Ultrasound transmitter with low distortion and concurrent reception

Abstract

An ultrasonic transceiver overcomes numerous defects of conventional ultrasonic transceivers by providing the ability to transmit high power and high frequency arbitrary waveforms with low distortion and the ability to monitor transmit signals through the receiver during a transmit period, the transceiver circuit having: a transducer element, the transducer element transmits an ultrasonic signal and receives a reflected ultrasonic signal; a transformer circuit having a transformer having a primary winding and a secondary winding coupled to the transducer element; an H-bridge transmit waveform circuit coupled to the primary winding of the transformer to generate a transmit waveform signal to the transducer element via the transformer; an FET clamp circuit coupled to the secondary winding of the transformer; and a receiver circuit having an input coupled to the FET clamp circuit.

Description

[0001] background Technical Field

[0002] The present disclosure relates to ultrasound imaging, and more particularly to a transceiver for use with an ultrasound transducer to transmit an arbitrary waveform at high power and high frequency with low distortion and with the ability to monitor the transmitted signal through a receiver during a transmit period.

[0003] Related technical description

[0004] Ultrasonic systems typically utilize multi-element transducers to transmit ultrasonic pulses into a medium and receive echo signals returning to the medium and from objects within the medium. Each transducer element may have its own independent transmitter and receiver or transceiver, thereby allowing electronic focusing and steering of the ultrasonic beam formed by the combination of transducer elements. In order to generate transmit pulses from piezoelectric transducer elements of sufficient power, the transmitter is typically operated at peak-to-peak voltage levels of up to several hundred volts. In contrast, the received echo signal level is significantly lower than the transmit pulse in signal strength, typically less than a few millivolts, which requires a high-gain receiver for adequate detection. Due to this large difference between the transmit and receive signals, the receiver must be protected from long recovery saturation, or worse, from damage by high transmit currents.

[0005] Most ultrasound systems employ a so-called transmit / receive (T / R) switch to protect the input of the receiver during transmit periods. Figure 1 , a representative ultrasound transceiver circuit 10 is shown, which includes a T / R switch 12 controlled by a control signal circuit 14. In response to the control signal circuit 14 switching the T / R switch 12 to an on state during a transmit period, the T / R switch 12 is coupled to the transducer element 16. The on state has the effect of achieving a low impedance path between the transmitter circuit 26 and the transducer element 16 and a high impedance path from the transmitter circuit 26 to the receiver circuit 20, which includes a variable gain amplifier 21 having an input 34. When the T / R switch 12 is in the on state, the receiver circuit 20 is provided with protection from the high voltage transmit waveform signal 22 transmitted from the transmit waveform signal generator 24 in the transmitter circuit 26.

[0006] After the transmitter circuit 26 has completed transmitting 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 in 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 protects the transmitter circuit 26 from attenuating or degrading the return echo signal. The receiver circuit 20 may have other limiting circuits at its input, such as a resistive connection to ground 36 to prevent large received signals, and Figure 1The back-to-back diode passive receiver protection circuit 30 and capacitor 38 are shown in FIG.

[0007] Figure 1 The transceiver circuit of has several problems that limit its effectiveness. Most ultrasound systems use a single T / R control signal 32 for all transceivers. In the case of a multi-element transducer, the transmit waveform 22 can be transmitted at various delay times to enable the ultrasound beam to be guided and focused in the medium (not shown). This usually requires a transmit period in which all transceivers remain in transmit mode until the last transmitter has transmitted. Therefore, there is a small area in the medium in front of the transducer in which the echo 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 receive signal set. In addition, the T / R switch 12, which is usually implemented with diodes and transistors, usually imparts some nonlinear characteristics to the transmit waveform 22, resulting in some small distortion of the waveform shape. For example, a sine wave transmit waveform 22 may be distorted in a way that generates higher harmonics, which can cause undesirable effects in the medium. Finally, due to current limitations and thermal effects in the electronic switch, the T / R switch 12 usually limits the amount of electrical power that can be applied to the transducer 16 in the transmit mode. Summary of the invention

[0008] The present disclosure relates to ultrasound systems and methods including ultrasound transceivers that overcome most of the deficiencies of conventional ultrasound transceivers by providing the ability to transmit arbitrary waveforms at high power and high frequency with low distortion and the ability to monitor the transmitted signal through the receiver during the transmit period.

