Bipolar drive circuit and impedance matching method for an ultrasonic transducer

Abstract

The present invention relates to a bipolar drive circuit and an impedance matching method for an ultrasonic transducer, belonging to the technical field of ultrasonic transducer drive. The drive circuit divides the primary circuit into two parts through the center tap of the transformer, and two field effect transistors S1 and S2 are used to control the opening or closing of the two parts of the circuit respectively. At the same time, two diodes D1 and D2 are used to ensure that the two parts of the circuit work independently; capacitors C1 and C2 are also provided in the circuit as the leakage inductance absorption branch of the transformer, and an inductor L1 is connected to the center tap of the primary side of the transformer T1 to achieve impedance matching of the drive circuit. The present invention places the matching inductor on the primary side of the transformer, and uses the characteristics of the transformer to greatly reduce the value of the matching inductor, reduce the volume of the inductor, and facilitate the selection and manufacture of the inductor.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultrasonic transducer driving, and relates to a bipolar driving circuit and an impedance matching method for an ultrasonic transducer. Background Art

[0002] The function of an ultrasonic transducer is a device that converts the input electrical energy into mechanical energy and emits it in the form of sound waves; the driving circuit of an ultrasonic transducer is the basis of the entire ultrasonic measurement circuit. The role of the driving circuit is to generate a regular electrical pulse with a certain power, a certain pulse width, and a certain frequency to excite the ultrasonic transducer, and then the transducer converts it into ultrasonic waves and emits them outward.

[0003] Impedance matching reflects the power transmission relationship between the input circuit and the output circuit. When the circuit achieves impedance matching, the coupling condition of the circuit is the best and the output power is the largest. On the contrary, reflected power is generated, the energy obtained by the transducer is relatively small, the energy loss is relatively large, and the circuit is easily burned out, causing damage to the circuit. Therefore, impedance matching must be performed on the driving circuit.

[0004] Currently, the driving circuits that provide alternating voltage for ultrasonic transducers are mainly divided into the following forms:

[0005] (1) Driving by using a transformer. The driving circuit mainly includes MOS transistors and a transformer. Generally, the driving circuit is designed on the primary side of the transformer, while the ultrasonic transducer is arranged on the secondary side of the transformer. This driving method controls the on or off of the MOS transistor through a control pulse. When the MOS transistor is on, a high voltage is generated on the secondary side of the transformer. When the MOS transistor is off, the voltage on the secondary side of the transformer is zero.

[0006] (2) Driving by using a push-pull driving circuit. The structure of this driving circuit is relatively complex and the implementation cost is relatively high.

[0007] (3) Driving by using a dedicated chip. In this driving method, among the two pins of the ultrasonic transducer, one pin is grounded and the other pin is connected to the driving chip. The output of the chip is controlled through a control pulse, and an alternating driving voltage is provided for the ultrasonic transducer through the chip. Since the input voltage of the chip is small, for a device power supply circuit with high requirements for the driving voltage, its complexity increases; at the same time, in order to obtain ultrasonic signals with consistent energy, it is necessary to keep the driving voltage of the ultrasonic transducer stable, which leads to the need to add a voltage stabilizing circuit in the circuit to keep the driving voltage stable when using the chip for driving, and this undoubtedly increases the complexity of the circuit and is not conducive to the design of the driving circuit.

[0008] When driven by a transformer, the ultrasonic transducer can have a relatively high emission sound intensity. The transducer is capacitive at the resonant frequency point. If direct drive is used, it will not only cause excessive energy loss, but also reduce the electro-acoustic conversion intensity and efficiency. Therefore, impedance matching technology is adopted to introduce a series inductor in the mH level to make the transducer circuit approximately present a pure resistive state near the resonant frequency point. However, in this case, the required inductor has a large volume and often needs to be customized, which increases the circuit cost and is not conducive to circuit design. Therefore, the present invention designs the drive circuit of the ultrasonic transducer to reduce the matching inductor value and facilitate the selection of the inductor. Summary of the Invention

[0009] In view of this, the purpose of the present invention is to provide a bipolar drive circuit for an ultrasonic transducer and a method for matching the impedance of the drive circuit to reduce the matching inductor value of the drive circuit and facilitate the selection of the inductor.

[0010] To achieve the above object, the present invention provides the following technical solutions:

[0011] A bipolar drive circuit for an ultrasonic transducer, the drive circuit includes a transformer T1, capacitors C1, C2, diodes D1, D2, field effect transistors S1, S2, and an inductor L1.

