JP2010226559A - High-frequency switch and receiving circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-frequency switch which reduces generation of a self-mixing signal in a simple configuration, and to provide a receiving circuit employing the high-frequency switch. <P>SOLUTION: A high-frequency switch includes: a field-effect transistor in which the gate terminal is connected to an input terminal side, the drain terminal is connected to an output terminal side and the source is grounded; either a gate bias voltage-regulating means connected to the gate terminal side of the field effect transistor or a drain bias voltage-regulating means connected to the drain terminal side; and a matching circuit provided at least between the gate terminal and the input terminal or between the drain terminal and the output terminal. The high-frequency switch is configured to make reflection characteristics in a conducted state approximately equal to reflection characteristics in a shutoff state. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a high-frequency switch for switching high-frequency signals such as microwaves and millimeter waves, and a receiving circuit using the same.

  In wireless communication devices and radar devices, a high-frequency carrier wave such as a microwave or a millimeter wave is modulated with a signal used for communication or exploration, and this is transmitted as a radio frequency (RF) signal. In a receiving system that receives such an RF signal, the RF signal is down-converted to a low-frequency signal using a mixer by various methods such as a direct conversion receiving method and a superheterodyne method.

  There are various types of mixers, such as a double balance type and a Gilbert cell type, used for down-converting an RF signal. However, these mixers have a problem of self-mixing due to leakage of local signals. In an ideal state where the circuits of each mixer are perfectly balanced, such a problem does not occur, but in reality, it is extremely difficult to perfectly balance the circuits of each mixer. Therefore, a local signal leaks from the RF input terminal of the mixer, and this signal is reflected by a circuit such as an LNA (low noise amplifier circuit) and input again to the mixer. The leaked signal returned to the mixer is multiplied with the local signal to generate a signal called self-mixing.

  The self-mixing signal has a static component and a dynamic component. The static component is a component that does not vary with time and is generated depending on the reflection points at various points in the circuit. In addition, the dynamic component is caused by the time variation of the reflection point, such as when the output impedance of the receiving antenna varies depending on the environment surrounding the antenna, or when the component includes a circuit that operates in a time-sharing manner. It is a component generated due to this.

  As an example, in the receiving circuit 900 shown in FIG. 17, the LO signal 906 generated by the local (LO) signal source 901 leaks from the mixer 902, which reaches the receiving antenna 904 via the amplifier 903 and is reflected there. The reflected wave 907 returns to the mixer 902 again, where it is multiplied with the LO signal 906 to generate a self-mixing signal 908. In this case, when the output impedance of the receiving antenna 904 fluctuates due to the influence of components or the like arranged in the vicinity, the reflection characteristics of the receiving antenna 904 change and the reflected wave 907 fluctuates with time. As a result, the dynamic component is included in the self-mixing signal 908.

  FIG. 18 illustrates a receiving circuit 910 in which a high frequency switch 911 is provided between an amplifier 903 and a mixer 902, and the high frequency switch 911 is time-division controlled to repeat opening and closing. In this case, the reflected wave 912 reflected by the high frequency switch 911 is multiplied by the LO signal 906 by the mixer 902 to generate a self-mixing signal 913. Since the high frequency switch 911 fluctuates in a time division manner, the self-mixing signal 913 includes a dynamic component.

  For static components included in the self-mixing signal, DC cut or HPF (High Pass Filter) when the baseband signal is relatively wide is provided to remove the self-mixing signal including the DC component. It is possible. As an example of a receiving circuit configured to remove a self-mixing signal, in Patent Document 1, a dummy circuit configured in the same manner as a basic circuit including an amplifier 922 and a mixer 923 is provided as shown in FIG. The self-mixing signal generated in each is canceled out.

  On the other hand, since the dynamic component of the self-mixing signal is a signal having a frequency component that changes with time, an HPF having a cutoff characteristic corresponding to this is required. However, since the necessary amount of information may be lost from the baseband signal when the HPF is passed, the HPF cannot be used in such a case. As a prior art for solving such a problem, for example, the one described in Non-Patent Document 1 is known.

  In Non-Patent Document 1, for the purpose of reducing the leak signal of the local signal before reaching the reflection point, as shown in FIG. 20, the front of the LNA 932 serving as the reflection point of the leak signal leaked from the mixer 931 (mixer A buffer amplifier 933 is provided on the (931 side). By adding a buffer amplifier 933 in front of the LNA 932, the leak signal is reduced by the buffer amplifier 933 before reaching the LNA 932 at the reflection point. Further, even with the method of providing the dummy circuit of Patent Document 1, it is possible to cancel the dynamic component depending on the portion to be applied.

