RU2314495C1 - Interface arrangement for a micro mechanical gyroscope - Google Patents

Abstract

FIELD: the invention refers to micro mechanical sensors of speed rotating in which Coriolis effect is used particularly to micro mechanical gyroscopes of vibratory type.

SUBSTANCE: the interface arrangement has transresistive amplifiers whose inputs are connected with the opposite electrodes, two sources of alternating voltage, in-series connected a differential amplifier and a demodulator. At that the inputs of the differential amplifier are connected with the outputs of the transresistive amplifiers. The output of the first source of alternating voltage fulfilled as a source of saw-tooth voltage is connected with a mobile mass of the micro mechanical gyroscope, the output of the second source of alternating voltage fulfilled as a source of rectangular voltage is connected with the input for the reference signal of the demodulator. At that the frequencies and the phases of the first and of the second sources of alternating voltage are equal.

EFFECT: the stability of the phase of the signal at the output of the interface arrangement is increased due to reducing the constant time of the low frequency filter of the demodulator.

5 dwg

Description

The present invention relates to micromechanical rotational speed sensors that use the Coriolis effect, in particular to vibration-type micromechanical gyroscopes.

Known interface device for a micromechanical gyroscope (MMG) according to US Pat. US No. 6467346 (see Fig. 5), containing a differential transresistive amplifier (DTU), the inputs of which are connected to electrodes located on opposite sides of the rotor on a torsion bar or moving mass (PM), while a voltage source is connected to the PM. DTU in this device is made on two operational amplifiers (op-amps) 22 with resistors connected between the output of each op-amp and its differential input and an additional op-amp with resistive dividers between the output and inputs of the op-amp. Since the capacitance of the capacitors formed by the electrodes and the PM changes during PM oscillations in this MMG, a current flows through the electrodes to which the op-amp inputs are connected, the magnitude of which depends on the amplitude (or rather, on the speed) of the PM motions. By transresistive amplifiers, this current is converted to voltage, the difference of which is allocated by an additional op-amp. The output signal of the DTU is proportional to the speed of movement of the PM, and at a constant frequency of oscillation, a signal proportional to the movements of the PM can be isolated from this signal.

The disadvantage of this device is the low accuracy of determining the movement of the PM in those MMGs in which the resonance frequency of the PM suspension is low and the allowable voltage in the gap between the PM and the electrodes is low.

This and other options for interface devices for MMG are described in US Pat. US No. 6253612 (fig. 3, 4). Fig.3a of this patent shows an interface device with a rectangular voltage source, which in the MMG interface device can be connected to a PM or electrodes. The use of an AC voltage source can significantly increase the amount of current flowing through the electrodes, and thereby increase the accuracy of determining the position or displacements of the PM. At the same time, the accuracy gain for sufficiently fast op-amp is equal to the ratio of the frequency of the AC voltage source to the resonant frequency of the PM suspension. However, as noted in US Patent Application No. US 2005 / 0166675A1, it is advisable to use a sinusoidal voltage source as an alternating voltage source used to drive the interface device. This allows us to improve the signal-to-noise ratio at the MMG output by an order of magnitude or more. Fig. 7 of this application shows that a band-pass filter can be applied to convert the voltage of a rectangular source into a sinusoidal one, which complicates the electronic part of the MMG.

Closest to the proposed device is an interface device described in the work of Peshekhonov et al. Results of the development of a micromechanical gyroscope. XII S. Petersburg International Conference on Integrated Navigation Systems May 23-25, 2005 p. 268-274. This interface device is adopted as a prototype. The structural diagram shown in Fig. 6 of this work shows that it includes a DTU, the inputs of which are connected to opposite electrodes, an AC voltage source (3 MHz), the output of which is connected to the PM, and a demodulator, one input of which is connected to the output of a transistor amplifier, and the other input is connected to an AC voltage source. The demodulator in this device is made on an analog multiplier, to the output of which a low-pass filter (LPF) is connected [see circuit shown in the Handbook of Nonlinear Circuits. Under. ed. Sheingold, M., Mir, 1977, Fig.2.4.9, p.147]. The amplitude of the variable component at the output of such a demodulator is equal to the value of the constant component. Note that, as a reference voltage, both a sinusoidal and a rectangular voltage can be supplied to the demodulator. As applied to MMG interface devices, this means that the AC voltage sources used in it can have a different output signal form. For example, a voltage source whose output is connected to the PM (let's call this voltage source first) may have a sinusoidal shape, and the second, which is connected to the demodulator input, may have a rectangular shape.