[0009] According to one aspect of the present disclosure, a circuit is provided, comprising: a transducer element configured to transmit 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 being 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 and configured to be coupled to the transducer element.

[0010] According to another aspect of the present invention, the transmit waveform circuit is an H-bridge circuit.

[0011] According to further aspects of the present disclosure, the circuit comprises a clamp circuit coupled between the secondary winding of the transformer and the input of the receiver circuit.Preferably, the clamp circuit comprises an active clamp circuit having a pair of FET switches coupled in parallel with the input of the receiver circuit.

[0012] According to yet another aspect of the invention, each of the FET switches in a pair of FET switches has a control terminal coupled to a transmit waveform generation circuit to receive a turn-on signal related to a duration of a transmit waveform signal.

[0013] According to another aspect of the present disclosure, there is provided an ultrasonic device, comprising:

[0014] a transducer circuit configured to transmit an ultrasonic signal and receive a corresponding echo signal and generate a return echo signal;

[0015] a variable gain receiver having an input coupled to the transducer circuit;

[0016] A transceiver capable of generating a peak-to-peak waveform of more than 100 volts across a transducer and receiving a return echo signal from the transducer of a peak-to-peak waveform of less than 1 volt, the transceiver comprising:

[0017] a transformer having a primary winding and a secondary winding, the primary winding coupled to the transducer;

[0018] a transmitter circuit coupled to the transducer through 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 the secondary is connected on one side to the transducer circuit and on the other side to an input of a variable gain receiver, wherein the maximum gain is at least 30 dB; and

[0019] a protection circuit coupled between the secondary winding of the transformer and the input of the variable gain receiver and configured such that when the protection circuit is active, the protection circuit provides an impedance in the range of 0.1 ohms 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;

[0020] The variable gain receiver can be active during the transmit period and can amplify the small voltage across the protection circuit to monitor the amplitude and duration of the transmit waveform. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The foregoing and other features and advantages of the present disclosure will be better understood and more clearly understood from the following detailed description when taken in conjunction with the accompanying drawings, in which:

[0022] Figure 1 is a schematic diagram of a conventional ultrasonic transceiver having a transmit / receive circuit;

[0023] Figure 2 is a schematic diagram of an ultrasonic transceiver having a transmit / receive (T / R) switch with a transformer instead of a T / R circuit according to the present disclosure;

[0024] Figure 3 A T / R circuit with an H-bridge circuit according to the present disclosure Figure 2 Schematic diagram of an ultrasonic transceiver;

[0025] Figure 4 The invention is a device having a T / R circuit according to the present invention. Figure 3 A schematic diagram of an ultrasonic transceiver circuit, wherein the T / R circuit utilizes a clamp circuit for receiver circuit protection;

[0026] Figure 5 is used for Figure 4 The control signal of the clamping circuit together with the control signal of the clamping circuit formed according to the present disclosure Figure 4 Behavioral waveform diagrams of response waveform signals of components of an ultrasonic transceiver circuit; and

[0027] Figure 6 is a schematic diagram of a control circuit for a transmitter circuit having a waveform formed in accordance with a representative embodiment of the present disclosure. DETAILED DESCRIPTION

[0028] In the following description, certain specific details are set forth in order to provide a thorough understanding of the various disclosed embodiments. However, those skilled in the relevant art will recognize that these embodiments can be implemented without one or more of these specific details, or with other methods, components, materials, etc. In other cases, well-known structures associated with switches, transducers, amplifiers, control signal generators, programmable logic devices, memories, and transformers are not shown or described in detail to avoid unnecessarily obscuring the description of these embodiments.

[0029] Unless the context requires otherwise, throughout this specification and the claims that follow, the word "comprise" and variations such as "include" and "comprising" should be construed in the open inclusive sense, ie, "including, but not limited to."

[0030] Throughout the specification, references to "one embodiment" or "an embodiment" mean that a particular feature, structure, or characteristic described in conjunction with that embodiment is included in at least one embodiment. Therefore, the phrases "in one embodiment" or "in an embodiment" appearing in various places throughout this specification do not necessarily all refer to the same embodiment. In addition, in one or more embodiments, the particular features, structures, or characteristics may be combined in any suitable manner. It should be understood that for simplicity and clarity of illustration, reference numerals may be repeated between the drawings to indicate corresponding or similar elements or steps, where deemed appropriate.

