JPH1174813A - Tuner circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tuner circuit in which malfunction of a PLL synthesizer is improved. SOLUTION: Variable band pass filters VPF 51-53 whose characteristic is varied with a control voltage Vt are provided between an output of an oscillator buffer amplifier 32 and an input of a PLL synthesizer 33. The characteristic of the variable BPF 51 has a characteristic to select a local oscillating frequency at a channel selection of a VHF low band and the variable BPF 52 has a characteristic to select a local oscillating frequency at a channel selection of a VHF high band and the variable BPF 53 has a characteristic to select a local oscillating frequency at a channel selection of a UHF band. Furthermore, only one of switching circuits 41, 42, 43 provided to the input of the variable BPFs 51, 52, 53 is controlled to be active in response to a selected frequency band by switching voltages VL, VH, U.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tuner circuit, and more particularly to a tuner circuit for converting a high-frequency television signal of a desired channel into an intermediate frequency signal by a double heterodyne system.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram showing an example of a conventional tuner circuit. This tuner circuit is a tuner circuit for a television signal (hereinafter, referred to as a TV tuner circuit).
HF block 1 and UHF block 2 and IF amplifier 3
1. Oscillator buffer amplifier 32, phase locked loop (PLL) synthesizer 33, and video / audio processing system 34
It is composed of

In this conventional circuit, an RF reception signal 1a received by a VHF antenna 11 is amplified at a high frequency by a VHF RF amplifier 12, and then a VHF tuning circuit 13 extracts a TV signal in a VHF band.
And is frequency-converted (down-converted) to a local oscillation frequency 1b from a VHF oscillator (local oscillator) 15 to produce an intermediate frequency signal (IF signal) 1c.

Similarly, the RF reception signal 2a received by the UHF antenna 21 is amplified at a high frequency by a UHF RF amplifier 22, then a UHF tuning circuit 23 extracts a UHF band TV signal, and is further supplied to a mixer 24 to be supplied to a UHF A local oscillation frequency 2b from an oscillator (local oscillator) 25 is frequency-converted (down-converted) to an intermediate frequency signal (IF signal) 2c.

On the other hand, the local oscillation frequency 1b from the VHF oscillator 15 and the local oscillation frequency 2b from the UHF oscillator 25 are input to the oscillator amplifier 32 and amplified, respectively, and then transmitted to the PLL synthesizer 33 via the coupling capacitor C. Supplied. PLL synthesizer 33
Are VHF tuning circuit 13, VHF tank circuit 17, UH
This is a frequency synthesizer that outputs a control voltage Vt to the F tuning circuit 23 and the UHF tank circuit 27, respectively.

Further, the PLL synthesizer 33 has a VHF
The low-band switching voltage VL and the VHF high-band switching voltage VH are generated and supplied to the VHF tank circuit 17, and the UHF-band switching voltage U is generated and supplied to the UHF tank circuit 27. , 27 are controlled.

As described above, when the VHF low band or the VHF high band is selected, the intermediate frequency signal 1c extracted from the mixer 14 is buffer-amplified by the buffer amplifier 16 and then amplified by the IF amplifier 31. Is supplied to a video / audio processing system 34 to be demodulated into a video signal and an audio signal. When the UHF band is selected, the intermediate frequency signal 2c extracted from the mixer 24 is
After being buffer-amplified by the buffer amplifier 26, the IF amplifier 3
The video / audio processing system 34 after the intermediate frequency amplification by 1
And demodulated into a video signal and an audio signal.

[0008]

However, in the above-described conventional tuner circuit, spurious signals generated by frequency conversion by the mixers 14 and 24 are input to the PLL synthesizer 33 together with the local oscillation frequencies 1b and 2b. Therefore, when a strong electric field signal is received from the antennas 11 and 21, the spurious signal level increases,
The malfunction of the PLL synthesizer 33 may be caused.

It is known that a high-pass filter is provided on the input side of the PLL synthesizer 33 in order to reduce the above-mentioned spurious signal.
No. 32), when spurious signals occur frequently due to reception of a strong electric field signal from the antennas 11 and 21, the spurious signals cannot be sufficiently suppressed.

[0010] The present invention has been made in view of the above points,
An object of the present invention is to provide a tuner circuit capable of improving a malfunction of a PLL synthesizer.

[0011]

In order to achieve the above object, the present invention provides a high frequency reception signal received via an antenna, which is mixed with a local oscillation frequency from a local oscillator by a mixer to obtain a predetermined intermediate frequency. In order to variably control the output local oscillation frequency of the local oscillator to a predetermined local oscillation frequency corresponding to the selected channel by a frequency synthesizer to which the output local oscillation frequency of the local oscillator is input while outputting after converting into an intermediate frequency signal. A tuner circuit for generating and outputting the control voltage of the variable bandpass filter, wherein a variable passband filter is provided in which a pass center frequency is variably controlled to a predetermined local oscillation frequency corresponding to a selected channel by a control voltage output from a frequency synthesizer. Configuration of inputting local oscillation frequency of local oscillator to frequency synthesizer through filter One in which the.

