CN1858564A - Phase-lock closed loop system of resistance vibration pickup type silicon micro mechanical resonant sensor - Google Patents

Abstract

The phase-locked closed-loop system of the resistance-pick-up silicon micromachined resonant sensor includes: a loop filter, a voltage-controlled oscillator and an excitation amplifier. A phase-locked loop is composed of a pick-up resistor with a sensitive structure, a loop filter and a voltage-controlled oscillator. The pick-up resistor acts as a phase detector of the phase-locked loop. The signal output by the pick-up resistor is amplified, filtered and The integral acts on the voltage-controlled oscillator; the signal output by the voltage-controlled oscillator is used as the reference signal of the pickup resistor, and the signal output by the voltage-controlled oscillator is amplified by the excitation amplifier and used as the excitation signal of the excitation element in the sensitive structure. In the system, the phase detector in the phase-locked loop structure is replaced by the pick-up resistor, which simplifies the closed-loop circuit of the resistance-pick-up silicon micromechanical resonant sensor.

Description

Phase-locked closed-loop system of resistance-pickup silicon micromachined resonant sensor

technical field

The invention relates to a phase-locked closed-loop system of a silicon micro-mechanical resonant sensor, in particular to a phase-locked closed-loop system of a resistance pickup type silicon micro-mechanical resonant sensor.

Background technique

Resistive pick-up silicon micromechanical resonant sensors use piezoresistive effect to detect the vibration signal of the sensor's sensitive structural resonator, and the pick-up resistance can be realized by thin film resistors or diffused resistors.

The sensitive structure of the resonant sensor needs to be combined with a closed-loop system to work. The usual closed-loop system includes an amplitude control link and a phase shift link. The amplitude controller is used to adjust the gain of the entire closed loop to meet the amplitude conditions of the resonant sensor self-excited closed loop. The phase link is used to adjust the phase shift of the entire closed loop to meet the phase conditions of the self-excited closed loop of the resonant sensor. However, due to the small size of the silicon micromechanical resonant pressure sensor, the output signal of its sensitive structure is very weak. Taking a resistance pickup type silicon micromechanical resonant pressure sensor as an example, at its resonant frequency, a larger excitation signal is used to excite the sensor. For the resonator of the sensor, the change rate of its pick-up resistance is less than 1/10 ⁵ . Therefore, in the closed-loop system of the silicon micro-mechanical resonant sensor, the problem of weak signal detection must be solved first. Phase-locked loop is an effective method to detect periodic weak signals, and it is widely used in weak signal detection of silicon micro-mechanical resonant sensors. A phase-locked loop is usually composed of a phase detector, a loop filter and a voltage-controlled oscillator, and the phase detector is usually realized by an analog multiplier.

Usually, the closed-loop system of the silicon micro-mechanical resonant sensor based on the phase-locked loop structure first needs to amplify and filter the vibration signal through the pre-filter, and then detect it by the analog multiplier, and then amplify, filter or integrate the signal through the loop filter. , control the voltage-controlled oscillator to output a sinusoidal signal with the same frequency as the pickup signal and a certain phase difference. This signal is fed back to the analog multiplier as a reference signal for the phase detector. After the signal is amplified, it is output to the silicon microelectronics through the phase shift link The excitation element of a mechanically resonant pressure sensor excites the resonator to vibrate.

The output DC bias of the analog multiplier is generally greater than the microvolt level. When the signal of the sensor is weak, the DC signal output by the phase detector, which represents the phase difference between the vibration pickup signal and the reference signal, is sometimes as low as microvolts. Using an analog multiplier for phase detection, the output DC bias of the analog multiplier will cause a large error in the phase difference between the vibration pickup signal and the reference signal, so that the closed loop of the sensor cannot accurately track the change of the natural frequency of the sensor, thereby introducing measurement errors. The pre-filter is usually realized by sampling a band-pass filter, and the vibration pickup signal passes through the pre-filter, which will generate a certain phase shift, which needs to be compensated by a phase shifting link. However, the pre-filter and phase-shift link cannot guarantee a constant phase-shift characteristic within the operating frequency band of the sensor, and their characteristics will also drift due to the influence of temperature and other factors. The phase drift generated by the pre-filter and the phase-shifting link must be compensated by the phase shift of the sensitive structure of the resonant sensor, which will cause the resonant frequency of the entire closed-loop system to drift, and cannot accurately track the natural frequency of the sensitive structure of the resonant sensor. Measurement errors are generated; and the phase shifting link is more complicated in circuit implementation, and it is also difficult to compensate the phase drift generated by the phase shifting link in the circuit.

