JPWO2011062032A1 - Oscillator circuit and sensor - Google Patents

Abstract

One end of the SAW device (111) constituting the resonance unit (101) is connected to the ground, and the other end is connected to the base of the transistor (Tr2) of the amplification unit (122). The emitter of the transistor (Tr2) is connected to the base of the transistor (Tr1) of the amplifying unit (121) via the decoupling capacitor (Cd1). The emitter of the transistor (Tr1) is connected to the ground via the resonance capacitor (C2). A resonance capacitor (C1) is connected between the emitter and base of the transistor (Tr1). Thus, by providing the amplification unit (122) including another transistor (Tr2) in the previous stage of the amplification unit (121) including the transistor (Tr1) and the resonance capacitors (C1, C2), the resonance unit (101). As a result, the negative resistance as viewed from the amplifying unit side increases.

Description

  The present invention relates to an oscillation circuit using a SAW device as a resonance part.

  Conventionally, as a general oscillation circuit that oscillates a signal of a predetermined frequency, there is a Colpitts oscillation circuit as shown in Non-Patent Document 1. A general Colpitts oscillation circuit includes a semiconductor amplifying element such as a transistor, one inductor, and two capacitors, as described in non-patent literature.

  By the way, when such an oscillation circuit is used for a biosensor or the like, since the detection object is sensed based on a change in the oscillation frequency, a configuration in which the oscillation frequency changes according to the amount of the detection object attached is necessary. is there. In order to realize this, conventionally, an oscillation circuit using a crystal resonator or a SAW device instead of the above-described inductor has been devised.

“Product Lineup, Oscillator”, [online], Murata Manufacturing website, [searched on November 9, 2009], Internet <URL: http://www.murata.co.jp/products/resonator/basic/ ceralock / principle.html>

  However, when a general Colpitts oscillation circuit using a conventional SAW device is used, the oscillation frequency to be output may become unstable during the change of the oscillation frequency, or the oscillation may stop in some cases. .

  An object of the present invention is to realize an oscillation circuit that continues to oscillate reliably and stably even in an oscillation circuit that changes the oscillation frequency using a SAW device.

  The present invention relates to an oscillation circuit including a resonance unit including a SAW device and a first amplification unit including a first amplification element. In this oscillation circuit, a second amplifying unit including a second amplifying element having a characteristic of increasing the negative resistance is inserted between the SAW device and the amplified signal input terminal of the first amplifying element. It becomes.

In general, the oscillation circuit can be represented by an equivalent circuit as shown in FIG. FIG. X1 is a general equivalent circuit diagram of the oscillation circuit. As shown in FIG. 6, the oscillation circuit includes a resonance unit composed of a series circuit of an inductor (L) and a resistor (R _L ), and an amplification unit composed of a series circuit of _a capacitor (C) and a negative resistance (−R _a ). With. An oscillation circuit is configured by forming a closed circuit by the resonance unit and the amplification unit. Here, in the oscillation circuit to which the present invention is applied, the inductor (L) is a resonance inductor and is composed of the inductance of the SAW device, and the resistance (R _L ) is composed of the resonance resistance of the SAW device. The capacitor (C) is composed of the capacitance of a resonance capacitor provided in the amplification unit, and the negative resistance (−Ra) depends on the amplification factor of the amplification unit including the amplification element. Then, by setting the negative resistance (−Ra) of the amplifying unit to be larger than the resistance (R _L ) of the resonating unit and setting the phase of the resonating unit and the amplifying unit to coincide, The circuit oscillates and outputs a signal at the oscillation frequency.

When the SAW device is used, the resonance resistance (R _L ) may be increased although there is a feature that the frequency change amount can be increased as compared with the crystal resonator. Similarly, the resonator resistance may increase to increase the sensor sensitivity. However, if the second amplifying unit is inserted as in this configuration to increase the negative resistance of the amplifying unit on the equivalent circuit. Stable oscillation can be obtained.

  In the oscillation circuit of the present invention, the first amplifying element and the second amplifying element are grounded emitter transistors. One end of the SAW device is connected to the ground, and the other end of the SAW device is connected to the base of the transistor that serves as the second amplifying element. The emitter of the transistor serving as the second amplifying element is connected to the base of the transistor serving as the first amplifying element. A resonance capacitor is connected to the emitter of the transistor serving as the first amplifying element.

