Patent ID: 12231097

DETAILED DESCRIPTION

Aspects of the present application relate to amplification circuitry for an ultrasound device. An ultrasound device may include one or more ultrasonic transducers configured to receive ultrasound signals and produce electrical output signals. Thus, the ultrasonic transducers may be operated as ultrasound sensors. The ultrasound device may include one or more amplifiers for amplifying the electrical output signals. The power consumed by, the noise generated by, and the linear signal amplification quality provided by, the amplifier may depend on an amount of current consumed by the amplifier. In some embodiments, the amplifier has a variable current source. The variable current source is adjusted during acquisition of an ultrasound signal to maintain the noise level of the amplifier below the signal level and to maintain linear amplification, while at the same time reducing the amount of power consumed by the amplifier. In some embodiments, the amplifier is a TIA.

The aspects and embodiments described above, as well as additional aspects and embodiments, are described further below. These aspects and/or embodiments may be used individually, all together, or in any combination of two or more, as the application is not limited in this respect.

FIG.1illustrates a circuit for processing received ultrasound signals, according to a non-limiting embodiment of the present application. The circuit100includes N ultrasonic transducers102a. . .102n, wherein N is an integer. The ultrasonic transducers are sensors in some embodiments, producing electrical signals representing received ultrasound signals. The ultrasonic transducers may also transmit ultrasound signals in some embodiments. The ultrasonic transducers may be capacitive micromachined ultrasonic transducers (CMUTs) in some embodiments. The ultrasonic transducers may be piezoelectric micromachined ultrasonic transducers (PMUTs) in some embodiments. Further alternative types of ultrasonic transducers may be used in other embodiments.

The circuit100further comprises N circuitry channels104a. . .104n. The circuitry channels may correspond to a respective ultrasonic transducer102a. . .102n. For example, there may be eight ultrasonic transducers102a. . .102nand eight corresponding circuitry channels104a. . .104n. In some embodiments, the number of ultrasonic transducers102a. . .102nmay be greater than the number of circuitry channels.

The circuitry channels104a. . .104nmay include transmit circuitry, receive circuitry, or both. The transmit circuitry may include transmit decoders106a. . .106ncoupled to respective pulsers108a. . .108n. The pulsers108a. . .108nmay control the respective ultrasonic transducers102a. . .102nto emit ultrasound signals.

The receive circuitry of the circuitry channels104a. . .104nmay receive the electrical signals output from respective ultrasonic transducers102a. . .102n. In the illustrated example, each circuitry channel104a. . .104nincludes a respective receive switch110a. . .110nand an amplifier112a. . .112n. The receive switches110a. . .110nmay be controlled to activate/deactivate readout of an electrical signal from a given ultrasonic transducer102a. . .102n. More generally, the receive switches110a. . .110nmay be receive circuits, since alternatives to a switch may be employed to perform the same function. The amplifiers112a. . .112n, as well as amplifier300ofFIG.3(described below), may be TIAs in some embodiments. One or more of the amplifiers112a. . .112nmay be variable current amplifiers. As will be described further below, the current of the amplifiers may be varied during an acquisition period, thus adjusting the power consumption, noise level, and linearity of the amplifiers. The amplifiers112a. . .112nmay output analog signals.

The circuit100further comprises an averaging circuit114, which is also referred to herein as a summer or a summing amplifier. In some embodiments, the averaging circuit114is a buffer or an amplifier. The averaging circuit114may receive output signals from one or more of the amplifiers112a. . .112nand may provide an averaged output signal. The averaged output signal may be formed in part by adding or subtracting the signals from the various amplifiers112a. . .112n. The averaging circuit114may include a variable feedback resistance. The value of the variable feedback resistance may be adjusted dynamically based upon the number of amplifiers112a. . .112nfrom which the averaging circuit receives signals. In some embodiments, the variable resistance may include N resistance settings. That is, the variable resistance may have a number of resistance settings corresponding to the number of circuitry channels104a. . .104n. Thus, the average output signal may also be formed in part by application of the selected resistance to the combined signal received at the inputs of the averaging circuit114.

The averaging circuit114is coupled to an auto-zero block116. The auto-zero block116is coupled to a programmable gain amplifier118which includes an attenuator120and a fixed gain amplifier122. The programmable gain amplifier118is coupled to an ADC126via ADC drivers124. In the illustrated example, the ADC drivers124include a first ADC driver125aand a second ADC driver125b. The ADC126digitizes the signal(s) from the averaging circuit114.