The disadvantages of the prototype are the complexity of the implementation of the voltage source of the sinusoidal shape and the instability of the phase of the output signal due to changes in the parameters of the elements on which the low-pass filter is implemented. The instability of the phase of the output signal leads to the fact that during subsequent synchronous detection (using the demodulator D3) of the signal coming from the output of the demodulator (D2, see FIG. 6 of the prototype), connected through the DTU to the electrodes located on the output axis, using the reference the signal coming from the output of the demodulator (D1, see Fig.6), connected through a DTU with electrodes located on the axis of the drive channel, the degree of suppression of quadrature noise is deteriorated and the scale factor MMG is changed. All this causes a deterioration in the accuracy of MMG.

The objective of the invention is to simplify the design of the interface device and increase the phase stability of the signal at the output of this interface device.

Improving these characteristics when using the proposed interface device in MMG will improve accuracy and reduce the size and cost of the latter.

The task is achieved in that in the interface device of the micromechanical gyroscope containing transresistive amplifiers, the inputs of which are connected to opposite electrodes, the first and second AC voltage sources, series-connected differential amplifier and demodulator, while the inputs of the differential amplifier are connected to the outputs of transresistive amplifiers, the output of the first AC voltage source connected to the moving mass of the micromechanical gyroscope, the output of the second source As the AC voltage is connected to the input for the reference signal of the demodulator, the first AC voltage source is designed as a sawtooth voltage source, the second AC voltage source is made as a rectangular voltage source, while the frequencies and phases of the first and second AC voltage sources are equal.

In addition, the task is achieved by the fact that in the interface device of the micromechanical gyroscope, the demodulator is made according to the push-pull key demodulator.

The main advantage of the present invention is due to the fact that the execution of the first source as a voltage source with a sawtooth shape allows you to get the voltage at the output of a rectangular DTU, which when demodulated is converted into a signal with a low ripple level, which allows you to use the low-pass filter with a lower time constant to obtain the desired variable level component of the output voltage. By reducing the time constant of the low-pass filter, an increase in the phase stability of the signal at the output of the interface device is achieved.

The claimed combination of features allows to increase the accuracy of MMG by increasing the accuracy of suppressing quadrature interference when using the proposed interface device with a higher phase stability of the output signal, to simplify the MMG by using a simpler circuit interface device.

Figure 1 shows a block diagram of the inclusion of the proposed interface device in MMG.

In figure 1, the following notation:

1 - moving mass

2, 3 - electrodes of a capacitive displacement sensor located along the axis of the primary oscillations or drive

4, 5 - electrodes of a capacitive displacement sensor located along the axis of the secondary oscillations or the output axis

6, 7 - electrodes of the comb engine located along the axis of the primary oscillations or drive

8, 9 - additional electrodes located along the axis of secondary vibrations or the output axis

10 - DTU connected to the electrodes of the capacitive displacement sensor, located along the axis of the primary vibrations

11 - DTU connected to the electrodes of a capacitive displacement sensor located along the axis of the secondary vibrations

12 - amplifier

13, 14 - resistors

15, 16, 20 - demodulators

17 - the first source of alternating voltage

18 - second source of alternating voltage

19 - phase shifter

Figure 2 shows an example implementation of the proposed interface device on industrial elements.

In figure 2, the following notation:

21 - capacitor formed by the electrode 2 and PM

22 - capacitor formed by the electrode 3 and PM

10 - DTU connected to the electrodes of the capacitive displacement sensor, located along the axis of the primary vibrations

15 - demodulator

17 - the first source of alternating voltage

18 is a second source of alternating voltage

23, 24 - Shelter

25, 26, 29 - resistors

27 - differential amplifier

28 - analog multiplier

30 - capacitor

Figure 3 shows the signals at the output of the transresistive amplifier with different forms, but the same signal amplitude of the first AC voltage source.

In figure 3, the following notation:

31 - signal with a rectangular voltage shape of the first AC voltage source

32 - signal with a sinusoidal voltage shape of the first AC voltage source

33 - signal when the sawtooth voltage of the first AC voltage source

Figure 4 shows an example implementation of a push-pull key demodulator.

In figure 4, the following notation:

34 - op amp

35-38 - resistors

39 - key

40 - input source

Figure 5 shows the alternating components of the ripple voltage at the output of the demodulator of the proposed interface device.