  This configuration shows a specific configuration of the resonance unit and the amplification unit of the oscillation circuit described above. By using a transistor as the amplifying element, an oscillation circuit can be configured with a relatively easy material and a simple configuration. Although a transistor is used as the amplifying element, a FET may naturally be used, and a similar configuration can be realized.

  In the oscillation circuit of the present invention, a capacitor is inserted between the SAW device and the amplified signal input terminal of the second amplifying element.

  In this configuration, the DC bias voltage of the second amplifying element is cut off by the capacitor and is not applied to the SAW device. As a result, the deterioration of the SAW device due to the DC bias can be prevented.

  In the oscillation circuit of the present invention, a resistive element is connected in parallel to the SAW device.

  In this configuration, the resistance element connected in parallel to the SAW device can discharge charges that cause abnormal polarization due to the pyroelectric effect of the SAW device. Thereby, pyroelectric breakdown of the SAW device can be prevented.

  In the oscillation circuit according to the present invention, the second amplifying unit is connected in a plurality of stages.

  In this configuration, the negative resistance can be further increased by connecting the above-described second amplifying units in a plurality of stages. Thereby, more reliable and stable oscillation can be obtained.

  In the oscillation circuit of the present invention, the number of connections of the second amplifying units is determined based on the values of the inductance and negative resistance of the SAW device.

  In this configuration, a setting criterion for connecting a plurality of stages is shown. That is, if the number of stages increases, the negative resistance increases correspondingly, but the stray capacitance increases and the oscillation condition may deteriorate. In this case, in consideration of the relationship between the obtained negative resistance and the generated stray capacitance, it is possible to determine the number of stages as appropriate and to cancel by inserting a matching inductor, microstrip circuit, etc. It can oscillate.

  The sensor of the present invention includes the above-described oscillation circuit and a frequency detection circuit that detects an oscillation frequency of the oscillation circuit.

  In this configuration, a sensor including the above-described oscillation circuit is shown. If an oscillation circuit such as that described above is used, an oscillation signal can be obtained reliably and stably, so that reliable and stable sensing is possible.

  Moreover, the sensor of this invention is provided with the sensing part which makes the surface of a SAW device the sensing surface of a to-be-detected body.

  This configuration shows a more specific configuration of the sensor. Further, by using the surface of the SAW device as described above as a sensing surface, an oscillation signal can be stably obtained even if the frequency changes according to the sensing state of the detected object, and reliable and stable sensing is possible. A sensor can be configured.

  According to the present invention, even in an oscillation circuit using an SAW device whose oscillation frequency changes, an oscillation signal can be continuously generated and output reliably and stably.

1 is a circuit diagram of an oscillation circuit according to a first embodiment. It is the figure which showed the frequency component of the real component and imaginary component of the impedance of the amplifier circuit by this application structure and a conventional structure, ie, the resistance component of an amplifier circuit, and a phase. It is the figure which showed the time characteristic of the output frequency of the oscillation circuit at the time of sensing with this-application structure and the conventional structure. It is a circuit diagram of the oscillation circuit 10A of the second embodiment. It is a circuit diagram of oscillation circuit 10B of a 3rd embodiment. It is a general equivalent circuit diagram of an oscillation circuit.

  An oscillation circuit according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of an oscillation circuit 10 of the present embodiment.

  The oscillation circuit 10 includes a SAW device 111. The SAW device 111 is realized, for example, by forming an IDT electrode and a reflection electrode on a piezoelectric substrate. One end of the SAW device 111 is connected to the ground, and the other end of the SAW device 111 is connected to the base of the transistor Tr2. The SAW device 111 constitutes the resonance unit 101.

  The transistor Tr2 corresponds to the “second amplification element” of the present invention, and the emitter is connected to the ground via the resistor R23. The above-mentioned SAW device 111 is connected to the base of the transistor Tr2, and the drive voltage input terminal 104 is connected via a resistor R21. The drive voltage input terminal 104 is connected to the collector of the transistor Tr2 via a resistor R22.

  The transistor Tr2 and the bias resistors R21, R22, and R23 constitute an amplifying unit 122 (corresponding to the “second amplifying unit” in the present invention). The amplifying unit 122 amplifies and outputs the signal input to the transistor Tr2 at a predetermined amplification factor when a predetermined driving voltage is applied from the driving voltage input terminal 104.

  The emitter of the transistor Tr2 is connected to the base of the transistor Tr1 via the decoupling capacitor Cd1.