[0031] As used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. It should also be noted that the term "or" is generally used in its broadest sense, meaning "and / or," unless the content clearly dictates otherwise.

[0032] Overview

[0033] Ultrasound systems typically utilize 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 be able to receive the very small voltage signal generated by the returning echo. Some ultrasound applications also require the generation of specific transmit waveforms with very low distortion to obtain adequate results. An ultrasound transceiver is described that overcomes most of the deficiencies of conventional ultrasound transceivers, has the ability to transmit arbitrary waveforms of high power and high frequency with low distortion, and has the ability to monitor the transmit signal passing through the receiver during the transmit period.

[0034] Improved transceiver design

[0035] Elimination of T / R Switches - One improvement that can be made to conventional transceiver designs is to eliminate the T / R switch entirely. Figure 2As shown in the transceiver circuit 42 of FIG. 1 , this can be achieved by coupling the transmit waveform to the transformer 40 in the receive path. During transmit, the high voltage transmit waveform 42 (having 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. The input signal is not completely grounded because there is a voltage drop of approximately + / -0.8 across the back-to-back diodes 30, but this is typically too small to damage the receiver circuit 20 and has minimal effect on the transmit waveform. When an echo signal from the medium is received through the transducer element 16, the transmit drive signal from the transmitter circuit 26 is zero and the transformer 40 becomes a short circuit. The echo signal level received at the transducer element 16 is typically below the conduction threshold of the back-to-back diodes 30, causing the diodes to be at high impedance, thereby allowing the received signal to flow to the input 34 of the receiver circuit 20. A typical variable gain receiver circuit 20 will have a maximum gain greater than 30 dB.

[0036] Eliminating the T / R switch 12 provides several advantages. First, no transmit period is required because transmission at the transducer element 16 can occur at any time, even when the receiver circuit 26 is active or other transceivers are transmitting or receiving. This allows applications that employ multiple transmissions during the echo signal acquisition period from the same or different groups of transducer elements 16. Second, the echo signal reception period can begin before any transmission occurs at the transducer element 16, thereby allowing some transducer elements to receive signals before they transmit, thus effectively eliminating any dead zone in front of the transducer element 16. Third, because the receiver circuit receives a very attenuated version of the transmit waveform, the transmit waveform can be monitored to detect a faulty transmitter circuit 26 or a failed transducer element 16. In addition, the transformer 40 provides good isolation of the high voltage circuits of the transmitter circuit 26 from the transducer element 16, which is typically in close contact with a live subject. Therefore, a fault in the transmitter circuit 26 is prevented from becoming a shock hazard to the scanned subject.

[0037] H-bridge transmitter generator - Figure 3 A further improved transceiver circuit 50 is shown in FIG. Figure 1 A typical transmit waveform generator or transmitter circuit 26 used in generating arbitrary acoustic waveforms 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 electrical power that is radiated as heat. The transmit power of an ultrasound system with a large number of transmit channels and its own transmitter circuit 26 will be limited by the ability to cool the circuit.

[0038] like Figure 3As shown, the transformer isolation of the "no T / R switch" design allows the use of high voltage field effect transistor (FET) switches 52, 54, 56, 58 to generate the transmit waveform instead of expensive high power linear amplifiers. The switches 52, 54, 56, 58 are arranged in an H-bridge circuit 60, and each of the switches 52, 54, 56, 58 is independently controlled so that the voltage driven to the transducer element 16 can be one of three levels, namely +HV, 0 or -HV. These levels can be obtained from a single HV power supply of 100 volts or more, which is conducive to waveform symmetry between positive and negative outputs-an important characteristic required to minimize even harmonic distortion. The H-bridge circuit 60 also allows the zero state to be effectively driven, which suppresses the ringing of the transducer element 16 and improves channel-to-channel uniformity. The effectively driven zero state is also critical for generating accurate arbitrary acoustic waveforms from the three-state transmitter (H-bridge circuit) 60.

