Dynamic receive beamformer with oversampling for medical diagnostic ultrasound
Receive beamformers for receive beamforming ultrasound information include a plurality of channels. The received signals for each channel are oversampled for conversion to digital form, such as sampling with a sigma-delta converter. The reconstruction of the samples into data at the Nyquist or other rate is performed in stages. Partial reconstruction to a rate less than the oversampling rate, but greater than the Nyquist rate, occurs prior to summation across channels. Delays are implemented by selecting data from the sample stream. After summation, the samples are reconstructed at a Nyquist or other rate.
1. A receive beamformer system for beamforming ultrasound information, the receive beamformer system comprising:
first and second receive channel paths each comprising:
an oversampling analog-to-digital converter; and
a first decimation circuit connected with an output, of the converter;
a summer connected with the first and second receive channel paths; and
a second decimation circuit connected with an output of the summer;
wherein the first decimation circuit is operable to dynamically decimate under control of a dynamic delay controller.
2. The receive beamformer system of claim 1 wherein the oversampling converter is a sigma-delta analog-to-digital converter operable with an oversampling ratio of at least 10 and output with a bit width of one or more.
3. The receive beamformer system of claim 1 wherein the first decimation circuit comprises a filter operable to output signals oversampled less than output by the sigma-delta analog-to-digital converter and more than output by the second decimation circuit and operable to output signals with a bit width greater than output by the sigma-delta analog-to-digital converters and less than output by the second decimation circuit.
4. The receive beamformer of claim 3 wherein the filter is a poly-phase filter operable to effectively interpolate an input signal to a higher time resolution than a sampling interval of the oversampling analog-to-digital converter.
5. The receive beamformer system of claim 3 wherein the second decimation circuit is operable to output signals substantially at a Nyquist rate.
6. The receive beamformer system of claim 1 wherein the first decimation circuit comprises a comb filter of an order one above an order of the oversampling analog-to-digital converter.
7. The receive beamformer system of claim 1 wherein the first and second decimation circuits comprise a reconstruction filter, the first decimation circuit being a first partial reconstruction filter and the second decimation circuit being a second partial reconstruction filter.
8. The receive beamformer system of claim 1 further comprising a controller operable to select stored data from the memory as a function of a delay, the selected data being provided to the first decimation circuit; and
wherein the first and second receive channel paths each further comprise:
a memory operable to store data output by the converter;
a multiplier operable to amplify an output to the summer.
9. The receive beamformer system of claim 1 wherein the first and second receive channel paths each further comprise analog mixers operable for in-phase and quadrature paths, each of the sigma-delta analog-to-digital converters comprising a pair of low-pass converters.
10. The receive beamformer system of claim 1 wherein the oversampling analog-to-digital converter comprises a band-pass converter.
11. The receive beamformer system of claim 1 wherein the first and second receive channel paths are operable to time multiplex for forming a plurality of beams from the same received signals.
12. A method for receive beamforming ultrasound information, the method comprising:
oversampling received signals in at least two channels;
partially reconstructing, in the at least two channels, first higher bit width signals from the oversampled received signals, the first higher bit width signals having a higher bit width than the oversampled received signals;
summing the first higher bit width signals from the at least two channels; and
reconstructing second higher bit width signals from the summed first higher bit width signals, the second higher bit width signals having a higher bit width than the first higher bit width signals;
wherein partially reconstructing comprises filtering and decimating by at least two but less than an oversampling ratio.
13. The method of claim 12 wherein oversampling comprises oversampling with a ratio of sampling rate to Nyquist rate of at least 10.
14. The method of claim 12 wherein oversampling and partially reconstructing comprise oversampling and partially reconstructing in at least sixteen channels, and wherein summing comprises summing from the at least sixteen channels.
15. The method of claim 12 wherein reconstructing the second higher bit width signals comprises filtering and decimating such that the second higher bit width signals are substantially at a Nyquist rate.
16. The method of claim 12 wherein summing comprises summing at a data rate less than output by the oversampling and greater than the second higher bit width signals.
17. The method of claim 12 further comprising:
mixing the received signals prior to oversampling, the mixed received signals comprising in-phase and quadrature signals.
18. The method of claim 12 further comprising:
relatively delaying the oversampled signals of the at least two channels prior to summing; and
relatively apodizing the oversampled signals of the at least two channels prior to summing.
19. A system for receive beamforming ultrasound information, the system comprising:
an oversampling analog-to-digital converter;
a first low pass filter operable to construct first samples with a greater bit width than output from the converter;
a summer operable to sum the greater bit width samples with other samples; and
a second low pass filter operable to construct second samples from an output of the summer, the second samples having a greater bit width than the first samples.
20. The system of claim 19 wherein the converter is operable to output third samples at a rate at least 10 times a Nyquist rate and a bit width less than the first samples, wherein the first low pass filter is operable to output the first samples at a rate less than the third samples, and wherein the second low pass filter is operable to output the second samples at a rate less than the first samples.
21. The system of claim 19 further comprising:
a memory operable to store third samples output from the converter; and
a controller operable to select the third samples for outputting to the first low pass filter as a function of a delay for a beam.