JP5079541B2 - Physical quantity sensor - Google Patents

Description

  The present invention relates to a physical quantity sensor in which an output signal is constant regardless of a temperature change even when a resistance element of a current / voltage conversion circuit that converts an output current of a sensor element into a voltage has temperature characteristics.

  Conventionally, a vibration gyro sensor that detects angular velocity as a physical quantity using a vibrator is an indispensable sensor for car navigation systems, robot posture control, camera shake correction, etc. As the market expands, the demand for vibration gyro sensors has also increased rapidly.

  FIG. 12 is a diagram showing the principle of a general angular velocity sensor. In the illustrated example, drive electrodes 2a and 2b for excitation (drive) and detection electrodes 3a and 3b for Coriolis force detection are provided on the surface of a piezoelectric vibrator 1 made of a tuning fork type crystal vibrator. An oscillation circuit 2 is connected to the drive electrodes 2a and 2b, and an alternating drive voltage is supplied from the oscillation circuit 2. A detection circuit 3 is connected to the detection electrodes 3a and 3b.

  An orthogonal coordinate system including the X axis, the Y axis, and the Z axis is set as shown in FIG. When a drive voltage is applied from the oscillation circuit 2 to the drive electrodes 2a and 2b, the piezoelectric vibrator 1 vibrates at a predetermined frequency in the B direction along the X axis. At this time, when an angular velocity ω is applied around the Y axis, a Coriolis force F is generated in the Z axis direction. When the mass of the piezoelectric vibrator 1 is m and the vibration speed of the piezoelectric vibrator 1 is represented by v, the Coriolis force F is equal to 2 mvω.

  That is, the Coriolis force is determined in proportion to the magnitude of the angular velocity ω. Therefore, when the Coriolis force is generated, a current is generated in the detection electrodes 3a and 3b when the piezoelectric vibrator 1 is distorted in the Z-axis direction. Then, by detecting the generated current by the detection circuit 3, the magnitude of the angular velocity ω of the piezoelectric vibrator 1 can be obtained.

  By the way, especially as an application of an angular velocity sensor, since a car navigation system or the like is an in-vehicle device, a required operating temperature range is extremely wide, and generally, about −40 ° C. to + 85 ° C. is required.

  For this reason, there is a demand for a highly accurate gyro sensor that has a wide operating temperature range and is stable with respect to temperature. To meet these demands, a vibration gyro equipped with an operational amplifier that cancels the temperature characteristics of the sensor is required. It is disclosed.

  In addition, the current output from the sensor is often converted into a voltage signal by a current / voltage conversion circuit and then subjected to signal processing by a filter, an amplification circuit, or the like. An oscillation circuit and a detection circuit using the current / voltage conversion circuit are often used. Many have been disclosed (for example, see Patent Document 1).

  Hereinafter, Patent Document 1 as a conventional technique will be described with reference to the drawings. FIG. 13 is a circuit diagram of a conventional vibration gyro, which includes a driving electrode 8, an excitation current output electrode 9, and Coriolis output detection electrodes 10 and 11 on the tuning fork type piezoelectric vibrator 1. The output Xout of the oscillation circuit is connected to the drive electrode 8 to oscillate at a predetermined oscillation frequency.

The excitation current Iosc output from the excitation current output electrode 9 is converted into a voltage signal V11 by the current / voltage conversion circuit 12. By connecting the voltage signal V11 to the amplitude control circuit 1301, the amplitude control circuit 1301 can maintain the drive voltage Xout so that the voltage level of the voltage signal V11 becomes constant even if the characteristics of the tuning fork vibrator 1 change due to temperature or the like. Control the amplitude.

  The Coriolis output detection electrodes 10 and 11 are connected to the current / voltage conversion circuits 21 and 22, and the detection currents Is1 and Is2 are converted into voltage signals Vs1 and Vs2. The voltage signals Vs1 and Vs2 are input to the differential amplifier circuit 23, and after removing common-mode noise, synchronous detection is performed by the reference signal V11 which is an oscillation signal, and the angular velocity is detected.

  Here, the operation of the current / voltage conversion circuits 12, 21, and 22 will be described with reference to FIG. When the output current Is (Iosc, Is1, Is2) of the sensor element 1403 is input to the current / voltage conversion circuit 1401, the input impedance of the operational amplifier 1402 is very large, so that most of the current flows through the feedback resistor Rf. The voltage drop Rf × Is generated here is output from the output V of the current-voltage conversion circuit. Since the input of the operational amplifier 1402 is connected to the inverting input, V = −Rf × Is in consideration of the phase. Therefore, the voltage signal V is proportional to Rf.

