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 ultrasound imaging, and more particularly to a transceiver used with an ultrasound transducer to transmit high power and high frequency arbitrary waveforms with low distortion, and having the ability to monitor the transmitted signal via a receiver during transmission. [Background technology]

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

[0003] Most ultrasound systems use what is known as a transmit / receive (T / R) switch to protect the receiver input during transmission. A typical ultrasound 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 elements 16 in response to the control signal circuit 14 switching the T / R switch 12 to an ON state during transmission. The ON state has the effect of providing a low impedance path between the transmitter circuit 26 and the transducer elements 16 and a high impedance path from the transmitter circuit 26 to a receiver circuit 20 including a variable gain amplifier 21 having an input 34. Protection from high voltage transmit waveform signals 22 transmitted from a transmit waveform generator 24 in 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 transmitting the waveform signal 22, the T / R switch 12 is switched by the control signal 14 from a transmit state to a receive state 28 (indicated by the dashed line in the T / R switch 12), which provides a low impedance path from the transducer elements 16 to the receiver circuit 20 and also isolates the transmitter circuit 26 from attenuating or degrading the returning echo signal. The receiver circuit 20 may have a resistive connection to ground 36 at its input to protect against large received signals, as well as other limiting circuitry, 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 ultrasound 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 with various delay times to allow steering and focusing of the ultrasound beam in the medium (not shown). This generally requires a transmit period during which all transceivers remain in transmit mode until the last transmitter transmits. Thus, there is a small area in the medium in front of the transducer that cannot receive echoes 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 receive signals. Furthermore, the T / R switch 12, which is typically implemented with diodes and transistors, generally imparts some nonlinear characteristics to the transmit waveform 22, producing some small distortion of the waveform shape. For example, a sinusoidal transmit waveform 22 may 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 power that can be applied to the transducer 16 in transmit mode (on state) due to current limitations and heating effects in electronic switches. Summary of the Invention

[0006] The present disclosure is directed to ultrasound systems and methods, including ultrasound transceivers, that overcome many of the shortcomings of conventional ultrasound transceivers by providing the ability to transmit high power and high frequency arbitrary waveforms with low distortion and the ability to monitor the transmitted signal through a receiver during transmission.

[0007] According to one aspect of the present disclosure, a circuit is provided that includes a transducer element configured to emit ultrasonic signals and receive reflected ultrasonic signals; a transformer circuit coupled to the transducer element, the transformer circuit including a transformer having a primary winding and a secondary winding, the secondary winding coupled to the transducer element; a transmit waveform circuit coupled to the primary winding of the transformer and configured to generate a transmit 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, the receiver circuit configured to be coupled to the transducer element.

[0008] According to another aspect of the present disclosure, the transmit 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 yet 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 transmit waveform generation circuit for receiving an on signal that is tied to the duration of the transmit waveform signal.

[0011] According to yet another aspect of the present disclosure, there is provided an ultrasound device, comprising: 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 waveform of greater than 100 volts peak-to-peak across the transducer and receiving a returning echo signal from the transducer of less than 1 volt peak-to-peak, the transceiver comprising: a transformer having a primary winding and a secondary winding, the primary winding coupled to the transducer; a transmitter circuit coupled to the transducer via a transformer, the transmitter circuit comprising a transmit waveform generator configured to generate a transmit waveform, the transmit waveform generator coupled to a primary winding of the transformer such that the primary winding is driven by the transmit waveform generator, and a secondary winding connected to the 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 the secondary winding of the transformer and the input of the variable gain receiver, the protection circuit being configured, when active, to provide an impedance in the range of 0.1 to 1.0 ohms from the input of the variable gain receiver to ground during a transmit period of the transceiver, such that the input of the variable gain receiver provides an effective ground for the secondary winding of the transformer during the transmit period; An ultrasound device is provided in which a variable gain receiver can be active during transmission, amplifying a small voltage across a protection circuit and monitoring the transmit waveform for amplitude and duration. [Brief explanation of the drawings]

