Ultrasonic transmitter with low distortion and simultaneous reception

Abstract

An ultrasonic transceiver that overcomes many of the drawbacks of conventional ultrasonic transceivers by providing the ability to transmit arbitrary waveforms with low distortion, high power, and high frequency, and the ability to monitor the transmitted signal via a receiver during the transmission period. The transceiver circuit includes a transducer element that emits an ultrasonic signal and receives the reflected ultrasonic signal, a transformer circuit having a transformer with a secondary winding and a primary winding coupled to the transducer element, an H-bridge transmission waveform circuit coupled to the primary winding of the transformer to generate a transmission waveform signal to the transducer element via the transformer, an FET clamp coupled to the secondary winding of the transformer, and a receiver circuit having an input coupled to the FET clamp.

Description

Technical Field

[0001] The present disclosure relates to ultrasonic imaging, and more particularly to a transceiver that is used with an ultrasonic transducer to transmit arbitrary waveforms with high output and high frequency with low distortion and has the ability to monitor the transmitted signal via a receiver during the transmission period.

Background Art

[0002] Ultrasonic systems typically utilize multi-element transducers to transmit ultrasonic pulses into a medium and receive echo signals returning from objects in the medium back into the medium. Each transducer element can have its own independent transmitter and receiver, or transceiver, which enables electronic focusing and steering of the ultrasonic beam formed from a combination of transducer elements. To generate transmit pulses from piezoelectric transducer elements with sufficient output, the transmitter typically operates at peak-to-peak voltage levels up to several hundred volts. In contrast, the received echo signal levels are significantly lower in signal strength than the transmit pulses, generally less than a few millivolts, and require a high-gain receiver for proper detection. Due to this large mismatch between the transmit and received signals, the receiver must be protected from long recovery saturation and, in the worst case, from damage due to high transmit currents.

[0003] Most ultrasonic systems use what is known as a transmit / receive (T / R) switch to protect the input of the receiver during the transmit period. A representative ultrasonic transceiver circuit 10 is shown in FIG. 1 and includes a T / R switch 12 controlled by a control signal circuit 14. The T / R switch 12 is coupled to the transducer element 16 in response to the control signal circuit 14 switching the T / R switch 12 to the on state during the transmit period. The on state has the effect of realizing a low impedance path between the transmitter circuit 26 and the transducer element 16 and a high impedance path to the receiver circuit 20 including a variable gain amplifier 21 having an input 34 from the transmitter circuit 26. Protection from the high voltage transmit waveform signal 22 transmitted from the transmit waveform signal generator 24 within the transmitter circuit 26 is provided to the receiver circuit 20 when the T / R switch 12 is in the on state.

[0004] After the transmitter circuit 26 has completed transmission of the waveform signal 22, the T / R switch 12 is switched from the transmit state to the receive state 28 (shown by the dashed line within the T / R switch 12) by the control signal 14, which provides a low impedance path from the transducer element 16 to the receiver circuit 20 and further isolates the transmitter circuit 26 so as not to attenuate or degrade the return echo signal. The receiver circuit 20 can have at its input a resistive connection to ground 36 for protection against large received signals, as well as other limiting circuits such as the back-to-back diode passive receiver protection circuit 30 and capacitance 38 shown in FIG. 1.

[0005] The transceiver circuit of FIG. 1 has several problems that limit its effectiveness. Most ultrasonic systems utilize a single T / R control signal 32 for all transceivers. In the case of a multi-element transducer, the transmit waveform 22 may be emitted at various delay times to enable steering and focusing of the ultrasonic beam in a medium (not shown). This generally requires a transmit period in which all transceivers remain in the transmit mode until the last transmitter transmits. Thus, there is a small region in front of the transducer where echoes cannot be received during the transmit period. Similarly, it is not possible to transmit on an element or group of elements during the receive process without interrupting the entire set of received signals. Further, the T / R switch 12 is typically implemented with diodes and transistors and generally imparts some non-linear characteristics to the transmit waveform 22, generating some small distortion of the waveform shape. For example, a sinusoidal transmit waveform 22 can be distorted to generate higher harmonics that can have undesirable effects in the medium. Finally, the T / R switch 12 generally limits the amount of electrical power that can be applied to the transducer 16 in the transmit mode (on state) due to current limiting and heating effects in the electronic switch. SUMMARY OF THE INVENTION