[0012] Among them, the positive electrode of the diode D1 is connected to the source electrode of the field effect transistor S1, and the negative electrode of D1 is respectively connected to one end of the capacitor C1 and the negative electrode of the power supply; the other end of the capacitor C1 is respectively connected to the drain electrode of the field effect transistor S1 and one end of the primary side of the transformer T1; the gate electrode of S1 is connected to a control signal.

[0013] Among them, the positive electrode of the diode D2 is connected to the source electrode of the field effect transistor S2, and its negative electrode is respectively connected to one end of the capacitor C2 and the negative electrode of the power supply; the other end of the capacitor C2 is respectively connected to the drain electrode of the field effect transistor S2 and one end of the primary side of the transformer T1; the gate electrode of the field effect transistor S2 is connected to a control signal; one end of the inductor L1 is connected to the positive electrode of the power supply, and the other end is connected to the center tap of the primary side of the transformer T1.

[0014] The secondary side of the transformer T1 is connected to the ultrasonic transducer.

[0015] The capacitors C1 and C2 respectively serve as leakage inductance absorption branches of the primary side of the transformer T1; the diodes D1 and D2 are used to make the two primary side circuits of the transformer T1 work independently; the inductor L1 is used to achieve impedance matching of the drive circuit.

[0016] Further, the field effect transistors S1 and S2 are controlled by complementary square wave signals.

[0017] Further, the impedance matching method of the drive circuit is specifically as follows: The transformer T1 is analyzed using a linear model to perform impedance matching of the inductor L1 of the bipolar drive circuit, specifically as follows:

[0018] The overall equivalent impedance Z of the secondary side of transformer T1 T2 is:

[0019] Z T2 = Re2 + Le2s + Z u

[0020] s = j(2πf)

[0021] When Z T2 is equivalent to the primary side of transformer T1, it is:

[0022]

[0023] The equivalent impedance Z of the primary side of the transformer T1 is:

[0024]

[0025] Then the value of inductance L1 is:

[0026]

[0027] In the above formula, Re2 represents the equivalent series resistance of the secondary side of the transformer, j represents the imaginary unit, f represents the resonant frequency of the ultrasonic transducer, Le2 represents the leakage inductance of the secondary side of the transformer, and Z u represents the equivalent impedance of the ultrasonic transducer at the operating point, n represents the turns ratio of the primary and secondary sides of the transformer as 1:n, Re1 represents the equivalent series resistance of the primary side of the transformer, Le1 represents the leakage inductance of the primary side of the transformer, and L m represents the exciting inductance, and Lm[Z T1 is the imaginary part of Z T1 .

[0028] The beneficial effect of the present invention is that: based on a transformer with a center tap, the present invention designs a bipolar drive circuit for an ultrasonic transducer, makes the matching inductance located on the primary side of the transformer, and according to the characteristics of the transformer, the value of the matching inductance is greatly reduced, eliminating the need to customize a large-sized inductance. At the same time, there is a rich variety of inductances in the market, making it easy to select an inductance.

[0029] Other advantages, objectives, and features of the present invention will be described to some extent in the subsequent specification, and to some extent, will be obvious to those skilled in the art based on the study of the following text, or can be learned from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be described in detail preferably with reference to the accompanying drawings, where:

[0031] Figure 1 It is a bipolar ultrasonic transducer driving circuit with impedance matching;

[0032] Figure 2 It is the equivalent circuit when the ultrasonic transducer is near the resonance frequency point;

[0033] Figure 3 It is the linear equivalent model of the transformer;

[0034] Figure 4 It is the working process of the driving circuit. Specific implementation manners

[0035] The following uses specific specific examples to illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the diagrams provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0036] Among them, the attached drawings are only for illustrative purposes, showing only schematic diagrams, not physical diagrams, and cannot be understood as a limitation to the present invention; in order to better illustrate the embodiments of the present invention, some components in the attached drawings will be omitted, enlarged or reduced, which do not represent the dimensions of the actual product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the attached drawings may be omitted.

[0037] In the attached drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "rear", etc. indicating the orientation or positional relationship, it is based on the orientation or positional relationship shown in the attached drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the attached drawings are only for illustrative purposes and cannot be understood as a limitation to the present invention. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0038] The bipolar ultrasonic transducer driving circuit proposed by the present invention is as Figure 1As shown, the primary side of the transformer in the drive circuit has a center tap, the turns ratio of the transformer is 1:n, the field effect transistors S1 and S2 are controlled by complementary square wave signals, the capacitors C1 and C2 are respectively the leakage inductance absorption branches on the primary side of the transformer, the diodes D1 and D2 ensure that the two primary side circuits of the transformer work independently, and the inductor L1 realizes the impedance matching of the drive circuit.