[0012] The foregoing and other features and advantages of the present disclosure will be more readily appreciated as the same becomes better understood from the following detailed description taken in conjunction with the accompanying drawings. [Figure 1] FIG. 1 is a schematic diagram of a conventional ultrasonic transceiver with transmit / receive circuitry. [Figure 2] 1 is a schematic diagram of an ultrasound transceiver with a transmit / receive (T / R) circuit that replaces the T / R switch with a transformer in accordance with the present disclosure. [Figure 3] 3 is a schematic diagram of the ultrasound transceiver of FIG. 2 with a T / R circuit utilizing an H-bridge circuit in accordance with the present disclosure. [Figure 4] FIG. 4 is a schematic diagram of the ultrasound transceiver circuit of FIG. 3 with a T / R circuit utilizing a clamp circuit for receiver circuit protection in accordance with the present disclosure. [Figure 5]5 is a waveform diagram of control signals for the clamp circuit of FIG. 4 along with response waveform signals for components of the ultrasound transceiver circuit of FIG. 4 formed in accordance with the present disclosure. [Figure 6] FIG. 1 is a schematic diagram of a control circuit for a transmitter circuit having waveform plots formed in accordance with exemplary implementations of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0013] In the following description, certain specific details are set forth to provide a thorough understanding of various disclosed implementations. However, one skilled in the art will recognize that implementations can be practiced without one or more of these specific details, or with other methods, components, materials, etc. In other instances, well-known structures related to switches, transducers, amplifiers, control signal generators, programmable logic devices, memories, and transformers have not been shown or described in detail to avoid unnecessarily obscuring the description of the embodiments.

[0014] Unless the context otherwise requires, throughout the specification and the claims that follow, the word "comprise" and variations thereof (such as "comprises" and "comprising") are to be construed in an open-ended and inclusive sense, i.e., "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 with respect to an implementation is included in at least one implementation. Thus, the appearances of the phrase "in one implementation" or "in an implementation" in various places throughout this specification do not necessarily all refer to the same implementation. Furthermore, in one or more implementations, particular features, structures, or characteristics may be combined in any suitable manner. It will be understood that for simplicity and clarity of description, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or similar elements or steps.

[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 to mean "and / or" unless the context clearly dictates otherwise.

[0017] overview Ultrasound systems typically utilize a transceiver connected to a transducer or transducer elements to transmit ultrasonic energy into a medium and receive echo signals that return to the transducer. The transceiver must be capable of generating a high-voltage signal to drive the transducer and receiving the very small voltage signals generated by the returning echoes. Some ultrasound applications also require the generation of specific transmit waveforms with very low distortion to achieve adequate results. An ultrasonic transceiver is described that overcomes most of the shortcomings of conventional ultrasonic transceivers, has the ability to transmit high-power, high-frequency, arbitrary waveforms with low distortion, and has the ability to monitor the transmit signal via a receiver during the transmit period.

[0018] Improved Transceiver Design Eliminating the T / R Switch—One improvement that can be made to conventional transceiver designs is to eliminate the T / R switch entirely. This can be accomplished using a transformer 40 that couples the transmit waveform to the receive path, as shown in transceiver circuit 42 in FIG. 2. During transmission, the high-voltage transmit waveform 42 (with a peak-to-peak voltage of over 100 volts) causes the back-to-back diodes 30 to conduct, which protects the receiver circuit 20 at its input 34 by effectively grounding the input signal. While the input signal is not perfectly grounded, there is a voltage drop of approximately + / - 0.8 across the back-to-back diodes 30, but this is generally small enough not to damage the receiver circuit 20 and has only a minimal effect on the transmit waveform. Upon receiving an echo signal from the medium by the transducer elements 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 elements 16 is typically below the conduction threshold of the back-to-back diodes 30 so that the diodes are 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 of greater than 30 dB.