[0006] The present disclosure is directed to an ultrasonic system and method that includes an ultrasonic transceiver that overcomes most of the drawbacks of conventional ultrasonic transceivers by providing the ability to transmit arbitrary waveforms with low distortion, high output, and high frequency, and the ability to monitor the transmit signal through the receiver during the transmit period.

[0007] According to one aspect of the present disclosure, there is provided a circuit including a transducer element configured to emit an ultrasonic signal and receive the reflected ultrasonic signal, a transformer circuit coupled to the transducer element, the transformer circuit having a primary winding and a secondary winding, the transformer circuit including a transformer in which the secondary winding is coupled to the transducer element, a transmission waveform circuit coupled to the primary winding of the transformer and configured to generate a transmission waveform signal to the transducer element via the transformer circuit, and a receiver circuit having an input coupled to the secondary winding of the transformer and configured to be coupled to the transducer element.

[0008] According to another aspect of the present disclosure, the transmission waveform circuit is an H-bridge circuit.

[0009] According to a further aspect of the present disclosure, the circuit includes a clamp circuit coupled between the secondary winding of the transformer and the input of the receiver circuit. Preferably, the clamp circuit includes an active clamp circuit having a pair of FET switches coupled in parallel to the input of the receiver circuit.

[0010] According to still a further aspect of the present disclosure, each of the FET switches in the pair of FET switches has a control terminal coupled to the transmission waveform generation circuit to receive an on signal associated with the duration of the transmission waveform signal.

[0011] According to yet another aspect of the present disclosure, there is provided an ultrasonic device, including a transducer circuit configured to transmit an ultrasonic signal, receive a corresponding echo signal, and generate a return echo signal, a variable gain receiver having an input coupled to the transducer circuit, a transceiver capable of generating a peak-to-peak waveform exceeding 100 volts across the transducer and receiving a return echo signal from the transducer with a peak-to-peak of less than 1 volt, the transceiver including a transformer having a primary winding and a secondary winding, the primary winding being coupled to the transducer, A transmitter circuit coupled to a transducer via a transformer, comprising a transmission waveform generator configured to generate a transmission waveform, the transmission waveform generator being coupled to a primary winding of the transformer such that the primary winding is driven by the transmission waveform generator, and a secondary winding of the transformer being connected to a transducer circuit on one side and to an input of a variable gain receiver on the other side with a maximum gain of at least 30 dB. A protection circuit coupled between a secondary winding of the transformer and an input of the variable gain receiver, the protection circuit providing an impedance in the range of 0.1 to 1.0 ohm from the input of the variable gain receiver to ground during a transmission period of the transceiver when the protection circuit is active, thereby configuring the input of the variable gain receiver to provide an effective ground for the secondary winding of the transformer during the transmission period. A variable gain receiver is provided that can be active during a transmission period and amplifies a small voltage across the protection circuit to monitor the transmission waveform for amplitude and duration.

Brief Description of the Drawings

[0012] The foregoing and other features and advantages of the present disclosure will be better understood and will be more readily understood from the following detailed description when taken in conjunction with the accompanying drawings.

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Mode for Carrying Out the Invention

[0013] In the following description, specific specific details are described so that a complete understanding of the various disclosed implementation forms can be obtained. However, those skilled in the art will recognize that the implementation forms can be implemented without using one or more of these specific details, or using other methods, components, materials, etc. In other examples, well-known structures related to switches, transducers, amplifiers, control signal generators, programmable logic devices, memories, and transformers are not shown in detail or described in order to avoid unnecessarily obscuring the description of the embodiments.

