CN110311684B - An Automatic Tuning Bandpass Sigma-Delta Interface Circuit Based on MEMS Gyroscope - Google Patents

Abstract

The invention relates to an automatic tuning band-pass Σ-Δ interface circuit based on a microelectromechanical gyroscope, which comprises a C/V conversion module, a loop filter module, an observer, a quantizer and a DAC feedback module; The output end is connected to the input end of the DAC feedback module through the quantizer, and the output end of the DAC feedback module is connected to the input end of the loop filter module to form a closed-loop structure, forming a Sigma-delta modulator; the existing detection module The detected capacitance signal is converted into a proportional voltage signal by the C/V conversion module, and the voltage signal and the feedback analog signal output by the DAC feedback module are input into the Sigma-delta modulator after logical operation to realize noise Shape and quantize the output; the observer generates a control voltage and acts on the loop filter module to realize automatic tuning. The invention can adjust the center frequency point in real time, track the change of the resonance frequency of the MEMS gyroscope, significantly improve the environmental adaptability of the MEMS gyroscope, and improve the overall accuracy.

Description

An Automatic Tuning Bandpass Sigma-Delta Interface Circuit Based on MEMS Gyroscope

technical field

The invention relates to the technical field of integrated circuits, in particular to an automatic tuning band-pass sigma-delta (Sigma-delta) interface circuit used in the field of inertial sensors for micro-electromechanical (MEMS) gyroscopes.

Background technique

Compared with conventional inertial sensors, MEMS inertial sensors have the advantages of small size, light weight, low power consumption and mass production. In recent years, MEMS inertial sensors have developed rapidly, and their performance has been continuously improved in terms of measurement accuracy and stability. They are widely used in military and civilian fields, such as missiles, vehicle navigation, and smart mobile devices. At the same time, the interface circuit design of high-performance MEMS inertial sensors is also developing towards the direction of high precision, low power consumption and small area.

Due to the deviation of the MEMS process during processing, the different components of the same batch are not completely consistent, and the resonant frequency will deviate; at the same time, affected by the external environment, temperature, etc., the resonant frequency of the MEMS gyroscope will also change. In addition, the circuit using continuous-time technology has low power consumption, small phase error, and will not introduce folding noise, but it will be affected by factors such as the uncertainty of ASIC processing errors and temperature, which makes the Sigma-Delta modulator noise-shaping center frequency point. Deviations will occur. All of the above factors will reduce the overall accuracy of the MEMS gyroscope.

SUMMARY OF THE INVENTION

In view of the above problems, the purpose of the present invention is to provide an automatic tuning band-pass sigma-delta interface circuit based on a micro-electromechanical gyroscope, which can overcome the influence of temperature and processing errors on the noise shaping frequency of continuous-time band-pass sigma-delta ADC. problems, improve the signal-to-noise ratio in different environments, and improve the overall accuracy of the gyro.

In order to achieve the above object, the present invention adopts the following technical solutions: a kind of automatic tuning band-pass Σ-Δ interface circuit based on micro-electromechanical gyroscope, it is characterized in that: comprise C/V conversion module, loop filter module, observer, quantizer and the DAC feedback module; the output end of the loop filter module is connected to the input end of the DAC feedback module through the quantizer, and the output end of the DAC feedback module is connected to the input end of the loop filter module to form a closed-loop structure , forming a sigma-delta modulator; the existing detection module converts the detected capacitance signal into a proportional voltage signal through the C/V conversion module, and the voltage signal and the feedback analog signal output by the DAC feedback module perform logical operations Then, it is input to the sigma-delta modulator to realize noise shaping and quantized output; the observer generates a control voltage and acts on the loop filter module to realize automatic tuning.

Further, the C/V conversion module includes an OTA operational amplifier, a feedback capacitor, a feedback resistor and a switch demodulation module; the capacitance signal is input to the OTA operational amplifier, and the connection between the forward end and the output end of the OTA operational amplifier is The feedback capacitor and the feedback resistor are connected in parallel, and the output end of the OTA operational amplifier is connected to the loop filter module in the sigma-delta modulator through the switch demodulation module.

Further, it includes a first MOS adjustable resistor, a first operational amplifier, a second MOS adjustable resistor, a second operational amplifier, a first capacitor and a second capacitor; the output of the C/V conversion module is the same as the first One end of a MOS adjustable resistor is connected to one end, the other end of the first MOS adjustable resistor is connected to the forward end of the first operational amplifier, and the output end of the first operational amplifier is connected to the second MOS adjustable resistor through the second MOS adjustable resistor. The forward end of the second operational amplifier is connected, and the output end of the second operational amplifier is connected to the quantizer; the first capacitor is connected in parallel between the forward end and the output end of the first operational amplifier , the second capacitor is connected in parallel between the forward end and the output end of the second operational amplifier; the resistance of the MOS adjustable resistor is determined by the control voltage output by the observer.