[0039] FETs 52, 54, 56, 58 are controlled by digital signals A, B, C, D (see, e.g., Figure 3 and Figure 6 ) is driven by a digital control signal. The digital control signal can be easily generated by a programmable logic device or by a digital value read from a storage device. These devices are readily commercially available and will not be described or illustrated in detail here. The digital signal can program the transition to a new output state timed by a high frequency clock (typically in the range of 250 MHz to 500 MHz).

[0040] For example, by turning on FETs 52, 58 via control signals A and D and turning off FETs 54, 56 control signals B and C, a high voltage HV is applied across the primary winding 62 of the transformer 40 in the positive direction. Turning off FETs 52, 58 control signals A and D and turning on FETs 54, 56 control signals B and C applies a high voltage HV across the primary winding 62 of the transformer 40 in the reverse direction, thereby generating a negative output. Similarly, turning off control signals A and B and turning on control signals C and D grounds both sides of the primary winding 62 and creates 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, such as Figure 6 By controlling the configuration and timing of the four H-bridge FETs 52, 54, 56, 58 using control signals A, B, C, D, a three-state output waveform with arbitrarily timed state transitions can be generated, thereby generating an arbitrary acoustic waveform in the medium acoustically coupled to the transducer element 16 when filtered by the impulse response of the transducer element 16.

[0041] Thus, this transceiver circuit 50 is able to generate an acoustic waveform that matches the acoustic waveform from a high power linear amplifier. (See Flynn, J. et al., “Method and System for Arbitrary Waveform Generation Using a Tri-State Transmit Pulser,” PCT / US2014 / 047080.) In addition to being lower cost, the advantage of the tri-state approach is that it can generate very high power arbitrary acoustic waveforms with low power dissipation in the transmitter circuit itself, thereby reducing the power and cooling requirements of the transmit circuit.

[0042] Reducing nonlinear effects and distortion - Many ultrasound applications require high linearity in the transmit waveform and low distortion in the receiver to achieve their purpose. For example, there are ultrasound applications that encode the transmit waveform in order to uniquely identify its signal in a mix of acoustic signals and noise. In order to decode the transmitter's signal in the receive signal processing, it is critical to have good linearity in the transmit waveform and in the signal path before the receiver's input.

[0043] In previous "no T / R switch" designs of transceiver circuits 42 and 50, back-to-back diodes 30 were employed to protect the receiver circuit input 34 from large voltages and to serve as a ground path for the secondary winding 64 of the transmitter transformer 40 when transmission was active. While effective in protecting the receiver circuit 20 during transmission, these back-to-back diodes 30 introduced slight distortion and non-linear characteristics in the transmit waveform into the signal path used to receive the echo signal at the transducer element 16.

[0044] To improve linearity and reduce distortion, such as Figure 4As shown in the transceiver circuit 70 of FIG. 1 , 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 the FETs 72, 74 are turned on, they present a very low resistance (approximately 0.1 ohms). This resistance is also fairly constant over the entire output current range of the transmitter circuit 60. This active clamp circuit 76 will eliminate the crossover distortion of the passive clamp diode 30, as well as increase the dynamic range of the receiver circuit 20, since a typical receiver can receive signals greater than + / -0.8 volts. 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, as well as detect faulty transmitter circuits or transducer elements. This monitoring can be achieved without additional circuitry by capturing the non-saturated output signal of the receiver only during the transmit period and estimating the transmit power based on 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 readily determined by one skilled in the art and will not be described in detail herein.

[0045] Figure 5 It is shown in Figure 4 The control signal of the clamp circuit and Figure 4 The response waveform signal behavior of the components of the ultrasonic transceiver circuit is shown in the waveform diagram. The control of the active clamp circuit 30 is indicated by the signals E and F which are usually turned on together. The clamp control signal is generated to correspond to the transmit duration shown in the second waveform, and it minimizes the signal level at the point of the variable gain amplifier in the receiver circuit 20. Although this adds additional complexity to the design, it can be related to the transmit waveform duration and is automatically generated by the digital transmit signal generator circuit 60 for most waveforms. The ability to transmit at any time during the receive period is still retained. Figure 5 The figure in FIG. 1 also shows the receiver circuit 20 outputting with a third waveform and the transducer element 16 outputting with a fourth waveform. Note that there is a small signal at the output of the receiver during transmission, which can be used to estimate the transmission power. This signal can be slightly amplified if necessary.

