JPH02250524A - High frequency switch circuit - Google Patents

Abstract

PURPOSE:To constitute a high frequency switch circuit without using a capacitor by providing a bias circuit which sets one of two transistors in a conductive state and the other transistor in a nonconductive state after applying the adverse bias voltage between the collector and the emitter of the latter transistor. CONSTITUTION:A constant voltage source 23 is provided together with a bias circuit consisting of resistances 241, 242, 251, 252, and 27. The bias circuit sets a 1st transistor TR 221 in a conductive state and at the same time applies the adverse bias voltage between the collector and the emitter of a 2nd TR 222. Thus a 1st high frequency signal is outputted from an output terminal 11 via the emitter and the collector of the TR 221. On the other hand, a 2nd high frequency signal is not outputted from the terminal 11 owing to a high impedance of the TR 222. As a result, a high frequency switch circuit is obtained with no use of a capacitor.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a high frequency switch circuit that inputs two high frequency signals and outputs one of the signals in a tuner of a television receiver or the like.

``Prior Art'' FIG. 5 is a block diagram showing an example of the configuration of a tuner of a television receiver. In this figure, 1 is an antenna, 21 and 22 are television signals in the VHF band and UHF band (hereinafter referred to as bandpass filters (hereinafter referred to as BPF'), 31 and 3, which pass the TV signal);
．． are high frequency amplifiers that amplify the output signals of I3 P l'' 21 and 2, respectively, and 41 and 4 are BPFs that pass output No. 11 of the high frequency amplifiers 31 and 3, respectively.

In addition, 5 is a frequency conversion I that converts the TV signals of the V HF band and UHF' band into intermediate frequency signals and outputs the signals.
C, and in IC5, 61 and 6. 71 and 7. are local oscillators that output local oscillation signals in the V HF' band and U ) [F band, respectively. are each BPF4+
and 4. The output signal of V I-IF band and IJ
A mixer mixes the signals with local oscillation signals in the HF band and converts them into intermediate frequency signals, and reference numeral 8 denotes an intermediate frequency amplifier that amplifies the intermediate frequency signals.

Further, reference numeral 9 denotes a high frequency switch circuit which inputs local oscillation signals in the VHF band and the UHF band and outputs either one of the signals, and 101 and 10. is an input terminal, and ■■ is an output terminal.

In addition, I2 is an IC for the PLL circuit, which inputs the local oscillation signal output from the high frequency switch circuit 9 and outputs a selection control voltage according to the selected channel to the local oscillator 6.
．． or 6. is applied to the control voltage input terminal of the oscillator to control the frequency of the local oscillation signal.

Next, an example of a specific circuit of the high frequency switch circuit 9 is shown in FIG. In this figure, parts corresponding to those in FIG. 5 are given the same reference numerals, and their explanations will be omitted. 6th
In the figure, 131 and +3. 141 and 14. are transistors forming an emitter follower circuit; is a constant voltage source, 151 and 15t are base resistors, 16. and 16. is the collector resistance.

Also, 17. and 17t are transistors forming a constant current source; +8. and +8. is current control (immediate resistance, 1
9. and 19. is a constant voltage source, 20. and 20, the common terminal Tc is connected to the bases of the transistors 17□ and 17, respectively, and the terminal Ta is connected to the constant voltage source +9. and 19t, and switches 2+ and 21. whose terminals Tb are respectively grounded. is a DC blocking capacitor.

In such a configuration, in order to receive the 'rv signal in the VHF band, switch 20. The common terminal 'II' of the switch 20. is connected to the terminal T, and the switch 20. The common terminal Tc of is connected to the terminal T,. This causes transistor 17. is a constant voltage of 11tl9. The bias is supplied by
Becomes a constant current source, transistor 13. operates as an emitter 7-lower. On the other hand, transistor 17. has its base grounded and is in an off state, and the transistor 13t is also in an off state. Therefore, the local oscillation signal in the V I-IF band input from the input terminal 101 is transmitted to the transistor 13.
．． and the output terminal 1 via the DC blocking capacitor 211.
Output from 1. On the other hand, input terminal 10. The U11F band local oscillation signal input from transistor 13. The signal is blocked at the output terminal If, and is hardly output from the output terminal If.

In addition, to receive the 'I'V signal of the UHI' band,
Switch 20. Connect the common terminal Tc of the terminal T to the switch 20. The common terminal 'rc of is connected to the terminal Tb.

The subsequent operations are the same as those described above, so the explanation will be omitted.

In addition, in the tuner shown in Fig. 5, 'I of the Vl-IF band
' When receiving the V signal, the local oscillator 6. The oscillation of Ut[
When receiving F-band TV signals, local oscillator 6. The oscillations of each are stopped.