[0014] Throughout the specification and the following claims, unless the context requires otherwise, the word "comprise" and its variations ("comprises" and "comprising", etc.) are to be construed in a non-limiting and inclusive sense, that is, "including but not limited to".

[0015] References throughout this specification to "one implementation" or "an implementation" mean that a particular feature, structure, or characteristic described in connection with the implementation is included in at least one implementation. Thus, appearances of the phrases "in one implementation" or "in an implementation" in various places throughout this specification are not necessarily all referring to the same implementation. Furthermore, in one or more implementations, the particular features, structures, or characteristics may be combined in any suitable manner. It will be understood that, for the sake of brevity and clarity, reference numerals may be repeated between drawings to indicate corresponding or analogous elements or steps where appropriate.

[0016] As used in this specification and the appended claims, the singular forms "a", "an", and "the" include plural referents unless the content clearly dictates otherwise. It should also be noted that the term "or" is generally used in its broadest sense in the context of meaning "and / or" unless the context clearly dictates otherwise.

[0017] Summary An ultrasonic system typically utilizes a transceiver connected to a transducer or transducer element to transmit ultrasonic energy into a medium and receive an echo signal returning to the transducer. The transceiver must be able to generate a high voltage signal to drive the transducer and must be able to receive the very small voltage signal generated by the returning echo. Some ultrasonic applications also require generating a particular transmit waveform with very low distortion to obtain suitable results. An ultrasonic transceiver is described that overcomes most of the drawbacks of conventional ultrasonic transceivers and has the ability to transmit arbitrary waveforms with low distortion, high output, and high frequency, and also has the ability to monitor the transmit signal through a receiver during the transmit period.

[0018] Improved Transceiver Design Removal of the T / R Switch - One improvement that can be made to a conventional transceiver design is to completely remove the T / R switch. This can be achieved using a transformer 40 that couples the transmit waveform to the receive path, as shown in the transceiver circuit 42 of FIG. 2. During transmission, a high-voltage transmit waveform 42 (having a peak-to-peak voltage exceeding 100 volts) conducts the back-to-back diodes 30, which protects the receiver circuit 20 at its input 34 by effectively grounding the input signal. The input signal has a voltage drop of approximately + / -0.8 volts across the back-to-back diodes 30 and is thus not completely grounded, but this is generally small enough not to damage the receiver circuit 20 and has a minimal impact on the transmit waveform. When an echo signal is received from the medium by the transducer element 16, the transmit drive signal from the transmitter circuit 26 is zero and the transformer 40 becomes a short circuit. The received echo signal level at the transducer element 16 is typically below the conduction threshold of the back-to-back diodes 30 such that the diodes are at a high impedance and allow the received signal to flow to the input 34 of the receiver circuit 20. A typical variable gain receiver circuit 20 has a maximum gain greater than 30 dB.

[0019] Removal of the T / R switch 12 provides several advantages. First, transmission in the transducer element 16 can be performed at any time, even while the receiver circuit 26 is active or while another transceiver is transmitting or receiving, so that no transmission period is required. This enables applications where multiple transmissions can be used during the echo signal acquisition period from the same or different sets of transducer elements 16. Second, the echo signal reception period can start before transmission occurs in the transducer element 16, allowing some transducer elements to receive signals before being transmitted, thus effectively eliminating the previous dead zone of the transducer element 16. Third, since the receiver circuit receives a very attenuated version of the transmission waveform, it can monitor the transmission waveform to detect a faulty transmitter circuit 26 or a faulty transducer element 16. Further, the transformer 40 provides good isolation of the high voltage circuit of the transmitter circuit 26 from the transducer element 16, which is often in close contact with the body. Therefore, a fault in the transmitter circuit 26 is prevented from posing a risk of electric shock to the object being scanned.

[0020] H - bridge transmission generator - An improved transceiver circuit 50 is shown in FIG. 3. The typical transmission waveform generator or transmitter circuit 26 of FIG. 1 for generating any acoustic waveform consists of a digital waveform signal generator 24, followed by a digital - to - analog converter (not shown), and then a power amplifier 25. Since the power amplifier 25 consumes a significant amount of power dissipated as heat, it is difficult to generate high output levels in this manner. An ultrasonic system having multiple transmission channels with its own transmitter circuit 26 has its transmission power limited by its ability to cool the circuits.

