Trans-impedance amplifier (TIA) for ultrasound devices

A variable-current trans-impedance amplifier (TIA) for an ultrasound device is described. The TIA may be coupled to an ultrasonic transducer to amplify an output signal of the ultrasonic transducer representing an ultrasound signal received by the ultrasonic transducer. During acquisition of the ultrasound signal by the ultrasonic transducer, one or more current sources in the TIA may be varied. The variable-current trans-impedance amplifier may include multiple stages, including a first stage having N-P transistor pairs configured to receive an input signal and produce a single-ended amplified signal.

BACKGROUND

Field

The present application relates to ultrasound devices having an amplifier for amplifying received ultrasound signals.

Related Art

Ultrasound probes often include one or more ultrasound sensors, which sense ultrasound signals and produce corresponding electrical signals. The electrical signals are processed in an analog or a digital domain. Sometimes, ultrasound images are generated from the processed electrical signals.

BRIEF SUMMARY

According to an aspect of the present technology described herein, an ultrasound apparatus is provided, comprising an ultrasound sensor and a variable-current trans-impedance amplifier (TIA). The variable current TIA is coupled to the ultrasound sensor and configured to receive and amplify an output signal from the ultrasound sensor. The variable-current TIA has a variable current source.

According to an aspect of the present technology, a method is provided, comprising acquiring an ultrasound signal with an ultrasound sensor during an acquisition period and outputting, from the ultrasound sensor, an analog electrical signal representing the ultrasound signal. The method further comprises amplifying the electrical signal with a variable-current trans-impedance amplifier (TIA), including varying a current of the variable-current TIA during the acquisition period.

According to an aspect of the present application, a method is provided, comprising acquiring an ultrasound signal with an ultrasound sensor during an acquisition period, and outputting, from the ultrasound sensor, an analog electrical signal representing the ultrasound signal. The method further comprises amplifying the electrical signal with a variable-current trans-impedance amplifier (TIA), including decreasing a noise floor of the variable current TIA during the acquisition period.

According to an aspect of the present technology, an ultrasound apparatus is provided, comprising a variable current trans-impedance amplifier (TIA) configured to receive and amplify an output signal from an ultrasound sensor and having a variable-current source and a differential input stage comprising two pairs of N-P transistors.

According to an aspect of the present technology, an ultrasound apparatus is provided, comprising an ultrasound sensor, a variable-current trans-impedance amplifier (TIA) coupled to the ultrasound sensor and configured to receive and amplify an output signal from the ultrasound sensor. The variable-current TIA has a variable current source with an input quadrature transistor arrangement with current sharing.

According to an aspect of the present technology, an ultrasound apparatus is provided, comprising an ultrasound sensor, and a variable-current trans-impedance amplifier (TIA) coupled to the ultrasound sensor and configured to receive and amplify an electrical signal representing an output signal from the ultrasound sensor. The variable-current TIA has an input stage with a first pair of N and P transistors each having a control terminal configured to receive the electrical signal and a second pair of N and P transistors each having a control terminal configured to receive a bias signal.

DETAILED DESCRIPTION

Aspects of the present technology described herein 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. An amount of power consumed by an amplifier, a noise generated by the amplifier, and a linear signal-amplification quality provided by the amplifier may depend on an amount of current consumed by the amplifier. In some embodiments, the amplifier may have a variable current source. The variable current source may be adjusted during acquisition of an ultrasound signal to maintain the noise level of the amplifier below the amplifier's signal level and to maintain a linear amplification of the signal while at the same time reducing the amount of power consumed by the amplifier. In some embodiments, the amplifier may be a TIA.

According to an aspect of the present technology, a variable-current TIA is provided that exhibits beneficial power performance for a given noise level. The variable-current TIA may include an input stage configured to receive a signal at transistors of opposite polarities, such as N-type and P-type MOSFETs. The transistors of opposite polarities may be arranged in input pairs, as a quad input configuration, with an input pair representing two transistors of opposite polarities (e.g., one N-type MOSFET and one P-type MOSFET) configured to receive a same input voltage at control terminals thereof. Current through the input pairs of transistors may be controlled to be substantially equal, thus providing reduced noise for a given power consumption of the variable-current TIA. In this manner, improved performance may be provided.

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 present technology described herein is not limited in this respect.

FIG.1illustrates a circuit100for processing received ultrasound signals, according to some non-limiting embodiments of the present technology. The circuit100comprises N ultrasonic transducers102a. . .102n(sometimes collectively denoted “102” herein), wherein N is an integer, and N=n. In some embodiments, the ultrasonic transducers102may be sensors that produce electrical signals representing received ultrasound signals. The ultrasonic transducers102may also transmit ultrasound signals in some embodiments. The ultrasonic transducers102may be capacitive micromachined ultrasonic transducers (CMUTs) in some embodiments. The ultrasonic transducers may be piezoelectric micromachined ultrasonic transducers (PMUTs) in some embodiments. As will be appreciated, alternative types of ultrasonic transducers may be used for the ultrasonic transducers102in other embodiments.