  As an example of a circuit provided with a high frequency switch, when a buffer amplifier is provided in front of the high frequency switch as in Non-Patent Document 1 for the receiving circuit 910 shown in FIG. 18 (hereinafter referred to as Conventional Example 1), In the case of providing a dummy circuit (including a high frequency switch) as in Patent Document 1 (hereinafter referred to as Conventional Example 2), how the self-mixing signal is reduced will be described with reference to FIG. FIG. 21 is an explanatory diagram schematically showing that the self-mixing signal is reduced by each means.

  FIG. 21A shows an example of the LO signal generated by the LO signal source 901. Here, it is assumed that the switch 911 is turned on / off at a period T by making the time length of on (closed) equal to the time length of off (open). The waveform of the desired signal that has passed through the switch 911 when it is on is shown in the left diagram of FIG. 21B, and the spectrum of the baseband signal obtained by down-converting this with the LO signal is shown in the right diagram of FIG. Each is shown. Separately from the desired signal, the LO signal leaks from the mixer 902, is reflected by the switch 911, and returns to the mixer 902. The reflected wave waveform is down-converted to the left in FIG. The spectrum of the self-mixing signal is shown on the right side of FIG. The spectrum shown in the right diagrams of FIGS. 21B and 21C is the spectrum of the signal formed by the envelope of the signal waveform shown in the left diagram.

  Since the reflection characteristic of the switch 911 is large when the switch 911 is off and is small when the switch 911 is on, the leak signal from the mixer 902 is off when the switch 911 is off as shown in the left diagram of FIG. When the switch 911 is on, the light is reflected without being reflected. Further, since the switch 911 is repeatedly turned on and off for the same time length, the spectrum of the self-mixing signal generated from the reflected wave reflected by the switch 911 (the right diagram in FIG. 21C) is shown in FIG. It is almost equal to the spectrum of the desired signal shown in the right figure of b). Thus, when the spectrum of the desired signal and the spectrum of the self-mixing signal have similar frequency components, they cannot be distinguished on the frequency axis. Therefore, the self-mixing signal cannot be removed using a filter.

  On the other hand, in the case of the conventional case 1 in which a buffer amplifier is provided between the switch 911 and the mixer 902, the leak signal reaching the switch 911 is reduced by the buffer amplifier, so that the left diagram of FIG. As shown, the power of the reflected wave returning to the mixer 902 is greatly reduced. Also, in the spectrum of the self-mixing signal shown in the right diagram of FIG. 21 (d), each frequency component is greatly reduced.

  In the case of the conventional case 2 in which the dummy circuit including the switch 911 is provided, as shown in the left diagram of FIG. 21 (e), the self-mixing signal generated on the basic circuit side is the opposite phase dummy signal generated on the dummy circuit side. In this way, the power of the self-mixing signal is greatly reduced. Also, in the spectrum of the self-mixing signal shown in the right diagram of FIG. 21 (e), each frequency component is greatly reduced.

JP 2007-208466 A

S. Tanaka et al. "GSM / DCS1800 Dual Band Direct-Conversion Transceiver IC with a DC Offset Calibration System," IEEE, Proceedings of the 27th ESSCIRC pp.492-495 Sep.2001

  However, in the case of the conventional example 1 in which a buffer amplifier is added, although there is an effect in reducing the self-mixing signal, the addition of the buffer amplifier increases the number of parts, and there are problems such as an increase in size and an increase in power consumption. is there. In particular, it is not preferable to add a buffer amplifier from the viewpoints of component cost, buffer performance, power efficiency, and the like in radio equipment and radar devices that use high frequency band signals such as quasi-millimeter waves and millimeter waves.

  Even in the case of the conventional case 2 in which the dummy circuit is provided, as in the case of the conventional case 1, there are problems such as the number of parts, circuit scale, and power consumption. In addition, this method has a problem that the number of components of the dummy circuit increases as the location where the dynamic self-mixing signal is generated is further away from the mixer, which makes it more difficult to apply.

  Accordingly, the present invention has been made to solve the above-described problems, and an object thereof is to provide a high-frequency switch that reduces the generation of a self-mixing signal with a simple configuration and a receiving circuit using the same.

  A first aspect of the high-frequency switch according to the present invention is a high-frequency switch that switches between a conductive state in which a high-frequency signal input from an input terminal is conducted to an output terminal and a cut-off state in which the high-frequency signal is cut off. The reflection characteristic in the state is substantially equal.

  Another aspect of the high-frequency switch according to the present invention is characterized in that a matching circuit for adjusting the reflection characteristic is provided on at least one of the input terminal side and the output terminal side.