[Problem to be Solved by the Invention MJ] By the way, in the conventional tuner described above, in the high frequency switch circuit 9 of the frequency conversion IC 5 (well, it is necessary to form capacitors 21. and 21. on the depth of the IC. , the emitter potentials of transistors 13 and I3. change each time switches 20° and 20. are switched, so these capacitors 21+ and 21.
．． However, there is a problem in that it is difficult to use a transistor that utilizes the junction capacitance of a transistor, and a transistor formed of an MO8 structure must be used.

Therefore, there was a drawback that the IC chip area became large.

By the way, since transistors have junction capacitance, when the transistor is turned off,
It does not turn off completely for band signals. Therefore, transistor 13. and 13°, when one is operating as an emitter follower, the other transistor is connected to the capacitors 211 and 21 . There was a problem in that it had an adverse effect on the operating transistors.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a high-frequency switch circuit that can be constructed without using a capacitor and has high isolation.

"Means for Solving the Problem" In the present invention, first and second high frequency signals are respectively input, and by a switching operation, one of the first and second high frequency signals is output from an output terminal. In a high frequency switch circuit, a first transistor has an emitter input with a first high frequency signal and a collector connected to an output terminal, and a second transistor has an emitter input with a second high frequency signal and a collector connected to an output terminal. Depending on the switching operation, one of the first and second transistors is made conductive, and a reverse bias voltage is applied between the collector and emitter of the other transistor. The device is characterized in that it includes a bias circuit that brings the device into a non-conductive state.

"Operation" According to the present invention, when the first transistor is made conductive by the bias circuit and a reverse bias voltage is applied between the collector and emitter of the second transistor,
The first high frequency signal is output from the output terminal via the emitter and collector of the first transistor. On the other hand, the second high-frequency signal is not output from the output terminal because the second transistor has high impedance.

"Embodiment" Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing the configuration of a high frequency switch circuit according to a first embodiment of the present invention. In this figure, parts corresponding to those in FIG. 6 are given the same reference numerals,
The explanation will be omitted.

In FIG. 1, 221 and 22. The emitters of each input terminal 10. and 10. 23 is a constant voltage source, 241 and 24 . One end of each is a constant voltage source 2
3, and the other end is connected to transistors 221 and 22.3.
a resistor connected to the emitter of 25. and 25. are connected at one end to the constant voltage source 23, and at the other end to the transistor 22. and 22. resistor connected to the base of , 2
6 is the terminal 1pa or the transistor 22. The terminal T is connected to the emitter of the transistor 22. This is a switch connected to the emitter of , and whose common terminal 'rc is grounded via a resistor 27.

In addition, the constant voltage source 23a and the resistor 24 242.25 25
．． and 27 (hereinafter collectively referred to as a bias circuit), the common terminal T e of the switch 26 is connected to the terminal T
When the connection is made, the transistor 221 is turned on,
Transistor 22. from emitter to collector? 1XI
Flow A, and connect the common terminal of switch 26 to terminal II.
When connected to Iゎ, transistor 22. is set in advance to a value that turns on the transistor 221 and causes a current to flow from the emitter to the collector of the transistor 221.

In such a configuration, in order to receive a TV signal in the VHF band, the common terminal Tc of the switch 26 is connected to the terminal 'l'6.
Connect to. At this time, the terminals T1 and 'I゛ in FIG.
Let the potentials at be potentials v1 and V, respectively.
By setting the bias circuit as described above, the relationship between the potential (1) and V becomes as shown in the following equation.

V + < V 2...■ As a result, the constant voltage source 23 is connected to the resistor 24. Current flows through transistor 22. flows from the emitter of transistor 22. will flow out from the emitter of transistor 22. and 22! The operating points of are points U and b in FIG. 2, respectively. Therefore, transistor 22. is turned off and becomes a high impedance to high frequency signals. On the other hand, transistor 22. turns on and becomes a low impedance to high frequency signals. As a result, input terminal 10. A local oscillation signal in the VHF band inputted from the VHF band is outputted from the output terminal 11 via the transistor 221. On the other hand, U input from the input terminal 10
The IIF band local oscillation signal is transmitted through transistor 22. has high impedance to high frequency signals, so output terminal 1
There is almost no output from 1.

In addition, to receive UHF band TV signals, switch 2
The common terminal Tc of 6 is connected to the terminal Tb.

The subsequent operations are the same as those described above, so the explanation will be omitted.

Next, a second embodiment of the invention will be described. Third
This figure is a circuit diagram showing the configuration of a high frequency switch circuit according to a second embodiment of the present invention. In this figure, parts corresponding to those in FIG. 6 are given the same reference numerals, and their explanations will be omitted. In the high frequency switch circuit shown in this figure, capacitors 21 and 21 . In place of the transistor 22. described in FIG. and 22. , resistance 2
5° and 25. Additionally, a constant voltage source 28 is newly provided.