The circuit100further comprises N circuitry channels104a. . .104n. The circuitry channels may correspond to respectively to the ultrasonic transducers102a. . .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 receive circuitry of the circuitry channels104a. . .104nmay receive the electrical signals output respectively from the ultrasonic transducers102a. . .102n. In the illustrated example, each circuitry channel104a. . .104nincludes a respective receive switch110a. . .110nand a respective amplifier112a. . .112n. The receive switches110a. . .110nmay be controlled to activate/deactivate readout of respective electrical signals from the ultrasonic transducers102a. . .102n. As will be appreciated, the receive switches110a. . .110nmay be receive circuits, because alternative circuit structures, which may perform one or more function(s) of a switch, may be employed to perform a same or similar function as a switch. The amplifiers112a. . .112n, as well as an amplifier300ofFIG.3(described below), may be TIAs in some embodiments. One or more of the amplifiers112a. . .112nmay be variable-current amplifier(s). As will be described further below, a current of the amplifiers112a. . .112nmay be varied during an acquisition period, thus enabling any one or any combination of: power consumption, noise level, and amplifier linearity to be adjusted. The amplifiers112a. . .112nmay output analog signals.

The circuit100further comprises an averaging circuit114, which may also be referred to herein as a summer or a summing amplifier. In some embodiments, the averaging circuit114may be a buffer or an amplifier. The averaging circuit114may receive output signals from one or more of the amplifiers112a. . .112nand may output or 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. A value of the variable feedback resistance may be adjusted dynamically based upon a number of the amplifiers112a. . .112nfrom which the averaging circuit114receives signals. In some embodiments, the variable feedback resistance may include N resistance settings. That is, the variable feedback resistance may have a number of resistance settings corresponding to a number of the circuitry channels104a. . .104n. Thus, the average output signal may also be formed in part by application of a selected resistance to a combined signal inputted to the averaging circuit114.

The averaging circuit114may be coupled to an auto-zero block116. The auto-zero block116may be coupled to a programmable gain amplifier118, which may include an attenuator120and a fixed gain amplifier122. The programmable gain amplifier118may be coupled to an ADC126via ADC drivers124. In the illustrated example, the ADC drivers124include a first ADC driver125aand a second ADC driver125b. The ADC126may digitize the signal(s) from the averaging circuit114.

AlthoughFIG.1illustrates a number of components as part of a circuit of an ultrasound device, it should be appreciated that aspects of the present technology described herein are not limited to the exact components or configurations of components illustrated. For example, aspects of the present technology may relate to the amplifiers112a. . .112n, and one or more component(s) illustrated downstream of the amplifiers112a. . .112nin the circuit100may be 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 substrates128a,128bmay 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 other illustrated circuitry may be monolithically integrated on a same semiconductor die. Such integration may be facilitated by using CMUTs as the ultrasonic transducers102a. . .102n.

According to an embodiment, the components ofFIG.1may form part of an ultrasound probe. The ultrasound probe may be sized and structured to be handheld. In some embodiments, the components ofFIG.1may form 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 amplifiers112a. . .112nofFIG.1. For context, the ultrasonic transducer102aand the averaging circuit114are also illustrated inFIG.2, whereas for simplicity the receive switch110ais omitted fromFIG.2.

In this non-limiting embodiment, the amplifier112ais implemented as a two-stage operational amplifier (“op-amp” for short). A first stage202may be coupled to the ultrasonic transducer102a. The second stage204may be coupled between the first stage202and the averaging circuit114. The second stage204may provide an output signal of the amplifier112a, in this non-limiting example.

The first stage202and the second stage204may each have a variable current source203,205. The variable current source203may be provided for the first stage202and may sink a current I1. The variable current source205may be provided for the second stage204and may sink a current I2. Although the variable current sources203and205are illustrated as distinct from the respective stages202and204, they may be considered part of the respective stages202and204.

With a two-stage amplifier construction as shown inFIG.2, the noise and the linearity of the amplified signal may be controlled independently. The noise of the amplifier112amay be impacted primarily by the first stage202. The linearity of the amplifier112amay be 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 may be impacted primarily by the first stage and the linearity of the amplifier may be impacted primarily by the last stage. The inventors have appreciated that during acquisition of an ultrasound signal, referred to herein as an acquisition period, the noise and the linearity of the amplified signal may vary in importance. When the ultrasound signal is initially received, early in the acquisition period and corresponding to relatively shallower depths from which reflected ultrasound waves forming the ultrasound signal as a reflected signal, the noise associated with this early or initial acquisition period will be relatively lower in amplitude compared to the amplitude of the received signal, but the linearity of the amplified signal may be of relatively higher importance. However, later during the acquisition period and corresponding to relatively greater depths from which reflected ultrasound waves forming the ultrasound signal as a reflected signal, the ultrasound signal is likely to be relatively smaller in amplitude, 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. Such 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 operate to control the noise of the amplified signal202to a lesser extent than that to which it is capable. Later in the acquisition period, the variable current source203may be controlled to sink an increased amount of current while the variable current source205may be controlled to sink a decreased amount of current. 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 more specifically the dynamic biasing of the first stage202and the second stage204, may be implemented to control power, noise, and linearity characteristics of the amplifier112aduring an acquisition period.

