JPH0450670Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field This invention relates to the front-end circuit of a receiver, and in particular, to a receiver that is suitable for obtaining the best reception condition depending on the reception condition. Regarding front-end circuits.

(b) Prior art The front end circuit of a conventional receiver is as follows:
For example, the block shown in FIG. 3 has been provided.

In the figure, 11 is an RF amplifier section, 22 is a mixer section, 33 is a local oscillation section, 44 is a relay switching section,
44a is RF amplifier input switching relay, 44b is RF
The amplifier output switching relay 55 is a receiving antenna.

As for the circuit configuration, the receiving antenna 55 is connected to the common terminal of the RF amplifier input switching relay 44a, and one contact of this relay is connected to the RF amplifier 11.
connected to the input side of the

The output side of the RF amplifier 11 is connected to the mixer section 22 via an RF amplifier output switching relay 44b.

The output signal of the local oscillator 33 is added to the mixer section 22, mixed with the output signal from the RF amplifier 11, and an IF signal is output.

The relay switching unit 44 receives the switching command and controls the RF amplifier input switching relay 44a and the RF amplifier output switching relay 44b.

In the operation of the circuit, the signal induced by the receiving antenna 55 is normally connected to the RF amplifier 11 via the RF amplifier input switching relay 44a, amplified by a predetermined amount, and then output from the output side of the RF amplifier 11. It is applied to the mixer section 22 via the RF amplifier output switching relay 44b.

In the mixer section 22, the input signal from the RF amplifier 11 and the tuning signal from the local oscillation section 33 are mixed, and the mixer section 22 outputs an IF signal.

Among the RF signals induced in the receiving antenna 55,
In particular, when a strong electric field signal is input to the mixer section 22 through the RF amplifier 11, the frequency conversion action of the mixer section 22 enters a non-linear operating state, resulting in a signal with distorted amplitude and frequency, which becomes an IF signal. Therefore, even if the desired signal frequency is selected, the desired signal becomes unclear due to the signal distortion generated in the mixer section 22, resulting in a so-called cross-modulation state. Become.

If the reception state is such that cross-modulation occurs, the relay switching unit 44 is controlled to switch the contacts of the RF amplifier input switching relay 44a and the RF amplifier output switching relay 44b from the RF amplifier 11 side. Switch to the side that is directly connected to RF amplifier 11
The signal induced by the receiving antenna 55 is applied directly to the mixer section 22 without passing through the signal.

By configuring the circuit as described above, the signal applied to the mixer section 22 is reduced by the gain of the RF amplifier 11, the cross-modulation characteristics are improved, and the desired frequency can be clearly received.

(c) Problems that the invention aims to solve However, in the front-end circuit of the conventional receiver described above, the RF amplifier section 11 is separated to prevent cross modulation as shown in Figure 3, so the reception The mixer section 22 is directly connected to the antenna 55, which has the drawback that the frequency component of the tuning signal from the local oscillation section 33 is unnecessarily radiated from the receiving antenna 55.

This idea was made in view of the above points, and its purpose is to eliminate the drawbacks of the conventional example, prevent the deterioration of unnecessary radiation without disconnecting the RF amplifier section, and provide a method that is effective against cross modulation. It provides the front end circuitry of the receiver.

(d) Means for solving the problem The front-end circuit of the receiver according to this invention is composed of an RF amplifier section, a mixer section, and a local oscillation section. The mixer section is divided into two mixer sections: a mixer section that prioritizes sensitivity characteristics and a mixer section that prioritizes cross-modulation characteristics, and can be switched and used depending on the purpose.

(E) Effect According to this invention, the mixer section can be divided into a mixer section that prioritizes improvement of cross-modulation characteristics and a mixer section that prioritizes sensitivity characteristics, and can be operated by switching as appropriate, and the RF amplifier section can be separated. Therefore, when the reception condition becomes such that cross-modulation occurs, the circuit is switched to the mixer side that prioritizes the cross-modulation characteristics, thereby preventing the deterioration of the reception condition due to cross-modulation. In addition, since the mixer section is not directly connected to the receiving antenna, unnecessary radiation of the tuning signal frequency from the local oscillator section is not increased.