[0039] The ultrasonic transducer is usually a capacitive element. When it works near the resonant frequency, its approximate equivalent circuit is as Figure 2 shown. Then the equivalent impedance Z u at the operating point of the ultrasonic transducer is:

[0040]

[0041] Zs=j(2πf) (2)

[0042] In the formula, j represents the imaginary unit, and f is the resonant frequency of the ultrasonic transducer.

[0043] The transformer is analyzed using a linear model, and it is assumed that the two primary sides of the transformer with the center tap separated are completely symmetrical. Its equivalent model is as Figure 3 shown. The relevant parameters in the figure are: primary side leakage inductance Le1, primary side equivalent series resistance Re1, magnetizing inductance Lm, secondary side leakage inductance Le2, secondary side equivalent series resistance Re2, and the turns ratio of the primary and secondary sides of the transformer is 1:n. Then according to Figure 3 it can be obtained that the overall equivalent impedance of the secondary side of the transformer is:

[0044] Z T2 =Re2+Le2s+Z u (3)

[0045] The equivalent impedance of Z T2 to the primary side impedance of the transformer is:

[0046]

[0047] The primary side impedance of the transformer is:

[0048]

[0049] Then the value of the matching inductor L1 in the drive circuit can be obtained according to Equation (5):

[0050]

[0051] The working process of the bipolar drive circuit is as Figure 4 shown. First, the field effect transistor S1 is turned on and S2 is turned off. This process lasts for Then the field effect transistor S2 is turned on and S1 is turned off, and the duration is

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the present technical solution, and they should all be covered within the scope of the claims of the present invention.

Claims

1. An impedance matching method for a bipolar drive circuit of an ultrasonic transducer. The bipolar drive circuit includes a transformer T1, capacitors C1, C2, diodes D1, D2, field effect transistors S1, S2, and an inductor L1; The positive electrode of diode D1 is connected to the source electrode of field effect transistor S1, and the negative electrode of D1 is respectively connected to one end of capacitor C1 and the negative power supply terminal; the other end of capacitor C1 is respectively connected to the drain electrode of field effect transistor S1 and one end of the primary side of transformer T1; the gate electrode of S1 is connected to a control signal; the positive electrode of diode D2 is connected to the source electrode of field effect transistor S2, and its negative electrode is respectively connected to one end of capacitor C2 and the negative power supply terminal; the other end of capacitor C2 is respectively connected to the drain electrode of field effect transistor S2 and one end of the primary side of transformer T1; the gate electrode of field effect transistor S2 is connected to a control signal; one end of inductor L1 is connected to the positive power supply terminal, and the other end is connected to the center tap of the primary side of transformer T1; the secondary side of transformer T1 is connected to the ultrasonic transducer; the capacitors C1, C2 respectively serve as leakage inductance absorption branches of the primary side of transformer T1; the diodes D1, D2 are used to enable the two primary side circuits of transformer T1 to work independently; the inductor L1 is used to achieve impedance matching of the drive circuit; It is characterized in that This impedance matching method uses a linear model to analyze transformer T1 to perform impedance matching of the inductor L1 of the bipolar drive circuit, specifically as follows: The overall equivalent impedance Z of the secondary side of transformer T1 T2 is as follows: Z T2 = Re2 + Le2s + Z u s = j(2πf) Equivalent to Z T2 on the primary side of transformer T1 is: The equivalent impedance \(Z\) of the primary side of the transformer T1 is as follows: Then the value of inductor L1 is: In the above formula, Re2 represents the equivalent series resistance of the secondary side of the transformer, j represents the imaginary unit, f represents the resonance frequency of the ultrasonic transducer, Le2 represents the leakage inductance of the secondary side of the transformer, and Z u represents the equivalent impedance of the ultrasonic transducer at the operating point. The turns ratio of the primary and secondary sides of the transformer T1 is 1:n. Re1 represents the equivalent series resistance of the primary side of the transformer, Le1 represents the leakage inductance of the primary side of the transformer, and L m represents the exciting inductance, and Lm[Z T1 is the imaginary part of Z T1 .

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