WhileFIG.1illustrates a number of components as part of a circuit of an ultrasound device, it should be appreciated that the various aspects described herein are not limited to the exact components or configuration of components illustrated. For example, aspects of the present application relate to the amplifiers112a. . .112n, and the components illustrated downstream of those amplifiers in circuit100are optional in some embodiments.

The components ofFIG.1may be located on a single substrate or on different substrates. For example, as illustrated, the ultrasonic transducers102a. . .102nmay be on a first substrate128aand the remaining illustrated components may be on a second substrate128b. The first and/or second substrates may be semiconductor substrates, such as silicon substrates. In an alternative embodiment, the components ofFIG.1may be on a single substrate. For example, the ultrasonic transducers102a. . .102nand the illustrated circuitry may be monolithically integrated on the same semiconductor die. Such integration may be facilitated by using CMUTs as the ultrasonic transducers.

According to an embodiment, the components ofFIG.1form part of an ultrasound probe. The ultrasound probe may be handheld. In some embodiments, the components ofFIG.1form part of an ultrasound patch configured to be worn by a patient.

FIG.2illustrates a non-limiting example of the amplifier112aofFIG.1in greater detail. The same configuration may be used for the other amplifiers112nofFIG.1. For context, the ultrasonic transducer102aand averaging circuit114are also illustrated, while for simplicity the receive switch110ais omitted.

In this non-limiting embodiment, the amplifier112ais implemented as a two-stage operational amplifier (“op-amp” for short). The first stage202is coupled to the ultrasonic transducer102a. The second stage204is coupled between the first stage202and the averaging circuit114. The second stage204provides the output signal of the amplifier112a, in this non-limiting example.

The first stage202and second stage204each have a variable current source. The variable current source203is provided for the first stage202and sinks a current I1. The variable current source205is provided for the second stage204and sinks a current I2. Although the variable current sources203and205are illustrated as distinct from the respective stages202and204, they may be considered part of the respective stages.

With a two-stage amplifier construction as shown inFIG.2, the noise and linearity of the amplified signal may be controlled independently. The noise of the amplifier112ais impacted primarily by the first stage202. The linearity of the amplifier112ais impacted primarily by the second stage204. More generally, the same may be true for a multi-stage amplifier having two or more stages, such that the noise of the amplifier is impacted primarily by the first stage and the linearity of the amplifier is impacted primarily by the last stage. Applicant has appreciated that during acquisition of an ultrasound signal, referred to herein as an acquisition period, the noise and linearity of the amplified signal may vary in importance. When the ultrasound signal is initially received, early in the acquisition period and corresponding to shallow depths when the ultrasound signal is a reflected signal, the associated noise will be relatively low compared to the received signal amplitude, but the linearity of the amplified signal may be of relatively high importance. However, later during the acquisition period, corresponding to greater depths when the ultrasound signal is a reflected signal, the ultrasound signal is likely to become smaller, and thus the noise of the signal is of increased importance. Thus, the amplifier112aofFIG.2is designed to allow for independent and variable control of noise and linearity. The control may be provided via the variable current sources203and205.

Early during an acquisition period, the variable current source203may be controlled to sink a relatively small amount of current, while the current source205may be controlled to sink a relatively large amount of current. In such a scenario, the second stage204may operate to control the linearity of the amplified signal produced by the amplifier112a, while the first stage202may control the noise of the amplified signal202to a lesser extent than that to which it is capable. Later in the acquisition period, the current sunk by the variable current source203may be increased while the current sunk by the variable current source205may be decreased. As the current sunk by the variable current source203is increased, the first stage202may operate to control the noise of the amplifier112ato a greater extent. As the current sunk by the variable current source205is decreased, the second stage204may operate to control the linearity of the amplifier112ato a lesser extent. Thus, dynamic current biasing of the amplifier112a, and first stage202and second stage204more specifically, may be implemented to control the power, noise, and linearity characteristics of the amplifier during an acquisition period.

The dynamic control of current sources203and205may be achieved using a digital controller, an example being shown inFIG.3A. The variable current sources203and205may each include two or more programmable current settings. The greater the number of settings, the greater the control over the current sunk by the current sources203and205.

The amplifier112aalso includes a variable feedback impedance206. In some embodiments, the variable feedback impedance is a variable RC feedback circuit. An example of the variable RC feedback circuit is illustrated inFIG.3Aand described in connection with that figure. The feedback impedance determines the transimpedance gain of the transimpedance amplifier, such that the input current signal may be converted into an output voltage of varying amplitude.

