JPH0227643Y2 - - Google Patents

Description

[Detailed explanation of the invention] (a) Industrial application field This invention electronically switches the antenna coil.
The present invention relates to an antenna input circuit for a multi-band receiver capable of receiving multiple broadcast bands. (b) Prior art An antenna input circuit in which the antenna coil is switched electronically is disclosed in Utility Model Application Publication No. 57-151041, for example.
It is stated in the No. FIG. 1 shows the antenna input circuit, which allows reception of two bands by switching a band changeover switch 1. In that case, to receive a high frequency broadcast band, switch the band switch 1.
Connect to terminal 2. Then, the switching diode 3 and the switching transistor 4 are turned on, and the connection point between the first antenna coil 5 and the second antenna coil 6 is grounded, so that both ends of the second antenna coil 6 are grounded, and the second antenna coil 6 is in operation. I won't. As a result, among the received signals received by the loop antenna 7, the first antenna coil 5, the variable capacitor 8, and the first padding. A signal with a frequency corresponding to the tuning frequency determined by capacitor 9 is applied to switching diode 3 and coupling capacitor 1.
0 to the next stage, and high frequency broadcast bands can be received. On the other hand, to receive a low frequency broadcast band, the band changeover switch 1 is connected to the terminal 11. Then, the switching diode 3 and the switching transistor 4 are turned off, and the switching diode 12 is turned on, so that both the first and second antenna coils 5 and 6 become operational. As a result, the first and second antenna coils 5 and 6, the variable capacitor 8, the first and second padding . A signal with a frequency corresponding to the tuning frequency determined by capacitors 9 and 13 is supplied to the next stage via switching diode 12 and coupling capacitor 14, so that a low frequency broadcast band can be received. However, when the above circuit receives a low frequency broadcast band, when a strong signal is received by the loop antenna 7, a large signal is generated in the first and second antenna coils 5 and 6, and the negative polarity side of the circuit generates a large signal. This has the disadvantage that the switching diode 3 and the switching transistor 4 which are in the off state are turned on and the output signal is distorted. (c) Purpose of the invention The present invention was developed in view of the above points, and aims to apply a reverse bias to the band switching switching element of the antenna input circuit to prevent non-linear distortion at the time of a large signal. It is something. (d) Structure of the invention The antenna input circuit of the multi-band receiver according to the invention includes a series circuit consisting of a plurality of antenna coils connected in series with each other, and is connected to each connection point of the antenna coils to receive signals. Turns on depending on the broadcast band. A switching element that is turned off and a DC cutting capacitor inserted between one end of the series circuit and the ground, an output signal being taken out from the other end of the series circuit, and a connection between the series circuit and the DC cutting capacitor. The switching element is configured to apply a direct current voltage to a point and apply a reverse bias to the switching element via the antenna coil. (E) Example Figure 2 shows an example of the present invention .
18 is a switching transistor whose collector is connected to the connection point of the first and second antenna coils 16 and 17; 19 is a series circuit consisting of first and second antenna coils 16 and 17 connected in series; A band switching terminal connected to the base of the switching transistor 18; 20 a DC cut capacitor inserted between the second antenna coil 17 and the ground; 21 the series circuit 15 and the DC bias capacitor 20; 22 is a coupling capacitor connected in series to the series circuit 15 , and 23 is a high impedance buffer circuit connected to the coupling capacitor 22. . The above-described circuit is configured to be able to receive two bands, for example, a medium wave band (MW) and a long wave band (LW), by controlling the band switching terminal 19. That is, when receiving MW, which is a higher frequency broadcast band, a positive DC voltage is applied to the band switching terminal 19. Then, the switching transistor 18 is turned on and the first
Since the connection point between the antenna coil 16 and the second antenna coil 17 is grounded, both ends of the second antenna coil 17 are grounded in terms of high frequency, and the second antenna coil 17 does not operate. As a result, among the received signals received by the loop antenna 24, the first antenna coil 16,
variable capacitance diode 25, and first padding.
An output signal having a frequency corresponding to the tuning frequency determined by the capacitor 26 is transmitted to the first antenna coil 1.
6, and is supplied to the next stage high frequency amplification circuit (not shown) via the coupling capacitor 22 and buffer circuit 23 , where the MW is received. The capacitance of the variable capacitance diode 25 changes with the tuning voltage applied from the terminal 27, and the DC cut capacitor 28 connected to the variable capacitance diode 25 prevents current from flowing into the series circuit 15 due to the tuning voltage. I have to. In addition, LW, which is the lower frequency broadcast band,
When receiving, without applying a positive DC voltage to the band switching terminal 19,
8 is turned off. Then, both the first and second antenna coils 16 and 17 become operational.
As a result, the first and second antenna coils 16
and 17, a variable capacitance diode 25, first and second trimmers. An output signal having a frequency corresponding to the tuning frequency determined by the capacitors 26 and 29 is generated in the first and second antenna coils 16 and 17, and the output signal is transmitted to the next stage via the coupling capacitor 22 and the buffer circuit 23 . will be supplied and the LW will be received. At this time, a DC voltage (+B) is applied to the collector of the off-state switching transistor 18 from one end point A of the lower impedance of the second antenna coil 17. A DC voltage (+B) is applied via 17. Therefore, even if a large signal is generated in the first and second antenna coils 16 and 17, the negative polarity side of the large signal is connected from the ground to the capacitor 30, the resistor 31, and the base of the switching transistor 18. No current flows into the series circuit 15 through the collectors. In this case, the switching transistor 1
Even if DC voltage (+B) is applied to the collector of 8,
DC cut capacitor 20, coupling capacitor 2
2, and the first by the DC cut capacitor 28.
Only the current of the high-frequency signal flows through the second antenna coils 16 and 17, and the signal is not adversely affected. In addition, in this invention, the connection with the next stage has high input impedance and low output impedance.
Since this is done with a boost-strap source follower circuit using FET 32, it is possible to take out the output signals of both the high frequency broadcast band and the low frequency broadcast band from the output end point B of the high impedance series circuit 15. A high-frequency amplifier circuit connected to the stage can use one with low input impedance. (f) Effects of the invention As described above, according to the invention, since a reverse bias is applied to the switching element for switching the broadcast band of the antenna input circuit, non-linear distortion can be prevented when a large signal is generated. It has the advantage of Furthermore, since a high impedance buffer circuit is used so that output signals of different broadcast bands can be obtained from a common output terminal, there is an advantage that a switching element for extracting the output signals is not required.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an antenna input circuit of a conventional multi-band receiver, and FIG. 2 is a circuit diagram showing an embodiment of the present invention. Explanation of main figure numbers, 15 ...Series circuit, 16,1
7... Antenna coil, 18... Switching element, 20... DC cut capacitor, 23 ...
Batsuhua circuit.

Claims (1)

[Scope of utility model registration request] A series circuit consisting of a plurality of antenna coils connected in series with each other, a band switching terminal to which a switching voltage is applied depending on the broadcast band to be received, and a band switching terminal that is turned on and off according to the switching voltage applied to the band switching terminal. The device also includes a switching element for selectively grounding the connection point between the antenna coils, and a DC cutting capacitor inserted between one end of the series circuit and the ground, so as to connect one end of the series circuit to high frequency. An antenna for a multi-band receiver, characterized in that the switching element is grounded, a DC voltage is applied to a connection point between the series circuit and the DC cut capacitor, and a reverse bias is applied to the switching element via the antenna coil. input circuit.