  Since the amplitude control circuit 1301 of the oscillation circuit 2 controls the drive voltage Xout so that the level of the output V11 of the current / voltage conversion circuit 12 is constant, V11 is always constant regardless of the temperature. However, the original purpose is to make the excitation current Iosc constant so as to drive the vibration amplitude of the driving leg of the tuning fork vibrator 1 constant. As described above, since the voltage output V of the current / voltage conversion circuit 1401 is Rf × Is, it depends on the stability of the feedback resistor Rf. Therefore, the feedback resistor Rf is usually a metal film resistor having very high accuracy and temperature characteristics.

  Further, since the detection currents Is1 and Is2 output from the Coriolis output detection electrodes 10 and 11 are also converted into voltage signals Vs1 and Vs2 by the current / voltage conversion circuits 21 and 22, the accuracy and temperature characteristics of the feedback resistor Rf are gyro. Since it affects the sensitivity temperature characteristic, it is desirable to use a resistor with good accuracy and temperature characteristic as the feedback resistance Rf of the current / voltage conversion circuits 21 and 22 of the detection circuit 3.

  Therefore, both the oscillation circuit 2 and the detection circuit 3 use the elements having good accuracy and temperature characteristics for the feedback resistors Rf of the current / voltage conversion circuits 12, 21 and 22, so that the vibration amplitude is constant regardless of the temperature. It is possible to realize a gyro sensor with constant characteristics.

Japanese Unexamined Patent Publication No. 2000-292175 (5th page, FIG. 5)

  However, in the feedback resistor Rf of the current / voltage conversion circuits 12, 21, and 22 of the conventional oscillation circuit 2 and the detection circuit 3 of Patent Document 1, the operating temperature range of the vibration gyro sensor is particularly in car navigation systems and the like. Since it is a vehicle-mounted device, the operating temperature range is extremely wide and a stable temperature characteristic is required. Therefore, a metal film resistor having good accuracy and temperature characteristic is often used.

  The metal film resistance is 0.5% accuracy or less and the temperature characteristic is very good with a temperature coefficient of 50ppm / ° C. It is essential to realize a vibration gyro sensor that requires stable temperature characteristics over a wide operating temperature range. Although it is an element, the price is several yen / unit (a resistance element with poor accuracy is about 0.1 yen / unit), which is very expensive and causes an increase in cost, which hinders the cost reduction of the vibration gyro sensor. There is a fear.

Further, the feedback resistance Rf of the current / voltage conversion circuits 21 and 22 of the detection circuit 3 can output a larger voltage as the resistance value is larger, which is effective in improving the S / N of the angular velocity detection sensitivity. For this reason, a high resistance is often used, but the high resistance element has only poor accuracy and temperature characteristics, and there is a problem in that the sensitivity variation of the vibration gyroscope and the temperature characteristics are adversely affected.

  An object of the present invention is to solve the above-mentioned problems and to provide a physical quantity sensor that can obtain a constant output regardless of a change in ambient temperature.

  In order to solve the above problems, the physical quantity sensor of the present invention employs the following configuration.

  A physical quantity sensor according to the present invention includes a sensor element having a drive electrode and a detection electrode, a current-voltage conversion circuit that converts an output current from the drive electrode into a voltage, and an AGC that makes the output voltage from the current-voltage conversion circuit constant. A physical quantity sensor comprising: an oscillation circuit including a circuit; and a detection circuit including an external force applied to the sensor element as a detection current from the detection electrode and converting the detection current into a voltage. The current-voltage conversion circuit of the oscillation circuit and the current-voltage conversion circuit of the detection circuit each include a resistance element, and these resistance elements are resistance elements having the same temperature characteristics. To do.

  According to this configuration, even if the resistance value of the resistance element of the current-voltage conversion circuit in the oscillation circuit and the detection circuit changes depending on the temperature, the rate of change is the same. Therefore, a constant output can be obtained regardless of the ambient temperature change.

  Further, it is desirable that the resistance element in the current-voltage conversion circuit of the oscillation circuit and the resistance element in the current-voltage conversion circuit of the detection circuit have the same resistance value.

When the resistance value of the resistance element of the current-voltage conversion circuit is increased, the output from the physical quantity sensor is increased, so it is conceivable to increase the resistance value of the resistance element. However, if the resistance value of the resistance element is increased, a peak occurs in the frequency characteristics of the current-voltage converter circuit due to the effect of stray capacitance on the input terminal, etc., and the frequency of each current-voltage converter circuit of the oscillation circuit and the detection circuit The characteristics may be different.
However, even if the frequency characteristics differ depending on the resistance value as described above, if the resistance elements having the same resistance value are used as in the present invention, the frequency characteristics of the current-voltage conversion circuit can be made the same. The frequency characteristics of the circuit can be canceled out, and the output value from the physical quantity sensor can be made constant.

  Further, the resistance element in the current-voltage conversion circuit of the oscillation circuit and the resistance element in the current-voltage conversion circuit of the detection circuit may be formed on the same semiconductor substrate, and the resistance elements may be formed with the same pattern width and the same pattern length. desirable.