The dynamic control of the current sources203and205may be achieved using a digital controller330, in an example arrangement 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 may include a variable feedback impedance206. In some embodiments, the variable feedback impedance206may be a variable RC feedback circuit. An example of such a variable RC feedback circuit is illustrated inFIG.3Aand described in connection with that figure. Feedback impedance may determine a transimpedance gain of a transimpedance amplifier (TIA), such that an 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 present technology may provide 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 the second stage204ofFIG.2, respectively. The first stage306includes an NMOS transistor310having a gate configured to receive the signal at the input302. A PMOS transistor312and a PMOS transistor314may have their gates coupled, with the drain of the PMOS transistor312coupled to the drain of the NMOS transistor310. The gate of the transistor312may be coupled to its drain. The transistors312and314may also be configured to receive a power supply voltage VDDA. The first stage306may further comprise an 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 two resistors; the other of the two resistors may receive the power supply voltage VDDA. The drain of the PMOS transistor314may be coupled to the drain of the 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 the PMOS transistor318is coupled to a node between the transistors314and316of the first stage306. The source of PMOS the transistor318receives the power supply voltage 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. The variable impedance circuit320may provide stable operation of the amplifier300when a gain of the amplifier300, or when currents of variable current sources321,325, are varied. Thus, the variable impedance circuit320may be provided to maintain a stable operation of the amplifier300for all magnitudes of currents sunk by the variable current sources321and325. That is, values of the variable capacitor CCand the variable resistor RZmay be adjusted during operation of the amplifier300to account for different current settings that may be programmed by the digital controller330

More specifically, 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. The current source322asinks a current IA, the current source322bsinks a current 2IA, and the current source322csinks a current 4IA. The current sources322a-322care coupled to the first stage306by respective switches324a,324b, and324c, which effectively provide 3 bits (8 states) of current control. 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. The current source326asinks a current IB, the current source326bsinks a current 2IB, and the current source326csinks a current 4IB. The current sources326a-326care coupled to the second stage308by respective switches328a,328b, and328c, which effectively provide 3 bits (8 states) of current control. The current IBmay equal 50 microAmps, or +/−20% of that value, or any value or range of values within such ranges, as examples.

AlthoughFIG.3Aillustrates variable current sources each including three parallel-coupled current sources, it should be appreciated that not all aspects of the present technology 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 current sources may have magnitudes that may be different than those disclosed herein. Any suitable magnitude(s) may be provided to allow for operation over a desired range of currents.

The digital controller330may be configured to control operation of the variable current sources321and325. The digital controller330may provide control signals to (digitally) program the currents of the variable current sources321,325. In the illustrated example ofFIG.3A, 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, an amount of current sunk by the variable current sources321,325may be varied independently during operation of the amplifier300, for example during an acquisition period. According to a non-limiting example, the digital controller330decreases an amount of current sunk by the variable current source325during the acquisition period and increases an amount of current sunk by the 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 controller330may 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, the digital controller300may be configured to control more than one component of the circuit ofFIG.1, any of which may be the amplifiers112a. . .112n.

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

The variable feedback impedance332and the variable impedance circuit320may be controlled in any suitable manner. In one embodiment, the digital controller330may set values of feedback impedances. However, alternative 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 technology. The variable impedance circuit320includes a number of switches340a. . .340narranged 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 of the switches340a. . .340nis coupled in series with a respective capacitor CCand a respective resistor RZ. An 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 of the switches340a. . .340nand capacitance and resistance values of the capacitors CCand the resistors RZprovided in the signal paths may be selected to provide sufficient control of the variable feedback impedance332, to obtain variable operation of the amplifier300across a range of operating scenarios resulting from variation of the variable current sources321,325. 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 the variable impedance circuit320based on a given gain set by the 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 technology. The variable impedance circuit332includes a number of complementary switches350a,350b, . . .350n. The complementary switches350a,350b, . . .350nreceive respective control signals SLa, SLb . . . SLn and SHa, SHb . . . SHn. The control signals SLa, SLb . . . SLn and SHa, SHb . . . SHn may be provided by the digital controller330in some embodiments, although alternatives may be used. The complementary switches350a,350b, . . .350nare coupled to respective parallel-connected RC circuits Cf, Rf. While three complementary switches350a,350b,350nare 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.