(F) Embodiment An embodiment of the front-end circuit of a receiver according to this invention will be described based on FIGS. 1 and 2.

Figures 1 and 2 are block diagrams of this invention.

In the figure, 1 is an RF amplifier section, 2 is an A mixer, 3 is a B mixer, 4 is a local oscillation section, 5 is a relay switching section,
5a is a mixer section input switching relay, 5b is a mixer section output switching relay, and 6 is a receiving antenna.

In the circuit configuration, the receiving antenna 6 is connected to the input side of the RF amplifier 1, and the output side of the RF amplifier 1 is connected to the common terminal of the mixer input switching relay 5a.

One contact of the mixer section input switching relay 5a is
It is connected to the input side of an A mixer 2 that prioritizes sensitivity characteristics, and the other contact is connected to the input side of a B mixer 3 that prioritizes cross-modulation characteristics. The output sides of these two A and B mixers 2 and 3 are connected to contacts of a mixer section output switching relay 5b.

Further, the mixer section input/output switching relays 5a and 5b are controlled by a relay switching section 5.

As for circuit operation, the signal induced by the receiving antenna 6 is amplified by a predetermined amount in the RF amplifier section 1, and is normally inputted to the A mixer 2 via the mixer section input switching relay 5a, where it is output to the local oscillator section 4. The output signal of the sum or difference is mixed with the generated tuning signal.
The IF signal is passed through the mixer output switching relay 5b.
Send to IF amplifier section.

If the signal induced by the receiving antenna 6 is a particularly strong electric field signal and the A mixer 2 causes non-linear operation, a distorted signal will be output as an IF signal and the desired signal will be interfered with, resulting in an unclear state. This results in a state where so-called cross-modulation occurs.

When the reception state is such that cross-modulation occurs, it is possible to control the relay switching section 5 to switch the mixer section input/output switching relays 5a and 5b to the B mixer 3 side to improve the cross-modulation characteristics, if necessary.
Moreover, since the RF amplifier section 1 is not separated, it is possible to prevent the tuning signal frequency generated by the local oscillation section 4 from being directly radiated from the receiving antenna 6.

In addition, as shown in FIG. 2, the mixer section input/output switching relays 5a and 5b are switched to transmit the tuning signal from the local oscillation section 4, which is applied to the A mixer 2 and B mixer 3. It is also possible to switch to add it to the selected A mixer 2 or B mixer 3 at the same time as it is selected. Furthermore, mixer section input/output switching relays 5a, 5
(b) Local oscillator output switching relay 5c and relay switching section 5 may be replaced by switching means such as a diode switch.

(G) Effect of the invention According to the front-end circuit of the receiver according to this invention, the mixer section can be divided into a B mixer section with good cross-modulation characteristics and an A mixer section with good sensitivity characteristics. Since it is configured so that it can be switched, it is possible to switch the
This has the effect of improving cross-modulation characteristics without separating the RF amplifier section and worsening unnecessary radiation from the receiving antenna.

Furthermore, it has excellent features such as a simple structure, and can be constructed at low cost, making it easy to implement.

[Brief explanation of drawings]

1 and 2 show an embodiment of the front end circuit of a receiver according to this invention, and FIGS. 1 and 2 are block diagrams. FIG. 3 is a block diagram of a conventional example. Explanation of main symbols, 1...RF amplifier, 2...A
Mixer, 3... B mixer, 4... Local oscillator, 5
...Relay switching section, 5a...Mixer section input switching relay, 5b...Mixer section output switching relay, 5c...
...Local oscillator output switching relay, 6...Receiving antenna.

Claims (1)

[Claim for Utility Model Registration] In a receiver front-end circuit consisting of an RF amplifier section, a mixer section, and a local oscillation section, a mixer section in which the sensitivity of the above mixer section is prioritized;
A receiver front-end circuit characterized in that it is divided into two mixer sections, a mixer section that gives priority to cross-modulation characteristics, and a mixer section that is switched between them depending on the purpose.