In figure 5, the following notation:

41 - ripple with a sinusoidal voltage shape of the first AC voltage source

42 - ripple when the sawtooth voltage of the first source of alternating voltage

In MMG in figure 1 from different sides of the PM are the electrodes 2, 3 of the capacitive PM displacement sensor along the drive axis, the electrodes 4, 5 of the capacitive PM displacement sensor along the output axis. The electrodes of the comb engine 6, 7 are also located on different sides of the PM along the drive axis, and the electrodes 8, 9 are located on different sides of the PM on the output axis. DTU 10, 11 are connected by inputs respectively to electrodes 2, 3 and electrodes 4, 5. DTU 10 is formed by an amplifier 12 with resistors 13, 14 connected between the output of amplifier 12 and the inverting and non-inverting inputs of amplifier 12. DTU 11 is made on similar elements, which and DTU 10. The output of each of DTU 10, 11 is connected respectively to the inputs of demodulators 15, 16. The first AC voltage source 17 is made as a sawtooth voltage source and connected to the PM, and the second AC voltage source 18 is made as a rectangular voltage source Ia and connected to the inputs of the demodulators 15, 16. The output of demodulator 15 via fazovraschatelnoe device 19, and the output of the demodulator 16 are connected directly to the demodulator 20 inputs.

The proposed interface device operates as follows.

When the PM moves along the drive axis, capacitances formed by the PM and electrodes 2, 3 change in opposite directions. This causes changes in the currents flowing through the electrodes 2, 3. The difference of the currents flowing through these electrodes is converted to a square voltage, the amplitude of which proportional to the movements of the PM along the axis of the drive. This voltage is converted by the demodulator 16 into a voltage whose magnitude is proportional to the PM movements along the drive axis. The output signal of the demodulator 15 is supplied to both the primary oscillation excitation device or the drive, and through the phase shifter 19 to the demodulator 20 as a reference signal. The primary excitation or drive excitation device is not shown in FIG. 1. His work is described in detail in the literature, for example, in US Pat. US No. 6067858, No. 6253612. When the device for excitation of primary vibrations PM1 on the electrodes 6, 7, an alternating voltage is generated, which creates a force or moment acting on the PM and causing PM oscillations. When MMG rotates around the sensitivity axis, the Coriolis acceleration acts on the PM, causing PM vibrations along the output axis, i.e. between the electrodes 4, 5. Changes in the distance between the PM and electrodes 4, 5 cause changes in the capacitances of the capacitors formed by the PM and electrodes 4, 5, and accordingly, the voltage change at the output of the DTU 11. The shape of these voltages coincides with the shape of the voltage at the output of the DTU 11. After at the output of the latter, the demodulation by the demodulator 16 contains a useful component, the amplitude of which is proportional to the speed of rotation of the MMG around the axis of sensitivity, and a component whose phase is shifted 90 ° relative to the useful component, the so-called quadrature interference. The nature of the quadrature interference is described in more detail in US Pat. US No. 6067858. One of the main methods for suppressing quadrature interference is synchronous phase-sensitive detection or demodulation, in which it is possible to completely suppress this interference. However, if there are elements in the signal conversion channels that change the phase of the signal, then the instability of these elements can lead to a phase drift of one signal supplied to the input of the demodulator relative to another. The exclusion of these elements from the circuit or the reduction of their time constant eliminates or reduces, accordingly, their influence on the degree of suppression of the quadrature noise and improves the accuracy of the MMG.

An embodiment of a DTU 10 and a demodulator 15 are shown in FIG. 2.

The inputs of the DTU 10 are connected to the capacitors 21, 22, the combined output of which is connected to the first source of alternating voltage 17. The DTU 10 is formed by an op-amp 23, 24, between the outputs and inverting inputs of which resistors 25, 26 are connected. The outputs of the op-amp 23, 24 are connected to the differential inputs amplifier 27. The demodulator 15 is formed by an analog multiplier 28 and an LPF on a resistor 29 and a capacitor 30. The inputs of the analog multiplier 28 are connected to the output of the differential amplifier 27 and a second AC voltage source 18.

The circuit in figure 2 works as follows. Transistor amplifiers on the op amp 23, 24 convert the input current into voltages, the difference of which is extracted by the differential amplifier 27. The values of the input currents are proportional to the input capacitances, which depend on the distances between the PM and electrodes 2, 3. Accordingly, the amplitude of the output voltage of the differential amplifier 27 is proportional to the movements of the PM. A signal proportional to the amplitude of the output voltage of the differential amplifier 27 is allocated by the demodulator 15. The low-pass filter at the resistor 29 and the capacitor 30 provides suppression of the high-frequency component of the signal at the output of the analog multiplier 28. The higher the time constant of this low-pass filter, the higher the degree of suppression of the high-frequency component of the signal. However, the instability of the time constant of the low-pass filter (the absolute value of its change due to aging of elements or the influence of temperature) also increases, impairing the accuracy of the MMG. Note that other LPF implementations are possible (of a higher order, using active elements, on switched capacitors, etc.). On the other hand, the circuit on the OA 23 with a resistor 25 and a capacitor 21 is a differentiation circuit of the input signal (see J. Rutkovsky. Integrated operational amplifiers. M., Mir, 1978, pp. 180-184). Therefore, when the voltage of the source 17 is rectangular, the output voltage of the op-amp 23 will represent narrow pulses, the duration of which is determined by the duration of the edges of the input voltage pulses.