Contents of the invention

The technical problem of the present invention is: to overcome the deficiencies of the prior art, to provide a phase-locked closed-loop system of the resistance-pick-up type silicon micro-mechanical resonant sensor, which simplifies the closed-loop control circuit of the sensor, and avoids the need for phase detectors, front-end Errors introduced by setting filters and phase shifting links.

The technical solution of the present invention: the phase-locked closed-loop system of the silicon micro-mechanical resonant sensor with resistance pick-up vibration, which is characterized in that it includes a loop filter, a voltage-controlled oscillator and an excitation amplifier, and consists of a pick-up resistance of a sensitive structure, a loop The filter and the voltage-controlled oscillator form a phase-locked loop, and the pickup resistor acts as a phase detector of the phase-locked loop. The signal output by the pickup resistor is amplified, filtered and integrated by the loop filter, and acts on the voltage-controlled oscillator; The output signal of the controlled oscillator is divided into two channels, one is used as the reference signal of the pickup resistor, and the other is amplified by the excitation amplifier, and used as the excitation signal of the excitation element in the sensitive structure to excite the resonator. The invention replaces the phase detector in the phase-locked loop structure with the vibration-pickup resistance, and simplifies the closed-loop circuit of the resistance-pick-up type silicon micro-mechanical resonant sensor.

The principle of the present invention: the present invention adopts the pick-up resistance of the resistance pick-up type silicon micro-mechanical resonant sensor as the phase detector of the phase-locked loop. The resistance value of the pickup resistance can be expressed as R(1+ε), and the change amount εR of the resistance value of the pickup resistance reflects the vibration signal of the resonator. According to Ohm's theorem, the voltage U at both ends of the pickup resistor, through the pickup resistance The relationship between the current I and the pickup resistance R(1+ε) can be expressed as U=IR(1+ε), or I=U/R(1+ε)≈UR(1-ε)/R ² . It can be seen that when the reference signal is a current, the pickup resistor is equivalent to an analog multiplier, which outputs a voltage signal; when the reference signal is a voltage, the pickup resistor is approximately equivalent to an analog multiplier, which outputs a current signal, thus realizing the lock The function of the phase detector in the phase loop structure.

The structure of the loop filter is shown in Figure 3, the frequency characteristics of the resonator are shown in Figure 4, and the voltage control characteristics of the voltage-controlled oscillator are shown in Figure 5.

Suppose the signal output by the voltage-controlled oscillator is U ₁ (t)=cos(ωt), the signal output after being amplified by the amplifier is U ₂ (t)=Bcos(ωt), the resonator is excited, and the vibration signal of the resonator is x (t)=A(ω,t)Bcos(ωt+φ). The signal output by the voltage-controlled oscillator is U ₁ (t)=cos(ωt) and it is used as the reference signal of the pickup resistor, and the signal output by the pickup resistor is X(t)=A(ω,t)Bcos(ωt+φ )cos(ωt)=A(ω,t)B[cos(2ωt+φ)+cos(φ)]/2. The loop filter filters out the AC component of X(t), and integrates its DC component X _d (t)=A(ω,t)Bcos(φ)/2.

Let ω _r be the natural frequency of the resonator. According to the phase-frequency characteristics of the resonator, when ω=ω _r , φ=-90°, X _d (t)=0, the output of the loop filter is constant, and the voltage The frequency of the output signal of the controlled oscillator is stable at ω _r . When ω<ω _r , it can be seen from the phase-frequency characteristics of the resonator, φ>-90°, then X _d (t)>0, so that the output signal of the loop filter increases, and the voltage-controlled characteristics of the voltage-controlled oscillator It can be seen that the frequency of the voltage-controlled oscillator output signal will increase until when ω=ω _r , the closed-loop loop of the entire sensor is stable at the natural frequency ω _r of the resonator. When ω>ω _r , φ<-90°, X _d (t)<0, so that the output signal of the loop filter decreases, and the frequency of the output signal of the voltage-controlled oscillator will also decrease until when ω=ω When _r , the closed-loop loop of the whole sensor is stable on the natural frequency ω _r of the resonator.