  In another aspect of the high frequency switch of the present invention, the anode side is connected to the input terminal, the anode side is connected to the output terminal, and the cathode side is connected to the cathode side of the first PIN diode. A second PIN diode, and one or more third PIN diodes whose anode side is connected between the cathode side of the first PIN diode and the cathode side of the second PIN diode, and whose cathode side is grounded It is characterized by providing.

  Another aspect of the high frequency switch of the present invention is characterized in that the matching circuit is connected to an anode side and a cathode side of at least one of the first PIN diode and the second PIN diode. .

  In another aspect of the high-frequency switch of the present invention, the matching circuit includes a capacitor and a resistor connected in series, and the anode side and the cathode side of the first PIN diode or the second PIN diode are respectively connected to the first and second PIN diodes. The capacitor is connected to the resistor.

  Another aspect of the high frequency switch of the present invention is a field effect transistor having a gate terminal connected to the input terminal side, a drain terminal connected to the output terminal side, and a source grounded, and a gate terminal of the field effect transistor At least one of gate bias voltage adjusting means connected to the drain terminal and drain bias voltage adjusting means connected to the drain terminal side.

  In another aspect of the high frequency switch of the present invention, the matching circuit is connected to at least one of the gate terminal and the input terminal and the drain terminal and the output terminal. And

  In another aspect of the high frequency switch of the present invention, the matching circuit includes an inductor connected in series between the input side and the output side, one end connected in parallel between the inductor and the output side, and the other end grounded And a capacitor.

  According to a first aspect of the receiving circuit of the present invention, there is provided a receiving circuit for inputting a high frequency signal received by a receiving antenna and converting the high frequency signal into a predetermined baseband signal. 8. The high frequency switch according to any one of aspects 8, a mixer having a high frequency signal input terminal connected to an output terminal side of the high frequency switch, and a DC cutoff means connected to a low frequency signal output terminal side of the mixer And a local oscillator connected to the local signal input end side of the mixer, and a control frequency for switching between conduction and interruption of the high-frequency signal by the high-frequency switch is at least one of the frequencies of the baseband signal It is characterized by being consistent with the part.

  According to the present invention, it is possible to provide a high-frequency switch that reduces the generation of self-mixing signals with a simple configuration and a receiving circuit using the same by suppressing a change in reflection characteristics accompanying the opening and closing operation of the high-frequency switch. it can.

It is a block diagram which shows the structure of the high frequency switch which concerns on the 1st Embodiment of this invention. It is a block diagram which shows the structure of the conventional reflection type high frequency switch. It is a Smith chart which shows the reflective characteristic of the high frequency switch of 1st Embodiment, and the conventional high frequency switch. 1 is a block diagram showing a demodulation circuit according to a first embodiment of the present invention. It is explanatory drawing explaining the reduction of the self-mixing signal by the high frequency switch of 1st Embodiment using a signal waveform and a frequency spectrum. It is explanatory drawing explaining the change of the reflective characteristic and self-mixing signal strength accompanying ON / OFF of a switch. It is a block diagram which shows the structure of the receiving circuit of a comparative example. It is explanatory drawing explaining the influence which the change of the reflective characteristic of the high frequency switch of 1st Embodiment has on the intensity | strength of a self-mixing signal. It is a graph which shows the change of the self-mixing signal intensity when the change of the reflective characteristic of the high frequency switch of 1st Embodiment is used as a parameter. It is a block diagram which shows the structure of the high frequency switch of 2nd Embodiment using a field effect transistor. It is a circuit diagram which shows an example of an input matching circuit. It is a graph which shows the reflective characteristic of the high frequency switch using the conventional field effect transistor which is not provided with a matching circuit. It is a graph which shows the reflective characteristic of the high frequency switch using the conventional field effect transistor in which the gain matching at the time of conduction | electrical_connection was performed. It is a graph which shows the reflective characteristic of the high frequency switch of 2nd Embodiment. It is a graph which shows the change of the self-mixing signal strength when the amount of change of the reflection characteristic of the high frequency switch of the second embodiment is used as a parameter. It is a graph which shows the comparison of the self-mixing signal strength of the conventional receiving circuit which performed gain matching at the time of conduction | electrical_connection, and used the buffer amplifier, and the high frequency switch of 2nd Embodiment. It is explanatory drawing explaining generation | occurrence | production of the self-mixing signal in the conventional receiver circuit. It is explanatory drawing explaining generation | occurrence | production of the self-mixing signal in the receiver circuit provided with the high frequency switch. It is explanatory drawing of the conventional receiving circuit which provided the dummy circuit and made it cancel a self-mixing signal. It is explanatory drawing of the conventional receiving circuit which reduced the self-mixing signal with the buffer amplifier. It is explanatory drawing explaining the generation | occurrence | production of a self-mixing signal using a signal waveform and a frequency spectrum.