  The transistor Tr1 corresponds to the “first amplifying element” of the present invention, and the emitter is connected to the ground via the resistor R14. The emitter of the transistor Tr1 is connected to the ground via the resonance capacitor C2, and is connected to the base of the transistor Tr1 via the resonance capacitor C1. The base of the transistor Tr1 corresponds to the “amplified signal input terminal” of the present invention.

  In addition, a connection point (voltage dividing point) between the resistor R11 and the resistor R12 is connected to the base of the transistor Tr1. In the voltage dividing circuit of the resistors R11 and R12, the resistor R11 side is connected to the drive voltage input terminal 104, and the resistor R12 side is connected to the ground.

  A drive voltage input terminal 104 is connected to the collector of the transistor Tr1 through a resistor R13. The collector of the transistor Tr1 is connected to the output terminal 103 via the output capacitor Co.

  The transistor Tr1, the bias resistors R11, R12, R13, and R14, the resonance capacitors C1 and C2, and the output capacitor Co correspond to the amplification unit 121 (corresponding to the “first amplification unit” of the present application). Make up. The amplifying unit 121 amplifies and outputs the signal input to the transistor Tr1 at a predetermined amplification factor when a predetermined driving voltage is applied from the driving voltage input terminal 104. The amplifier 121 is connected to one end of the SAW device 111 via the ground via the resonance capacitor C2, and also functions as a feedback circuit at the time of oscillation.

  The amplifiers 121 and 122 constitute an amplifier circuit 102 corresponding to the resonance unit 101 in the oscillation circuit 10.

  With this configuration, the Colpitts oscillation circuit 10 having the resonance capacitors C1 and C2 is realized using the SAW device 111 as a resonance inductor in the frequency band in which the SAW device 111 acts as an inductor.

  Further, by providing the amplification unit 122 having a predetermined amplification factor in the preceding stage of the amplification unit 121 having the resonance capacitors C1 and C2, the negative resistance as the amplification circuit 102 increases, and only the conventional amplification unit 121 is provided. Compared with the configuration of FIG. 8, the negative resistance when the amplifier circuit side is viewed from the resonance unit 101 having the SAW device 111 can be increased.

  FIG. 2 is a diagram showing the frequency characteristics of the real component and the imaginary component of the impedance of the amplifier circuit, that is, the resistance component of the amplifier circuit and the phase in the present configuration and the conventional configuration. In FIG. 2, the horizontal axis indicates the frequency, and the vertical axis indicates the resistance value and the phase. In the figure, the thin solid line indicates the imaginary component Im, the thick solid line indicates the real component Re (this application) according to the configuration of the present invention, and the thick broken line indicates the real number component Re (conventional) according to the conventional configuration.

  Here, in order to oscillate, the imaginary component Im, that is, the phase needs to be “0”. Under the phase condition, the absolute value is larger than the resistance value (resonance resistance) of the resonance unit 101 including the SAW device 111. A large negative resistance value must be obtained. Furthermore, if the negative resistance value is large, more stable oscillation is possible.

  As shown in FIG. 2, when the imaginary component Im (phase) is “0”, in the conventional configuration, the resistance value is a negative resistance of “about −6Ω”. On the other hand, in the configuration of the present application, the resistance value is a negative resistance of “about −31Ω”. Here, since the resonance resistance of a SAW device 111 of a type called a 1-port type SAW device capable of shifting over a wide frequency range is generally about 10Ω at present, the resistance value of the resonance unit 101 is considered to be about 10Ω or more.

  Therefore, in the case of the conventional configuration, the absolute value of the negative resistance of the amplifier circuit is smaller than the resistance value of the resonance unit 101. On the other hand, in the case of the configuration of the present application, the absolute value of the negative resistance of the amplifier circuit is significantly larger than the resistance value of the resonance unit 101.

  Here, in order to experimentally stabilize the oscillation, it is known that the absolute value of the negative resistance of the amplifier circuit should be about three times or more the resistance value of the resonance unit. Therefore, if the configuration of the present application is used, such an oscillation condition can be satisfied, and reliable and stable oscillation can be continuously realized.

  FIG. 3 is a diagram showing time characteristics of the output frequency of the oscillation circuit during sensing in the present configuration and the conventional configuration. In FIG. 3, the horizontal axis represents the elapsed time t, and the vertical axis represents the amount of frequency change based on the oscillation frequency before the elapsed time t = 0. The experimental result shows a state in which the object to be detected starts to be sensed by the sensing unit including the SAW device 111 at the timing of time t = 0, and the oscillation frequency changes over time.