It should be appreciated fromFIG.2and the foregoing description that an embodiment of the application provides a multi-stage TIA having two or more independently controllable variable current sources, with a variable feedback impedance. The variable current sources may allow for dynamic current biasing of the TIA, for example during an acquisition period. Thus, the power consumption, noise, and linearity of the amplifier may be adjusted during the acquisition period.

FIG.3Ais a circuit diagram illustrating an implementation of the amplifier112aofFIG.2, according to a non-limiting embodiment of the present application. The amplifier300has an input302and an output304. The input302may be coupled to an ultrasonic transducer or a receive switch, as described previously in connection withFIGS.1and2, and may receive an electrical signal representing an ultrasound signal received by the ultrasonic transducer. The output304may provide an amplified output signal of the amplifier112a, and may be coupled to an averaging circuit or other component to which it is desired to provide the amplified output signal.

The amplifier300includes a first stage306and a second stage308, which may be implementations of the first stage202and second stage204ofFIG.2, respectively. The first stage306includes an NMOS transistor310having a gate configured to receive the signal at input302. PMOS transistor312and PMOS transistor314have their gates coupled, with the drain of PMOS transistor312coupled to the drain of NMOS transistor310. The gate of transistor312is coupled to its drain. Transistors312and314are also configured to receive a power supply voltage VDDA. The first stage306further comprises NMOS transistor316having a gate configured to receive a bias voltage provided by an RC circuit. The RC circuit includes two resistors, of value R, with a capacitor Cbcoupled in parallel with one of the resistors. The other resistor receives the power supply voltage VDDA. The drain of PMOS transistor314is coupled to the drain of NMOS transistor316. An example value for R is 50 kOhm and an example value for Cbis 10 pF, although alternatives for both are possible, such as +/−20% of those values listed, or any value or range of values within such ranges.

The second stage308includes a PMOS transistor318configured to receive the output of the first stage306. In particular, the gate of PMOS transistor318is coupled to a node between transistors314and316of the first stage306. The source of PMOS transistor318receives VDDA. A variable impedance circuit320is also provided in the second stage308. The variable impedance circuit320includes a variable capacitor CCin series with a variable resistor RZ, and thus is a variable RC circuit in this embodiment. Variable impedance circuit320may provide stable operation of the amplifier300when the gain of the amplifier, or the currents of the currents sources, are varied. Thus, the variable impedance circuit may be provided to maintain stable operation of the amplifier300for all the current magnitudes sunk by the variable current sources321and325. That is, the values of CCand RZmay be adjusted during operation of the amplifier300to account for the different current settings programmed by the digital controller330

A variable current source is provided for each of the stages306and308. The variable current source321for the first stage306includes three parallel connected current sources322a,322b, and322c. Current source322asinks a current IA, current source322bsinks a current 2IA, and current source322csinks a current 4IA. The current sources322a-322care coupled to the first stage306by respective switches324a,324b, and324c, which effectively provides 3 bits (8 states) of control of the current. The current IAmay equal 100 microAmps or +/−20% of that value, or any value or range of values within such ranges, as examples.

The variable current source325for the second stage308includes three parallel connected current sources326a,326b, and326c. Current source326asinks a current IB, current source326bsinks a current 2IB, and current source326csinks a current 4IB. The current sources326a-326care coupled to the second stage308by respective switches328a,328b, and328c, which effectively provides 3 bits (8 states) of control of the current. The current IBmay equal 50 microAmps or +/−20% of that value, or any value or range of values within such ranges, as examples.

WhileFIG.3Aillustrates variable current sources each include three parallel-coupled current sources, it should be appreciated that not all aspects of the present application are limited in this manner That is, variable current sources may be implemented in various manners, including alternative manners to those illustrated. For example, more or fewer than three current sources may be coupled in parallel to create a variable current source. Also, the magnitudes of the current sources may be different than those illustrated inFIG.3A. Any suitable magnitudes may be provided to allow for operation over a desired range of currents.

A digital controller330is provided to control operation of the variable current sources321and325. The digital controller provides control signals to (digitally) program the currents of the variable current sources. In the illustrated example, the digital controller330provides one or more switching signals S1to control operation of the switches324a-324c, and one or more switching signals S2to control operation of the switches328a-328c. In this manner, the amount of current sunk by the variable current sources may be varied independently during operation of the amplifier300, for example during an acquisition period. According to a non-limiting example, the digital controller330decreases the current sunk by variable current source325during the acquisition period and increases the current sunk by variable current source321during the acquisition period through suitable operation of the switching signals S1and S2.