From the above analysis, it can be seen that the closed loop of the whole sensor works stably at the natural frequency of the resonator, thus realizing the closed loop of the sensor.

The advantages of the present invention compared with the prior art: because the present invention has adopted the pick-up resistance of the resistance pick-up type silicon micro-mechanical resonant sensor as the phase detector of the phase-locked loop, in the closed-loop system of the sensor, there is no pre-filter It simplifies the closed-loop control circuit of the sensor and avoids the errors introduced by the phase detector, pre-filter and phase-shifting link.

Description of drawings

Fig. 1 is a structural representation of the present invention;

Fig. 2 is a structural schematic diagram of a traditional resonant sensor closed loop;

Fig. 3 is a schematic structural diagram of a loop filter in the present invention;

Fig. 4 is the frequency characteristic curve diagram of the resonator in the present invention, wherein Fig. 4a amplitude-frequency characteristic curve diagram, Fig. 4b is the phase-frequency characteristic curve diagram;

FIG. 5 is a graph of the voltage control characteristics of the voltage controlled oscillator in the present invention.

Detailed ways

As shown in Figure 1, the phase-locked closed-loop system 2 of the resistance-pick-up silicon micro-mechanical resonant sensor is composed of a loop filter 5, a voltage-controlled oscillator 4 and an excitation amplifier 3, and the signal output by the pick-up resistor 6 of the sensitive structure 1 After being amplified by the loop filter 5, low-pass filtered and integrated, it acts on the voltage-controlled oscillator 4; the signal output by the voltage-controlled oscillator 4 is used as the reference signal of the pickup resistor 6, and the other signal output by the voltage-controlled oscillator 4 After being amplified by the excitation amplifier 3 , the resonator 7 is excited as the excitation signal of the excitation element 8 in the sensitive structure 1 .

The pickup resistor 6 of the sensitive structure 1, the loop filter 5 and the voltage-controlled oscillator 4 constitute a phase-locked loop. The phase detector in the PLL structure is realized by the pickup resistor 6 of the sensitive structure 1 .

As shown in Figure 3, loop filter 5 of the present invention is made up of low-pass filter and integrator, and low-pass filter is used for amplifying the direct current signal that pickup resistance 6 outputs, and filters out alternating current signal, and integrator is used for picking up The integration of the DC signal output by the vibration resistor 6. The low-pass filter and integrator can be realized by common operational amplifiers, such as OP27 or OP07, selected according to bandwidth, noise and other indicators, and can also be realized by integrated circuits or ASICs.

The voltage-controlled oscillator 4 can be realized by an integrated circuit, such as MAX038 of Maxim Integrated Products, Inc.

The excitation amplifier 3 can be realized by a common operational amplifier, and it must be ensured that it cannot produce large phase drift.

Claims (2)

1, the phase-lock closed loop system of resistance vibration-pickup type silicon micro-mechanical resonate sensor, it is characterized in that: phase-locked closed-loop control system (2) is made up of loop filter (5), voltage controlled oscillator (4) and penultimate amplifier (3), pick-up resistance (6), loop filter (5) and voltage controlled oscillator (4) by sensitive structure constitute a phaselocked loop, wherein the pick-up resistance (6) of sensitive structure is as the phase detector of phaselocked loop, the signal of pick-up resistance (6) output of sensitive structure (1) acts on voltage controlled oscillator (4) through loop filter (5) amplification, filtering and integration; The signal of voltage controlled oscillator (4) output is divided into two-way, one tunnel reference signal as pick-up resistance (6), and amplify through overdriven amplifier (3) on another road, as the excitation signal energizes resonator (7) of exciting element (8) in the sensitive structure (1).

2, the phase-lock closed loop system of resistance vibration-pickup type silicon micro-mechanical resonate sensor according to claim 1, it is characterized in that: described loop filter (5) is made up of low-pass filter and integrator, low-pass filter is used to amplify the direct current signal of pick-up resistance (6) output, and filtering AC signal, integrator is used for the direct current signal integration to pick-up resistance (6) output.

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