[0019] Eliminating the T / R switch 12 offers several advantages. First, there is no need for a transmit period because transmission at the transducer elements 16 can occur at any time, even while the receiver circuit 26 is active or other transceivers are transmitting or receiving. This enables applications in which multiple transmissions can be used during an echo signal acquisition period from the same or different sets of transducer elements 16. Second, the echo signal reception period can begin before a transmission occurs at the transducer elements 16, allowing some transducer elements to receive a signal before it is transmitted, thus effectively eliminating a dead zone in front of a transducer element 16. Third, because the receiver circuit receives a highly attenuated version of the transmit waveform, the transmit waveform can be monitored to detect a faulty transmitter circuit 26 or a faulty transducer element 16. Furthermore, the transformer 40 provides good isolation of the high-voltage circuitry of the transmitter circuit 26 from the transducer elements 16, which are often in close contact with the living body. Therefore, a failure of the transmitter circuit 26 is prevented from becoming an electric shock hazard to the subject being scanned.

[0020] A further improved H-bridge transmit generator transceiver circuit 50 is shown in FIG. 3. A typical transmit 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) followed by a power amplifier 25. It is difficult to generate high power levels with this approach because the power amplifier 25 consumes a significant amount of power that is dissipated as heat. Ultrasound systems with multiple transmit channels, each with its own transmitter circuit 26, are limited in transmit power by the ability to cool the circuit.

[0021] As shown in Figure 3, the transformer isolation of the "no T / R switch" design allows the transmit waveform to be generated using high-voltage field-effect transistor (FET) switches 52, 54, 56, and 58 rather than expensive high-power linear amplifiers. The switches 52, 54, 56, and 58 are arranged within an H-bridge circuit 60, each of which is independently controlled so that the voltage driven to the transducer elements 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, facilitating waveform symmetry between the positive and negative outputs—a key characteristic required to minimize even harmonic distortion. The H-bridge circuit 60 also allows the 0 state to be actively driven, which damps ringing in the transducer elements 16 and improves channel-to-channel uniformity. An actively driven 0 state is also critical for generating accurate, arbitrary audio waveforms from the tri-state transmitter (H-bridge circuit) 60.

[0022] FETs 52, 54, 56, and 58 are driven by digital signals A, B, C, and D (see, e.g., FIGS. 3 and 6) that control the transmitter circuit output states. The digital control signals can be readily generated by programmable logic devices or by digital values ​​read from storage devices. These devices are readily available commercially and will not be described or illustrated in detail here. The digital signals can be programmed to transition to new output states that are timed by a high frequency clock, typically in the range of 250-500 MHz.

[0023] For example, turning on FETs 52, 58 with control signals A and D and turning off control signals B and C for FETs 54, 56 applies a high voltage HV in a positive direction to primary winding 62 of transformer 40. Turning off control signals A and D for FETs 52, 58 and turning on control signals B and C for FETs 54, 56 applies a high voltage in the reverse direction to primary winding 62 of transformer 40, generating a negative output. Similarly, turning off control signals A and B and turning on control signals C and D grounds both sides of primary winding 62, generating a zero voltage state. Because signals A and C, and signals B and D, are always complementary, they can be generated by a single drive signal, as shown in FIG. 6. By using control signals A, B, C, and D to control the configuration and timing of the four H-bridge FETs 52, 54, 56, and 58, it is possible to generate a tri-state output waveform with arbitrarily timed state transitions which, when filtered by the impulse response of the transducer element 16, will generate an arbitrary acoustic waveform in the medium acoustically coupled to the transducer element 16.

[0024] Thus, this transceiver circuit 50 can generate acoustic waveforms that match those from high-power linear amplifiers. (See Flynn, J. et al., "Method and System for Arbitrary Waveform Generation Using a Tri-State Transmit Pulser," PCT / US2014 / 047080.) In addition to lower cost, an advantage of the tri-state approach is that it can generate very high-power arbitrary acoustic waveforms with low power consumption in the transmitter circuitry itself, thereby reducing power and cooling requirements for the transmitter circuitry.