According to this configuration, even when the resistance value of the current-voltage conversion circuit increases as described above, the pattern areas of the resistance elements of the current-voltage conversion circuit in the oscillation circuit and the detection circuit can be made the same. Since the generated stray capacitance is also increased, the frequency characteristics of the current-voltage conversion circuit of the oscillation circuit and the detection circuit can be made the same.
As a result, even if a peak occurs in the frequency characteristics of the current-voltage conversion circuit due to the influence of stray capacitance, the current-voltage conversion circuit having the same frequency characteristics can be used, so that the frequency characteristics of the current-voltage conversion circuit can be offset. The output value from the physical quantity sensor can be made constant.

The physical quantity sensor is preferably a vibration type gyro sensor in which the sensor element is formed of a crystal resonator. According to this configuration, since the crystal oscillator can obtain a stable oscillation frequency, the vibration frequency of the vibrator is also stable against changes in the surrounding temperature, and a vibration type gyro sensor with better temperature characteristics is realized. be able to.

  Further, by using the physical quantity sensor of the present invention, it is possible to provide a vibration gyro sensor suitable for an in-vehicle navigation system and the like having a wide operating temperature range, high accuracy and excellent reliability, at low cost.

  As described above, according to the present invention, since the temperature characteristics of the resistance elements of the current-voltage conversion circuit in the oscillation circuit and the detection circuit can be canceled, a physical quantity sensor that obtains a constant output regardless of the ambient temperature change can be provided. Can be provided.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a circuit diagram of a vibration type gyro sensor implemented as a physical quantity sensor showing a first embodiment of the present invention. FIG. 2 is a graph showing the temperature characteristics of the feedback resistor Rf of the current-voltage conversion circuit used in the oscillation circuit of the vibration gyro sensor of the present invention.

  FIG. 3 is a graph showing the relationship between the feedback resistance Rf of the current-voltage conversion circuit used in the oscillation circuit of the vibration gyro sensor of the present invention and the excitation current Iosc of the piezoelectric vibrator. FIG. 4 is a graph showing the relationship between the excitation current Iosc and the detection current Is of the piezoelectric vibrator of the vibration type gyro sensor of the present invention.

  FIG. 5 is a graph showing the relationship between the resistance value of the feedback resistor Rf of the current-voltage conversion circuit used in the oscillation circuit of the vibration type gyro sensor of the present invention and the detection current Is of the piezoelectric vibrator. FIG. 6 is a graph showing the relationship between the detected output voltage and the feedback resistor Rf of the current-voltage conversion circuit of the oscillation circuit and the detection circuit of the vibration gyro sensor of the present invention.

  FIG. 7 is a circuit diagram showing a configuration of a current-voltage conversion circuit showing the second embodiment of the present invention. FIG. 8 is a diagram showing frequency characteristics of the current-voltage conversion circuit showing the second embodiment of the present invention. FIG. 9 is a cross-sectional view of an IC showing a structure of a polysilicon resistor formed on a semiconductor substrate showing a third embodiment of the present invention.

  FIG. 10 is a graph showing temperature characteristics of resistance values of polysilicon resistors formed on a semiconductor substrate showing the third embodiment of the present invention. FIG. 11 is a pattern diagram of polysilicon resistors formed on a semiconductor substrate showing a third embodiment of the present invention.

(First embodiment)
First, a circuit diagram of a vibration gyro sensor implemented as a first embodiment of a physical quantity sensor of the present invention will be described with reference to FIG. In FIG. 1, reference numeral 1 denotes a crystal resonator as a piezoelectric resonator that detects a physical quantity of angular velocity. The crystal resonator 1 has a drive electrode 8, an excitation current output electrode 9, and detection electrodes 10 and 11. The excitation output current Iosc output from the excitation current output electrode 9 of the crystal resonator 1 is input to the current-voltage conversion circuit 12 and converted into the voltage signal V11.

  The voltage signal V11 is input to the low-pass filter (LPF) 13 and the AGC circuit 16, and the AGC circuit 16 detects the voltage signal V11 of the current-voltage conversion circuit 12 even if the impedance of the crystal unit 1 changes due to variations in temperature or manufacturing process. The variable gain amplifying circuit 14 is controlled so that the voltage level becomes constant. The low-pass filter (LPF) 13 has the purpose of eliminating the harmonic component because the oscillation phase condition is satisfied.

  The output V14 of the variable gain amplifier circuit 14 is input to the amplifier circuit 15 to amplify the signal so that the oscillation gain condition can be satisfied, and the drive electrode 8 of the crystal resonator 1 is applied as the drive signal Xout. The current-voltage conversion circuit 12, the low-pass filter (LPF) 13, the variable gain amplification circuit 14, the amplification circuit 15, and the AGC circuit 16 constitute the oscillation circuit 2. The output V11 of the current-voltage conversion circuit 12 is also input to the phase circuit 17, performs phase adjustment, and is output as a reference signal V15 for synchronous detection.

