Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-04-26
2002-09-17
Bockelman, Mark (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C600S509000
Reexamination Certificate
active
06453200
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
An early method for working with a high frequency carrier signal is disclosed in the German patent application DE 196 01 866.
Various methods and devices are known to transmit signals between a medical device, in particular an implanted one, and an external transmitter or receiver. For example, modern cardiac pacemakers can record an intracardial electrocardiogram (IECG) using the pacemaker electrodes and can transmit it, using a telemetry unit, to an extracorporeal control device.
2. Description of Related Art
In modern signal transfer methods that are known for implanted cardiac pacemakers, e.g. from the book by John G. Webster (Editor): “Design of Cardiac Pacemakers”, section 12 “External Programming”, IEEE Press Book Series, New York 1995, the digital signal that is to be transferred wirelessly is modulated onto the high frequency carrier signal in bit sequences by a modulator in the transmitter. It is then transmitted across a distance to the receiver, which contains a corresponding demodulator for recovery of the data signal. The carrier signal is in a comparatively low frequency range, since it has to penetrate the body and must not interfere with neighbouring medical devices.
All such methods have the disadvantage that the quality of the data signal that is recovered on the receiver side strongly deteriorates with the distance between transmitter and receiver, and with interference in the transmission path.
The transmitting power must not fall below a definite value, so that a desired range with a prescribed certain noise immunity can be achieved in an information transfer over a noisy transmission path.
This required high transmitting power, on one hand, has the disadvantage that the energy consumption during the transmitting operation is correspondingly high, which is of disadvantage for battery operated devices, such as the previously mentioned cardiac pacemakers, due to rapid battery exhaustion. On the other hand, one is concerned that the electromagnetic radiation emitted from the transmitter can lead to harm to the human body, which must in particular be considered for implanted medical devices due to the extremely low distance from the patient.
SUMMARY OF THE INVENTION
The objective of this invention is to create a method of the previously mentioned type and an arrangement for the implementation of that method, which allows a lowering of the transmitting power and an increase in range for medical implants—while at least maintaining the transmission quality.
The invention incorporates the technical principle, to subject the pulses, modulated with the information, using a known method of telecommunications, to an angle modulation in the transmitter. (Angle modulation is to be read as a generic term for phase and frequency modulation) These angle modulated pulses are time compressed in the receiver by introducing a time delay using suitable means, so that the duration of the pulses is shortened and they experience an amplitude enhancement. This pulse compression can be carried out using a dispersion filter. The information can be recovered from the pulses processed in this manner by a corresponding demodulation, whereby the demodulation can be carried out with an improved signal
oise ratio, due to the increase in amplitude. The actual information can be imprinted onto the pulse by a pulse modulation method, or by carrying out the pulse compression in a discernibly different manner for pulses sequential in time, so that the information is contained in this variation of the angle modulation.
Thus a signal is available after the demodulation, that otherwise could only be obtained by using higher transmitting power, if not using any other costly methods to improve reception, such as diversity reception or signal encoding, which occupies a larger frequency range or a longer transmission time due to redundant components, so that the available data channel would show a lower data throughput or could only be used by a lower number of users.
In this invention, the angle modulation of the pulses in the transmitter is carried out according to a modulation that, during the pulse duration, determines a change in frequency, in case of a frequency modulation, or a shift in phase, in case of a phase modulation. Phase and frequency modulation are both treated under the common generic term of angle modulation.
While the modulation of the pulses can be achieved using different pulse modulation methods, in the variable angle modulation a special angle modulation time characteristic is used, corresponding to a “modulation characteristic curve”.
Hereby, the modulation characteristic curve—here referred to as modulation characteristic—determines the time behaviour of the frequency during the pulse duration. Preferably, the frequency of the transferred signal decreases linearly during the pulse duration, from a value above the carrier frequency to a value below the carrier frequency. The filter on the receiver side is matched to the employed modulation characteristic by a corresponding differential, frequency dependent delay time response, in such a manner so that the generated signal components of different phase position superpose to form a nearly coincident signal.
The imprinting of the information to be transmitted can occur either by varying or selecting the modulation characteristic, or by any other conventional modulation method that has no effect on the signal delay time, or only to a secondary degree. A preferred option is the modification of the amplitude of the transmitted signal dependent on the input signal—i.e. amplitude modulation, or all types of encoding in which the transmitted information is determined by the type, number, position, or sequence of the transferred pulses.
The invention offers in an advantageous manner the possibility to transmit signals to devices, in particular implanted ones, using higher frequencies than customary until now, without affecting the tissue on one hand, and without electromagnetic interference (EMI) to other devices used in the clinical environment on the other hand. Until now this was the main problem in the use of devices emitting electromagnetic waves in clinical surroundings. Until now these conditions ruled out, for example, the use of portable telephones etc. Additionally, this invention's method offers the advantage that a signal transfer can be made across larger distances (for example within a patient's room), so that programming devices etc. do not have to be attached directly to the patient's body. When appropriate codes are selected, it is also possible to communicate in parallel with several devices without mutual interference. Since the used signals can be transmitted with low amplitude, they do not rise above the surrounding noise level, or only negligibly. Thus the mutual interaction between them is low.
In a preferred embodiment of the invention the imprinting of the information of the input signal occurs by selecting or modifying a modulation characteristic dependent on the input signal. If the input signal has a high-level, then, for example, a modulation characteristic linearly falling with the signal is used, which leads to a frequency modulated pulse in which the frequency decreases during the pulse duration. For a low-level of the input signal a linearly rising modulation characteristic is used, which correspondingly leads to a pulse with frequency that increases during the pulse duration. The filter means on the receiver side are appropriately matched.
The invention is not limited to linear modulation characteristics, but can be implemented with modulation characteristics of any shape, whereby it is only necessary to assign distinct modulations to different levels of the input signals, so that a subsequent signal discrimination is possible in the receiver.
It is also possible to use more than two modulation characteristics for the input signal, so that every pulse transmits a larger information content. If, for example, four different modulation
Altera Law Group LLC
Bockelman Mark
Nanotron Gesellschaft fur Mikrotechnik mbH
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