Ultrasonic transmitting circuit capable of adjusting frequency

Abstract

The invention discloses an ultrasonic transmitting circuit capable of adjusting frequency. The ultrasonic transmitting circuit comprises a voltage division circuit, a comparator module, a DFF trigger and a current mirror structure. The voltage division circuit performs voltage division on a power supply through a resistor R1 and a resistor R2 to generate two reference voltages; the comparator module is connected with the voltage division circuit and controls charging and discharging of a capacitor through a P-type MOS tube and an N-type MOS tube so as to generate an oscillation signal; the DFF trigger performs frequency division shaping on the oscillation signal, outputs a pulse signal, and adjusts the oscillation signal to a frequency suitable for working of the transducer; the current mirror structure provides a constant current source for charging and discharging of the capacitor. By optimizing signal generation and power management, more efficient energy utilization and more reliable signal emission are realized, and different working frequencies of the ultrasonic transducer are met.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultrasonic flow measurement, and particularly relates to an ultrasonic transmitting circuit with adjustable frequency. Background Art

[0002] The ultrasonic transmitting circuit is used to drive the ultrasonic transducer to emit signals, and its performance directly affects the measurement accuracy and stability of the flowmeter. Most of the existing ultrasonic transmitting circuits are based on crystal oscillators. Its working principle is that the crystal oscillator drives the ultrasonic transducer to emit ultrasonic signals through a stable frequency output. This circuit usually includes a frequency generation module, a power amplification module, and a drive circuit. Frequency generation is achieved through a crystal oscillator, a digital frequency synthesizer, or an oscillator based on an LC circuit. The signal is amplified from low power to a level suitable for driving the transducer through a power amplifier. An operational amplifier or a dedicated amplifier is commonly used to drive the ultrasonic transducer (such as a piezoelectric crystal) to work and generate ultrasonic signals. The current ultrasonic transmitting circuit often has the following defects in practical applications: high power consumption: the traditional circuit cannot dynamically adjust the power, resulting in energy waste and difficulty in meeting the low-power requirements of portable devices; poor signal stability: frequency drift and waveform distortion are likely to occur during high-frequency operation; weak anti-interference ability: the signal is easily interfered in a complex electromagnetic environment, reducing the measurement reliability; complex adjustment: frequency adjustment depends on complex circuits or external devices, lacking flexibility. Therefore, there is an urgent need to develop an ultrasonic transmitting circuit that can adjust the amplitude and center frequency of the ultrasonic wave according to requirements and is suitable for ultrasonic transducers with different operating frequencies. Summary of the Invention

[0003] Object of the Invention: To solve the above technical problems, the present invention provides an ultrasonic transmitting circuit with adjustable frequency. By optimizing signal generation and power management, more efficient energy utilization and more reliable signal transmission are achieved, meeting the operating frequencies of different ultrasonic transducers.

[0004] Technical Solution: An ultrasonic transmitting circuit with adjustable frequency provided by the present invention includes:

[0005] A voltage division circuit that divides the power supply voltage VDD through resistors R1 and R2 to generate two reference voltages: a high reference voltage Vhigh and a low reference voltage Vlow;

[0006] A comparator module connected to the voltage division circuit, which controls the charging and discharging of the capacitor through a P-type MOS transistor and an N-type MOS transistor to generate an oscillation signal;

[0007] A DFF flip-flop that divides and shapes the oscillation signal and outputs a pulse signal to adjust the oscillation signal to a frequency suitable for the transducer to work;

[0008] A current mirror structure that provides a constant current source for the charging and discharging of the capacitor.

[0009] Further, the pulse signal is a square wave signal with a duty cycle of 50% to improve the working efficiency and stability of the transducer.

[0010] Further, the resistances of the resistors R1 and R2 are both greater than 10 kΩ.

[0011] Further, the voltage dividing circuit reduces power consumption through a small current and a diode-structured MOS transistor.

[0012] Further, the voltage difference between the high reference voltage Vhigh and the low reference voltage Vlow is 0.5 V - 3 V to avoid the influence of overshoot on the actual pressure difference.

[0013] Further, the high reference voltage Vhigh and the low reference voltage Vlow are used for the inverting input terminal (VIN-) of the comparator as a comparison reference. By adjusting the values of Vhigh and Vlow, the charging and discharging time of the capacitor can be controlled, thereby adjusting the frequency of the oscillator.

[0014] Further, the voltage dividing circuit further includes two-stage operational amplifiers. The two-stage operational amplifiers amplify and stabilize the reference voltage generated by the voltage dividing circuit to ensure its accuracy and stability, and then output the reference voltage to the inverting input terminal (VIN-) of the comparator module.

[0015] Further, the pulse signal is a square wave signal with a duty cycle of 50%.

[0016] Further, in the voltage dividing circuit, R1 = 36 kΩ, R2 = 85 kΩ; Vhigh = 3.3 V, Vlow = 2.7 V.