  A high-frequency switch and a receiving circuit using the same according to a preferred embodiment of the present invention will be described in detail with reference to the drawings. Each component having the same function is denoted by the same reference numeral for simplification of illustration and description. The present invention relates to a high-frequency switch configured so that reflection characteristics are substantially constant regardless of an open / closed state, and a receiving circuit using the high-frequency switch. Such a receiving circuit is suitable for application to a receiving circuit of a radio communication device or a radar device.

  A high-frequency switch according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing the configuration of the high-frequency switch 100 of the present embodiment. The high-frequency switch 100 according to this embodiment includes a PIN diode 103 and 104 connected in series between an input terminal 101 and an output terminal 102, and three PIN diodes connected in parallel between the PIN diodes 103 and 104. 111 to 113, a first matching circuit 120 including a capacitor 121 and a resistor 122, and a second matching circuit 130 including a capacitor 131 and a resistor 132. Note that the number of PIN diodes connected in parallel is not limited to three, as long as the number of PIN diodes is appropriately changed depending on the required high-frequency characteristics.

  When the high-frequency switch 100 is turned on (conductive state), the PIN diodes 103 and 104 are turned on, while all the PIN diodes 111 to 113 are turned off. When the high frequency switch 100 is turned off (shut off state), the PIN diodes 103 and 104 are turned off, while all the PIN diodes 111 to 113 are turned on. In the high frequency switch 100 of this embodiment, the matching circuits 120 and 130 are appropriately adjusted so that the high frequency signal input from the input terminal 101 is not reflected by the high frequency switch 100 regardless of conduction / cutoff. It is configured as an absorption type switch.

  For comparison with the high frequency switch 100 of this embodiment, the configuration of a conventional reflective high frequency switch is shown in FIG. In the conventional high frequency switch 940 shown in the figure, three PIN diodes 945 to 947 are connected in parallel between an input end 941 and an output end 942. When the high-frequency switch 940 is on, the PIN diodes 945 to 947 are turned off. When the high-frequency switch 940 is off, the PIN diodes 945 to 947 are turned on and shorted. In a state where the PIN diodes 945 to 947 are short-circuited, signals input from either the input end 941 side or the output end 942 side are totally reflected. Note that the number of PIN diodes connected in parallel is not limited to three, as long as the number of PIN diodes is appropriately changed depending on the required high-frequency characteristics.

  The reflection characteristics of the high-frequency switch 100 of this embodiment and the conventional high-frequency switch 940 are shown in FIG. FIG. 3A is a Smith chart showing the reflection characteristics of the high-frequency switch 100, and FIG. 3B is a Smith chart showing the reflection characteristics of the high-frequency switch 940. In the reflection characteristics of the high-frequency switch 100 shown in FIG. 3A, the impedance is matched to the characteristic impedance regardless of whether the high-frequency switch 100 is on or off, and both show no reflection. Thus, the high frequency switch 100 of the present embodiment is configured such that the reflection characteristics are constant regardless of on / off.

  A first matching circuit 120 and a second matching circuit 130 are provided in order to keep the reflection characteristic constant regardless of whether the high-frequency switch 100 is on or off. By adjusting the capacitances of the capacitors 121 and 131 and the resistance values of the resistors 122 and 132 constituting the first matching circuit 120 and the second matching circuit 130, the impedance at the time of conduction and the impedance at the time of interruption are as follows: Both can be matched to the characteristic impedance. Note that the first matching circuit 120 and the second matching circuit 130 of the present embodiment are both configured by combining capacitors and resistors, but the present invention is not limited to this.

  On the other hand, in the reflection characteristics of the conventional high frequency switch 940 shown in FIG. 3B, when the high frequency switch 940 is on, the impedance matches the characteristic impedance and no reflection occurs, whereas when the high frequency switch 940 is off, the total reflection occurs. Has been shown to be. That is, in the conventional high-frequency switch 940, the impedance changes between when it is on and when it is off, and the reflected wave reflected by the high-frequency switch 940 is associated with the dynamic frequency corresponding to the control frequency of the high-frequency switch 940. Ingredients will be included.

  As described above, in the high-frequency switch 100 of the present embodiment, the reflection characteristics can be made sufficiently small regardless of on / off. In addition, even when there is reflection, the reflection characteristics can be adjusted to be constant between on and off, and even if a self-mixing signal is generated by a reflected wave reflected by the high-frequency switch 100, the mixing signal is dynamically generated. Ingredients can be excluded.

