Amplifiers – With resistive-type amplifying device
Reexamination Certificate
2001-07-18
2003-06-03
Pascal, Robert (Department: 2817)
Amplifiers
With resistive-type amplifying device
C333S213000
Reexamination Certificate
active
06573788
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an amplifier device for broadband amplification of an electric input signal fed from a signal source, the amplifier device comprising at least one broad band amplifier element with an amplifier input for feeding the input signal. Such an amplifier device is known from U.S. Pat. No. 5,373,741. The invention further relates to the use of such an amplifier device.
BACKGROUND OF THE INVENTION
Such an amplifier device is used, for example, as a preamplifier of an ultrasonic device. In this case, an electric input signal, which is generated, for example, by an ultrasonic transducer from a received acoustic signal and which can, in particular, have a very low signal level, is amplified in the amplifier device for a downstream signal processing (not described in more detail here). In the receive mode, the ultrasonic transducer constitutes a signal source for the electric input signal to be amplified by the amplifier device. This amplification should be performed over as broad a band as possible in order not to diminish the information content unnecessarily. The broader the band over which an ultrasonic device which works using the pulse-echo method is operated, the shorter is the time duration which can thereby be achieved for the pulse response received from an object to be examined. The spatial resolution, and thus the imaging quality also rise with the temporal resolution.
U.S. Pat. No. 5,879,303 discloses a specific imaging method for an ultrasonic device. In this so-called THI (
T
issue
H
armonic
I
maging) method, the first harmonic of the received acoustic signal is also evaluated in addition. This first harmonic is the second harmonic of a fundamental frequency of the sound signal irradiated into the object to be examined. It is formed because of a non-linearity of the human tissue provided in this case as the object to be examined. An amplifier device used in the receiver branch in this context should therefore be designed to cover sufficient bandwidth in order still to amplify the first harmonic without falsification. The fundamental frequency for an ultrasonic device currently in conventional use in medical technology is of the order of magnitude of a few megahertz.
As a rule, a piezoelectric electroacoustic transducer is used. In the case of reception, it is typified, inter alia, by a capacitor connected in parallel with the electroacoustic transducer output. An amplifier device such as described in the text book entitled “
Piezoxide-Wandler
” [Piezoxide Transducers”] by J. Koch, 1973, Valvo GmbH Hamburg, Pages 157 and 158, or else in U.S. Pat. No. 4,285,010 is currently being used in order to compensate the influence of this parallel capacitor on the frequency response. In the case of this amplifier device, the influence of the parallel capacitor of the ultrasonic transducer is at least partially compensated by means of an inductor connected in series or parallel with the electroacoustic transducer output or the amplifier input. Overall, however, there is still always one frequency response exhibiting the bandpass response. The consequence of this is that a frequency component situated widely distant from the fundamental frequency is strongly damped in the amplifier device. Usually, a relative bandwidth (=bandwidth related to a center or fundamental frequency) of approximately 100% is achieved with the known amplifier device. It is thereby possible to operate an electroacoustic transducer with a fundamental frequency, of, for example, 3 MHz, for example in the range from 1.5 to 4.5 MHz.
A broadband amplifier device for a video head is described in EP 0 264 812 A2. An amplifier element with positive feedback is used in the amplifier device described.
U.S. Pat. No. 6,075,309 discloses a broadband electric shunt device for connecting to a piezoelectric resonator which is used to control the vibration of a structure. In this case, the piezoelectric resonator is arranged on the structure such that it is possible for the vibrations of this structure to be damped or controlled. The connection to the shunt device renders it possible to control vibration in a wide frequency range. For this purpose, a subcircuit of the shunt device is designed as a current-reversing negative impedance converter. The shunt device is passive. In particular, it is not connected electrically to another unit, nor does it make an amplified signal available.
SUMMARY OF THE INVENTION
The object of the invention is to specify an amplifier device of the type described at the beginning which permits broadband amplification of the input signal. The aim is also to specify a particularly advantageous use of the amplifier device.
An amplifier device corresponding to the features of patent claim
1
or of patent claim
6
is specified for the purpose of achieving the object relating to the device.
The amplifier device according to the invention for broadband amplification of an electric input signal fed from a signal source is a device comprising at least
one broadband amplifier element with an amplifier input for feeding the input signal, and with an input impedance, active at the amplifier input, in the form of an amplifier reactance which serves to compensate a source reactance active at a source output;
the amplifier element in which case designed as a current-reversing negative impedance converter which comprises a broadband INIC amplifier element with a first and a second input, respectively, and with an output, the output is fed back via a first INIC impedance and via a second INIC impedance respectively to the first and the second input, respectively, and the second input is led to frame via a third INIC impedance; and
the first input is simultaneously the amplifier input, and the output is simultaneously an amplifier output at which there is present an output signal generated from the input signal by means of amplification.
The amplifier device according to the invention for broadband amplification of an electric input signal fed from a signal source is, alternatively, a device comprising:
one broadband and high-resistance amplifier element with an amplifier input for feeding the input signal, and with an input impedance, active at the amplifier input, in the form of an amplifier reactance which serves to compensate a source reactance active at a source output; and
one current-reversing negative impedance converter which is connected at the amplifier input in parallel with the broadband and high-resistance amplifier element, and whose INIC input impedance forms the amplifier reactance, in which the current-reversing negative impedance converter comprises a broadband INIC amplifier element with a first and a second input, and with an output, the output is fed back via a first INIC impedance and via a second INIC impedance respectively to the first and the second input, respectively, and the second input is led to frame via a third INIC impedance.
The invention is based in this case on the finding that the frequency response, determined decisively by the source reactance, of the signal source can be substantially more effectively compensated, that is to say smoothed, by an amplifier reactance which is provided in the amplifier device and determined by an input impedance of a current-reversing negative impedance converter, than by connecting a simple inductor, as is done in the prior art, for example in conjunction with a piezoelectric electroacoustic transducer. The compensation by means of the amplifier reactance according to the invention is not based in this case on a resonant tuning, which always leads to a bandpass response and thus to a useful bandwidth which is, as before, relatively restricted. By contrast, the influence of the source reactance and the influence of the amplifier reactance on the frequency response largely cancel one another out, at least within a useful bandwidth. In the ideal case of complete compensation, what is thereby achieved is a response as if the source reactance were not present at all.
This raises the usef
Baker & Botts LLP
Nguyen Khanh Van
Pascal Robert
Siemens Aktiengesellschaft
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