[0017] Further, the frequency division ratio of the DFF flip-flop is 2, and the output frequency is 1 / 2 of the oscillation frequency.

[0018] Beneficial effects: Compared with the prior art, the technical solution of the present invention has the following remarkable advantages: (1) Low power consumption. Through dynamic power management and current mirror constant current control, the power consumption is reduced by more than 30%; (2) High stability. Monte Carlo simulation shows that the average value of the output frequency is 1.01 MHz, and the standard deviation < 2%, with strong anti-interference ability; (3) Adjustable frequency. It supports adjustment in the range of 100 kHz to 9 MHz and is suitable for a variety of transducers; (4) Simple structure. It does not require high-voltage power supply, has a small area, and the cost is reduced by 40%. Description of the Drawings

[0019] Figure 1 It is a schematic diagram of the ultrasonic transmitting circuit with adjustable frequency of the present invention;

[0020] Figure 2 It is a schematic diagram of the two-stage operational amplifier circuit of the present invention;

[0021] Figure 3 This is the Monte Carlo simulation diagram of the output frequency for Embodiment 1 of the present invention. Detailed implementation manners

[0022] The following further elaborates on the technical solution of the present invention through specific embodiments. However, it is necessary to point out that the following embodiments are only used for the description of the invention content and do not constitute a limitation to the protection scope of the present invention.

[0023] Embodiment 1

[0024] As Figures 1 - 3 shown, an adjustable-frequency ultrasonic transmitting circuit includes:

[0025] A voltage-dividing circuit divides the power supply voltage VDD through resistors R1 and R2 to generate two reference voltages: a high reference voltage Vhigh and a low reference voltage Vlow;

[0026] A comparator module is connected to the voltage-dividing circuit and controls the charging and discharging of a capacitor through a P-type MOS transistor and an N-type MOS transistor to generate an oscillation signal;

[0027] A DFF flip-flop divides the frequency and shapes the oscillation signal, outputs a pulse signal, and adjusts the oscillation signal to a frequency suitable for the transducer to work;

[0028] A current mirror structure provides a constant current source for the charging and discharging of the capacitor.

[0029] Taking driving a 1MHz ultrasonic transducer as an example, the final required oscillator frequency is 1MHz. In order to make the duty cycle 50%, it is necessary to divide the frequency and shape it through a DFF flip-flop. Therefore, the frequency output by this structure should be 2MHz, and the discharge time should be controlled within 500ns as much as possible.

[0030] The specific parameter settings of the ultrasonic transmitting circuit are as follows: the power supply voltage VDD = 5V, the voltage-dividing resistors R1 = 36kΩ, R2 = 85kΩ, generating a voltage difference of 2.7V between Vhigh and Vlow; the capacitor C2 = 3pF, the discharge current is 20μA, and the frequency division ratio of the DFF flip-flop is 2.

[0031] The working process is as follows: The ultrasonic transmitting circuit charges the capacitor and discharges it with a constant current through the current mirror structure, thereby generating pulses to excite the ultrasonic transducer. When the capacitor C2 is charged to Vhigh, Vout jumps to a high level, and when it is discharged to Vlow, it jumps back to a low level, forming a 2MHz oscillation; the DFF flip-flop divides the frequency and outputs a 1MHz square wave to drive the transducer to emit ultrasonic waves.

[0032] The power supply VDD is divided by the resistors R1 and R2 to generate two reference voltages Vhigh and Vlow respectively, where VDD > Vhigh > Vlow. VIN+ is the non-inverting input terminal of the comparator, and VIN- is the inverting input terminal of the comparator. The two reference voltage signals are sequentially input to VIN-.

[0033] In the initial state, Vout outputs a low level:

[0034] 1. The PM1 transistor is turned on, and the reference voltage Vhigh is input to the inverting input terminal VIN- of the comparator;

[0035] 2. The PM2 transistor is turned on, and the capacitor C2 is charged. The NM2 transistor discharges with a constant current through a current mirror structure. Since the size of the PM2 transistor is larger than that of the NM2 transistor, the drain current of the PM2 transistor is greater than the drain current of the NM2 transistor, that is, the charging current > the discharging current. The capacitor C2 can store charge, causing the voltage of the non-inverting input terminal VIN+ of the comparator to rise.

[0036] When the non-inverting input terminal VIN+ of the comparator > the inverting input terminal VIN- of the comparator, Vout jumps to a high level:

[0037] 1. The NM1 transistor is turned on, and the reference voltage Vlow is input to the inverting input terminal VIN- of the comparator;

[0038] 2. The PM2 transistor is turned off. At this time, the charge at the non-inverting input terminal VIN+ of the comparator releases the charge stored in the capacitor through the NM2 transistor.

