JP2007082806A - Ultrasonic diagnostic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide small and inexpensive ultrasonic diagnostic apparatus by adopting a new-type AD converter which has a dynamic range which can be applied to CW Doppler signal processing and whose circuit scale is small. <P>SOLUTION: According to an image rendering mode and an ultrasonic probe 11 to be used, each of the center frequency Fc, the band width Bw and the dynamic range of a controlled bandpass type sigma delta AD converter 154 is controlled freely by a resonator controller 16. Thus, a reception beam former corresponding to all modes by one reception system can be achieved, so that a CW Doppler mode dedicated analog signal processing circuit required conventionally can be deleted. As the result, the reception beam former and the ultrasonic diagnostic apparatus smaller and less expensive than conventional ones are achieved. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ultrasonic diagnostic apparatus capable of imaging in a CW (Continuous Wave) Doppler mode, a B mode, and the like.

  Recent ultrasonic diagnostic apparatuses have been digitized extensively regardless of their class. For example, the reflected echo received by the probe is converted into a digital signal immediately after being amplified by the preamplifier, and then necessary processing is performed by digital signal processing. When digitized in this way, it is freed from errors such as component variations and temperature changes that cannot be avoided by analog components, and the device can be produced uniformly within the designed accuracy range. In addition, it is possible to build a wide range of processing circuits in one IC due to the fact that digital circuits are suitable for IC integration and recent significant advances in LSI technology. Therefore, it has become possible to provide users with small and low-priced products.

  The background of such a situation is largely due to the fact that high-speed, high-precision AD converters (ADC) have become available at a relatively low price. For example, when a digital ultrasonic diagnostic apparatus appeared in the world, AD converters that can be adopted even for high-end machines were about 8-bit 20 MSPS. However, at present, 10-bit 40 MSPS is often adopted even in the popular machine class, and more than 12-bit 40 MSPS is becoming natural in high-end machines.

  By the way, even in such a digitization situation, the CW Doppler signal processing must be relied on an old analog signal processing circuit. This is due to the following operational circumstances unique to CW Doppler signal processing. That is, the target of the Doppler method is blood flow, and the ultrasonic reflector is a minute object such as a blood cell. Therefore, the received signal is weak when compared with a B mode or the like having a reflector as a tissue. In the CW Doppler method, a transmission wave is always sent into the body. For this reason, the transmission amplitude is limited for safety, and the amplitude of the received signal is also limited from this point. Furthermore, there is a limit to the amplification of the received signal by the amplifier. This is because a carrier component having a relatively large amplitude on which a Doppler signal component is superimposed has a problem that it is saturated by amplification.

  Under these circumstances, the AD converter that handles the received signal in the CW Doppler signal processing is required to have a large dynamic range that can express from a weak Doppler signal component to a carrier component. However, there is no conventional AD converter that satisfies this requirement at present. Therefore, the subsequent digital signal processing circuit cannot be shared with the signal processing system of another imaging mode (for example, B mode), and a dedicated analog signal processing circuit is required for processing the CW Doppler signal. .

  That is, an ultrasonic diagnostic apparatus compatible with CW Doppler has at least two signal processing systems. Hereinafter, a signal processing system of a conventional ultrasonic diagnostic apparatus compatible with CW Doppler will be described with reference to FIG.

  A signal received in the CW Doppler mode is subjected to beam forming processing in a CW beam former 51 which is a dedicated analog circuit composed of various and various analog parts. The subsequent signal processing / image generation unit 53 calculates the Doppler frequency and the blood flow rate by fast Fourier transform processing or the like based on the signal subjected to the beam forming processing.

  On the other hand, a signal received in another imaging mode, for example, the B mode, is converted into digital data by, for example, 10-bit 40 MSPS in the AD converter 52a of the signal receiving unit 52, and beam formation is performed by the Rx beamformer 52b. Receive processing for. Conventionally, as an AD converter for such a purpose, a so-called “pipeline type” is used. This is (1) the input signal is converted to a digital quantity by a “flash” AD converter of several bits, (2) it is converted back to an analog quantity by a DA converter, and the residual is obtained by subtracting from the input signal. (3) The process of (1) to (3) of amplifying the residual appropriately and inputting it to the “flash type” AD converter in the next stage is performed several times to obtain final converted data. .