  In addition, the angular velocity is detected, and the currents Is1 and Is2 output from the detection electrodes 10 and 11 are converted into voltage signals V20 and V21, which are input to the differential amplifier circuit 23 to remove common-mode noise. The output V22 of the differential amplifier circuit 23 is synchronously detected with reference to the oscillation signal V15. Then, the harmonic component is removed from the synchronously detected signal V23 by a low-pass filter (LPF) 25, and the resultant signal is output as a detection signal Vout.

  Here, the characteristics of the circuit used in the vibration type gyro sensor of the present invention will be described. Feedback resistors as resistance elements of the current-voltage conversion circuits 12, 21, and 22 used in the oscillation circuit 2 and the detection circuit 3 described above. Rf5, 6 and 7 use resistance elements having the same temperature characteristics. In the present embodiment, a current-voltage conversion circuit that uses a resistance element as a feedback resistor will be described. However, the present invention can be applied to a circuit other than a feedback resistor, for example, a circuit that performs current-voltage conversion using an input resistor. Can do.

  By using resistance elements having the same temperature characteristics for the feedback resistors Rf5, 6, and 7 of the current-voltage conversion circuits 12, 21, and 22 of both the oscillation circuit 2 and the detection circuit 3, the feedback resistor Rf5 is used as the output of the vibration type gyro sensor. , 6 and 7, a constant output can be obtained without being affected by the change in resistance value due to the temperature. The reason for this will be described below with reference to FIGS.

  FIG. 2 is a graph showing temperature characteristics of the feedback resistors Rf5, 6, and 7 of the current-voltage conversion circuits 12, 21, and 22 in the oscillation circuit 2 and the detection circuit 3 of the vibration type gyro sensor used in the first embodiment. The resistance element used in the first embodiment has a positive temperature characteristic in which the resistance value linearly changes with temperature. FIG. 3 shows the relationship between the feedback resistor 5 of the current-voltage conversion circuit 12 in the oscillation circuit 2 and the excitation current Iosc output from the crystal resonator 1.

As described above, the oscillation circuit 2 is configured so that the voltage output V11 of the current-voltage conversion circuit 12 is constant even when the impedance of the crystal unit 1 varies due to temperature change, manufacturing process, or the like due to the operation of the AGC circuit 16. Operate. The voltage output V11 of the current-voltage conversion circuit 12 is from FIG.
V11 = −Iosc × Rf5 ------------------ (1)
Because V11 is constant
Iosc = V11 (constant) / Rf5 --------- (2)
From the above formulas (1) and (2), as shown in FIG. 3, Iosc has an inversely proportional relationship to Rf5.

  Next, in FIG. 4, the relationship between the excitation current Iosc of the crystal unit 1 and the detected output current Is is shown. The excitation current Iosc and the vibration amplitude of the crystal resonator 1 are in a proportional relationship. The greater the excitation current Iosc is oscillated, the greater the vibration amplitude of the crystal resonator 1 is. Here, as the vibration amplitude increases, the detection sensitivity of the Coriolis force generated at the angular velocity increases, and the detection output currents Is1 and Is2 increase. Therefore, the excitation current Iosc and the detection output currents Is1 and Is2 are in a proportional relationship, and a graph as shown in FIG. 4 is obtained.

The following relational expression is established between the excitation current Iosc and the detection output currents Is1 and Is2 using a certain proportional coefficient K. The proportional coefficient K is a coefficient independent of temperature, which is determined by the vibration amplitude of the vibrator and the characteristics of the device.
K x Iosc = Is1, Is2 ------------------ (3)
A sensor with a high S / N can be realized by setting the vibration amplitude to be large, but the vibration amplitude cannot be increased so much in consideration of linear detection with respect to the bending or angular velocity of the vibrator.

FIG. 5 is a graph showing the relationship between the resistance value of the feedback resistor Rf5 of the current-voltage conversion circuit 12 in the oscillation circuit 2 and the detection output currents Is1 and Is2 of the crystal unit 1. Substituting the above equation (2) into equation (3)
Is1, Is2 = K × V11 (constant) / Rf5 ------- (4)
As described above, since V11 and the proportional coefficient K are constant, the detected output currents Is1 and Is2 are in an inversely proportional relationship with the feedback resistor Rf5 and affect the change in the resistance value of the feedback resistor Rf5.