In addition, constant voltage source 143.14! and a voltage EBl of 28,
Eal and Eaa are set in advance so as to satisfy the relational expression shown below.

Ea+=E□...◆...■ E aa> E a+, E am...■ Also, the common terminal Tc of the switch 201 is connected to the terminal T.

and switch 20. Constant voltage sources 19+ and 192 and resistors 16, 116 . ．． The values of 18t and 18 are set in advance.

fct>ICs...-■ In such a configuration, in order to receive the VHF band TV += signal, the switch 20. common terminal Tc of terminal T
6 and switch 20. common terminal Tc of terminal T,
Connect to. At this time, assuming that the potentials at terminals rr1 and T in FIG. 3 are potentials v1 and V, respectively, transistor 13. and 17. are both off, but the transistor! 3. Since a minute current is removed by the constant voltage source 1/L, the potential V and the voltage E8. The relationship is as shown in the following equation.

■, Masu EB!・ ・ ・■ On the other hand, transistors 131 and 17. Since both are in the on state, resistor 15. The voltage drop at transistor 13. From the base-emitter voltage Veg+ of
The relationship between the potential v1 and the voltage E al is as shown in the following equation.

V I<E a+-・・■ Therefore, from 2〇, ■, and ■, the following relationship is obtained.

EBe>Eat, Eaz勺V t>V r'”
``■ As a result of the above, the emitter current of transistor 13. flows into the emitter of transistor 22□ and flows out from the emitter of transistor 22., and the operating points of transistors 22. and 22° are the same as in the first embodiment. , respectively, resulting in points a and b in FIG. As a result, the local oscillation signal in the VHF band input from the input terminal 10 is transmitted to the transistor 13.
, and 22. The signal is then output from output terminal II. On the other hand, input terminal 10. The UHF band local oscillation signal input from transistor 13. is sufficiently attenuated at
There is almost no output from the output terminal 11.

In addition, in order to receive the 'r■ signal in the UHF band, switch 20. The common terminal Tc of the switch 20+ is connected to the terminal T, and the common terminal Tc of the switch 20+ is connected to the terminal T. The subsequent operations are the same as those described above, so the explanation will be omitted.

Next, a third embodiment of the invention will be described. Fourth
This figure is a circuit diagram showing the configuration of a high frequency switch circuit according to a third embodiment of the present invention. In this figure, parts corresponding to those in FIG. 3 are given the same reference numerals, and their explanations will be omitted. In the high frequency switch circuit shown in this figure, transistor 13. and! 39. Constant voltage source 14. and 14° and base resistance 15. and 15. are removed, and input terminals 10I and 10t, one ends of resistors 161 and 16, and the emitters of transistors 221 and 22° are connected at one point, respectively.

Note that the operation is almost the same as that of the second embodiment, so a description thereof will be omitted.

As explained above, VHF band and U I (P band T
Switch 26 when receiving one of the V signals
(In the second and third embodiments, switches 20 and 2
0t), transistor 22. and 22
．． The side that is not received has a high impedance and high isolation, so the received signal will not be adversely affected by the other signal.

"Effects of the Invention" As explained above, according to the present invention, there is an effect that a high frequency switch circuit can be configured without using a capacitor. Therefore, the chip area of Ic can be reduced and the yield of IC can be improved. Additionally, there is an effect of high isolation. Therefore, there is an effect that when one signal is being output, the other signal does not have an adverse effect.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of a high frequency switch circuit according to a first embodiment of the present invention, and FIG.
and 22. Figures 3 and 4 show examples of the characteristics of
The figures are circuit diagrams showing the configurations of high-frequency switch circuits according to second and third embodiments of the present invention, FIG. 5 is a block diagram showing an example of the configuration of a tuner for a television receiver, and FIG. 6 is a conventional high-frequency switch. FIG. 2 is a circuit diagram showing an example of a circuit configuration. 4! , 19+119g, 23, 28...6
I 16,, Emperor 8 I 182, 242
53.27...Resistance, 17. ．． 122,...
...transistor, 20 2...switch. 14,, l Constant voltage source, 1 24, . 2511 72.22. ．． 02.26・

Claims (1)

[Claims] A high frequency switch circuit in which first and second high frequency signals are respectively input and one of the first and second high frequency signals is outputted from an output terminal by a switching operation, wherein the first high frequency signal is input to an emitter. a first transistor to which a signal is input and whose collector is connected to the output terminal; a second transistor to which the emitter receives the second high-frequency signal and whose collector is connected to the output terminal; and the switching operation. A bias that makes one of the first and second transistors conductive and applies a reverse bias voltage between the collector and emitter of the other transistor to make it non-conductive in response to A high frequency switch circuit comprising a circuit.