The digital controller330may be any suitable type of controller. The digital controller may include integrated circuitry. In some embodiments, the digital controller330may include or be part of an application specific integrated circuit (ASIC). In some embodiments, the digital controller330may not be specific to the amplifier300. For example, a digital controller may be provided to control more than one component of the circuit ofFIG.1, one of which may be the amplifiers112a. . .112n.

The amplifier300further includes a variable feedback impedance332formed by variable capacitor Cfand variable resistor Rf. The capacitor Cfand resistor Rfmay be coupled between the output304and the input302, and may be in parallel with each other. The variable feedback impedance332may control the gain of the amplifier300. Thus, the values of Cfand Rfmay be adjusted to vary the amplifier's gain.

The variable feedback impedance332and the variable impedance circuit320may be controlled in any suitable manner. In one embodiment, the digital controller330may set the values of the feedback impedances. However, alternatives manners of control may be used.

It should be appreciated that the described groupings of components in connection withFIG.3Aare not limiting. For example, while certain components illustrated in that figure are described as being part of a first stage or a second stage, the identification of the first and second stages is not limiting. The first and second stages may include more, fewer, or different components than those illustrated.

FIG.3Bis a circuit diagram of an implementation of the variable impedance circuit320ofFIG.3A, according to a non-limiting embodiment of the present application. The variable impedance circuit320includes a number of switches340a. . .340nconfigured in parallel and configured to receive respective control signals SWa . . . SWn. In some embodiments, the digital controller330may provide the control signals SWa . . . SWn, although alternatives may be used. Each switch is coupled in series with a respective capacitor CCand resistor RZ. The impedance of the variable impedance circuit320may be adjusted during an acquisition period through suitable provision of the control signals SWa . . . SWn. Any suitable number of parallel signal paths may be provided, so that the illustrated example of two parallel signal paths is non-limiting. The number of parallel signal paths and the capacitance and resistive values provided may be selected to provide sufficient control of the feedback impedance to account for the variable operation of the amplifier across the range of operating scenarios resulting from the variation of the variable current sources. For example, for a given amplifier gain dictated by variable feedback impedance332, appropriate settings of variable impedance circuit320may be selected. In some embodiments, a lookup table may be utilized to determine the appropriate settings of variable impedance circuit320based on a given gain set by variable feedback impedance332.

In bothFIGS.3A and3B, the values of CCand RZmay be selected to provide desired operating characteristics. As examples, RZmay be equal to 3 kOhms in some embodiments, and CCmay be equal to 300 fF. Alternatives for both are possible. For example, they may assume values within +/−20% of those values listed, or any value or range of values within such ranges.

FIG.3Cis a circuit diagram of an implementation of the variable impedance circuit332ofFIG.3A, according to a non-limiting embodiment of the present application. The variable impedance circuit332includes a number of complementary switches350a,350b. . .350n. Each switch receives respective control signals SLa, SLb . . . SLn and SHa, SHb . . . SHn. The control signals may be provided by the digital controller330in some embodiments, although alternatives may be used. The complementary switches are coupled to respective parallel-connected RC circuits Cf, Rf. While three complementary switches are shown inFIG.3C, any suitable number may be provided to allow for sufficient control of the gain of the amplifier300.

In bothFIGS.3A and3C, the values of Cfand Rfmay be selected to provide desired operating characteristics. As examples, Rfmay be equal to 180 kOhms in some embodiments, and Cfmay be equal to 84 fF. Alternatives for both are possible. For example, they may assume values within +/−20% of those values listed, or any value or range of values within such ranges.

FIG.4is a graph illustrating the behavior of two variable current sources of a variable current amplifier during an acquisition period, as may be implemented by the amplifier ofFIGS.2and3A, which again may be a TIA. For example, the illustrated behavior may be implemented by the variable current sources203and205ofFIG.2. The x-axis represents time during an acquisition period, ranging from t0to t8. The y-axis represents the current of the current source, having values ranging from I0to I8. The values of t0-t8and I0-I8may be any suitable values for operation of a given ultrasound system, as the various aspects described herein are not limited to implementation of any specific time or current values. Also, the number of time intervals during an acquisition period is non-limiting, as more or fewer may be implemented. The number of current values which may be implemented is non-limiting, as more or fewer may be implemented.