  In FIG. 6, the detected output currents Is1 and Is2 are converted into voltage signals V20 and V21 by current-voltage conversion circuits 21 and 22, common-mode noise is removed by a differential amplifier circuit 23, and then detected by a synchronous detection circuit 24 and then a low-pass filter (LPF). ) The relationship between the detection output Vout from which harmonics have been removed at 25 and the resistance values of the feedback resistors Rf5, 6, and 7 of the current-voltage conversion circuits 12, 21, and 22 in the oscillation circuit 2 and the detection circuit 3 is shown.

The voltage outputs V20 and V21 of the current-voltage conversion circuits 21 and 22 of the detection circuit 3 are
V20 = -Rf6 × Is1 -------------------- (5)
V21 = -Rf7 × Is2 -------------------- (6)
Substituting Equation (4) into Equation (5) and Equation (6) above gives the following.
V20 = −K × V11 (constant) × (Rf6 / Rf5) ---- (7)
V21 = −K × V11 (constant) × (Rf7 / Rf5) ---- (8)

  Therefore, when the detected output currents Is1 and Is2 are converted into voltage signals V20 and V21 by the current-voltage conversion circuits 21 and 22, the temperature characteristics of Rf6 and Rf7 are effective, and the feedback resistance Rf5 of the current-voltage conversion circuit 12 of the oscillation circuit 2 The temperature characteristics of the feedback resistors Rf6 and Rf7 of the current-voltage conversion circuits 21 and 22 of the detection circuit 3 are canceled out.

  That is, the AGC circuit 16 of the oscillation circuit 2 operates normally, the level of the voltage output V11 of the current-voltage conversion circuit 12 is constant, the feedback resistor Rf5 of the current-voltage conversion circuit 12 of the oscillation circuit 2 and the feedback of the detection circuit 3 If the temperature characteristics of the resistors Rf6 and Rf7 are the same, (Rf6 / Rf5) and (Rf7 / Rf5) are constant from the above equations (7) and (8), and the resistance value change due to the temperature change can be canceled out. I understand.

  For example, when the feedback resistors Rf5, Rf6, and Rf7 have the same temperature characteristics, the rate of change of the resistance values of Rf5, Rf6, and Rf7 is also the same, so that (Rf6 / Rf5), (Rf7 / Rf5) becomes constant. As a result, the voltage outputs V20 and V21 of the current-voltage conversion circuits 21 and 22 of the detection circuit 3 become constant without being affected by ambient temperature changes.

  A differential amplifier circuit 23, a synchronous detection circuit 24, and a low-pass filter (LPF) 25 are provided between the output from the detection circuit 3 and the outputs of the current-voltage conversion circuits 21 and 22, but the temperature characteristics such as gain are improved. It is easy to make it constant, and as a result, the output Vout of the detection circuit 3 can be made constant without being affected by ambient temperature changes.

In addition, the temperature characteristics of the feedback resistors Rf5, 6, and 7 were also those in which the temperature characteristics of the resistance element used in the first embodiment changed linearly with respect to the temperature as shown in FIG. Even if the element has higher-order characteristics than the next, if the elements have the same temperature characteristics, the temperature characteristics of the feedback resistors Rf5, 6 and 7 are offset in the detection output Vout, and the ambient temperature change is affected. It is clear that it can be kept constant without being affected.

  Therefore, even if a resistance element having a poor temperature characteristic is used for the feedback resistors Rf5, 6, and 7 of the current-voltage conversion circuits 12, 21, and 22 of the oscillation circuit 2 and the detection circuit 3, it is constant even if the ambient temperature changes. A vibration type gyro sensor that can obtain an output can be realized, and a vibration type gyro sensor that is low in cost can be provided.

  Although the sensor element used in the vibration type gyro sensor of the first embodiment has been described using a crystal resonator, the sensor element may be a piezoelectric element other than the crystal resonator. For example, it is clear that the effect of the present invention can be exhibited even with a ceramic type vibrator such as PZT, and a vibration type gyro sensor that obtains a constant output even when the ambient temperature changes can be realized.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 7 shows a current-voltage conversion circuit 71 that converts the current I output from the excitation current output electrode 9 and the detection electrodes 10 and 11 of the crystal resonator 1 into a current voltage. Since the current I output from the crystal unit 1 has a very large input impedance of the operational amplifier 72, most of the current flows through the feedback resistor Rf74.

  The voltage drop Rf × I generated here is output from the output V of the current-voltage conversion circuit 71. Since the input of the operational amplifier 72 is connected to the inverting input, V = −Rf × I in consideration of the phase. Therefore, the voltage signal V is proportional to Rf. Here, at the input of the current-voltage conversion circuit 71, there exists a stray capacitance 73 parasitic to the signal wiring, the input protection circuit of the operational amplifier 72, etc., and a low-pass filter is formed with the feedback resistor Rf 74, and the current-voltage conversion circuit 71. In some cases, the frequency characteristics of the above are deteriorated.