According to the present invention, even if a spurious signal component is mixed in the local oscillation frequency input to the frequency synthesizer, the channel is selected by the variable bandpass filter using the control voltage for controlling the local oscillation frequency which originally exists. Since only the predetermined local oscillation frequency corresponding to the channel is selected, unnecessary frequency components lower than the local oscillation frequency as well as spurious signal components higher than the local oscillation frequency are removed. it can.

Further, the present invention relates to a VHF low band, VH
In a tuner circuit for receiving a television signal transmitted in the F high band and the UHF band, three variable band filters are provided exclusively for each of the three bands. Since the switching means for extracting the local oscillation frequency from only one of the three variable bandpass filters is provided, the influence of the output noise of the other two variable bandpass filters can be prevented.

[0014]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration diagram of an embodiment of a tuner circuit according to the present invention. 4, the same components as those of FIG. 4 are denoted by the same reference numerals, and the description thereof will be omitted. The embodiment shown in FIG.
, And an input of the PLL synthesizer 33, a first series circuit including a capacitor C1, a switching circuit 41, a variable bandpass filter (BPF) 51 and a capacitor C4, a capacitor C2, a switching circuit 42, a variable bandpass filter ( A second series circuit including a BPF) 52 and a capacitor C5 is connected in parallel with a third series circuit including a capacitor C3, a switching circuit 43, a variable bandpass filter (BPF) 53, and a capacitor C6. Output switching voltage V
L, VH, and U are connected to input terminals of switching circuits 41, 42, and 43 via resistors R1, R2, and R3, and
The output control voltage Vt of the PLL synthesizer 33 is
It is characterized in that it is connected to the control voltage input terminals of the variable BPFs 51, 52, 53 via 4, R5, R6.

Here, the variable BPF 51 has the characteristic that the frequency of the local oscillation frequency can be selected when the VHF low band is selected, and the variable BPF 52 has the characteristic that the local oscillation frequency can be frequency selected when the VHF high band is selected. Further, the variable BPF 53 has such a characteristic that the local oscillation frequency can be selected when the UHF band is selected.

Next, the operation of this embodiment will be described. First, of the three variable BPFs 51, 52, and 53, one desired frequency band (VHF low band, VHF
Variable BPF corresponding to high band and UHF band)
In order to operate only the switching circuit, the switching voltage V for switching the tank circuit output from the PLL synthesizer 33 is used.
L, VH and U are used. This switching voltage V
As shown in FIG. 2, when only VL is at a high level (High) and the other two VHs and U are at a low level (Low), only the switching circuit 41 is turned on. Variable BP corresponding to low band
Only F51 is set to the operation state.

Similarly, as shown in FIG. 2, when only VH is at a high level (High) and the other two VL and U are at a low level (Low), only the switching circuit 42 is turned on. Variable B corresponding to band
Only the PF 52 is set to the operation state. As shown in FIG. 2, only U is at a high level (High) and the other two VLs are at a high level.
When VH is at a low level (Low), only the switching circuit 43 is turned on, so that only the variable BPF 53 corresponding to the UHF band is in the operating state.

The local oscillation frequency control voltage Vt of the PLL synthesizer 33 is supplied to the variable BPFs 51, 52, and 53 via resistors R4, R5, and R6, respectively, to adjust the resonance frequencies of the variable BPFs 51, 52, and 53. Tune to the local oscillation frequency required to select a desired channel. Therefore, for example, when a television broadcast of a VHF low band channel (that is, 1 to 3 channels) is selected, the PLL synthesizer 33 outputs the high-level switching voltage VL and the low-level switching voltages VH and U, respectively. Then, a local oscillation frequency control voltage Vt for outputting a local oscillation frequency necessary for selecting a desired channel is output.

A predetermined local oscillation frequency is output from the VHF oscillator 15 by the local oscillation frequency control voltage Vt, and a television signal of a desired channel of the VHF low band is output from the mixer 14 to a predetermined intermediate frequency signal (IF signal). And is extracted. This I
The F signal is supplied to the video / audio processing system 34 via the buffer amplifier 16 and the IF amplifier 31 and subjected to well-known signal processing to be demodulated into a video signal and an audio signal.

At this time, the switching voltage VL,
By using VH and U, only the variable BPF 51 among the variable BPFs 51 to 53 is brought into the operating state, and the center frequency of the variable BPF 51 passing through the VHF low band is selected using the local oscillation frequency control voltage Vt. It is variably set to a predetermined local oscillation frequency at the station.