  A receiving circuit according to an embodiment of the present invention will be described with reference to FIG. FIG. 4 is a block diagram showing a receiving circuit 10 using the high frequency switch 100 of the present embodiment. The receiving circuit 10 includes a mixer 11, a local oscillator 12, an amplifier 13, and a capacitor 14 in addition to the high frequency switch 100, and is connected to the receiving antenna 20.

  The receiving circuit 10 amplifies the received signal received by the receiving antenna 20 by the amplifier 13 and inputs the amplified signal to the mixer 11 via the high frequency switch 100. The received signal input to the mixer 11 is multiplied with the LO signal input from the local oscillator 12 and down-converted to a baseband signal. The capacitor 14 blocks and outputs the DC component of the signal output from the mixer 11. The baseband signal demodulated in this way is processed by a predetermined signal processing unit to extract data.

  The high frequency switch 100 is controlled at a frequency that overlaps at least a part of the frequency band of the baseband signal. Since the high frequency switch 100 of this embodiment is configured so that the reflection characteristics are constant between on and off, even if the LO signal leaks from the mixer 11 and reaches the high frequency switch 100, the high frequency switch 100 The reflected wave does not contain a dynamic component. In particular, in the present embodiment, since the high frequency switch 100 is configured as an absorption type switch, reflected waves reflected by the high frequency switch 100 are sufficiently reduced.

  As described above, since the reflection characteristics of the high-frequency switch 100 that operates in a time-sharing manner are constant, even if the LO signal leaked from the mixer 11 is reflected by the high-frequency switch 100, the reflected wave has almost no dynamic component. Not included. Further, the DC component can be blocked by the capacitor 15 which is a DC blocking means.

  FIG. 5 shows an example of a waveform of a reflected wave reflected by the high-frequency switch 100 and returning to the mixer 11 and a spectrum of a self-mixing signal generated when this reflected wave is multiplied by the LO signal by the mixer 11. FIG. 5A is a diagram schematically showing the waveform of the reflected wave reflected by the high-frequency switch 100, and FIG. 5B is a diagram showing the reflected wave reflected by the high-frequency switch 100 being down-converted by the mixer 11. It is a spectrum of a self-mixing signal. By using the high-frequency switch 100 of the present embodiment in which the reflection characteristics are constant, the dynamic component is reduced, and the DC component is also reduced by the capacitor 16. As a result, as shown in FIG. 5, the leak signal returning to the mixer 11 is sufficiently reduced, and the spectrum of the self-mixing signal hardly contains the same high frequency component as the desired signal.

  In the high-frequency switch 100 of this embodiment, the matching circuits 120 and 130 are adjusted so that | RON / ROFF | is approximately 1 when the reflection amount when the switch is off is ROFF and the reflection amount when the switch is on is RON. ing.

  For the receiving circuit 10 including the high-frequency switch 100 according to the present embodiment and the receiving circuit including the conventional reflective switch, the reflection characteristics and the self-mixing signal intensity change due to the ON / OFF of each switch are schematically illustrated. Is shown in FIG. As a receiving circuit having a conventional switch, a receiving circuit 950 (referred to as Comparative Example 1) having no means for reducing the self-mixing signal as shown in FIG. 7A and a receiving circuit shown in FIG. A receiving circuit 960 having such a buffer amplifier (referred to as Comparative Example 2) is compared with the receiving circuit 10 of the present embodiment.

  In the following, it is assumed that the level at which a local signal leaks from the RF input terminal of the mixer 11 is 0 dBm, and the conversion loss of the mixer 11 is 0 dB as an example. The reflection characteristics of the conventional reflective switch 951 are set to −20 dB when conducting and 0 dB when shutting off. The isolation performance (buffer amount) of the buffer amplifier 961 is 20 dB. Further, the reflection characteristic of the high-frequency switch 100 of the present embodiment is set to −20 dB at both on time and off time.

  FIG. 6A shows changes in the reflection characteristics (upper stage) and the self-mixing signal strength (lower stage) of the switch 951 in the receiving circuit 950 of the first comparative example. Here, 0 dB (complete reflection) is set when the reflection characteristic of the switch 951 is off, and −20 dB when the switch 951 is turned on. As a result, 0 dBm (complete reflection) is obtained when the intensity of the self-mixing signal is off, and It is supposed to change to -20 dBm.

  In the receiving circuit 960 of the comparative example 2, a buffer amplifier 961 is provided in front of the switch 951 having the above-described reflection characteristics. FIG. 6B shows the reflection characteristics of the switch 951 when the switch 951 is turned on / off. (Upper stage) and self-mixing signal intensity (lower stage) are shown. The change in the reflection characteristic of the switch 951 is the same as that shown in FIG. 6A, but the intensity of the self-mixing signal is reduced by −20 dBm compared to that shown in FIG. It changes to −20 dBm when 951 is off, and to −40 dBm when 951 is on.