  As shown in FIG. 3, in the conventional configuration, the oscillation stops due to the influence of the state change of the SAW device from the timing when the sensing starts, that is, after a lapse of a predetermined time from the start of the change of the oscillation frequency. In addition, although it is difficult to understand the detailed frequency fluctuation in the figure, in the conventional configuration, the frequency is shifted while being varied vertically (high and low). This is considered to be caused by the fact that the absolute value of the negative resistance of the amplifier circuit is low and hardly changes from the resistance value of the resonance part, resulting in unstable oscillation.

  On the other hand, in the configuration of the present invention, oscillation continues stably from the timing when sensing starts, that is, even when the change of the oscillation frequency starts. This is considered to be due to the fact that the negative resistance having an absolute value significantly larger than the resistance value of the resonance unit 101 can be obtained as an amplifier circuit as shown in FIG.

  As described above, by using the configuration of the present embodiment, even if a SAW device having a wide oscillation frequency change range and a relatively large resonance resistance is used for the resonance part, oscillation can be continued reliably and stably.

  Such an oscillation circuit is used for various sensors such as a biosensor. Specifically, for example, the surface of the SAW device can be used as a sensing surface, and can be used as a sensor that detects an object to be detected (liquid material or the like) that contacts the sensing surface.

  Such a sensor includes the above-described oscillation circuit and a frequency detection circuit. The frequency detection circuit is a known circuit, and detects the frequency of the oscillation signal output from the oscillation circuit.

  In such a sensor, if the object to be detected is not attached to the surface of the SAW device, an oscillation signal having an oscillation frequency according to the steady state of the SAW device is output from the oscillation circuit. On the other hand, when the object to be detected adheres to the surface of the SAW device, the resonance condition of the SAW device changes due to the object to be detected, and the oscillation frequency changes as shown in FIG.

  The frequency detection circuit detects the frequency of the output signal from such an oscillation circuit over time. The frequency detection circuit detects the detection target according to the detected frequency. For example, processing such as determining that the detected object exists if the frequency change amount is equal to or greater than a predetermined value, or determining that the detected object exists if the detected frequency reaches a specific frequency is performed.

  Further, by using an oscillation circuit having the above-described configuration for such a sensor, a reliable and stable oscillation signal can be obtained, so that the detection target can be detected reliably and stably.

  Next, an oscillation circuit according to a second embodiment will be described with reference to the drawings. FIG. 4 is a circuit diagram of the oscillation circuit 10A of the present embodiment. The oscillation circuit 10A of the present embodiment is obtained by adding various additional circuit elements to the oscillation circuit 10 of the first embodiment. Hereinafter, only the added circuit elements will be described.

  A capacitor Cv is inserted and connected between the SAW device 111 of the resonance unit 101 and the base of the transistor Tr2. By providing such a capacitor Cv, it is possible to prevent the DC bias voltage of the transistor Tr2 from being applied to the SAW device 111. As a result, the deterioration of the SAW device 111 due to the DC bias voltage can be prevented.

  Further, the resistor Rs is connected in parallel to the SAW device 111. That is, one end of the resistor Rs is connected to the ground, and the other end is connected to a terminal on the connection side of the SAW device 111 with the capacitor Cv. By providing such a resistor Rs, even if an unnecessary charge is generated in the SAW device 111 due to the pyroelectric property of the SAW device 111, the charge can be discharged to the ground via the resistor Rs. Thereby, pyroelectric breakdown of the SAW device 111 can be prevented.

  The resistor R21 connected to the base of the transistor Tr2 of the amplifying unit 122A and the resistor R22 connected to the collector are connected to the ends opposite to the side connected to the transistor Tr2. This connection point is connected to the ground via a decoupling capacitor C20, and is connected to the drive voltage input terminal 104 via a decoupling resistor R32.

  The resistor R11 connected to the base of the transistor Tr1 of the amplifier 121A and the resistor R13 connected to the collector are also connected to the ends on the opposite side to the side connected to the transistor Tr1. This connection point is connected to the ground via a decoupling capacitor C10, and is connected to the drive voltage input terminal 104 via a decoupling resistor R31.

  Furthermore, the drive voltage input terminal 104 is connected to the ground via a decoupling capacitor C30.

  By using these configurations, it is possible to more effectively suppress the oscillation signal from leaking from the amplifying units 121A and 122A to the drive voltage input terminal 104. Thereby, an amplifier circuit having more excellent amplification characteristics can be configured.

