JP3140398B2 - Tuner circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a tuner circuit incorporated in electronic equipment such as a television receiver, a video tape recorder, and a televideo.

[0002]

2. Description of the Related Art FIG. 4 shows a basic circuit configuration of a television tuner circuit A. That is, the RF signal input from the input terminal (ANTIN) 51 of the antenna is converted into the VHF frequency band and the UH frequency by the low-pass filter (LPF) 52 and the high-pass filter (HPF) 56, respectively.
F frequency band, and each filter 52, 5
6, a band-pass filter (BPF) 5 provided at the subsequent stage
3, 57, high-frequency amplifiers (RFAmp) 54, 58, and band-pass filters (BPF) 55, 59, and mixed with a local oscillation frequency from a local oscillator 61 in a mixing circuit (MIX) 60 to produce an intermediate frequency (IF). Is converted to
Thereafter, the signal passes through an intermediate frequency amplifier (IFAmp) 62 and a band-pass filter (BPF) 63 and passes through an output terminal (IFOmp).
UT) 64 to a demodulation circuit built in a television set (not shown).

FIG. 5 shows a tuner circuit A having a configuration in which an amplifier is added to the tuner circuit A having the above configuration to improve sensitivity.
1 is shown. That is, the input terminal of the antenna (AN
A broadband amplifier 71 is interposed between the TIN 51 and the low-pass filter (LPF) 52 and the high-pass filter (HPF) 56. That is, the input terminal (ANTIN)
The RF signal input from 51 is directly amplified by the broadband amplifier 71.

The tuner circuit A2 shown in FIG. 6 is different from the tuner circuit A1 shown in FIG.
1 and a damping circuit 81 in series with the damping circuit 8
In this configuration, a mechanical switch 82 is attached so as to bypass each of the resistance elements R1 to R3. That is, at the time of strong input (when the received electric field strength is strong), the switch 82 is turned off, and the signal is input to the broadband amplifier 71 after passing through the attenuation circuit 81. The switch 82 is turned on to let the attenuator 81 pass through and input to the broadband amplifier 71 as it is.

[0005]

However, in the tuner circuit A1 shown in FIG. 5, the input terminal (ANTIN)
The RF signal input from 51 is directly used as the broadband amplifier 7.
Because it is amplified by 1, there is no problem at the time of weak input,
At the time of strong input, there is a problem that distortion occurs in the wideband amplifier 71, and cross-modulation and inter-modulation occur.

The tuner circuit A2 shown in FIG. 6 solves the problem of intermodulation and intermodulation due to distortion, which has been a problem in the tuner circuit A1 shown in FIG. That you need to turn it off,
Since the mechanical switch 82 is added, there is a problem that the cost increases accordingly.

[0007] The present invention has been made in order to solve such problems, and its object is to increase the cost without increasing the cost.
An object of the present invention is to provide a tuner circuit that improves sensitivity at a weak input and improves distortion characteristics at a strong input.

[0008]

According to a first aspect of the present invention, there is provided a tuner circuit comprising: a parallel circuit comprising an amplifier and an attenuation circuit connected between an input terminal of an antenna and a tuner. In addition, switching means for switching the amplifier between an operating state and a non-operating state is provided. Thus, for example, when the amplifier is in the operating state at the time of weak input, the amplifier can be operated almost without being affected by the attenuation circuit connected in parallel with the amplifier, so that the sensitivity can be improved. In addition, when the amplifier is not operated at the time of strong input, the amplifier can be operated as an attenuation circuit, so that distortion characteristics can be improved.

In a tuner circuit according to a second aspect of the present invention, the switching means is means for turning on / off the power supply of the amplifier. This eliminates the need to add a mechanical switch as in the related art, thereby suppressing an increase in cost.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 are circuit block diagrams showing one embodiment of the tuner circuit of the present invention.

The tuner circuit A4 shown in FIGS. 1 and 2 is an input stage of the tuner 1 (ie, ANTIN in FIG. 4).
51 and an LPF 52 and an HPF 56) are connected to a parallel circuit composed of the broadband amplifier 2 and the attenuation circuit 3.

That is, the antenna input terminal (ANTIN) 11 is connected to the input terminal of the Amp 21 of the broadband amplifier 2 via the DC blocking capacitor C1.
The output terminal of p21 is connected to the tuner 1 via a DC blocking capacitor C2. The positive power supply terminal is a bypass capacitor C having one end connected to the ground.
3, and a negative power supply terminal is connected to the ground.