  On the other hand, in the receiving circuit 10 including the high-frequency switch 100 according to the present embodiment, as shown in the upper part of FIG. 6C, the reflection characteristic is −20 dB even when the high-frequency switch 100 is off, and the on / off is performed. Regardless of, the reflection characteristics are constant. As a result, the intensity of the self-mixing signal is always constant regardless of whether the high-frequency switch 100 is on or off, as shown in the lower part of FIG.

  In the above description, the high-frequency switch 100 of the present embodiment assumes that the reflection characteristics are always constant regardless of on / off, but there may be a case where the change in the reflection characteristics cannot be sufficiently reduced due to temperature fluctuations or manufacturing variations. It is done. Thus, a case where a difference in reflection characteristics occurs between the high frequency switch 100 when it is on and when it is off will be described below. FIG. 8 shows changes in the reflection characteristics and the self-mixing signal intensity when the reflection characteristics of the high-frequency switch 100 are turned on / off. Here, the difference in reflection characteristics that occurs when the high-frequency switch 100 is turned on / off is represented by X dB. FIG. 8 shows that the intensity of the self-mixing signal also changes by X dB as the reflection characteristic changes by X dB by turning on / off.

  FIG. 9 shows the change in the self-mixing signal intensity when the change X in the reflection characteristics due to the on / off of the high-frequency switch 100 is used as a parameter. In FIG. 9, for example, when the reflection characteristic of the high-frequency switch 100 changes by 5 dB (X = 5 dB) between on and off, it can be seen that a self-mixing signal is generated at about 10 mV. However, when one buffer amplifier is provided, a self-mixing signal of 20 mV is generated, so that the self-mixing signal can be further suppressed as compared with the case where one buffer amplifier is provided. As described above, the high-frequency switch 100 according to the present embodiment can obtain the effect of reducing the self-mixing signal as described above even when the reflection characteristics are not completely matched between the on time and the off time.

  The high-frequency switch of the present invention can be provided with a simple configuration using a field effect transistor. In the following, another embodiment of the high-frequency switch of the present invention configured using field effect transistors will be described with reference to FIG. FIG. 10 is a block diagram of a high-frequency switch 200 according to another embodiment configured using the field effect transistor 210. The high-frequency switch 200 operates the field effect transistor 210 as an amplifier and controls the amplification factor of the transistor, thereby enabling switching between signal conduction and interruption.

  The field effect transistor 210 has a gate terminal 211 connected to the input terminal 201 via the input matching circuit 220 and a drain terminal 212 connected to the output terminal 202 via the output matching circuit 230. Since the amplification factor of the transistor is controlled by adjusting at least one of the gate bias voltage and the drain bias voltage, the gate bias voltage adjusting unit 240 connected to the gate terminal 211 of the field effect transistor 210, and the field effect A drain bias voltage adjusting means 250 connected to the drain terminal 212 of the transistor 210 is provided. Only one of the gate bias voltage adjusting unit 240 and the drain bias voltage adjusting unit 250 may be provided.

を満たすように調整されている。 In the high-frequency switch 200 of this embodiment, when the reflection coefficient in the conduction state of the field effect transistor 210 is Γon and the reflection coefficient in the cutoff state is Γoff, at least one of the S parameters of the input matching circuit 220 and the output matching circuit 230 is

It is adjusted to meet.

  An example of the output matching circuit 230 is shown in FIG. The output matching circuit 230 shown in the figure is composed of two elements including an inductor 231 connected in series and a capacitor 232 connected in parallel. Since the reflection coefficients Γon and Γoff of the field effect transistor 210 are determined in advance, by adjusting the inductance of the inductor 231 and the capacitance of the capacitor 232 that are parameters of the matching circuit 230, the expression (1) To satisfy. Although the configuration of the output matching circuit 230 has been described here, the input matching circuit 220 can be configured similarly.

  A comparison between the reflection characteristic of the high-frequency switch 200 of the present embodiment and the reflection characteristic of a high-frequency switch using a conventional field effect transistor will be described below. Here, a case where a high frequency GaAs field effect transistor is used as a field effect transistor and operated as a switch of 20 GHz band will be described as an example. Since the high-frequency switch 200 is arranged between the receiving antenna 20 and the mixer 11 like the high-frequency switch 100 of the first embodiment, the output end side of the field effect transistor 210 that affects the strength of the self-mixing signal. The reflection characteristics will be described.