  FIG. 11 is a diagram illustrating a configuration of a pipelined AD converter. The flash type shown in the figure is the simplest configuration example. For example, in the case of 2 bits, a voltage obtained by dividing the input range into four parts is prepared, and the input voltage is compared with those to output a code from a close value. That's it. In this type, as many comparators as the number of divisions are required. Therefore, when the resolution is increased, the circuit scale and the power consumption are extremely increased. For example, if the resolution is increased from 8 bits to 10 bits, the number of comparators increases from 256 to 1024.

  Therefore, the pipeline type AD converter employs a method for obtaining final conversion data by repeating flash AD conversion for each range of several bits. According to this method, if the flash is composed of 4 stages in the case of 8 bits, the number of comparators can be increased by 4 even if the number of stages is increased by 10 bits. Although there is a disadvantage of output delay by the pipeline system, the data rate itself is the same as the sampling rate of the sample hold “S / H”, and high-speed conversion is possible.

  However, the conventional ultrasonic diagnostic apparatus corresponding to CW Doppler having the above configuration has the following disadvantages, for example.

  First, since the CW beamformer 51 includes many analog parts, the cost is high, and a certain amount of area is required for its mounting. Therefore, when the CW beamformer 51 is mounted, it is difficult to reduce the size and cost of the ultrasonic diagnostic apparatus.

  Second, although the pipeline AD converter has a smaller circuit scale than the flash type, it has many components as shown in FIG. Therefore, it is not suitable for incorporation into a highly integrated IC, and it is difficult to reduce the size and price of an ultrasonic diagnostic apparatus. In the case of an ultrasonic diagnostic apparatus, for example, there is a concept that an AD converter is incorporated into an ASIC of a reception beamformer. In the example of FIG. 10, this is a technique for developing a portion surrounded by a dotted line as a dedicated IC (ASIC). When the pipeline type AD converter is employed by this method, the circuit scale of the AD converter portion of the figure is not reduced, and the degree of integration is not increased. In other words, the number of channels that can be realized in one ASIC is limited, and this is also an impediment to developing a small and low-priced device.

  Thirdly, in a conventional ultrasonic diagnostic apparatus compatible with CW Doppler, at least two signal processing systems and a space for mounting them are required. This leads to an increase in size and cost of the ultrasonic diagnostic apparatus.

  There is also a movement to search for an AD converter applicable to the above-described CW Doppler signal processing. This is mainly achieved by increasing the resolution of the pipeline type. However, this approach would require something larger than 16 bits unless there is a technological breakthrough. At this level, when considering an ASIC with multiple channels, the circuit scale and power consumption become enormous, which may result in a high cost in spite of the low cost.

  The present invention has been made in view of the above circumstances, and has a dynamic range applicable to signal processing in Doppler mode and signal processing in other imaging modes, and a new AD conversion with a small circuit scale. The purpose is to provide a small-sized and low-priced ultrasonic diagnostic apparatus.

  In order to achieve the above object, the present invention takes the following measures.

  According to an aspect of the present invention, in an ultrasonic diagnostic apparatus that scans a predetermined part of a subject with an ultrasonic wave according to a predetermined imaging mode and acquires an ultrasonic image, the ultrasonic wave is transmitted to the subject. An ultrasonic probe that receives an echo signal from the control unit, a control unit that determines a frequency band and a dynamic range of a signal to be imaged according to the imaging mode, and a frequency band that is determined from the echo signal. An ultrasonic diagnostic apparatus comprising: signal conversion means for extracting a signal component and performing analog-digital conversion in the determined dynamic range to obtain a digital signal.

  As described above, according to the present invention, by adopting a new AD converter having a dynamic range applicable to signal processing in Doppler mode and signal processing in other imaging modes and having a small circuit scale, A small and low-priced ultrasonic diagnostic apparatus can be realized.

  Hereinafter, first and second embodiments of the present invention will be described with reference to the drawings. In the following description, components having substantially the same function and configuration are denoted by the same reference numerals, and redundant description will be given only when necessary.

  Further, in each of the following embodiments, a case where the present invention is applied to imaging using the CW Doppler mode is taken as an example in order to make the description concrete. However, regardless of this, the technical idea of the present invention can be applied to all imaging using the Doppler mode.

