Amplifiers – Interstage coupling – With electromechanical transducer
Reexamination Certificate
2000-05-22
2003-09-16
Nguyen, Patricia (Department: 2817)
Amplifiers
Interstage coupling
With electromechanical transducer
C330S110000, C330S141000, C330S254000, C330S278000
Reexamination Certificate
active
06621341
ABSTRACT:
BACKGROUND
In a medical ultrasound system, echoes received by an ultrasound transducer are amplified by a front-end subsystem, i.e., a set of circuitry that is first to receive and process the signals provided by the transducer. As shown in
FIG. 1
, the front-end
100
includes a first amplifier
102
, (“pre-amplifier”), cascaded with a variable gain amplifier
104
(“VGA”). The pre-amplifier
102
is coupled with a piezoelectric ultrasound transducer
106
. Since the combined impedance of the piezoelectric ultrasound transducer
106
and its connecting cable (not shown) is essentially capacitive, the purpose of the pre-amplifier
102
is to convert the high impedance charge input into a usable output voltage.
Generally, two pre-amplifier
102
topologies are used. The first, known as a charge sensitive amplifier, utilizes an operational amplifier (“Op Amp”).
FIG. 2
shows a pre-amplifier
200
which works as a charge integrator. The electrical charge from the transducer
202
is compensated by a charge of equal magnitude and opposite polarity, producing a voltage across the feedback capacitor
204
, labeled “C
FB
”. In effect, the charge sensitive amplifier
200
provides a C
T
/C
FB
voltage gain, where C
T
is the equivalent capacitance of the transducer
202
.
Another known pre-amplifier
300
architecture, shown in
FIG. 3
, employs a low-noise bipolar transistor
302
in a common-base configuration. Prior knowledge of the transducer
304
impedance is used to configure the pre-amplifier
300
so that the collector has an essentially capacitive load
314
, labeled “C
L
”. Having approximately unity current gain, this pre-amplifier
300
causes the output charge to be equal to the input. As a result, a C
T
/C
L
voltage gain is achieved.
Referring back to
FIG. 1
, to compensate for the attenuation of ultrasound energy at different depths, prior art systems further utilize a variable gain-controlled amplifier
104
. An exemplary VGA
104
is described in U.S. Pat. No. 4,331,929, entitled “GAIN-CONTROLLED AMPLIFIER” to Yokoyama. The VGA
104
adjusts the front-end gain as a function of time and/or attenuating characteristics of body tissues.
Maintaining an extensive signal range, the VGA
104
that is incorporated into a medical ultrasound system preferably provides both a low noise floor and the ability to attenuate exceptionally strong echoes while allowing progressively greater gain for echoes from deeper structures.
SUMMARY
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. By way of introduction, one aspect of the present invention is a method for controlling input gain in a diagnostic medical ultrasound system. The method comprises receiving a plurality of ultrasound signals from a piezo-electric ultrasound transducer; varying the gain of the signals utilizing a variable capacitance; and controlling the variance of the gain as a function of the variable capacitance.
Another aspect of the present invention is a gain controlled input stage for a diagnostic medical ultrasound system. The input stage includes an ultrasound transducer, a variable capacitance circuit and an amplifier coupled with the ultrasound transducer and the variable capacitance circuit wherein the gain of the amplifier is responsive to the variable capacitance circuit.
REFERENCES:
patent: 3972228 (1976-08-01), Mansson
patent: 4373394 (1983-02-01), Renzel et al.
patent: 4851791 (1989-07-01), Marotel
patent: 5603324 (1997-02-01), Oppelt et al.
patent: 5609154 (1997-03-01), Oppelt et al.
patent: 5641908 (1997-06-01), Hayakawa
patent: 5724312 (1998-03-01), Oppelt
patent: 6150649 (2000-11-01), Wake et al.
patent: 195 05 697 (1996-08-01), None
Burr-Brown® VCA610 specification brochure “Wideband Voltage Controlled Amplifier”, Jan., 1995, 12 pages.
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