摘要:
In a method for matching a transmission/reception antenna in a nuclear magnetic resonance imaging apparatus to the impedance of a high-frequency system which feeds the antenna, a directional coupler is used for acquiring respective signals corresponding to a forward voltage wave supplied to the antenna, and the associated return voltage wave. The amplitudes of the forward and return waves are calculated in a controller for all matching conditions of a transformation network, the transformation network being interconnected between the high frequency system and the antenna. When a tomogram is to be produced, the transformation network is set so that the antenna is matched as best as is possible to the high-frequency system. The same method can be used for matching an antenna which is only used for reception when producing tomograms.
摘要:
A high-frequency power amplifier has a high-frequency input, a high-frequency output and at least one power transistor connected therebetween. The power transistor has a first electrode serving as a control input, a cooling terminal connected to a second electrode and a third electrode. The third electrode is connected to a high-frequency reference potential conductor and the high-frequency reference potential conductor is connected in terms of high-frequency to the second electrode. An input signal applied to the high-frequency input is coupled out as an output signal at the high-frequency output.
摘要:
A high-frequency receiver with an analog input part has at least one analog mixer stage, this mixer stage being operable with an injection frequency, and a following digitalization stage. The digitalization stage includes an analog-to-digital converter for digitalizing a signal emitted by the analog input part with a sampling rate prescribed by a sampling frequency. A signal generator for generating the injection frequency or the sampling frequency is connected to the mixer stage and to the analog-to-digital converter, this signal generator generating the injection frequency or the sampling frequency only as a whole number multiple of a basic frequency.
摘要:
An analog-to-digital converter circuit has pre-sample and hold circuit for acquiring and temporarily storing a supplied analog input signal, and for outputting the temporarily stored input signal, at least two signal paths, which are arranged downstream relative to the pre-sample and hold circuit and which are switched in parallel with one another, the temporarily stored input signal sample from the pre-sample and hold circuit being subjected to respective fixed amplifications, which are different from one another, in said signal paths and a selection circuit arranged downstream relative to the signal paths for through-connecting only one of the signal paths, dependent on the respective signal levels, to an analog-to-digital converter that is arranged downstream relative to the selection circuit.
摘要:
A high-frequency power amplifier for feeding an antenna of a nuclear magnetic resonance tomography apparatus has at least one amplifier stage that can emit a maximum output power within a first frequency band. Circuitry for frequency-dependently altering the maximum output power is connected to the amplifier stage, whereby the maximum output power within a second frequency band, that is higher than the first frequency band is higher than within the first frequency band.
摘要:
An analog-to-digital converter circuit for digitalizing a high-frequency signal with large dynamics has a first analog-to-digital converter and a second analog-to-digital converter connected in parallel, a level converter connected to one of the two analog-to-digital converters, a level recognition element for determining a level range in which the high-frequency signal lies and for generating a control signal dependent on the level range, and a correction memory that is connected to the level recognition element, the correction memory having address inputs connected to outputs of the analog-to-digital converters. The control signal is used as a selection criterion which identifies which analog-to-digital converter address data are taken from for producing a digital output signal, the digital output signal being linearized according to a characteristic of the selected analog-to-digital converter in order to correct for distortion arising in the selected converter. The overall analog-to-digital converter circuit thus has an overall linear characteristic, even as the input signal varies between low and high amplitudes.
摘要:
A radio-frequency power amplifier is supplied by a voltage supply device. The voltage supply device has a voltage divider chain that is connected at the input side with a base potential and a ground voltage. The voltage divider chain has a number of Zener diodes connected in series, with which at least one capacitor is connected in parallel. Intermediate voltages that lie between the ground voltage and the base potential can be tapped at respective node points between each two immediately adjacent Zener diodes. A first supply input of the radio-frequency power amplifier is connected with the ground voltage. The voltage divider chain is connected with the radio-frequency power amplifier via a switching device. The switching device has a number of switching elements connected in parallel with one another, these switching elements being connected at the output side with a second supply input of the radio-frequency power amplifier. The base potential or one of the intermediate voltages is present at the input side of each switching element. The switching elements can be individually controlled by a control device, such that the second supply input can be selectively connected with the base potential and each of the intermediate voltages via the switching device.
摘要:
A radio-frequency power amplifier is supplied by a voltage supply device. The voltage supply device has a voltage divider chain that is connected at the input side with a base potential and a ground voltage. The voltage divider chain has a number of Zener diodes connected in series, with which at least one capacitor is connected in parallel. Intermediate voltages that lie between the ground voltage and the base potential can be tapped at respective node points between each two immediately adjacent Zener diodes. A first supply input of the radio-frequency power amplifier is connected with the ground voltage. The voltage divider chain is connected with the radio-frequency power amplifier via a switching device. The switching device has a number of switching elements connected in parallel with one another, these switching elements being connected at the output side with a second supply input of the radio-frequency power amplifier. The base potential or one of the intermediate voltages is present at the input side of each switching element. The switching elements can be individually controlled by a control device, such that the second supply input can be selectively connected with the base potential and each of the intermediate voltages via the switching device.
摘要:
A catheter for magnetic resonance-supported interventional procedures has an electric cable that connects a first electric component attached to one catheter end with a second electric component attached to the other catheter end, with the electric cable being coiled at least in sections thereof.
摘要:
An amplifier device has an amplifier circuit, an energy supply device, a switching matrix and a control device. A radio-frequency, low-energy signal pulse can be amplified into a high-energy power pulse by the amplifier circuit. The amplifier circuit is supplied with electrical energy by the energy supply device. The energy supply device has a number of electrical energy sources that are separated in terms of potential relative to one another in a state in which they are not connected to the amplifier circuit. The electrical energy sources can be selectively connected to the amplifier circuit by the switching matrix. The switching state of the switching matrix can be dynamically set for this purpose by the control device.