(First embodiment)
First, the configuration of the ultrasonic diagnostic apparatus according to the present embodiment will be described with reference to FIG.

  FIG. 1 is a block diagram of the ultrasonic diagnostic apparatus 10. As shown in the figure, the ultrasonic diagnostic apparatus 10 includes an ultrasonic probe 11, a T / R switch 13, a transmission / reception unit 15, a B-mode processing unit 17, a Doppler processing unit 19, an image generation unit 21, a display unit 23, and an input. A device 25 and a CPU 27 are included.

  The ultrasonic probe 11 generates ultrasonic waves based on a drive signal from the ultrasonic transmission / reception unit 15 and converts a reflected wave from the subject into an electric signal, and a matching layer provided in the piezoelectric vibrator. And a backing material for preventing the propagation of ultrasonic waves from the piezoelectric vibrator to the rear. When ultrasonic waves are transmitted from the ultrasonic probe 11 to the subject, the transmitted ultrasonic waves are successively reflected by the discontinuous surface of the acoustic impedance of the body tissue and received by the ultrasonic probe 11 as an echo signal. The amplitude of this echo signal depends on the difference in acoustic impedance at the discontinuous surface that is to be reflected. The echo when the transmitted ultrasonic pulse is reflected by the moving blood flow or the surface of the heart wall depends on the velocity component of the moving body in the ultrasonic transmission direction due to the Doppler effect. Receive a shift.

  The T / R switch 13 is a switch for switching a signal path between transmission and reception.

  The transmission / reception unit 15 includes a trigger generation circuit and a delay circuit (not shown), a pulser 150, and the like. In the pulsar 150, a rate pulse for forming a transmission ultrasonic wave is repeatedly generated at a predetermined rate frequency fr Hz (period: 1 / fr second). Further, in the delay circuit, a delay time necessary for focusing the ultrasonic wave into a beam shape for each channel and determining the transmission directivity is given to each rate pulse. The trigger generation circuit applies a drive pulse to the probe 11 at a timing based on this rate pulse.

  The transmission / reception unit 15 includes an LNA (Low Noise Amplifier) 152, a TGC (Time Gain Compensation) 153, a controlled bandpass sigma-delta AD converter 154 (hereinafter simply referred to as a “controlled bandpass sigma-delta AD conversion” A beam former 155). The LNA 152 amplifies the echo signal captured via the probe 11 with low noise for each channel. The TGC 153 amplifies the output signal of the LNA 152 with a controlled gain in accordance with the time when the amplified echo signal returns. Based on the control signal from the resonator controller 16, the control-type bandpass sigma-delta AD converter 154 performs filtering based on a predetermined center frequency and a predetermined dynamic range for each imaging mode, and outputs an analog signal in a predetermined band. Are extracted and AD converted (analog-to-digital conversion). The detailed configuration of this controlled bandpass sigma-delta AD converter 154 will be described later. The beamformer 155 gives a delay time necessary for determining the reception directivity to the AD converted echo signal, and then performs an addition process. By this addition, the reflection component from the direction corresponding to the reception directivity of the echo signal is emphasized, and a comprehensive beam for ultrasonic transmission / reception is formed by the reception directivity and the transmission directivity.

  The resonator controller 16 controls the bandwidth Bw and the center frequency Fc of the analog signal extracted by the controlled bandpass sigma-delta AD converter 154 according to the imaging mode based on the overall control of the CPU 27.

  The B-mode processing unit 17 receives the echo signal from the transmission / reception unit 15 and performs logarithmic amplification, envelope detection processing, and the like, and generates data in which the signal intensity is expressed by brightness. This data is transmitted to the image generation unit 21 and displayed on the display unit 23 as a B-mode image in which the intensity of the reflected wave is represented by luminance.

  The Doppler processing unit 19 performs frequency analysis on velocity information from the echo signal received from the transmission / reception unit 15, extracts blood flow, tissue, and contrast agent echo components due to the Doppler effect, and obtains blood flow information such as average velocity, dispersion, and power. Ask for multiple points. The obtained blood flow information is sent to the image generation unit 21 and displayed in color on the display unit 23 as an average velocity image, a dispersion image, a power image, and a combination image thereof.