[0046] The H-bridge circuit 60 can also be a source of distortion in the transmit waveform if not properly designed and programmed. The FETs 52, 54, 56, 58 do not switch instantaneously, and when one FET is on and another is off, there can be transient voltage effects that corrupt the waveform. These effects can be minimized by fine tuning the timing of the transitions. A small delay can be introduced to the control signal that can adjust for propagation delays and component variations. This small delay can be programmed at system startup using a calibration routine that minimizes distortion components.

[0047] For example, Figure 6 Shown for Figure 4 6 is a representative control circuit 66 of the transmitter circuit 60 shown. The control circuit 66 in this embodiment 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 its output formed into a C digital signal coupled directly to the gate of the N-FET 56. The P gate driver 70 output is an A digital signal which is also input to the gate of the P-FET 52 through a capacitor 74. The positive +HV bias rail is connected to the gate of the P-FET 52 through 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 through a capacitor 78 as a digital signal B. The +HV bias rail is also coupled to the gate of the P-FET 54 through a parallel diode-resistor circuit 80.

[0048] exist Figure 6 The bottom of FIG. 1 is a waveform diagram of the P output and N output and the A, B, C, D selection signals and the output signal Output received at the transducer element 16 changing with time.

[0049] Generally speaking, in the following claims, the terms used should not be interpreted to limit the claims to the specific embodiments disclosed in the specification and claims, but should be interpreted to include all possible embodiments and the full scope of equivalents to which these claims are entitled. Therefore, the claims are not limited by the present disclosure.

[0050] This application claims the benefit of priority to U.S. Application No. 17 / 747,398, filed on May 18, 2022, which is hereby incorporated by reference in its entirety.

Claims

1. A circuit, comprising: a transducer element configured to transmit 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 has an input coupled to the secondary winding of the transformer and configured to be coupled to the transducer element.

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

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

5. The circuit of claim 4, wherein each of the FET switches in the pair of FET switches has a control terminal coupled to the transmit waveform generator circuit to receive a turn-on signal related to a duration of a transmit waveform signal.

6. An ultrasonic device, comprising: a transducer circuit configured to transmit an ultrasonic signal and 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 of more than 100 volts across the transducer and receiving the return echo signal of less than 1 volt peak-to-peak waveform from the transducer, 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 through the transformer, the transmitter circuit comprising a transmit waveform generator configured to generate a transmit waveform, the transmit waveform generator coupled to the primary winding of the transformer such that the primary winding is driven by the transmit waveform generator and the secondary is connected on one side to the transducer circuit and on the other side to the input of the variable gain receiver, wherein a maximum gain is at least 30 dB; and a protection circuit coupled between the secondary winding of the transformer and the input of the variable gain receiver and configured such that when the protection circuit is active, the protection circuit provides an impedance in the range of 0.1 ohms 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 grounding for the transformer secondary winding during the transmit period; The variable gain receiver can be active during the transmit period and can amplify a small voltage across the protection circuit to monitor the amplitude and duration of the transmit waveform.

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

8. The ultrasound device of claim 6, wherein activation of the protection circuit on the input of the variable gain receiver is performed automatically based on a duration of the transmit waveform.

9. The ultrasound device of claim 6, wherein the transmitter circuit can be activated multiple times during a receive period while actively controlling the receiver input clamp so that the receiver is minimally affected during each activation.

10. The ultrasound device of claim 6, wherein the transmit waveform generator is configured to generate a three-state output waveform including -HV, 0, and +HV states, wherein HV can be set within a range from less than 2 volts to greater than 100 volts.

11. The ultrasound device of claim 10, wherein 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 is configured to be independently turned on and off.

12. The ultrasound device of claim 11, wherein the duration of each state in the tri-state output waveform is programmable to generate a tri-level output waveform that, when filtered by the impulse response of the transducer, produces a desired arbitrary acoustic output waveform.

13. The ultrasound device of claim 11, wherein the timing of turning on and off of each of the FETs can be adjusted with a small delay to minimize distortion in the output of the transmitter circuit.

Images