[0021] As shown in FIG. 3, transformer isolation in a "no T / R switch" design enables the generation of a transmit waveform using high voltage field effect transistors (FETs) 52, 54, 56, 58 instead of an expensive high power linear amplifier. The switches 52, 54, 56, 58 are arranged within an H-bridge circuit 60, and each of the switches 52, 54, 56, 58 is independently controlled such that the voltage driven to the transducer element 16 can be one of three levels, +HV, 0, or -HV. These levels can be derived from a single HV power supply of 100 volts or more, thereby facilitating waveform symmetry (an important characteristic necessary to minimize even harmonic distortion) between the positive and negative outputs. The H-bridge circuit 60 also enables the 0 state to be actively driven, which attenuates the ringing of the transducer element 16 and improves the uniformity between channels. The actively driven 0 state is also important for generating any accurate acoustic waveform from the tri-state transmitter (H-bridge circuit) 60.

[0022] The FETs 52, 54, 56, 58 are driven by digital signals A, B, C, D (see, for example, FIGS. 3 and 6) that control the transmitter circuit output state. The digital control signals can be easily generated by a programmable logic device or by digital values read from a memory device. These devices are readily commercially available and are not described or illustrated in detail herein. The digital signals can typically program the transition to a new output state that is timed by a high frequency clock in the range of 250 - 500 MHz.

[0023] For example, when the control signals A and D turn on the FETs 52 and 58 and turn off the control signals B and C of the FETs 54 and 56, a high voltage HV is applied in the positive direction to the primary winding 62 of the transformer 40. By turning off the control signals A and D of the FETs 52 and 58 and turning on the control signals B and C of the FETs 54 and 56, a high voltage is applied in the reverse direction to the primary winding 62 of the transformer 40, and a negative output is generated. Similarly, when the control signals A and B are turned off and the control signals C and D are turned on, both sides of the primary winding 62 are grounded, and a 0-voltage state is generated. Since the signals A and C, and the signals B and D are always complementary, as shown in FIG. 6, they can be generated by a single drive signal. By controlling the configuration and timing of the four H-bridge FETs 52, 54, 56, 58 using the control signals A, B, C, and D, it is possible to generate a tri-state output waveform having a state transition at an arbitrary timing, which, when filtered by the impulse response of the transducer element 16, generates an arbitrary acoustic waveform in the medium acoustically coupled to the transducer element 16.

[0024] Therefore, this transceiver circuit 50 can generate an acoustic waveform that matches the acoustic waveform from a high-output linear amplifier. (See "Method and System for Arbitrary Waveform Generation Using a Tri-State Transmit Pulser" by Flynn, J et al., PCT / US2014 / 047080). In addition to being less costly, the advantage of the tri-state approach is that it can generate an arbitrarily high-output acoustic waveform with low power consumption in the transmitter circuit itself, thereby reducing the power and cooling requirements for the transmitter circuit.

[0025] Reduction of Nonlinear Effects and Distortion - Many ultrasonic applications require high linearity in the transmitted waveform and low distortion in the receiver to achieve their objectives. For example, there are ultrasonic applications where the transmitted waveform is encoded to uniquely identify the signal in the mixture of the acoustic signal and noise. To decode the transmitter's signal in the received signal processing, it is important to have good linearity in both the transmitted waveform and the signal path before the receiver's input.

[0026] In the previous "no T / R switch" designs of the transceiver circuits 42 and 50, the back-to-back diodes 30 were used to protect the receiver circuit input 34 from large voltages and to serve as a path to ground for the secondary winding 64 of the transmitter transformer 40 when transmission was active. These back-to-back diodes 30 are effective in protecting the receiver circuit 20 during transmission, but introduce a slight distortion in the transmitted waveform and introduce non-linear characteristics into the signal path for receiving the echo signal by the transducer element 16.