  The image generation unit 21 converts a scanning line signal sequence of ultrasonic scanning into a scanning line signal sequence of a general video format typified by a television or the like, and generates an ultrasonic diagnostic image as a display image.

  The display unit 23 is a monitor or the like that displays a tissue image obtained by B-mode signal processing, a blood flow image obtained by Doppler signal processing or the like based on the video signal from the image generation unit 21.

  The input device 25 is connected to the apparatus main body, and includes various switches, buttons, trackballs, etc. for incorporating various instructions, conditions, region of interest (ROI) setting instructions, various image quality condition setting instructions, etc. from the operator into the apparatus main body. Has a mouse, keyboard, etc.

  The CPU 27 has a function as an information processing apparatus (computer) and is a control unit that controls the operation of the main body of the ultrasonic diagnostic apparatus.

(Bandpass sigma-delta AD converter)
Next, the configuration of the controlled bandpass sigma-delta AD converter 154 will be described in detail. This controlled band-pass sigma-delta A / D converter 154 controls the center frequency and band of the analog signal extracted by the control of the resonator controller 16, and uses an echo signal (analog signal) with an optimum value in each imaging mode. ) AD conversion is executed.

  FIG. 2 is a block diagram showing the configuration of the present controlled band-pass sigma-delta AD converter 154. As shown in the figure, the controlled bandpass sigma-delta AD converter 154 includes an adder 154a, a resonator 154b, a comparator 154c, a 1-bit DAC 154d, and a digital filter 154c.

  The adder 154a subtracts the 1-bit signal fed back and converted back to analog from the input analog signal. Thereby, the quantization noise is driven to the unused band, and the quantization noise of the frequency of interest is reduced.

  The resonator 154 b performs filtering (extraction) based on the center frequency Fc and the bandwidth Bw based on the control signal from the resonator controller 16. These Fc and Bw are controlled by the imaging mode. For example, in the case of the CW Doppler mode, a necessary signal band is narrow but a wide dynamic range is necessary. Therefore, the center frequency Fc corresponding to the probe 11 to be used and Bw for squeezing the band are supplied to the resonator 154b. Is done. In the B mode, since a signal having a wider frequency band is required, the center frequency Fc corresponding to the probe 11 to be used and Bw for expanding the band are supplied to the resonator 154b.

  The comparator 154c converts the resonator output signal into a 1-bit digital signal by comparing with a predetermined reference voltage.

  The 1-bit DAC 154d is provided in the feedback loop, converts the 1-bit digital signal generated by the comparator 154c from digital to analog, and sends it to the adder 154a for subtraction from the input signal.

  The digital filter 154c performs decimation on the digital signal (bit string) output from the comparator 154c. The digital signal of a predetermined band extracted by this decimation is sent to the beam former 155.

  Next, the operation of this controlled bandpass sigma-delta AD converter 154 will be described. The controlled band-pass sigma-delta AD converter 154 changes the bandwidth Bw and the center frequency Fc of the analog signal to be extracted according to the imaging mode based on the control of the resonator controller 16. Hereinafter, a Doppler mode, in particular a CW Doppler mode that requires a high dynamic range, and an imaging mode for imaging the amplitude itself (for example, a B mode, an A mode, an M mode, etc. The operation in both of them will be described.

  In the CW Doppler mode, the controlled band-pass sigma-delta AD converter 154 is controlled so as to extract a signal with a narrow band and a large dynamic range. In the Doppler mode, the necessary signal component is limited to a narrow band around the center frequency, and the band of the converter can be narrowed down. By using a narrow band, the noise reduction effect can be greatly increased, so that a wide dynamic range can be obtained.

  FIG. 3A is a control example of the controlled bandpass sigma-delta AD converter 154 in the CW Doppler mode, and the solid line in the figure indicates the signal transfer function of the controlled bandpass sigma-delta AD converter 154. The dotted line indicates the noise transfer function. As shown in the figure, in the CW Doppler mode, for example, a signal is extracted in a narrow band with a center frequency Fc = 2 MHz and a bandwidth Bw = 100 kHz. Thereby, the noise reduction effect can be increased and the S / N ratio can be increased. The center frequency Fc = 2 MHz is adjusted to the center frequency of the probe.