[0025] Reduced Nonlinear Effects and Distortion - Many ultrasound applications require high linearity in the transmit waveform and low distortion at the receiver to achieve their objectives. For example, there are ultrasound applications where the transmit waveform is coded to uniquely identify the signal in a mixture of acoustic signals and noise. In order to decode the transmitter signal in the receive signal processing, it is important to have good linearity in both the transmit waveform and the signal path prior to the receiver input.

[0026] In previous "T / R switchless" designs of transceiver circuits 42 and 50, 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. While these back-to-back diodes 30 are effective in protecting the receiver circuit 20 during transmission, they introduce slight distortion into the transmit waveform and nonlinear characteristics into the signal path for receiving the echo signal at the transducer elements 16.

[0027] To improve linearity and reduce distortion, as shown in transceiver circuit 70 of FIG. 4, the back-to-back diodes 30 can be replaced with two parallel-coupled 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 present very low resistance (approximately 0.1 ohms). This resistance is also fairly constant over the entire output current range of the transmitter circuit 60. Because a typical receiver can receive signals greater than ±0.8 volts, this active clamp circuit 76 eliminates the crossover distortion of the passive clamp diodes 30 and increases the dynamic range of the receiver circuit 20. With the active clamp circuit 76 providing a consistent, linear resistance, the attenuated transmit waveform signal at the input 34 of the receiver circuit 20 is an accurate representation of the transmit waveform and can be used to monitor transmit power and duration and to detect faulty transmitter circuits or transducer elements. This monitoring can be accomplished without additional circuitry by simply capturing the unsaturated output signal of the receiver during the transmit period and estimating the transmit power from the scaled-down signal from the receiver. This requires knowledge of the receiver gain (during transmit) and the attenuation factor of the clamp circuit, which can be easily determined by one skilled in the art and will not be described in detail herein.

[0028] The waveform diagrams for the control signals of the clamp circuit of Figure 4 are shown in Figure 5, along with the response waveform signals for the components of the ultrasound transceiver circuit of Figure 4. The control of the active clamp circuit 30 is shown by signals E and F, which are typically switched on together. The clamp control signal is generated to correspond to the transmit duration shown in the second waveform, minimizing the signal level at the variable gain amplifier in the receiver circuit 20. While this adds additional complexity to the design, it is tied to the transmit waveform duration and can be generated automatically by the digital transmit signal generator circuit 60 for most waveforms. The ability to transmit at any time during the receive period is still preserved. The diagram in Figure 5 also shows the receiver circuit 20 output in the third waveform and the transducer element 16 output in the fourth waveform. Note that there is a small signal at the receiver output during transmit, which can be used to estimate the transmit power. This can be scaled up somewhat if necessary.

[0029] The H-bridge circuit 60 can also be a source of distortion in the transmit waveform if not properly designed and programmed. FETs 52, 54, 56, and 58 do not switch instantaneously; there can be transient voltage effects that corrupt the waveform while one FET is on and another is off. These effects can be minimized by fine-tuning the timing of the transitions. Small delays can be introduced into the control signals that can be adjusted for propagation delays and component variations. Small delays can be programmed at system startup using a calibration procedure that minimizes distortion components.

[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 coupled to a P gate driver 70 and an N gate driver 72, respectively. The P gate driver 70 has an output forming a C digital signal coupled directly to the gate of N-FET 56. The output of the P gate driver 70 is also an A digital signal input to the gate of P-FET 52 via a capacitor 74. The positive +HV bias rail is connected to the gate of 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 N-FET 58 and to the gate of P-FET 54 via a capacitor 78 as digital signal B. The +HV bias rail is also coupled to the gate of P-FET 54 via a parallel diode-resistor circuit 80.

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

[0032] In general, the terms used in the following claims should not be construed to limit the claims to the specific implementations disclosed in the specification and claims, but should be construed to include all possible implementations along with the full range of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure herein.