  FIG. 12 shows the reflection characteristics of a conventional switch (conventional switch 1) using a field effect transistor without the matching circuits 220 and 230, where (a) shows decibels and (b) shows impedances. It is shown by. In any case, the conventional switch 1 has a large off-state reflection characteristic and a large difference from the on-state reflection characteristic. At a frequency of 20 GHz, the reflection characteristic at the on time is approximately −12.9 dB, whereas the reflection characteristic at the off time is approximately −1.20 dB, and a difference of 10 dB or more is observed between the two.

  In addition, FIG. 13 shows the reflection characteristics of a switch (conventional switch 2) adjusted using a conventional field-effect transistor so that the gain during conduction is matched. Also here, (a) shows the reflection characteristic in decibel notation, and (b) shows the reflection characteristic in impedance notation. In the case of the conventional switch 2, the reflection at the time of conduction is adjusted to be sufficiently suppressed and the gain is increased, but the reflection at the time of interruption is as large as that of the conventional switch 1. At a frequency of 20 GHz, the reflection characteristic at the time of conduction is sufficiently small at about −54.8 dB, whereas the reflection characteristic at the time of interruption is about −0.93 dB, which is greatly different from the reflection characteristic at the time of conduction.

  On the other hand, the high frequency switch 200 of this embodiment has a reflection characteristic as shown in FIG. FIG. 14 shows the reflection characteristics of the high-frequency switch 200, where (a) is in decibel notation and (b) is in impedance notation. In the high-frequency switch 200 of this embodiment, the matching circuits 220 and 230 are used to adjust the reflection characteristics during conduction and the reflection characteristics during interruption. As shown in FIG. 14A, the reflection characteristic at a frequency of 20 GHz is approximately −4.1 dB when conducting and approximately −4.1 dB when interrupting, so that the reflection characteristic is not changed by turning on / off the high-frequency switch 200. ing. This prevents the dynamic component from being included in the self-mixing signal.

  Next, the influence of the change in the reflection characteristics of the high-frequency switch 200 of this embodiment on the strength of the self-mixing signal will be described below. Here again, the level at which the local signal leaks from the RF input terminal of the mixer is 0 dBm, the conversion loss of the mixer is 0 dB, and the isolation performance of the buffer amplifier is 20 dB. FIG. 15 shows changes in the intensity of the self-mixing signal when the amount of change in the reflection characteristics of the high-frequency switch 200 is used as a parameter. FIG. 15A shows the intensity of the self-mixing signal when a 20 dB buffer amplifier is arranged in front of the conventional switch 1 as a comparison target, and FIG. 15B shows the conventional switch 2 as a comparison target. The intensity of the self-mixing signal when a 20 dB buffer amplifier is arranged in front of is shown.

  When the high-frequency switch 200 is used, the self-mixing signal intensity increases substantially in proportion to the amount of change in reflection characteristics. In FIG. 15A, the amount of change in the reflection characteristic of the high-frequency switch 200 of this embodiment matches the self-mixing signal intensity when the buffer amplifier of 20 dB is arranged in the conventional switch 1 (approximately). 0.9 dB) or less, it indicates that the high frequency switch 200 can reduce the cell mixing signal as compared with the countermeasures of the prior art. Similarly, in FIG. 15B, the amount of change in the reflection characteristic of the high-frequency switch 200 of the present embodiment is the amount of change in the reflection characteristic that matches the self-mixing signal intensity when a 20 dB buffer amplifier is arranged in the conventional switch 2. If it is (approximately 1.3 dB) or less, it indicates that the high-frequency switch 200 can reduce the self-mixing signal as compared with the measures according to the prior art.

  Therefore, even if the reflection characteristics of the field-effect transistor 210 or the matching circuits 220 and 230 change due to temperature fluctuations or manufacturing variations, if the change amount is about 0.9 dB or 1.3 dB or less, It can be seen that the high-frequency switch 200 of the embodiment can reduce the self-mixing signal. When the receiving circuit is configured using the high frequency switch 200, it is not necessary to provide a buffer amplifier in front of the receiving circuit, and thus a receiving circuit having a simple configuration can be provided.

  The buffer amplifiers arranged in front of the conventional switch 1 and the conventional switch 2 are known to have a forward gain that decreases and a reverse isolation that deteriorates as the frequency increases. It will be reduced. FIG. 16 shows a self-reception when a buffer amplifier is further applied to a conventional receiving circuit to which a field effect transistor switch (conventional switch 2) that performs gain matching during conduction is applied, and the buffer amount of the buffer amplifier is used as a parameter. The intensity of the mixing signal is compared with the intensity of the self-mixing signal in the receiving circuit to which the high frequency switch 200 is applied.