The cutoff frequency fc at which the influence of the low-pass filter occurs is
fc = 1 / (2π × stray capacitance C × feedback resistance Rf) ----- (9)
Determined by. When current-voltage conversion is performed on the currents Is1 and Is2 output from the detection electrodes 10 and 11, the larger the resistance value of the feedback resistor Rf74, the larger the output V, and as a result, the S / N ratio can be increased. The resistance value of the resistor Rf74 is often increased.

  From the above equation (9), when the resistance value of the feedback resistor Rf74 is small, there is no problem because the value of fc is higher than the vibration frequency of the crystal resonator 1, but when the resistance value of the feedback resistor Rf74 is large, In some cases, the cutoff frequency fc is not negligible with respect to the vibration frequency of the crystal resonator 1.

  FIG. 8 is a diagram showing the frequency characteristics of the current-voltage conversion circuit 71, where the horizontal axis represents frequency (Hz) and the vertical axis represents gain (dB). When the resistance value of the feedback resistor Rf74 of the current-voltage conversion circuit 71 is small (a), the gain is flat and 0 dB up to the limit of the frequency characteristic of the operational amplifier 72. However, when the resistance value of the feedback resistor Rf74 of the current-voltage conversion circuit 71 is large (b), the cutoff frequency fc of the low-pass filter formed by the stray capacitance 73 is reduced from the above equation (9), and the operational amplifier 72 A peak occurs in the frequency characteristic of and does not become flat.

Therefore, the excitation output current Iosc output from the excitation current output electrode 9 of the crystal resonator 1 shown in FIG. 1 is output from the feedback resistor 5 of the current-voltage conversion circuit 12 that converts current-voltage and the detection electrodes 10 and 11. When the resistance values of the feedback resistors 6 and 7 of the current-voltage conversion circuits 21 and 22 for converting the currents Is1 and Is2 into current-voltage are large and different, the resistance of the oscillation circuit 2 is affected by the stray capacitance 73 attached to the input terminal. The frequency characteristics of the current-voltage conversion circuit 12 and the current-voltage conversion circuits 21 and 22 of the detection circuit 3 may be different.

  As described above, when the frequency characteristics of the current-voltage conversion circuit 12 and the current-voltage conversion circuits 21 and 22 are different, even if the temperature characteristics of the feedback resistors 5, 6, and 7 are the same, as a result, the vibration type gyro sensor It becomes difficult to keep the output of the constant.

  Next, an example of the second embodiment according to the present invention will be described. The resistance values of the feedback resistors 6 and 7 of the current-voltage conversion circuits 21 and 22 in the detection circuit 3 are about 5 MΩ, and the stray capacitance 73 parasitic to the signal wiring attached to the input terminal, the input protection circuit of the operational amplifier 72, and the like is as follows. About 2 pF. In this case, fc is about 15 kHz from equation (9). Therefore, a peak occurs in the vicinity of 15 kHz for the frequency characteristics of the current-voltage conversion circuits 21 and 22 in the detection circuit 3.

  Here, since the vibration frequency of the crystal unit 1 is about 20 to 50 kHz, the output of the current-voltage conversion circuits 21 and 22 in the detection circuit 3 is adversely affected. On the other hand, since the resistance value of the feedback resistor 5 of the current-voltage conversion circuit 12 in the oscillation circuit 2 is about 100 kΩ and the stray capacitance 73 is the same 2 pF, fc is about 800 kHz from the equation (9).

  Accordingly, the peak frequency generated in the frequency characteristics of the current-voltage conversion circuit 12 in the oscillation circuit 2 and the current-voltage conversion circuits 21 and 22 in the detection circuit 3 (the current-voltage conversion circuit 12 of the oscillation circuit 2 is 15 kHz, the current of the detection circuit 3 is Since the voltage conversion circuits 21 and 22 are different from each other at 800 kHz, it becomes difficult to cancel the deterioration of the frequency characteristics of the current-voltage conversion circuit 12 and the current-voltage conversion circuits 21 and 22.

  In order to solve the above problem, the temperature characteristics of the feedback resistors 5, 6, and 7 of the current-voltage conversion circuits 12, 21, and 22 are made the same, and the resistance value is also made the same, so that the stray capacitance attached to the input terminal 73, even if a peak occurs in the frequency characteristics, the frequency characteristics of the current-voltage conversion circuits 12, 21, and 22 can be made the same. As a result, the deterioration of the frequency characteristics of the current-voltage conversion circuits 12, 21, 22 can be offset, and a constant output can be obtained.

(Third embodiment)
Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 9 shows an oscillation circuit 2 used in a vibration type gyro sensor implemented as a physical quantity sensor of the present invention, and feedback resistors Rf5, 6, and 7 of current-voltage conversion circuits 12, 21, and 22 of a detection circuit 3 formed on a semiconductor substrate. It is sectional drawing.