For this reason, the oscillator buffer amplifier 32
Local oscillation frequency input through the capacitor C1
Is supplied to the variable BPF 51 via the switching circuit 41, where a predetermined local oscillation frequency at the time of selecting a desired channel of the VHF low band is frequency-selected, and
After the spurious signal component is sufficiently suppressed, the signal is input to the PLL synthesizer 33 via the capacitor C4. Thus, even when spurious signals are generated frequently due to reception of a strong electric field signal from the antennas 11 and 21, spurious signals mixed in the local oscillation frequency can be sufficiently suppressed, thereby preventing the malfunction of the PLL synthesizer 33 beforehand. Can be prevented.

[0022]

Next, an embodiment of the present invention will be described.
FIG. 3 shows a circuit diagram of an embodiment of a main part of the present invention. In the figure, the same components as those of FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. In FIG. 3, diodes 61, 62 and 63 have anodes as capacitors C1 and R1, capacitors C2 and R2, and capacitors C3 and R3.
Of the switching circuit 4
1, 42 and 43.

A series circuit of a capacitor C7 and a varicap diode VD1 connected between a common connection point between the cathode of the diode 61 and the capacitor C1 and the ground, and a coil L1 connected in parallel to the series circuit. Is
A variable BPF 71 corresponding to the variable BPF 51 is configured. Similarly, the capacitors C8 and C9 and the varicap diode V are connected between the common connection point between the cathodes of the diodes 62 and 63 and the capacitors C2 and C3 and ground.
A series circuit of D2 and VD3 and coils L2 and L3 connected in parallel to the series circuit are connected to the variable BPF 52,
Variable BPFs 72 and 73 corresponding to 53 are configured.

Next, the operation of this embodiment will be described. Now, assuming that a desired channel of the VHF low band is selected, only VL of the switching voltages VL, VH and U is output at a high level from the PLL synthesizer 33 as shown in FIG. Out of the diodes 61 to 63, only the diode 61 is biased in the forward direction and turned on.

At this time, the PLL synthesizer 33
Are applied as respective reverse bias voltages to the respective cathodes of the varicap diodes VD1, VD2, and VD3 via resistors R4, R5, and R6, respectively, according to the voltages Vt. Control to the specified capacitance value. Of these, the variable BPF 71 connected to the cathode of the diode 61 turned on
The center frequency of the varicap diode VD1 is variably set to a predetermined local oscillation frequency when a desired channel of the VHF low band is selected by controlling the capacitance of the varicap diode VD1.

For this reason, the oscillator buffer amplifier 32
Local oscillation frequency input through the capacitor C1
And a variable BPF 71 via a diode 61. After a predetermined local oscillation frequency at the time of selecting a desired channel of the VHF low band is selected and a spurious signal component is sufficiently suppressed, a capacitor C4 is supplied.
Is input to the PLL synthesizer 33 via the.

Similarly, when a desired channel of the VHF high band is selected, the PLL synthesizer 33 outputs V out of the switching voltages VL, VH and U as shown in FIG.
Since only H is output at a high level, only the diode 62 of the diodes 61 to 63 in FIG. 3 is forward-biased and turned on. At the same time, the capacitance value of the varicap diode VD2 is variably controlled by the local oscillation frequency control voltage Vt output from the PLL synthesizer 33, so that the pass center frequency of the variable BPF 72 becomes the desired channel selection of the VHF high band. It is variably set to a predetermined local oscillation frequency at the time of station.

When a desired channel is selected in the UHF band, only U of the switching voltages VL, VH and U is output from the PLL synthesizer 33 at a high level as shown in FIG. Diodes 61 to
Of the 63, only the diode 63 is biased in the forward direction and turned on. At the same time, the capacitance value of the varicap diode VD3 is variably controlled by the local oscillation frequency control voltage Vt output from the PLL synthesizer 33, so that the pass center frequency of the variable BPF 73 becomes a desired channel in the UHF band. It is variably set to a predetermined local oscillation frequency at the time.

The present invention is not limited to the above embodiments and examples. For example, the switching circuits 41 to 43 can be provided in principle on the output sides of the variable BPFs 51 to 53.

[0030]

As described above, according to the present invention,
Even if spurious signal components are mixed in the local oscillation frequency input to the frequency synthesizer, a predetermined local frequency corresponding to the channel selected by the above-mentioned variable bandpass filter is used by using the control voltage for controlling the local oscillation frequency which originally exists. By selecting only the oscillation frequency, not only spurious signal components higher than the local oscillation frequency but also unnecessary frequency components lower than the local oscillation frequency are removed, so that the spurious signal components are sufficiently reduced. Can be suppressed
Therefore, even if spurious signals occur frequently due to reception of a signal of a strong electric field of the antenna, malfunction of the frequency synthesizer due to the spurious signals can be prevented.

