1b, resulting in the reception state of band 1 of band classification B shown in FIG.

When receiving Band 2, the FM} wrap circuit is in operation, but it is outside the reception band, so there is no problem, and when receiving Band 3, the UHF circuit 10 is in operation, and there is no FM at all.
It can operate without being affected by the trap circuit.

By using such an electronic tuner, band l
During reception, it is possible to receive the band that overlaps with the FM broadcast of the CATU band in the band classification shown in Fig. 2 without being affected by the FM wrap circuit. By using the output function of the band switching circuit, it is possible to configure a trap circuit in any reception band. Furthermore, PLL
By incorporating the integrated circuit 18, it is possible to form a high frequency block that prevents high frequency signals from going around to the outside, and since band division A shown in Fig. 4 is designated as band division B, the VHF band Interstage tuning circuit 12 and local oscillation circuit l! 13 configurations can be reduced, which can also contribute to a reduction in the number of parts.

Effects of the Invention As described above, according to the present invention, one of the remaining band switching circuits of the PLL integrated circuit is used for switching the trap circuit by dividing the band into three bands. A trap circuit can be set for any interference waves within the range, and a band that overlaps with the interference waves can be received. Furthermore, by changing the band divisions from band division A to band division B shown in FIG. 4, it is possible to reduce the interstage tuning circuit and local oscillation circuit configuration of the VHF band, and the number of parts can be reduced.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of a trap circuit and band switching circuit of an electronic tuner showing an embodiment of the present invention, Fig. 2 is a band division diagram of the electronic tuner, and Fig. 3 is a trap circuit and band switching circuit of a conventional electronic tuner. FIG. 4, which is a block diagram of the switching circuit, is a band division diagram of a conventional electronic tuner. 1... Antenna input terminal, 2... IF} wrap circuit, 3... Coupling capacitor, 4... Coil, 5...
Capacitor, 6...Switching diode, 7...
- Coupling capacitor, 8... Bias resistor, 9... Input tuning circuit, 10... UHF circuit, 11... RF amplifier, 12... Inter-stage tuning circuit, n... Local oscillation circuit, 14, 15, 16. 17... Band switching circuit, 18... PLL integrated circuit, l9.
... Active filter, 20... Control microcomputer, 2l... Switching diode.

Claims (1)

[Claims] 1. PLL (Phas) that supports frequency synthesizer tuning and has at least four built-in band switching circuits.
eLockedLoop) An electronic tuner in which an integrated circuit is provided in the same housing as a tuner circuit, the band classification of the tuner circuit is three bands or less, and one of the band switching circuits is a switching circuit for a specific band trap circuit.