  A field oxide film 92 is formed on a silicon substrate 91, a polysilicon element 93 is formed as a feedback resistor Rf5 on the field oxide film 92, a polysilicon element 94 is formed as a feedback resistor Rf6, and a polysilicon element is formed as a feedback resistor Rf7. 95 is formed.

  FIG. 10 shows an example of temperature characteristics of the polysilicon resistance element shown in FIG. In the case of an in-vehicle device such as a car navigation sensor, the required operating temperature range is generally required to be about −40 ° C. to + 85 ° C., and the resistance value changes by about 5%. The car navigation system may be required to have a performance of 1% or less. If the characteristics of the polysilicon resistance element are used as they are, the requirement cannot be satisfied.

Here, by applying the third embodiment of the present invention, it becomes possible to satisfy the specification of the temperature characteristic of the output. The polysilicon resistance element formed on the semiconductor substrate has a very high relative accuracy, and it is easy to make temperature characteristics uniform. Therefore, in the above-described formulas (7) and (8), the temperature characteristics of the feedback resistors Rf5 and Rf6 and Rf5 and Rf7 match, so that the temperature characteristics of the polysilicon resistance element can be offset. It is possible to realize a vibration type gyro sensor that can keep the output constant without being affected by ambient temperature changes.

  Here, in practice, it is difficult to perfectly match the temperature characteristics of the resistance elements, and some variation occurs. However, the temperature characteristic error of a plurality of polysilicon resistance elements formed on the same semiconductor substrate is 0.1% or less, and even if the temperature characteristics of the resistance elements cannot be completely canceled, the vibration type gyro sensor Since the temperature characteristic of the output is a difference between the temperature characteristics of the respective resistance elements, as a result, the temperature characteristic of the output of the vibration type gyro sensor becomes 0.1% or less. As a result, the temperature characteristic of 1% or less required for a car navigation system or the like can be sufficiently satisfied.

  By the way, when the feedback resistor Rf 74 of the current-voltage conversion circuit 71, for example, the polysilicon resistors 93, 94, 95 is formed on the silicon substrate 91, a stray capacitance 96 is generated between the silicon substrate 91. When the resistance value of the feedback resistor of the current-voltage conversion circuit is large, as described above, the cutoff frequency fc of the low-pass filter formed by the stray capacitance 96 is lowered, and a peak occurs in the frequency characteristics.

  As described above, even when the polysilicon resistor is formed on the silicon substrate, the frequency characteristic may be deteriorated if the resistance value of the feedback resistor of the current-voltage conversion circuit is large. This problem can be solved by making the pattern widths and pattern lengths of the polysilicon resistors 93, 94, and 95 the same. That is, when the pattern width and the pattern length are the same, the resistance value becomes the same, and at the same time, the area of the pattern of the polysilicon resistors 93, 94, and 95 becomes the same. This is because 96 can be the same.

  Therefore, the characteristics of the low-pass filter formed by the polysilicon resistors 93, 94, and 95 and the stray capacitance 96 are also the same, and the resistance values of the polysilicon resistors 93, 94, and 95 are increased so that the current-voltage conversion circuit 71 Even if a peak occurs in the frequency characteristics, the respective frequency characteristics are the same. Therefore, it is possible to cancel the deterioration of the frequency characteristics and to realize a vibration type gyro sensor that can keep the output constant.

  FIG. 11 shows an example of a pattern for improving relative accuracy when forming a polysilicon resistor on a semiconductor substrate. As shown in FIG. 11, the feedback resistor Rf5 of the current-voltage conversion circuit 12 of the oscillation circuit 2 is used as the polysilicon resistor 93, and the feedback resistors Rf6 and Rf of the current-voltage conversion circuits 21 and 22 of the detection circuit 3 are used as the polysilicon resistor 94. , 95 are always arranged next to each other, so that variations in ion implantation can be minimized and the relative accuracy of the polysilicon resistors 93, 94, 95 can be maximized.

  Further, by disposing dummy polysilicon resistors on both sides like the polysilicon resistor 1101 in FIG. 11, an error in resistance value due to etching variation can be reduced. As a result, it is possible to maximize the effects of the present invention.

  Note that the polysilicon resistors 93, 94, and 95 shown in the third embodiment of the present invention do not necessarily have the temperature characteristics shown in FIG. Since the accuracy is good, the temperature characteristics of the feedback resistance Rf5 of the current-voltage conversion circuit 12 of the oscillation circuit 2 and the feedback resistances Rf6 and Rf7 of the current-voltage conversion circuits 21 and 22 of the detection circuit 3 are canceled out and affect the ambient temperature change. It is possible to realize a vibration type gyro sensor that can keep the output constant without receiving it.

  In the present embodiment, the polysilicon resistor has been described as an example. However, any resistor element formed on the semiconductor substrate may be used, and the effect of the present invention can be realized by a diffused resistor, a well resistor, or the like.