[0027] To improve linearity and reduce distortion, as shown in the transceiver circuit 70 of FIG. 4, the back-to-back diode 30 can be replaced with two parallel-connected FET switches 72, 74 controlled by control signals E and F respectively to form an active clamp circuit 76. When FETs 72, 74 are switched on, they exhibit a very low resistance (about 0.1 ohm). This resistance is also fairly constant over the entire output current range of the transmitter circuit 60. Since a typical receiver can receive signals greater than + / - 0.8 volts, this active clamp circuit 76 removes the crossover distortion of the passive clamp diode 30 and increases the dynamic range of the receiver circuit 20. The attenuated transmitted waveform signal at the input 34 of the receiver circuit 20 is an accurate representation of the transmitted waveform due to the active clamp circuit 76 providing a consistent linear resistance and can be used to monitor the transmitted power and duration, as well as to detect a failed transmitter circuit or transducer element. This monitoring can be achieved without additional circuitry by simply capturing the non-saturated output signal of the receiver during the transmission period and estimating the transmitted power from the scaled-down signal from the receiver. This requires knowledge of the receiver gain (during transmission) and the attenuation factor of the clamp circuit, which can be easily determined by one skilled in the art and is not described in detail herein.

[0028] The behavior waveform diagram of the clamp circuit of FIG. 4 with respect to the control signal is shown in FIG. 5 together with the response waveform signal with respect to the components of the ultrasonic transceiver circuit of FIG. 4. The control of the active clamp circuit 30 is indicated by signals E and F, and these signals are typically switched on together. The clamp control signal is generated to correspond to the transmission duration shown in the second waveform, minimizing the signal level at the point of the variable gain amplifier in the receiver circuit 20. This adds additional complexity to the design, but it is tied to the transmission waveform duration and can be automatically generated by the digital transmission signal generator circuit 60 for most waveforms. The ability to transmit at any time during the reception period is still maintained. The figure of FIG. 5 also shows the output of the receiver circuit 20 in the third waveform and the output of the transducer element 16 in the fourth waveform. Note that a small signal at the receiver output exists during transmission and this can be used to estimate the transmission power. This can be amplified somewhat if necessary.

[0029] The H-bridge circuit 60 can also cause distortion of the transmission waveform if not properly designed and programmed. The FETs 52, 54, 56, 58 do not switch instantaneously, and there may be transient voltage effects that corrupt the waveform while one FET is turning on and another is turning off. These effects can be minimized by fine-tuning the timing of the transitions. A small delay can be introduced for the control signal that can be adjusted for propagation delay and component variations. The small delay can be programmed at system startup using a calibration procedure that minimizes the distortion component.

[0030] For example, FIG. 6 shows a representative control circuit 66 for the transmitter circuit 60 shown in FIG. 4. The control circuit 66 in this implementation includes a programmable logic device 68 having outputs P and N respectively coupled to a P-gate driver 70 and an N-gate driver 72. The P-gate driver 70 has an output that forms a C digital signal directly coupled to the gate of the N-FET 56. The output of the P-gate driver 70 is also an A digital signal that is input to the gate of the P-FET 52 via a capacitor 74. The positive +HV bias rail is connected to the gate of the P-FET 52 via a parallel diode-resistor circuit 76. Similarly, the output of the N-gate driver 72 is a D digital signal coupled to the gate of the N-FET 58 and coupled to the gate of the P-FET 54 as a digital signal B via a capacitor 78. The +HV bias rail is also coupled to the gate of the P-FET 54 via a parallel diode-resistor circuit 80.

[0031] At the bottom of FIG. 6, waveform plots versus time are shown for the P and N outputs, the A, B, C, D gate signals, and the output signal Output received by the transducer element 16.

[0032] Generally, the terms used in the following "claims" should not be construed as limiting the claims to the specific implementations disclosed in the specification and claims, but should be construed to include all possible implementations together with the full scope of equivalents that give rights to such claims. Therefore, the "claims" are not limited by the disclosure of this specification.