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

Claims

1. a transducer element configured to emit an ultrasonic signal and receive a reflected ultrasonic signal; a transformer circuit coupled to the transducer element, the transformer circuit comprising a transformer having a primary winding and a secondary winding, the secondary winding coupled to the transducer element; a transmit waveform circuit coupled to the primary winding of the transformer and configured to generate a transmit 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 via the secondary winding; a clamp circuit coupled between the secondary winding of the transformer and the input of the receiver circuit; It is equipped with The circuit, wherein the clamp circuit comprises an active clamp circuit having a pair of field effect transistor (FET) switches coupled in parallel to the input of the receiver circuit.

2. The circuit of claim 1 , wherein the transmit waveform circuit comprises an H-bridge circuit.

3. 3. The circuit of claim 2, wherein the H-bridge circuit comprises four FETs that generate a tri-state output waveform, each of the four FETs being independently switchable on and off.

4. 4. The circuit of claim 3, wherein the duration of each state in the tri-state output waveform is programmable to produce a three-level output waveform that, when filtered by the impulse response of the transducer circuit, produces any desired acoustic output waveform.

5. 4. The circuit of claim 3, wherein the timing of switching on and off each of the FETs can be adjusted with a small delay to minimize distortion in the output of the transmit waveform circuit.

6. 2. The circuit of claim 1, wherein each of the FET switches in the pair of FET switches has a control terminal coupled to the transmit waveform circuit for receiving an on signal tied to a duration of the transmit waveform signal.

7. 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 waveform of greater than 100 volts peak-to-peak across said transducer circuit and receiving said returning echo signal from said transducer circuit of less than 1 volt peak-to-peak; Equipped with The transceiver a transformer having a primary winding and a secondary winding, the secondary winding coupled to the transducer circuit; a transmitter circuit coupled to the transducer circuit via the transformer, the transmitter circuit comprising a transmit waveform generator configured to generate a transmit waveform, the transmit waveform generator coupled to a primary winding of the transformer such that the primary winding is driven by the transmit waveform generator, the secondary winding being connected to the transducer circuit on one side and to an 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, the protection circuit configured, when active, to provide an impedance in the range of 0.1 to 1.0 ohms from the input of the variable gain receiver to ground during a transmit period of the transceiver, such that the input of the variable gain receiver provides an effective ground for the transformer secondary winding during the transmit period; Including, the variable gain receiver may be active during the transmit period, amplifying a small voltage across the protection circuit and monitoring the transmit waveform for amplitude and duration; The ultrasonic device, wherein the protection circuit comprises an active clamp circuit having a pair of field effect transistor (FET) switches coupled in parallel to the input of the variable gain receiver.

8. 8. The ultrasonic device of claim 7, wherein the impedance of the protection circuit when active is resistive and constant over a range of currents at the transmitter circuit output.

9. 8. The ultrasonic device of claim 7, wherein the activation of the protection circuitry for the input of the variable gain receiver is performed automatically based on the duration of the transmit waveform.

10. 8. The ultrasonic device of claim 7, wherein the transmitter circuitry can be activated multiple times during a receive period using simultaneous active control of the protection circuitry, whereby the variable gain receiver is minimally affected during each activation.

11. 8. The ultrasonic device of claim 7, wherein the transmit waveform generator is configured to generate a tri-state output waveform including −HV, 0, and +HV states, where HV can be set over a range from less than 2 volts to more than 100 volts.

12. 12. The ultrasonic device of claim 11, wherein the three states of the tri-state output waveform are generated from four FETs configured in an H-bridge circuit, each of the four FETs being independently switchable on and off.

13. 13. The ultrasonic device of claim 12, wherein the duration of each state in the tri-state output waveform is programmable to produce a three-level output waveform that, when filtered by the impulse response of the transducer circuit, produces any desired acoustic output waveform.

14. 13. The ultrasonic device of claim 12, wherein the timing of switching on and off each of the FETs can be adjusted with a small delay to minimize distortion in the output of the transmitter circuit.

Images