  Further, in order to reduce the area of the polysilicon resistors 93, 94, 95, sheet resistance (Ω / □: resistance value per unit area) is used as the feedback resistors Rf6, 7 of the current-voltage conversion circuits 21, 22 of the detection circuit 3. Even if it is formed with a large polysilicon resistor, if the feedback resistor Rf5 of the current-voltage conversion circuit 12 of the oscillation circuit 2 is also composed of the same sheet resistance element, the temperature characteristics of the polysilicon resistor can be offset, so the area of the IC can be reduced. A vibration type gyro sensor that can be made small and has a constant output voltage Vout even when the ambient temperature changes can be realized at low cost.

It is a block diagram of the vibration type gyro sensor implemented as a physical quantity sensor which shows the 1st Embodiment of this invention. It is a graph which shows the temperature characteristic of the feedback resistance Rf of the current-voltage conversion circuit used for the oscillation circuit of the vibration type gyro sensor of this invention. It is a graph which shows the relationship between the feedback resistance Rf of the current-voltage conversion circuit used for the oscillation circuit of the vibration type gyro sensor of this invention, and the excitation current Iosc of a piezoelectric vibrator. It is a graph which shows the relationship between the excitation current Iosc of the crystal oscillator of the vibration type gyro sensor of this invention, and the detection current Is. It is a graph which shows the relationship between the resistance value of the feedback resistance Rf of the current-voltage conversion circuit used for the oscillation circuit of the vibration type gyro sensor of this invention, and the detection current Is of a crystal oscillator. It is a graph which shows the relationship between the feedback resistance Rf in the oscillation circuit of the vibration type gyro sensor of this invention, and the current voltage conversion circuit of a detection circuit, and the detection output voltage Vout. It is a circuit diagram which shows the structure of the current-voltage converter circuit which shows the 2nd Embodiment of this invention. It is a figure which shows the frequency characteristic of the current-voltage converter circuit which shows the 2nd Embodiment of this invention. It is sectional drawing of IC which shows the structure of the polysilicon resistance comprised on the semiconductor substrate which shows the 3rd Embodiment of this invention. It is a graph which shows the temperature characteristic of the resistance value of the polysilicon resistance comprised on the semiconductor substrate which shows the 3rd Embodiment of this invention. It is a pattern figure of the polysilicon resistance comprised on the semiconductor substrate which shows the 3rd Embodiment of this invention. It is a schematic diagram for demonstrating the principle of an angular velocity sensor. It is a block diagram which shows the structure of the circuit of the conventional angular velocity sensor. It is a circuit diagram which shows the structure of the conventional current-voltage conversion circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Crystal oscillator 2 Oscillation circuit 3 Detection circuit 4 Vibrating gyro sensor 5, 6, 7, 74 Feedback resistor 8 Drive electrode 9 Excitation current output electrode 10, 11 Detection electrode 12, 21, 22, 71, 1401 Current voltage conversion circuit DESCRIPTION OF SYMBOLS 13, 25 Low-pass filter 14 Gain variable amplifier circuit 15 Amplifier circuit 16 AGC circuit 17 Phase circuit 23 Differential amplifier circuit 24 Synchronous detection circuit 72, 1402 Operational amplifier 73 Floating capacitance 91 Silicon substrate 92 Field oxide film 93, 94, 95, 1101 Polysilicon resistor 1301 Amplitude control circuit 1302 Inversion circuit 1403 Sensor element

Claims (5)

A sensor element having a drive electrode and a detection electrode;
An oscillation circuit including a current-voltage conversion circuit that converts an output current from the drive electrode into a voltage, and an AGC circuit that makes the output voltage from the current-voltage conversion circuit constant;
In the physical quantity sensor having a detection circuit including a current-voltage conversion circuit that outputs an external force applied to the sensor element as a detection current from the detection electrode and converts the detection current into a voltage.
Each of the current-voltage conversion circuit of the oscillation circuit and the current-voltage conversion circuit of the detection circuit includes a resistance element, and the resistance elements are resistance elements having the same temperature characteristics. Sensor.   The physical quantity sensor according to claim 1, wherein the resistance element in the current-voltage conversion circuit of the oscillation circuit and the resistance element in the current-voltage conversion circuit of the detection circuit have the same resistance value.   The resistance element in the current-voltage conversion circuit of the oscillation circuit and the resistance element in the current-voltage conversion circuit of the detection circuit are formed on the same semiconductor substrate, and are formed with the same pattern width and the same pattern length. The physical quantity sensor according to claim 1 or 2, wherein   The physical quantity sensor according to claim 1, wherein the sensor element is a crystal resonator.   The physical quantity sensor according to claim 1, wherein the sensor element is a vibration gyro sensor that detects a Coriolis force generated in the sensor element.

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