The attenuation circuit 3 shown in FIG.
1, R2 and R3 are connected in a T-type, one end of a resistor R1 is connected to the input side of the wideband amplifier 2, one end of the resistor R2 is connected to the output side of the wideband amplifier 2, and one end of the resistor R3 is grounded. It is configured to be connected to FIG.
The resistor R1, R2, and R3 are connected in a π-type, the both ends of the resistor R2 are connected to the input side and the output side of the broadband amplifier 2, respectively, and one end is connected to the input end of the resistor R2. The other end of the connected resistor R1 and the other end of the resistor R3 whose one end is connected to the output terminal of the resistor R2 are connected to the ground. Note that tuner 1
The circuit configuration of this embodiment is exactly the same as that of the basic tuner circuit A shown in FIG.

In such a configuration, at the time of weak input, D
The C power supply is turned on, and the broadband amplifier 2 is operated. In this case, although the amplification gain is slightly reduced by the attenuating circuit 3 connected in parallel, the degree of the reduction is such that the reception sensitivity can be sufficiently improved.

Conversely, at the time of a strong input, the DC power supply is turned off to make the broadband amplifier 2 inactive and operate as the attenuation circuit 3. In this case, since the broadband amplifiers 2 connected in parallel have no amplifying action and the isolation between the input and output is about 30 dB, they can be ignored and can be operated purely as the attenuation circuit 3. At this time, the attenuating circuit 3 connected in parallel may be a T-type or a π-type as shown in FIGS. 1 and 2.
Since feedback occurs at N and oscillation occurs, it is necessary to set an appropriate attenuation. Specifically, the attenuation amount of the attenuation circuit 3 when the antenna side (ANTIN11 side) is viewed from the tuner 1 side is set to be larger than the amplification factor of the wideband amplifier 2 when the tuner 1 side is viewed from the antenna side. There is a need.

FIG. 3 shows the pass characteristics of the tuner circuit A4 according to the present invention when the DC power is turned on and off. Thus, according to the tuner circuit A4 of the present invention, without adding a circuit such as a mechanical switch,
By turning on and off the DC power supply, the broadband amplifier 2 and the attenuator 3 can be substantially switched.
Also, since there is no need to add a circuit such as a mechanical switch, it is possible to improve sensitivity at a weak input and improve distortion characteristics at a strong input without significantly increasing the cost. It is.

[0017]

According to the tuner circuit of the present invention, a parallel circuit comprising an amplifier and an attenuator is connected between an input terminal of an antenna and a tuner, and the amplifier is operated and is not operated. And a switching means for switching between. This makes it possible to operate the amplifier with little effect of the attenuation circuit connected in parallel when the amplifier is in the operating state at the time of weak input, so that the sensitivity can be improved and at the time of strong input. When the amplifier is in a non-operating state, the amplifier can be operated as an attenuation circuit, so that distortion characteristics can be improved.

Further, in the tuner circuit according to the second aspect of the present invention, since the switching means is means for turning on / off the power of the amplifier, it is necessary to add a circuit such as a conventional mechanical switch. Is eliminated, so that an increase in cost can be suppressed accordingly.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram showing one embodiment of a tuner circuit of the present invention.

FIG. 2 is a circuit block diagram showing one embodiment of a tuner circuit of the present invention.

FIG. 3 is a graph showing pass characteristics when the DC power is turned on and off by the tuner circuit of the present invention.

FIG. 4 is a block diagram illustrating a basic circuit configuration of a television tuner circuit.

FIG. 5 is a block diagram showing a configuration in which an amplifier is added to the tuner circuit shown in FIG. 4 to improve sensitivity.

6 is a block diagram showing a configuration in which an attenuating circuit is attached in series with an amplifier in the tuner circuit shown in FIG.

[Explanation of symbols]

 A4 Tuner circuit 1 Tuner 2 Broadband amplifier 3 Attenuation circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04B 1/18 H04B 1/16 H03J 3/02

Claims (2)

(57) [Claims] 1. A parallel circuit comprising an amplifier and an attenuation circuit is connected between an input terminal of an antenna and a tuner, and switching means for switching the amplifier between an operating state and a non-operating state is provided. A tuner circuit. 2. The switching means according to claim 1, further comprising:
2. The tuner circuit according to claim 1, wherein N is turned off.