According to an aspect of the present technology, an alternative two-stage variable-current TIA is configured to provide an increased transimpedance gain in a first stage and a reduced noise for a given power consumption. The variable-current TIA may utilize input N-type and P-type transistors (referred to herein as “N type” and “P type” for short), which share a same current, thus leading to performance characteristics as described above.FIG.3Dillustrates a non-limiting example.

More specifically,FIG.3Dillustrates a circuit diagram of an alternative to a portion of the first stage306of the amplifier300ofFIG.3A. Specifically, a first stage360shown inFIG.3Dis an alternative to the first stage306ofFIG.3A. The first stage360includes an amplification portion comprising transistors362a,362b,362c, and362d, a local feedback comprising a transistor364, a current source comprising transistors366and368, and the previously-described RC circuit including resistors having a resistance value R and a capacitance value Cb.

Amplification components of the first stage360may include two N-P transistor pairs, which may be considered more generally to be pairs of opposite polarity transistors. Namely, PMOS transistor362aand NMOS transistor362bform a first N-P transistor pair, and PMOS transistor362cand NMOS transistor362dform a second N-P transistor pair. These four transistors may also be referred to as a differential input quad, or an input quad (quadrature) transistor arrangement with current sharing, since a same current conducts through the two transistor pairs. The illustrated configuration of four transistors may also be referred to as a current-reused differential pair. As a result of the transistor pairs conducting substantially the same current as each other, the noise of the first stage360may be reduced by half for a given current consumption compared to the configuration of the first stage306inFIG.3A. Alternatively, for a given noise level, the first stage360may consume approximately half the power consumed by the first stage306.

As illustrated, an input signal InN is input to control terminals (e.g., gates) of the transistors362aand362b. Control terminals (e.g., gates) of the transistors362cand362dare biased by the illustrated RC network. That is, the transistors362aand362breceive a same input signal, and the transistors362cand362dreceive a same input signal (a bias signal). Arranging the transistors362a-362din this manner means that both N-type and P-type transistors of a given transistor pair are receiving a same input signal.

An amplified output signal Vampof the first stage360may be provided to a gate of the PMOS transistor318and the variable impedance circuit320, as inFIG.3A.

As described above, the first stage360includes a current source comprising transistors366and368. The illustrated current source represents an example of a variable current source. However, a variable current source structured like either of the variable current sources321,325ofFIG.3Amay be implemented instead. That is, multiple switchable current sources may be coupled together in the manner shown inFIG.3Afor current sources322a,322b, and322c, and used as the variable current source ofFIG.3Dinstead of the transistors366,368.

As described above, the first stage360also includes local feedback in the form of the transistor364. In the non-limiting example illustrated, the transistor364is a PMOS transistor. The local feedback operates to ensure that current through the two N-P transistor pairs is substantially equal. In theory, the local feedback is not needed for such a function, but in practice manufacturing differences between the transistors362a-362dof the two N-P transistor pairs may result in unequal currents through those N-P transistor pairs. The local feedback operates to correct that behavior.

The first stage360may be used with the other circuit components ofFIG.3A, in the same manner as the first stage306.

As with the amplifier300ofFIG.3Agenerally, the polarity of the transistors362a-362din the first stage360ofFIG.3Dmay be reversed. That is, the PMOS transistors may instead be NMOS transistors, and vice versa. Operation of such a polarity-reversed first stage would be substantially the same as that of the first stage360. Thus, it should be appreciated that the amplifiers illustrated and described herein are not limited to a particular polarity of transistors, and that a “reversed” polarity arrangement, in which the transistor polarities of a given circuit may be reversed, is contemplated as part of the present disclosure.

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 amplifiers ofFIGS.2and3A, which again may be TIAs. 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 a current of the current source, having values ranging from I0to I7. The values of t0-t8and I0-I7may 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 that may be implemented is non-limiting, as more or fewer may be implemented.

Curve402represents a current of a variable current source of a second stage of a variable current amplifier. Thus, the curve402may represent a current of the current source205ofFIG.2. Curve404represents a current of a variable current source of a first stage of the variable current amplifier. Thus, the curve404may represent a current of the 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, the curve402decreases moving from time t0to time t8, while the curve404increases during the same time span. As previously described in connection withFIG.2, the first and second stages of the variable current amplifier may impact different operational characteristics of the variable current amplifier, 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 amplifier (e.g., 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 a noise floor of an amplifier used to amplify the electrical signal502, and may correspond to a 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 that 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; in such situations it should be appreciated that operating with the constant noise floor506requires significantly more current (and therefore power) than operating according to the noise floor504. Thus, aspects of the present application enable a variable current amplifier to amplify ultrasound signals at 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 consumed by 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 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.