  In FIG. 16, as a comparative example, the self-mixing signal strength in the receiving circuit using the conventional switch 2 when the buffer effect of the buffer amplifier is 15 dB, 20 dB, 25 dB, and 30 dB is shown. Since the buffer effect of the buffer amplifier cannot be obtained at higher frequencies, the buffer effect is reduced from 30 dB to 15 dB as the frequency changes from low to high. Thus, the amount of reflection characteristic change allowed in the high-frequency switch 200 of this embodiment, that is, the amount of reflection characteristic change that can reduce the self-mixing signal when the high-frequency switch 200 is used increases as the frequency increases. Therefore, as the received signal becomes higher in frequency (for example, in the millimeter wave band or quasi-millimeter wave band), the effect of reducing the self-mixing signal by the high frequency switch 200 becomes more significant, and the temperature fluctuation allowed for the field effect transistor, the matching circuit, and the like. , Manufacturing variations and the like can be further increased.

  As described above, in order to reduce the self-mixing signal, in the conventional switch and receiving circuit, for example, it is necessary to add a transistor as a buffer amplifier, a mixer as a dummy circuit, and the like. Since the high-frequency switch and the receiving circuit can be handled only by the matching circuit, the configuration can be simplified and the cost can be reduced. As the element constituting the matching circuit, either a lumped constant component such as a chip component or a distributed constant component such as a stub using a microstrip line can be used.

  Note that the description in the present embodiment shows an example of the high-frequency switch and the receiving circuit according to the present invention, and the present invention is not limited to this. The detailed configuration and detailed operation of the high-frequency switch and the like in this embodiment can be changed as appropriate without departing from the spirit of the present invention.

10 receiving circuit 11 mixer 12 local oscillator 13 amplifier 20 receiving antenna 100, 200 high frequency switch 101, 201 input terminal 102, 202 output terminal 103, 104, 111-113 PIN diode 14, 121, 131, 232 capacitor 120 first matching Circuits 122 and 132 Resistor 130 Second matching circuit 210 Field effect transistor 211 Gate terminal 212 Drain terminal 220 Input matching circuit 230 Output matching circuit 231 Inductor 240 Gate bias voltage adjusting means 250 Drain bias voltage adjusting means

Claims (9)

A high-frequency switch that switches between a conducting state for conducting a high-frequency signal input from an input terminal to an output terminal and a blocking state for shutting off,
The high-frequency switch according to claim 1, wherein the reflection characteristic in the conductive state and the reflection characteristic in the cutoff state are substantially equal. The high-frequency switch according to claim 1, wherein a matching circuit for adjusting the reflection characteristic is provided on at least one of the input terminal side and the output terminal side. A first PIN diode having an anode connected to the input terminal;
A second PIN diode having an anode side connected to the output terminal and a cathode side connected to the cathode side of the first PIN diode;
One or more third PIN diodes having an anode side connected between a cathode side of the first PIN diode and a cathode side of the second PIN diode, and having a cathode side grounded, The high frequency switch according to claim 1 or 2. The high-frequency switch according to claim 3, wherein the matching circuit is connected to an anode side and a cathode side of at least one of the first PIN diode and the second PIN diode. The matching circuit includes a capacitor and a resistor connected in series,
5. The high-frequency switch according to claim 4, wherein an anode side and a cathode side of the first PIN diode or the second PIN diode are connected to the capacitor and the resistor, respectively. A field effect transistor having a gate terminal connected to the input terminal, a drain terminal connected to the output terminal, and a source grounded;
3. The device according to claim 1, further comprising at least one of a gate bias voltage adjusting unit connected to a gate terminal side of the field effect transistor and a drain bias voltage adjusting unit connected to a drain terminal side. High frequency switch. The high-frequency switch according to claim 6, wherein the matching circuit is connected to at least one of the gate terminal and the input terminal and the drain terminal and the output terminal. The matching circuit includes an inductor connected in series between an input side and an output side, and a capacitor having one end connected in parallel between the inductor and the output side and the other end grounded. The high frequency switch according to claim 7. A receiving circuit that inputs a high-frequency signal received by a receiving antenna and converts the high-frequency signal into a predetermined baseband signal,
The high-frequency switch according to any one of claims 1 to 8, wherein the high-frequency signal is input;
A mixer having a high-frequency signal input terminal connected to the output terminal side of the high-frequency switch;
DC blocking means connected to the low frequency signal output end side of the mixer;
A local oscillator connected to the local signal input end side of the mixer, and
A receiving circuit, wherein a control frequency for switching between conduction and interruption of the high-frequency signal by the high-frequency switch coincides with at least a part of the frequency of the baseband signal.

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