Curve402represents the current of a variable current source of a second stage of a variable current amplifier. Thus, curve402may represent the current of current source205ofFIG.2. Curve404represents the current of a variable current source of a first stage of the variable current amplifier. Thus, curve404may represent the current of current source203ofFIG.2.

FIG.4illustrates that the currents of the first and second stages of the variable current amplifier move in opposing directions during the acquisition period. That is, curve402decreases moving from time t0to time t8, while curve404increases during the same time. As previously described in connection withFIG.2, the first and second stages of the variable current amplifier may impact different characteristics of the variable current amplifier behavior, such as noise and linearity. Thus, when operating in the manner illustrated inFIG.4, the impact of the two stages of the variable current amplifier may vary during the acquisition period. That is, the impact of the second stage may be greater initially, up to time t4, while the impact of the first stage may be greater thereafter, from time t4to time t8.

As previously described in connection withFIG.3A, the currents of the two stages of a two-stage op-amp being used to implement a variable current amplifier may be controlled by digital codes. Thus, the current values I0-I7ofFIG.4may correspond to different digital codes set by a digital controller, such as digital controller330ofFIG.3A.

WhileFIG.4illustrates that the currents in the first and second stages of the amplifier switch at the same times, not all embodiments are limited in this respect. For example, the current in the second stage could be adjusted at times offset from those at which the current in the first stage is adjusted. Likewise, the currents of the two stages need not be adjusted the same number of times during an acquisition period.

As described previously, an aspect of the present application provides an amplifier with a variable current source which is controlled to adjust the noise of the amplifier during an acquisition period.FIG.5illustrates an example of such operation.

InFIG.5, the voltage of an electrical signal502output by an ultrasonic transducer, and thus representing a detected ultrasound signal, is illustrated as a function of time. Dashed line504represents the noise floor of an amplifier used to amplify the electrical signal502, and may correspond to the noise floor of an amplifier of the types described herein, such as amplifier112a. It can be seen that during the acquisition period, the magnitude of the electrical signal decreases. Likewise, the noise floor of the amplifier is decreased. Such a decrease in the noise floor may be achieved by controlling the current sunk by a variable current source of the amplifier in the manner described previously herein. For example, referring toFIG.2, the variable current source203may be increased during the acquisition period to decrease the noise floor of the amplifier112a. The noise floor may be adjusted to a level which provides an acceptable signal-to-noise ratio (SNR).

FIG.5also illustrates a constant noise floor506. It can be seen that while the constant noise floor506is at the same level as dashed line504toward the end of the acquisition period, the constant noise floor506is lower than the value of the dashed line504up to that point. As has been described herein, the noise level of an amplifier may be dependent on the current consumed by the amplifier, and in such situations it should be appreciated that operating with a constant noise floor506requires significantly more current (and therefore power) than operating according to dashed line504. Thus, aspects of the present application providing for a variable current amplifier to amplify ultrasound signals may provide substantial power savings compared to amplifiers operating with a constant noise level.

The amount of power savings may be significant. For example, in the circuit100, the amplifiers112a. . .112nmay consume a significant amount of power. In some embodiments, the amplifiers112a. . .112nmay consume more power than any other components of the circuit100. Accordingly, reducing the power consumption of the amplifiers112a. . .112nmay provide a significant reduction in power of the circuit100. In some embodiments, utilizing variable current amplifiers of the types described herein may provide up to a 25% power reduction, up to a 40% power reduction, up to a 50% power reduction, or any range or value within such ranges, in terms of the operation of the amplifier. The resulting power reduction for the circuit100may be up to 10%, up to 20%, up to 25%, or any range or value within such ranges.

Having thus described several aspects and embodiments of the technology of this application, it is to be appreciated that various alterations, modifications, and improvements will readily occur to those of ordinary skill in the art. Such alterations, modifications, and improvements are intended to be within the spirit and scope of the technology described in the application. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described.

As an example, certain embodiments described herein have focused on two-stage amplifiers. However, the techniques described herein may apply to multi-stage amplifiers having two or more stages. When more than two stages are used, the first stage may predominantly control the noise of the amplifier, while the last stage may predominantly control the linearity of the amplifier.

As described, some aspects may be embodied as one or more methods. The acts performed as part of the method(s) may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments.

All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms.

The phrase “and/or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases.

As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements.

As used herein, the term “between” used in a numerical context is to be inclusive unless indicated otherwise. For example, “between A and B” includes A and B unless indicated otherwise.

In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of” and “consisting essentially of” shall be closed or semi-closed transitional phrases, respectively.