  As described above, by using the configuration of the present embodiment, it is possible to realize an oscillation circuit having the operational effects as shown in the first embodiment and further excellent in operating characteristics.

  Next, an oscillation circuit according to a third embodiment will be described with reference to the drawings. FIG. 5 is a circuit diagram of the oscillation circuit 10B of the present embodiment. As illustrated in FIG. 5, the oscillation circuit 10 </ b> B according to the present embodiment is obtained by connecting two amplifying units 122 corresponding to the “second amplifying unit” illustrated in the first embodiment. Therefore, only portions having a circuit configuration different from that of the first embodiment will be described.

  The base of the transistor Tr3 of the amplification unit 222 is connected to the end of the SAW device 111 opposite to the end connected to the ground. The emitter of the transistor Tr3 is connected to the ground via a resistor R33. The base of the transistor Tr3 is connected to the drive voltage input terminal 104 via a resistor R31, and the collector of the transistor Tr3 is connected to the drive voltage input terminal 104 via a resistor R32. Thereby, an amplification unit 222 having the same configuration as that of the subsequent amplification unit 122 is formed.

  The emitter of the transistor Tr3 in the amplifying unit 222 is connected to the base of the transistor Tr2 in the amplifying unit 122 via the decoupling capacitor Cd2.

  With this configuration, the amplifier circuit 202 is connected to the amplifier 122 shown in the first embodiment in the previous stage of the amplifier 121 shown in the first embodiment, and further in the previous stage of the amplifier. 222 is connected. Thereby, the absolute value of the negative resistance as the amplifier circuit 202 can be further increased. As a result, an oscillation circuit that oscillates more reliably and stably can be configured.

  Note that the number of stages of amplifiers to be connected is not limited to two as shown in the present embodiment, and may be three or more. At this time, the number of amplification units to be connected may be set based on the obtained negative resistance value and the increasing floating capacitance. That is, if the number of connection stages is increased, the absolute value of the negative resistance is increased correspondingly, but stray capacitance corresponding to the number of stages is generated. The stray capacitance generated in this way may adversely affect the oscillation. Therefore, it is better to set the number of connection stages to the minimum number of stages at which a negative resistance of about three times or more of the resonance resistance of the SAW device can be obtained. In addition, by using the minimum number of stages as described above, the oscillation circuit can be formed as small as possible, and a sensor including the oscillation circuit can be formed in a small size accordingly.

  If it is necessary to increase the number of connection stages, a stray capacitance can be canceled by inserting a matching inductor, a microstrip line, or the like.

  In the above description, an example in which a transistor is used as an amplifying element is shown, but an FET, an OP amplifier, or the like may be used.

10, 10A, 10B-Oscillation circuit, 101-Resonance unit, 102-Amplification circuit, 121, 122, 121A, 122A, 221-Amplification unit, 103-Output terminal, 104-Drive voltage input terminal, 111-SAW device

Claims (8)

An oscillation circuit including a resonance unit including a SAW device and a first amplification unit including a first amplification element,
A second amplifying unit including a second amplifying element having a characteristic of increasing a negative resistance is inserted between the SAW device and the amplified signal input terminal of the first amplifying element; Oscillator circuit. The first amplifying element and the second amplifying element are grounded emitter type transistors,
One end of the SAW device is connected to ground,
The other end of the SAW device is connected to a base of a transistor serving as the second amplifying element,
The emitter of the transistor serving as the second amplifying element is connected to the base of the transistor serving as the first amplifying element,
The oscillation circuit according to claim 1, wherein a resonance capacitor is connected to an emitter of the transistor serving as the first amplifying element.   The oscillation circuit according to claim 1, wherein a capacitor is inserted between the SAW device and an amplified signal input terminal of the second amplification element.   The oscillation circuit according to claim 1, wherein a resistance element is connected in parallel to the SAW device.   The oscillation circuit according to claim 1, wherein the second amplification unit is connected in a plurality of stages.   The oscillation circuit according to claim 5, wherein the number of connection stages of the second amplification unit is determined based on an inductance of the SAW device and a value of the negative resistance. An oscillation circuit according to any one of claims 1 to 6,
A frequency detection circuit for detecting an oscillation frequency of the oscillation circuit.   The sensor according to claim 7, further comprising a sensing unit that uses a surface of the SAW device as a sensing surface of a detection target.

Images