  On the other hand, in the B mode, the controlled band-pass sigma-delta AD converter 154 is controlled so as to extract a signal in a wide band. The reason why such a wide band is used is that in the B mode or the like, it is important to use a received signal over a wide band in order to obtain a high-resolution image. Note that by extracting a signal in a wide band, the noise reduction effect is reduced as compared with CW Doppler. However, in the mode in which the amplitude of the reflected echo itself is imaged as in the B mode, this point is not as problematic as in the CW Doppler mode.

  FIG. 3B is an example of control of the controlled bandpass sigma-delta AD converter 154 in the B mode, and the solid line indicates the control-type bandpass sigma-delta AD converter 154 as in FIG. The signal transfer function and the dotted line indicate the noise transfer function. As shown in the figure, in the B mode, for example, the center frequency Fc = 10 MHz and the bandwidth Bw = 8 MHz, and the bandwidth is expanded so that necessary signals pass. This corresponds to reducing the Q value of the resonator 154b as a result. Therefore, as shown in the figure, the characteristic of the noise transfer function becomes “loose”, and the noise reduction effect is reduced as compared with the CW Doppler, but a wide band signal can be passed. The center frequency Fc = 10 MHz is adjusted to the center frequency of the probe.

  In modes other than the conventional CW Doppler, a 10-bit, high-end 12-bit pipeline AD converter is used. No more is needed for practical use. That is, if the S / N level of these AD converters can be realized, it is considered that the reduction in noise reduction effect in the high-band mode is not a problem.

  Next, the effect when the above-described controlled band-pass sigma-delta AD converter 154 is employed in the ultrasonic diagnostic apparatus 10 will be described from the viewpoint of comparison with the other two types of sigma-delta AD converters. .

  First, the first type sigma-delta AD converter will be described. FIG. 4 is a block diagram showing a configuration of the first type sigma-delta AD converter 50. FIGS. 5A to 5C are diagrams for explaining the characteristics of the first type sigma-delta AD converter 50. FIG.

  In the first type sigma-delta AD converter 50, as shown in FIG. 4, an integrator is incorporated in the modulator portion. Therefore, it is intended to pass quantization signal on the high frequency side through the low frequency side signal. In that sense, the first type sigma-delta AD converter 50 has a low-pass filter function.

  In general, in the sampling theory, the quantization noise is uniformly distributed in the Nyquist band as shown in FIG. 5A, and the total power is determined by the input range and resolution. Therefore, if sampling is performed at a frequency larger than the necessary band, and only the necessary band is extracted (decimation) later by the filter, the quantization noise is reduced by the band limitation by the filter as shown in FIG. it can. This is so-called oversampling.

  As shown in FIG. 5C, the first type sigma-delta A / D converter 50 further controls the noise distribution by sigma-delta modulation, passes it out of the band, and reduces the noise in the signal band. It is even smaller. With such a function, it is possible to reduce the quantization noise, which has been dominant as a noise source of the AD converter, to the same level or less as other noises.

  However, there is a problem in applying the first type sigma-delta AD converter 50 to an ultrasonic diagnostic apparatus in a simple manner. This is because the sigma-delta AD converter 50 is premised on oversampling. That is, since the frequency of a signal to be converted reaches a maximum of several tens of MHz, a clock frequency of several hundreds of MHz is required. There is a risk in generating and wiring such a high frequency on a circuit board, and an AD converter itself is required to operate at such a high rate, resulting in an increase in power consumption. This is the reason why the application of the conventional sigma-delta AD converter is limited to the audio band.

  There is a proposal to apply this type of AD converter to an ultrasonic diagnostic apparatus for the purpose of reducing the circuit scale due to its simplicity (for example, SE Noujaim, SL Garverick, and M. O'Donnell “Phased array ultrasonic beam forming using oversampled A / D converters, ”USP5,203,35, April 20, 1993, KWRigby“ Delta-sigma beamformers with minimal dynamic focusing artifacts, ”USP6,366,227, April2 2002, SRFreeman et al.,“ Delta -sigma oversampled ultrasound beamformer with dynamic delays, "IEEE Trans. Ultrasonic, Ferroelectrics and Frequency Control, vol. 46, pp 320-332, March 1999.). However, both are premised on the existence of a high frequency clock and operation at that frequency, and the practical problems described above are not considered.