Further, the loop filter module adopts a second-order MOS-C filter structure, the MOS adjustable resistor adopts a fully differential MOS resistor, and the time constant is determined by the fully differential MOS resistor and the capacitor.

Further, the fully differential MOS resistor is composed of four NMOS transistors operating in the linear region, wherein the sources of the NMOS transistor M1 and the NMOS transistor M4 are short-circuited, the drains of the NMOS transistor M1 and the NMOS transistor M3 are short-circuited, and the NMOS transistor M2 It is short-circuited with the source of the NMOS transistor M3, the drain of the NMOS transistor M2 and the NMOS transistor M4 is short-circuited, the gates of the NMOS transistor M1 and the NMOS transistor M2 are connected to the control voltage provided by the observer, the NMOS transistor M3 and the NMOS transistor The gate of the transistor M4 is connected to the control voltage provided by the external voltage source, the sources of the NMOS transistors M1 and M2 are the input terminals of the fully differential resistor, and the drains of the NMOS transistor M3 and the NMOS transistor M4 are the output terminals of the fully differential resistor.

Further, the observer includes a filter, two comparators, an XOR gate and an integrator; the observer has two input signals, and the first input signal is output by the C/V conversion module The signal is provided with the same amplitude and frequency as the signal input to the sigma-delta modulator. This input signal passes through the filter and a comparator in turn; the second input signal is generated by an existing external signal. It is a standard signal with the same frequency as the first input signal, and directly passes through the other comparator; the signals output by the two comparators are sequentially input to the XOR gate and the integrator to form a control The voltage acts on the MOS adjustable resistor in the loop filter module to control the resistance value of the resistor.

Further, the quantizer adopts an N-bit Flash ADC structure.

Further, the DAC feedback module includes 2 ^N resistors and 2 ^N switches, where N is the number of bits of the quantizer, and feeds back a digital signal to the input end of the sigma-delta modulator.

The present invention has the following advantages due to the adoption of the above technical solutions: 1. The present invention is based on a continuous-time band-pass Sigma-delta modulator, adopts a closed-loop structure, and is more suitable for high-precision digital quantization processing of gyro narrow-band signals. 2. The present invention uses a structure observer similar to the loop filter to generate a voltage control signal, which can automatically adjust the center frequency of the Sigma-Delta modulator, track the resonant frequency of the MEMS gyroscope in real time, and improve the signal-to-noise ratio. Improve the environmental adaptability of MEMS gyroscopes.

Description of drawings

Fig. 1 is the overall structure system block diagram of the present invention;

2 is a schematic diagram of an embodiment of the present invention;

3 is a schematic structural diagram of a C/V conversion module of the present invention;

Fig. 4 is the second-order MOS-C filter structural block diagram of the present invention;

Fig. 5 is the MOS adjustable resistance principle diagram of the present invention;

Figure 6a is a spectrogram of the output code stream of the quantizer at a temperature of 25°C;

Figure 6b is a spectrogram of the output code stream of the quantizer at a temperature of 60°C.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

Aiming at the characteristic that the output signal of the MEMS gyroscope is a narrow-band resonant frequency, as shown in Figures 1 and 2, the present invention provides an automatic tuning band-pass Σ-Δ interface circuit based on a microelectromechanical Capacitance changes are converted and digitally output, which includes a C/V conversion module 1, a loop filter module 2, an observer 3, a quantizer 4 and a DAC feedback module 5; wherein, the output end of the loop filter module 2 is processed by the quantizer 4 It is connected with the input end of the DAC feedback module 5, and the output end of the DAC feedback module 5 is connected with the input end of the loop filter module 2 to form a closed-loop structure, forming a Sigma-delta modulator. The existing detection module converts the detected capacitance signal into a proportional voltage signal through the C/V conversion module 1, and the voltage signal and the feedback analog signal output by the DAC feedback module 5 perform logical operations and then input into the Sigma-delta modulator to realize noise Functions to shape and quantize the output. The observer 3 generates a control voltage and acts on the loop filter module 2 in the sigma-delta modulator to realize the automatic tuning function and track the frequency of the MEMS gyroscope in real time.