According to the present invention, in a tuner circuit for receiving a television signal transmitted in a VHF low band, a VHF high band and a UHF band, three variable band filters are provided exclusively for the above three bands. By providing switching means for extracting a local oscillation frequency from only one of the three variable band filters according to the selected frequency band, the output of the other two variable band filters is provided. The influence of noise can be prevented, and the spurious interference characteristics can be further improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a diagram illustrating a logic of an output switching voltage of the PLL synthesizer of FIG. 1;

FIG. 3 is a configuration diagram of an embodiment of a main part of the present invention.

FIG. 4 is a configuration diagram of a conventional example.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 VHF block 2 UHF block 11 VHF antenna 13 VHF tuning circuit 14 VHF mixer 15 VHF oscillator 17 VHF tank circuit 21 UHF antenna 23 UHF tuning circuit 24 UHF mixer 25 UHF oscillator 27 UHF tank amplifier 31 UHF tank amplifier 31 UHF tank amplifier 32 UHF tank amplifier 32 UHF tank amplifier 31 UHF tank amplifier 34 video / audio processing system 41 VHF low band switching circuit 42 VHF high band switching circuit 43 UHF band switching circuit 51, 71 VHF low band variable band filter (B
PF) 52, 72 VHF high band variable bandpass filter (B
PF) 53, 73 Variable bandpass filter for UHF band (BP
F) 61 VHF low band switching diode 62 VHF high band switching diode 63 UHF band switching diode VD1, VD2, VD3 Varicap diode

Claims (4)

[Claims] 1. A high frequency reception signal received via an antenna is mixed with a local oscillation frequency from a local oscillator by a mixer, converted into an intermediate frequency signal of a predetermined intermediate frequency and output, and the output of the local oscillator is output. A tuner circuit for generating and outputting a control voltage for variably controlling an output local oscillation frequency of the local oscillator to a predetermined local oscillation frequency corresponding to a selected channel by a frequency synthesizer to which a local oscillation frequency is input, wherein the frequency synthesizer A variable bandpass filter whose passing center frequency is variably controlled to a predetermined local oscillation frequency corresponding to a selected channel is provided by the control voltage output from the control voltage, and an output local oscillation frequency of the local oscillator is set through the variable bandpass filter. A tuner circuit for inputting to a frequency synthesizer. 2. VHF received via a VHF antenna
A high frequency signal of the band is mixed with a local oscillation frequency from a first local oscillator by a first mixer, converted into a first intermediate frequency signal of a predetermined intermediate frequency, and output, and received via a UHF antenna. The high frequency signal in the UHF band is mixed with a local oscillation frequency from a second local oscillator by a second mixer, converted into a second intermediate frequency signal having a predetermined intermediate frequency, and output. A frequency synthesizer to which an output local oscillation frequency of a second local oscillator is input, for variably controlling output local oscillation frequencies of the first and second local oscillators to a predetermined local oscillation frequency corresponding to a selected channel. The control voltage and V are applied to the tank circuit connected to the first local oscillator.
Generating and outputting first and second tank circuit switching voltages for the HF low band and the VHF high band; and
UHF is connected to the tank circuit connected to the second local oscillator.
In a tuner circuit for generating and outputting a switching voltage for switching a third tank circuit of a band, the pass voltage is variably controlled to a predetermined local oscillation frequency corresponding to a selected channel by the control voltage output from the frequency synthesizer. A first variable bandpass filter for the VHF low band, a second variable bandpass filter for the VHF high band, and a third variable bandpass filter for the UHF band, which are provided in parallel with each other. A tuner circuit, wherein an output local oscillation frequency is input to the frequency synthesizer separately through the first to third variable bandpass filters. 3. A VHF low-band tuning method using the first to third tank circuit switching switching voltages output from the frequency synthesizer, the first to third variable band-pass filters of the first to third variable band filters. The output signal is taken out from only one variable bandpass filter, and the output signal is taken out only from the second variable bandpass filter among the first to third variable bandpass filters when the VHF high band is selected.
3. The tuner circuit according to claim 2, further comprising switching means for extracting an output signal only from said third variable band filter among said first to third variable band filters when selecting a band. . 4. A switching circuit, comprising: a first switching circuit provided before the local oscillation frequency input terminal of the first variable bandpass filter and controlled by a switching voltage for switching the first tank circuit;
A second switching circuit provided before the local oscillation frequency input terminal of the second variable bandpass filter and controlled by the second tank circuit switching switching voltage; and a local oscillation circuit of the third variable bandpass filter. 4. The tuner circuit according to claim 3, further comprising a third switching circuit provided before the frequency input terminal and switching-controlled by the third tank circuit switching switching voltage.