  Next, a second type band-pass sigma-delta AD converter will be described. FIG. 6A is a block diagram showing the configuration of the second type sigma-delta AD converter 60. In the second type sigma-delta AD converter 60, a resonator is incorporated in the modulator portion in place of the integrator as shown in FIG. Therefore, it is intended to pass only a signal having a predetermined center frequency (fixed) and a predetermined bandwidth (fixed) around it. In that sense, the second type sigma-delta AD converter 50 has a fixed band-pass filter function. In addition, a signal component existing in the center frequency ± set band and quantization noise controlled to be small at the center frequency appear in the output.

  The characteristics of the second type sigma-delta AD converter 60 will be described in comparison with the characteristics of the first type sigma-delta AD converter 50. FIG. 6B is a diagram showing the characteristics of the first type sigma-delta AD converter 50. FIG. 6C is a diagram showing characteristics (center frequency Fc, bandwidth Bw) of the second type sigma-delta AD converter 60. As can be seen by comparing FIG. 6B and FIG. 6C, the second type sigma-delta AD converter 60 has a high S / N ratio with respect to a predetermined center frequency Fc and a narrowband signal around it. AD conversion becomes possible. This characteristic can be said to be suitable for CW Doppler signal processing. This is because the Doppler signal component exists in the vicinity of a certain carrier frequency ± several tens of kHz, and conversely, other bands are not interesting if limited to Doppler signal processing. The oversampling ratio can be considered as a ratio between the set band and the sampling frequency. Therefore, according to the second type sigma-delta AD converter 60, it is possible to perform AD conversion of a high-frequency signal without taking an extremely high sampling frequency.

  However, the second type sigma-delta AD converter 60 has the following disadvantages when it is applied to an all-mode reception beamformer including the CW Doppler mode and other imaging modes. First, the center frequency of the second-type bandpass sigma-delta AD converter 60 is fixed. That is, the center frequency of the received echo signal in ultrasonic diagnosis depends on the probe. Therefore, the probe to be used is extremely limited as it is, and the degree of diagnosis is narrowed. Second, the second-type bandpass sigma-delta AD converter 60 cannot cover wideband signal processing. That is, the CW Doppler signal component has a narrow band, but a wide band is required in other modes. Therefore, it cannot cope with signal processing in the CW Doppler mode and signal processing in other imaging modes.

  Research on applying this type of AD converter to a beam former for an ultrasonic diagnostic apparatus has been reported in the past (for example, O. Norman, “A band-pass delta-sigma modulator for ultrasonic imaging at 160 MHz clock rate, "IEEE J. Solid-State Circuits, vol. 31, pp2036-2041, Dec. 1996). In this example, a method of controlling the band with an external element is adopted. For this reason, the degree of freedom of control is small, and the restriction that only one center frequency can be set is not escaped.

  The present controlled band-pass sigma-delta AD converter 154 overcomes these first-type and second-type band-pass sigma-delta AD converters and solves the above problems. In other words, the controlled band-pass sigma-delta AD converter 154 can freely control the center frequency, bandwidth Bw, and dynamic range, and extracts signals in the necessary band according to the imaging mode. Is possible.

  Therefore, the control-type bandpass sigma-delta AD converter 154 can realize an all-mode reception beamformer with one reception system, and eliminates the conventional CW Doppler mode dedicated analog signal processing circuit. Can do. As a result, it is possible to realize a reception beam former and an ultrasonic diagnostic apparatus that are smaller and less expensive than conventional ones.

Example 1
Next, an embodiment of the controlled band-pass sigma-delta AD converter 154 will be described. FIG. 7 is a diagram showing a controlled bandpass sigma-delta AD converter 154 according to the present embodiment. The band-pass sigma-delta AD converter 154 shown in the figure uses an analog / active filter called a Gm / C filter for the resonator 154b.

This Gm / C filter realizes a desired transfer function with a transconductor Gm _Q (bandwidth Bw control) or Gm _F (center frequency Fc control) and a capacitor C, thereby having a frequency characteristic as a filter. is there. The transconductor is a so-called V · I converter, but here, it is possible to make a V · I characteristic variable by a control voltage or current.