In the above embodiment, as shown in FIG. 3 , the C/V conversion module 1 includes an OTA operational amplifier, a feedback capacitor Cf, a feedback resistor Rf and a switch demodulation module. The capacitance signal is input to the OTA operational amplifier. A feedback capacitor Cf and a feedback resistor Rf are connected in parallel between the forward end and the output end of the OTA operational amplifier. The output end of the OTA operational amplifier is connected to the loop in the Sigma-delta modulator through the switch demodulation module Filter module 2 is connected. Among them, the switch demodulation module adopts the high frequency carrier switch demodulation technology, and outputs the voltage signal proportional to the input.

In the above-mentioned embodiments, as shown in FIG. 4 , the loop filter module 2 includes a first MOS adjustable resistor, a first operational amplifier OP1, a second MOS adjustable resistor, a second operational amplifier OP2, a first capacitor C1 and a second MOS adjustable resistor. Two capacitors C2. The output of the C/V conversion module 1 is connected to one end of the first MOS adjustable resistor, the other end of the first MOS adjustable resistor is connected to the forward end of the first operational amplifier OP1, and the output end of the first operational amplifier OP1 is connected to the second MOS The adjustable resistance is connected to the forward terminal of the second operational amplifier OP2 , and the output terminal of the second operational amplifier OP2 is connected to the quantizer 4 . The first capacitor C1 is connected in parallel between the forward end and the output end of the first operational amplifier OP1, and the second capacitor C2 is connected in parallel between the forward end and the output end of the second operational amplifier OP2. In this embodiment, the MOS adjustable resistor adopts a fully differential MOS resistor, and the time constant of the loop filter module 2 is determined by the fully differential MOS resistor and capacitor. The resistance value of the MOS adjustable resistor is determined by the control voltage output by the observer 3, thereby realizing that the change of the loop filter time constant affects the center frequency point of the noise shaping of the Sigma-delta modulator.

In a preferred embodiment, the loop filter module 2 adopts a second-order MOS-C filter structure, and the time constant is determined by a fully differential MOS resistor and capacitor. The resistance value of the voltage-controlled fully differential MOS resistor is determined by the control voltages V1 and V2, as shown in Figure 5. The control voltage V1 is provided by the observer 3, and the control voltage V2 is a constant voltage provided by an external voltage source. The fully differential MOS resistor is composed of four NMOS transistors working in the linear region. The sources of the NMOS transistor M1 and the NMOS transistor M4 are short-circuited, the drains of the NMOS transistor M1 and the NMOS transistor M3 are short-circuited, and the NMOS transistor M2 and the NMOS transistor M3 are short-circuited. The source of the NMOS transistor M2 and the NMOS transistor M4 are short-circuited, the gates of the NMOS transistor M1 and the NMOS transistor M2 are connected to the control voltage V1, the gates of the NMOS transistor M3 and the NMOS transistor M4 are connected to the control voltage V2, and the NMOS transistor M2 is connected to the control voltage V2. The sources of the transistor M1 and the NMOS transistor M2 are the input terminals of the fully differential resistor, and the drains of the NMOS transistor M3 and the NMOS transistor M4 are the output terminals of the fully differential resistor. The output voltage V1 of the observer 3 will change with temperature, process deviation, etc., thereby changing the resistance of the fully differential MOS resistor, that is, changing the time constant of the filter, and further, changing the noise shaping center frequency of the Sigma-delta modulator. .

In the above-mentioned embodiments, as shown in FIG. 2 , the structure and parameters of the observer 3 and the loop filter module 2 are the same. When the same signal passes through the observer 3 and the sigma-delta modulator, it is affected by the process error or temperature in the same way. . The observer 3 includes a filter H(s), two comparators, an XOR gate and an integrator. The observer 3 has two input signals. The first input signal AC1 is provided by the output signal of the C/V conversion module 1, and has the same amplitude and frequency as the signal input to the sigma-delta modulator. This input signal passes through in turn. Filter H(s) and the first comparator; the second input signal AC2 is provided by the existing external signal generator, which is a standard signal, and has the same frequency as the first input signal AC1, and directly passes through the second comparator. The signals output by the two comparators are input into the XOR gate and the integrator in turn to form a control voltage V1, which acts on the MOS adjustable resistor in the loop filter module 2 to control the resistance value of the resistor to change the filter's value. time constant.

In the above-mentioned embodiments, the quantizer 4 adopts an N-bit Flash ADC structure, performs parallel processing on the signals, and performs digital output.

In the above embodiments, the DAC feedback module 5 includes ^2N resistors and ^2N switches, where N is the number of bits of the quantizer 4, and feeds back the digital signal to the input end of the sigma-delta modulator.

In the above-mentioned embodiments, each module is powered by a single power supply, and the power supply is VDD, and the differential measurement is realized by the reference voltage Vref. In this embodiment, Vref=VDD/2.