[0033] This application claims the benefit of priority of U.S. Provisional Patent Application No. 17 / 747,398, filed on May 18, 2022, the entire disclosure of which is incorporated herein by reference.

Claims

1. A transducer element configured to emit an ultrasonic signal and receive the reflected ultrasonic signal, A transformer circuit coupled to the transducer element, comprising a transformer having a primary winding and a secondary winding, wherein the secondary winding is coupled to the transducer element, A transmission waveform circuit coupled to the primary winding of the transformer and configured to generate a transmission waveform signal to the transducer element via the transformer circuit, A receiver circuit having an input coupled to the secondary winding of the transformer and configured to be coupled to the transducer element A circuit comprising.

2. The circuit according to claim 1, wherein the transmission waveform circuit comprises an H-bridge circuit.

3. The circuit according to claim 2, further comprising a clamp circuit coupled between the secondary winding of the transformer and the input of the receiver circuit.

4. The circuit according to claim 3, wherein the clamp circuit comprises an active clamp circuit having a pair of FET switches coupled in parallel to the input of the receiver circuit.

5. The circuit according to claim 4, wherein each of the FET switches in the pair of FET switches has a control terminal coupled to the transmission waveform generator circuit for receiving an on signal associated with the duration of the transmission waveform signal.

6. A transducer circuit configured to transmit an ultrasonic signal, receive a corresponding echo signal, and generate a return echo signal, A variable gain receiver having an input coupled to the transducer circuit, A transceiver capable of generating a peak-to-peak waveform exceeding 100 volts across the transducer and receiving the return echo signal from the transducer with a peak-to-peak of less than 1 volt Comprising, The transceiver is, A transformer having a primary winding and a secondary winding, wherein the primary winding is coupled to the transducer, A transmitter circuit coupled to the transducer via the transformer, comprising a transmission waveform generator configured to generate a transmission waveform, wherein the transmission waveform generator is coupled to the primary winding of the transformer such that the primary winding is driven by the transmission waveform generator, and the secondary winding is connected to the transducer circuit on one side and to the input of the variable gain receiver on the other side with a maximum gain of at least 30 dB. A protection circuit coupled between the secondary winding of the transformer and the input of the variable gain receiver, wherein when the protection circuit is active, the protection circuit provides an impedance in the range of 0.1 to 1.0 ohm from the input of the variable gain receiver to ground during the transmission period of the transceiver, whereby the input of the variable gain receiver is configured to provide an effective ground for the secondary winding of the transformer during the transmission period. Including The variable gain receiver can be active during the transmission period and can amplify a small voltage across the protection circuit to monitor the transmission waveform in terms of amplitude and duration. An ultrasonic device.

7. The ultrasonic device according to claim 6, wherein the impedance of the protection circuit when active is resistive and constant over the current range of the transmitter circuit output.

8. The ultrasonic device according to claim 6, wherein the activation of the protection circuit for the input of the variable gain receiver is automatically performed based on the duration of the transmission waveform.

9. The transmitter circuit can be activated multiple times during the reception period using simultaneous active control of the receiver input clamp, whereby the receiver is minimally affected during each activation. The ultrasonic device according to claim 6.

10. The transmission waveform generator is configured to generate a tri-state output waveform including states of -HV, 0, and +HV, where HV can be set over a range from less than 2 volts to greater than 100 volts. The ultrasonic device according to claim 6.

11. The three states of the tri-state output waveform are generated from four FETs configured in an H-bridge circuit, and each of the four FETs can be independently switched on and off. The ultrasonic device according to claim 10. Claim 12 The ultrasonic device according to claim 11, wherein the duration of each state in the tri-state output waveform can be programmed to generate a three-level output waveform that generates an arbitrary desired acoustic output waveform when filtered by the impulse response of the transducer. Claim 13 The ultrasonic device according to claim 11, wherein the switching on and off timing of each of the FETs can be adjusted with a small delay to minimize distortion in the output of the transmitter circuit.

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