FIG. 8A shows an example of a transconductor having the most basic form in a CMOS (fixed characteristic type), for example. This is a basic source coupled differential input circuit. When the relationship between the output current and the input voltage is obtained, the following equation (1) is obtained.

Here, μ is the average electron mobility of the MOS-FET channel, Cox is the ratio between the dielectric constant and thickness of the oxide film, and W and L are the width and length of the channel, respectively. As shown in equation (1), the current is determined by the input voltage via fixed process parameters and bias current, so the circuit in the form of FIG. 8A can be a V · I converter. The transconductance gm can be obtained immediately by the following equation (2).

FIG. 8B shows an example (characteristic variable type) in which the characteristics of the transconductor shown in FIG. The newly added CMOS-M3 is equivalently operated as a voltage control resistor in the non-saturated region. When this resistance component is represented by R, the transconductor Gm of the circuit of FIG. 8B can be expressed by the following equation (3) using the original gm.

Here, since R is determined by the gate-source voltage of M3, it can be controlled by the gate voltage _Vtune . Therefore, the expression (3) can be expressed as the following expression (4), which is a variable transconductance.

  By using the elemental technology as described above, it is possible to realize a modulator as shown in FIG. 7, and thus a bandpass sigma-delta AD converter 154 capable of controlling the center frequency and the band can be obtained. .

(Example 2)
Next, another embodiment of the controlled band-pass sigma-delta AD converter 154 will be described. The AD converter 154 according to the present embodiment takes advantage of the characteristics of the sigma-delta AD converter that the circuit scale and power consumption are small, and is an example suitable for downsizing the apparatus.

  FIG. 9 is a diagram showing a reception beamformer 157 incorporating a controlled bandpass sigma-delta AD converter 154 according to the present embodiment. Corresponding to FIG. 1, the reception beamformer 157 includes a beamformer 155 as a digital reception beamformer ASIC and a controlled band-pass sigma-delta AD converter 154.

  A plurality of (eg, 128) control-type bandpass sigma-delta AD converters 154 are provided for each channel, and execute AD conversion with the above-described contents. The “Beamforming Logic” portion has a function equivalent to that of a conventional digital beamformer, and performs phasing addition and reception aperture control.

  As described above, the control-type bandpass sigma-delta AD converter 154 has a small circuit scale and power consumption, and can be said to be suitable for incorporating an IC. Therefore, when this is incorporated in the digital receive beamformer ASIC, more channels can be incorporated in one IC. That is, with respect to N of “Ch N” in FIG. 9, a larger value can be expected without increasing the size of the apparatus, and a high integration can be achieved as a reception beamformer circuit.

  Although the present invention has been described based on the embodiments, those skilled in the art can come up with various changes and modifications within the scope of the idea of the present invention. It is understood that it belongs to the scope of the present invention.

  For example, in the first embodiment, the implementation of the modulator using the Gm / C filter is shown, but the present invention is not limited to this. For example, it can be realized by a programmable switched capacitor circuit.

  Also, for example, the controlled bandpass sigma-delta AD converter in each of the above embodiments assumes 1 bit for the internal AD converter / DA converter of the constituent elements. However, the present invention is not limited to this and can be applied to a case of a plurality of bits.

  Furthermore, the control-type band-pass sigma-delta AD converter in each of the above embodiments is not limited to the ultrasonic diagnostic apparatus, and can be used for other devices (for example, communication devices such as radios and mobile phones). it can.

  Further, the embodiments may be combined as appropriate as possible, and in that case, the combined effect can be obtained. Furthermore, the above embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, even if some constituent requirements are deleted from all the constituent requirements shown in the embodiment, the problem described in the column of the problem to be solved by the invention can be solved, and the effect described in the column of the effect of the invention If at least one of the following is obtained, a configuration in which this configuration requirement is deleted can be extracted as an invention.

   As described above, according to the present invention, a small and inexpensive ultrasonic diagnostic apparatus is realized by adopting a new AD converter having a dynamic range applicable to CW Doppler signal processing and a small circuit scale. it can.