Lines 31, 32 and 33 in FIG. 3 correspond to the voltage forms at the output of the op-amp 23 for cases when the voltage of the AC voltage source connected to the PM has a rectangular shape (as in the analogue according to US Pat. No. 6253612, fig.3a, for of this case, when modeling in parallel with the resistor 25, a capacitor was turned on), sinusoidal (as in the prototype) and sawtooth. As can be seen from the graph, even with a sufficiently large capacitor capacitance in the feedback of the ОУ 23 (5 times larger than the capacitance of the electrodes), its output voltage changes significantly, which, when subtracting the voltages in the differential amplifier and demodulation, leads to errors and an increase in the noise of the MMG. In addition, the large value of the voltage pulses does not allow to increase the coefficient of conversion of current to voltage in a transresistive amplifier higher than the ratio of the supply voltage to the amplitude of this pulse. The voltage amplitudes 32 and 33 are close in magnitude to each other, the dynamic range of the signals is two orders of magnitude lower than with a rectangular voltage. Thus, the use of a source with a sawtooth shape of the output signal as an AC voltage source does not distort the signal at the output of the DTU, it allows to increase the coefficient of conversion of current to voltage in DTU by 2 orders of magnitude than in the analogue and, with low-noise opamps, significantly increase the sensitivity of MMG. Moreover, the implementation of the two sources 17 and 18 can be quite simple, for example, the source 17 can be formed on the op amp included as an integrator (see J. Rutkovsky. Integrated operational amplifiers, M., Mir, 1978, pp. 176-180), or a current source, for example, a field effect transistor and a capacitor connected to a square voltage source. Those. in fact, for the operation of the proposed interface device, it is sufficient to use a single source of rectangular voltage and a circuit for generating a sawtooth voltage from it.

In a push-pull demodulator (see Fig. 4), a resistor 35 is connected between the output of the op-amp 34 and its inverting input. A resistor 36 is connected between the inverting input and the common output of the power source. Resistors 37, 38 are connected between the output of the signal source 40 and the inverting and non-inverting inputs of the op-amp 34. The key 39 is connected between the non-inverting inputs of the op-amp 34 and the common output of the power source. When the resistance of the resistor 35 is twice as large as the rest of the resistors, the resistances of which are chosen equal to each other, when the key is closed and opened, the transmission coefficient of the circuit in Fig. 4 changes in sign. If the signal of the source 40 is in phase with the frequency of the signal that controls the state of the key, then shown in figure 4 will work as a demodulator. A detailed description of this scheme is given in B. Gutnikov. Integrated Electronics in Measuring Devices, L., Energoatomizdat, Leningrad Branch, 1988, p. 123, Fig. 4.4a).

If the input of this demodulator receives an alternating voltage of rectangular shape (line 33 in figure 3), then the output voltage is converted to constant. An insignificant transient at the leading edge of the signal can be filtered by the low-pass filter with a small time constant.

As can be seen from figure 5, the ripple in the sinusoidal form of the voltage of the first source of alternating voltage (curve 41) is the 2nd harmonic of the input signal, they are much larger for the same LPF time constant (left scale for curve 41, right scale for curve 42) than ripple in the sawtooth form of voltage of the first source of alternating voltage (curve 42).

Thus, the use of a sawtooth voltage source as the first alternating voltage source and a rectangular voltage source as the second one allows, along with a simpler implementation of the interface device circuit (in terms of sources 17, 18 and demodulators 15, 16), to reduce the time constant of the low-pass filter and to reduce the phase shift in phase of the output signal.

Claims (1)

An interface device of a micromechanical gyroscope containing a differential transresistive amplifier, formed by two transresistive amplifiers, the inputs of which are connected to opposite electrodes, the first and second AC voltage sources, series-connected differential amplifier and a demodulator formed by an analog multiplier and a low-pass filter, while the inputs of the differential amplifier are connected with transistor amplifier outputs, output of the first AC source voltage is connected to the moving mass of the micromechanical gyroscope, the output of the second AC voltage source is connected to the input for the reference signal of the demodulator, characterized in that the first AC voltage source is designed as a sawtooth voltage source, the second AC voltage source is made as a rectangular voltage source, with frequencies and phases the first and second alternating voltage sources are equal.

Images