[0039] When it drops to a certain node and the inverting input terminal VIN- of the comparator > the non-inverting input terminal VIN+ of the comparator, Vout jumps to a low level. In this way, the OSC oscillates to form a pulse.

[0040] The DFF flip-flop realizes the frequency division function and adjusts the duty cycle.

[0041] For this structure, the charging time is short and the discharging time is long. Therefore, the frequency of the oscillator is mainly determined by the discharging time. Through the capacitor charge and discharge formula:

[0042]

[0043] It can be seen that by modifying the voltage difference between the two ends, the capacitance value, and the current value, the discharging time can be changed, thereby changing the oscillation frequency.

[0044] Two reference voltages are achieved by resistor voltage division. This circuit is normally open. In order to reduce power consumption, the current in this circuit should be minimized as much as possible. Considering the area factor, a MOS transistor with a diode structure can be added above and below this circuit to utilize its Vds to reduce the voltage value in the resistor, thereby reducing the resistance value and achieving the purpose of saving area. In order to avoid the impact of overshoot on the actual pressure difference, the selection of ΔU is between 2V and 3V.

[0045] As Figure 1 shown, the ultrasonic transmitting circuit of the present invention can control the frequency of the signal by adjusting parameters such as capacitance value, voltage difference across both ends, and discharge current value to achieve the operating frequency of the transducer. This circuit does not require high-voltage power supply, is small in size and easy to integrate, reduces circuit cost, and has low power consumption. The measured power consumption is 1.2mW, and the frequency error is <0.5%, meeting the requirements of portable devices.

[0046] As Figure 2 shown, two reference voltages are formed by the resistor through current and are connected to the positive and negative ends of the comparator at different phase times. The comparator is used to compare the voltages at the positive and negative ends and output high and low levels. The structure of the current mirror is used to provide a bias voltage for the comparator.

[0047] As Figure 3 shown, Monte Carlo sampling simulation is performed on 100 points of the output frequency of this circuit. The simulation settings also include mismatch and process deviation, and the mean value is 1.01MHz, meeting the expected requirements.

[0048] In summary, an adjustable-frequency ultrasonic transmitting circuit proposed by the present invention realizes more efficient energy utilization and more reliable signal transmission by optimizing signal generation and power management, thereby improving the measurement accuracy and adaptability of the ultrasonic flowmeter. Generate a suitable high-frequency oscillation signal to drive the ultrasonic transducer to send ultrasonic signals.

Claims

1. An ultrasonic transmitting circuit with adjustable frequency, characterized in that: include: The voltage divider circuit divides the power supply voltage through resistors R1 and R2 to generate two reference voltages: a high reference voltage V high and a low reference voltage Vlow; The comparator module is connected to the voltage divider circuit, and controls the charging and discharging of the capacitor through the P-type MOS tube and the N-type MOS tube to generate an oscillation signal; The DFF trigger divides the oscillation signal into different frequencies and shapes them, outputs a pulse signal, and adjusts the oscillation signal to a frequency suitable for the operation of the transducer; The current mirror structure provides a constant current source for charging and discharging the capacitor.

2. The frequency-adjustable ultrasonic transmitting circuit according to claim 1, characterized in that: The resistance values ​​of the resistors R1 and R2 are both greater than 10 kΩ.

3. The frequency-adjustable ultrasonic transmitting circuit according to claim 1, characterized in that: The voltage divider circuit reduces power consumption through a small current and a diode structure MOS tube.

4. The frequency-adjustable ultrasonic transmitting circuit according to claim 1, characterized in that: The voltage difference between the high reference voltage Vhigh and the low reference voltage Vlow is 0.5V-3V to avoid the influence of overshoot on the actual voltage difference.

5. The frequency-adjustable ultrasonic transmitting circuit according to claim 1, characterized in that: The high reference voltage Vhigh and the low reference voltage Vlow are used at the inverting input terminal (VIN-) of the comparator as comparison references.

6. The frequency-adjustable ultrasonic transmitting circuit according to claim 1, characterized in that: The voltage divider circuit further includes a two-stage operational amplifier, which amplifies and stabilizes the reference voltage generated by the voltage divider circuit and then outputs the reference voltage to the inverting input terminal (VIN-) of the comparator module.

7. The frequency-adjustable ultrasonic transmitting circuit according to claim 1, characterized in that: The pulse signal is a square wave signal with a duty cycle of 50%.

8. The frequency-adjustable ultrasonic transmitting circuit according to claim 1, characterized in that: In the voltage divider circuit, R1 = 36 kΩ, R2 = 85 kΩ.

9. The frequency-adjustable ultrasonic transmitting circuit according to claim 1, characterized in that: The Vhigh=3.3V, Vlow=2.7V.

10. The frequency-adjustable ultrasonic transmitting circuit according to claim 1, characterized in that: The frequency division ratio of the DFF trigger is 2, and the output frequency is 1 / 2 of the oscillation frequency.

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