To sum up, when the present invention is used, the adjustment of the noise center frequency point can be realized at different temperatures. As shown in Fig. 6a and Fig. 6b, it is the spectrogram of the output code stream of the quantizer under different temperatures. The temperature is 25°C and 60°C. , after the signal passes through the sigma-delta modulator, the position of the resonant frequency can be near the lowest noise floor.

The above-mentioned embodiments are only used to illustrate the present invention, and the structure, size, setting position and shape of each component can be changed to some extent. and equivalent transformations shall not be excluded from the protection scope of the present invention.

Claims (7)

1. an automatic tuning band-pass Σ-Δ interface circuit based on a microelectromechanical gyroscope, is characterized in that: comprise C/V conversion module, loop filter module, observer, quantizer and DAC feedback module; Described loop filter The output end of the module is connected to the input end of the DAC feedback module through the quantizer, and the output end of the DAC feedback module is connected to the input end of the loop filtering module to form a closed-loop structure, forming a Sigma-delta modulator; the existing The detection module converts the detected capacitance signal into a proportional voltage signal through the C/V conversion module, and the voltage signal and the feedback analog signal output by the DAC feedback module perform logical operations and then input to the Sigma-delta modulator, Realize noise shaping and quantized output; the observer generates a control voltage and acts on the loop filter module to realize automatic tuning; The loop filter module includes a first MOS adjustable resistor, a first operational amplifier, a second MOS adjustable resistor, a second operational amplifier, a first capacitor and a second capacitor; the output of the C/V conversion module is the same as the One end of the first MOS adjustable resistor is connected, the other end of the first MOS adjustable resistor is connected to the forward end of the first operational amplifier, and the output end of the first operational amplifier is adjustable through the second MOS The resistor is connected to the forward end of the second operational amplifier, and the output end of the second operational amplifier is connected to the quantizer; the first operational amplifier is connected in parallel between the forward end and the output end of the first operational amplifier. A capacitor is connected in parallel between the forward terminal and the output terminal of the second operational amplifier; the resistance of the MOS adjustable resistor is determined by the control voltage output by the observer. 2. The interface circuit of claim 1, wherein the C/V conversion module comprises an OTA operational amplifier, a feedback capacitor, a feedback resistor and a switch demodulation module; the capacitance signal is input to the OTA operational amplifier, and the The feedback capacitor and the feedback resistor are connected in parallel between the forward end and the output end of the OTA operational amplifier, and the output end of the OTA operational amplifier is connected to the loop in the sigma-delta modulator through the switch demodulation module. The channel filter module is connected. 3. The interface circuit of claim 1, wherein the loop filter module adopts a second-order MOS-C filter structure, the MOS adjustable resistor adopts a fully differential MOS resistor, and the time constant is determined by a fully differential MOS resistor. and capacitance decision. 4. The interface circuit of claim 3, wherein the fully differential MOS resistor is composed of four NMOS transistors operating in a linear region, wherein the sources of the NMOS transistor M1 and the NMOS transistor M4 are short-circuited, and the NMOS transistor M1 It is short-circuited with the drain of the NMOS transistor M3, the source of the NMOS transistor M2 and the NMOS transistor M3 is short-circuited, the drain of the NMOS transistor M2 and the NMOS transistor M4 is short-circuited, and the gates of the NMOS transistor M1 and the NMOS transistor M2 are connected to the The control voltage provided by the observer, the gates of the NMOS transistor M3 and the NMOS transistor M4 are connected to the control voltage provided by the external voltage source, the sources of the NMOS transistor M1 and the NMOS transistor M2 are the input terminals of the fully differential resistor, the NMOS transistors M3 and The drain of the NMOS transistor M4 is the output end of the fully differential resistor. 5. The interface circuit of claim 1, wherein the observer comprises a filter, two comparators, an XOR gate and an integrator; the observer has two input signals, the first The input signal of the channel is provided by the output signal of the C/V conversion module, and the amplitude and frequency of the signal input to the sigma-delta modulator are the same. The input signal of the channel passes through the filter and compares the The second input signal is provided by the existing external signal generator, which is a standard signal with the same frequency as the first input signal, and directly passes through the other comparator; the signals output by the two comparators The XOR gate and the integrator are input in sequence to form a control voltage, which acts on the MOS adjustable resistor in the loop filter module to control the resistance value of the resistor. 6. The interface circuit according to any one of claims 1 to 5, wherein the quantizer adopts an N-bit FlashADC structure. 7. The interface circuit according to any one of claims 1 to 5, wherein the DAC feedback module comprises 2 ^N resistors and 2 ^N switches, and N is the number of digits of the quantizer, and the digital signal is fed back to the input of the sigma-delta modulator.

Images