Transmit circuit for imaging with ultrasound

• US 20040158147A1
• Filed: 02/10/2003
• Published: 08/12/2004
• Est. Priority Date: 02/10/2003
• Status: Active Grant

• Current Assignee: Siemens Medical Solutions USA Incorporated (Siemens AG)
• Original Assignee: Siemens Medical Solutions USA Incorporated (Siemens AG)
• Inventors: Shifrin, Lazar A.
• Granted Patent: US 6,808,494 B2
• Time in Patent Office: Days
• US Class Current: 600/437
• CPC Class Codes: G01S 7/52017 particularly adapted to short-range imaging G01S7/53 takes precedence
• CPC Class Codes: G01S 7/5202 for pulse systems

Abstract

A digital-to-analog converter with differential outputs is connected to two difference amplifiers through current splitters. The current splitters isolate the compliance voltage of the digital-to-analog converter so that larger resistances may be used with the difference amplifiers. The larger resistances allow for better signal-to-noise ratio performance of the transmit circuit. The difference amplifiers provide current signals to a push-pull output amplifier through their supply nodes. A single scaling resistor connects between the conventional outputs of two differential amplifiers to reduce mismatching between the positive and negative waveform paths. As a result of the feedback between the two difference amplifiers, a lower level of subharmonic and/or harmonic distortion products is achieved.

Claims

1. An ultrasound transmit circuit for generating a bi-polar waveform, the circuit comprising:

a first current splitter;

a digital-to-analog converter having an output connected with the first current splitter; and

an ultrasound transducer operatively connected to receive a signal responsive to the digital-to-analog converter.

2. The circuit of claim 1 further comprising a second current splitter wherein the digital-to-analog converter comprises a differential digital-to-analog converter, the first current splitter connected with one of a plurality of differential outputs of the digital-to-analog converter and the second current splitter connected with another of the plurality of differential outputs of the digital-to-analog converter.

3. The circuit of claim 2 wherein a first positive input of a first operational amplifier connects with a first collector terminal of the first current splitter while a first negative input of the first operational amplifier connects with a first collector terminal of the second current splitter.

4. The circuit of claim 3 wherein a second positive input of a second operational amplifier connects with a second collector terminal of the second current splitter while a second negative input of the second operational amplifier connects with a second collector terminal of the first current splitter.

5. The circuit of claim 1 wherein the first current splitter comprises first and second transistors with commonly connected emitters and bases where the commonly connected bases are grounded and where the commonly connected emitters connect to the output of the digital-to-analog converter output.

6. The circuit of claim 1 further comprising an output amplifier connected between the first current splitter and the ultrasound transducer.

7. The circuit of claim 1 further comprising first and second current drivers connected between the first current splitter and the ultrasound transducer.

8. The circuit of claim 7 further comprising a resistor connected between the first and second current drivers.

9. The circuit of claim 8 further comprising a transformer-coupled amplifier connected with the first and second current drivers;

wherein the first and second current drivers comprise first and second difference amplifiers, respectively, where a positive input of the first difference amplifier connects with the first current splitter and a negative input of the second difference amplifier connects with the first current splitter;

wherein the resistor connects with conventional outputs of the first and second difference amplifiers, respectively; and

wherein first and second supply nodes of the first and second difference amplifiers, respectively, connect with the transformer-coupled amplifier, and third and fourth supply nodes of the first and second difference amplifiers, respectively, connect with a voltage source.

10. The circuit of claim 8 wherein a positive input of the first current driver connects to the first current splitter and to a resistor;

and

further comprising a voltage source connected with the resistor.

11. An ultrasound transmit circuit for generating a bi-polar waveform, the circuit comprising:

an output amplifier having first and second inputs;

first and second difference amplifiers having respective first and second supply nodes connected with the first and second inputs, respectively;

an ultrasound transducer connected with the output amplifier;

first and second current splitters connected with inputs of the first and second difference amplifiers; and

a digital-to-analog converter having differential outputs, a first one of the differential outputs connected with the first current splitter and a second one of the differential outputs connected with the second current splitter.

12. The circuit of claim 11 wherein the first current splitter comprises first and second transistors and the second current splitter comprises third and fourth transistors, the first one of the differential outputs connected with the first and second transistors, the second one of the differential outputs connected with the third and fourth transistors, the first transistor connected with a positive input of the first difference amplifier, the second transistor connected with a negative input of the second difference amplifier, the third transistor connected with a negative input of the first difference amplifier, and the fourth transistor connected with a positive input of the second difference amplifier.

13. The circuit of claim 11 further comprising a resistor connected between first and second outputs of the first and second difference amplifiers, respectively.

14. The circuit of claim 11 further comprising a first resistor connected between an input of the first difference amplifier and a voltage source and a second resistor connected between an input of the second difference amplifier and the voltage source.

15. A method for generating a bi-polar ultrasound waveform with an ultrasound transmit circuit, the method comprising:

(a) splitting a current from a digital to analog converter;

(b) driving an output amplifier in response to at least part of the split current; and

(c) generating the bi-polar ultrasound waveform in response to (b).

16. The method of claim 15 wherein (a) comprises splitting the current at about a 50/50 ratio.

17. The method of claim 15 wherein (b) comprises driving the output amplifier with supply currents of first and second difference amplifiers responsive to the split current;

and

further comprising

(d) scaling supply currents of the first and the second difference amplifiers as a function of a resistor connected between first and second outputs of the first and second difference amplifiers, respectively.

18. The method of claim 15 wherein (a) comprises splitting a first current from a first output of the digital-to-analog converter and splitting a second current from a second output of the digital-to-analog converter, and wherein (b) comprises driving the output amplifier with first and second differential amplifiers each responsive to split first and second currents.