Beamformed ultrasonic imager with delta-sigma feedback control

• US 6,987,474 B2
• Filed: 10/26/2004
• Issued: 01/17/2006
• Est. Priority Date: 10/06/1997
• Status: Expired due to Term

• Current Assignee: Hittite Microwave, LLC (Analog Devices, Inc.)
• Original Assignee: Q-Dot, Inc. (Analog Devices, Inc.)
• Inventors: Desilets, Charles S., O'Donnell, Matthew, Freeman, Steven R., Morin, Marc A., Linnenbrink, Thomas E., Quick, Marshall K.
• Primary Examiner(s): Mai, Lam T.
• Application Number:
  US10/973,235
• Publication Number:
  US 20050219096A1
• Time in Patent Office: 448 Days
• Field of Search: 341/143
• US Class Current: 341/143
• CPC Class Codes: G01S 15/8927 using simultaneously or sequentially two or more subarrays or subapertures
• CPC Class Codes: G01S 7/52028 using digital techniques
• CPC Class Codes: G01S 7/52034 Data rate converters
• CPC Class Codes: G01S 7/52044 Scan converters
• CPC Class Codes: G01S 7/5208 with integration of processing functions inside probe or scanhead
• CPC Class Codes: G01S 7/52095 using multiline receive beamforming
• CPC Class Codes: H03M 3/324 characterised by means or methods for compensating or preventing more than one type of error at a time, e.g. by synchronisation or using a ratiometric arrangement
• CPC Class Codes: H03M 3/43 the quantiser being a single bit one
• CPC Class Codes: H03M 3/454 with distributed feedback, i.e. with feedback paths from the quantiser output to more than one filter stage

Abstract

A method and apparatus are provided for reducing distortion in a dynamically delayed digital sample stream of an imaging system. The method includes the steps of delta-sigma modulating an input analog signal of the imaging system at a frequency above the Nyquist frequency of the input analog signal to generate a digital sample stream and changing a length of the sample stream to delay a portion of the sample stream while maintaining synchronism between a delta-sigma modulator and a demodulator of the system.

Claims

1. A method of improving system noise performance of a delta-sigma based dynamically delayed beamformer receiving a plurality of analog signal streams from a plurality of transducers of a transducer array and providing an amplitude modulated output signal corresponding to a signal intensity as a function of range from the transducer array, such method comprising the steps of:

downconverting the plurality of analog signal streams on a plurality of processing channels by mixing each input signal stream of the plurality of analog input signal streams with a periodic signal having a fundamental frequency greater than zero Hertz but less than twice a carrier center frequency of the received analog sigal streams;

digitizing each mixed signal stream within a delta-sigma modulator;

dynamically delaying a corresponding set of samples among the digitized signal streams within independent delay lines to compensate each sample of the corresponding set of samples for a sample source'"'"'s geometric origin relative to a desired dynamic receive focus;

dynamically adjusting the phase of the periodic signal on each channel of the plurality of processing channels based upon a total delay applied to the sample stream of that channel;

summing the corresponding set of delayed samples; and

basebanding and low pass filtering the stream of summed samples to provide an output signal whose amplitude corresponds to the signal intensity of the formed beam as a function of range.

2. The method as in claim 1 further comprising the step of time gain compensating each analog signal of each analog signal stream of the plurality of analog signal streams based upon a distance of the signal from the transducer.

3. The method as in claim 1 wherein the step of digitzing each mixed signal stream within a delta-sigma modulator further comprising sampling the mixed signal stream above the Nyquist frequency for the signal steam.