FIG. 1 is a block diagram of the ultrasonic diagnostic apparatus 10. FIG. 2 is a block diagram showing the configuration of the present bandpass AD converter 154. FIG. 3A is an example of control of the bandpass AD converter 154 in the CW Doppler mode. FIG. 3B is an example of control of the bandpass AD converter 154 in the B mode. FIG. 4 is a block diagram showing the configuration of the sigma-delta AD converter 50. As shown in FIG. FIGS. 5A to 5C are diagrams for explaining the characteristics of the sigma-delta AD converter 50. FIG. FIG. 6A is a block diagram showing a configuration of a conventional bandpass sigma-delta AD converter. FIG. 6B is a diagram showing the characteristics of a sigma-delta AD converter 50 that is a low-pass type. FIG. 6C is a diagram illustrating the characteristics of the bandpass sigma-delta AD converter 154. FIG. 7 is a diagram showing an embodiment of the band-pass sigma-delta AD converter 154. FIG. 8A shows an example of the most basic form of transconductor in, for example, a CMOS. FIG. 8B shows an example in which the characteristics of the transconductor shown in FIG. FIG. 9 is a diagram showing another embodiment of the bandpass sigma-delta AD converter 154. In FIG. FIG. 10 is a block diagram showing a configuration of a conventional ultrasonic diagnostic apparatus 50. FIG. 11 is a diagram illustrating a configuration of a pipelined AD converter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Ultrasonic diagnostic apparatus, 11 ... Ultrasonic probe, 13 ... T / R switch, 15 ... Ultrasonic transmission / reception part, 16 ... Resonator controller, 17 ... B-mode processing part, 19 ... Doppler processing part, 21 ... Image generation , 23 ... display unit, 25 ... input device, 27 ... CPU, 150 ... pulsar, 152 ... LNA, 153 ... TGC, 154 ... controlled band-pass sigma-delta AD converter, 154a ... adder, 154b ... resonance 154c ... comparator, 154d ... 1bit-DAC, 154c ... digital filter, 155 ... beamformer

Claims (6)

In an ultrasonic diagnostic apparatus that scans a predetermined part of a subject with an ultrasonic wave according to a predetermined imaging mode and acquires an ultrasonic image,
An ultrasonic probe for transmitting an ultrasonic wave to the subject and receiving an echo signal from the ultrasonic wave;
Control means for determining a frequency band and a dynamic range of a signal to be imaged according to the imaging mode;
Signal conversion means for extracting a signal component belonging to the determined frequency band from the echo signal, performing analog-digital conversion in the determined dynamic range, and obtaining a digital signal;
An ultrasonic diagnostic apparatus comprising: The control means determines the frequency band based on a center frequency and a bandwidth of the image signal.
When the imaging mode is a Doppler mode, the predetermined bandwidth is set to be narrow so that the imaging signal becomes a narrowband signal,
When the imaging mode is a mode for imaging the amplitude of the echo signal itself, setting the predetermined bandwidth wide so that the imaging signal becomes a wideband signal;
The ultrasonic diagnostic apparatus according to claim 1.   The ultrasonic diagnostic apparatus according to claim 2, wherein the control unit controls the predetermined center frequency in accordance with a center frequency of the ultrasonic probe. The control means
When the imaging mode is a Doppler mode, set a wide dynamic range of the signal to be imaged,
When the imaging mode is a mode for imaging the amplitude of the echo signal itself, setting a dynamic range of the signal to be imaged narrowly;
The ultrasonic diagnostic apparatus according to claim 1, wherein: The signal converting means includes
An adder for inputting the echo signal;
A resonator that is provided at a subsequent stage of the adder and that passes only a first signal belonging to the frequency band among signals output by the adder;
A first converter for analog-to-digital conversion of the first signal;
A digital filter for decimation of the converted digital signal;
A second converter that is provided in a feedback loop that feeds back the digital signal output from the first converter to the input of the resonator, and that performs a digital-analog conversion on the digital signal to obtain a third signal; Have
The adder, the resonator, the first converter, and the second converter form a sigma-delta modulation system;
The ultrasonic diagnostic apparatus according to claim 1, wherein:   The ultrasonic diagnostic apparatus according to claim 1, wherein the signal conversion unit is an ASIC.

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