Pulse or digital communications – Transmitters – Angle modulation
Reexamination Certificate
1997-12-17
2001-02-06
Chin, Stephen (Department: 2734)
Pulse or digital communications
Transmitters
Angle modulation
C375S272000
Reexamination Certificate
active
06185264
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus and method for generating electromagnetic frequency shift keying signals.
BACKGROUND OF THE INVENTION
Frequency shift keying (FSK) transmitters convert incoming baseband binary data signals into corresponding frequency changes of an electromagnetic carrier signal. The modulated carrier signal is then decoded by a receiver into the original baseband binary data signals.
FSK transmitters typically include a resonant circuit which oscillates at the carrier frequency. Inductive reactive or capacitive reactive circuit elements are coupled to the resonant circuit through electronic switches. To achieve the frequency shifts of the carrier signal, the electronic switches selectively connect the reactive circuit elements to, and disconnect the reactive circuit elements from, the resonant circuit in response to the baseband binary data signals.
Conventional FSK transmitters introduce voltage transients, or “jitter”, into the modulated carrier signal when the carrier frequency is shifted. These transients are attributable to the asynchronous nature of the baseband binary data signals with respect to the carrier signal. Since the transmitter can be required to shift frequencies at any given moment, transients are introduced into the carrier signal if the initial conditions of the switched reactive circuit elements do not match the circuit conditions existing in the resonant circuit at the instant of the frequency shift.
Such voltage transients can be troublesome, particularly at high data transmission rates, because the transients can cause the receiver to produce bit errors in decoding the baseband data. Further errors can be introduced from the power source driving the resonant circuit if the magnitude of the carrier signal is allowed to fluctuate. Accordingly, it is desirable to eliminate both transients introduced into the carrier signal, and variations in magnitude of the carrier signal. It is also desirable, particularly where energy sources are limited, for the transfer of energy between the power source and the electromagnetic carrier signal to be as efficient as possible.
Various attempts have been made to eliminate frequency shift distortion from transients. For example, Baker (U.S. Pat. No. 3,249,896), Spiro (U.S. Pat. No. 3,451,012) and Andersen (U.S. Pat. No. 5,300,904) teach FSK transmitters each using a pair of magnetically-coupled inductors which are alternately coupled to a capacitor through a switch. Distortion introduced when the capacitor is switched from one inductor to the other is minimized since the magnetic fields in both inductors are continuously in phase. However, the cost of magnetically-coupled inductors unnecessarily increases the cost of the circuits. Furthermore, the circuits are inefficient since two magnetic fields must be continually maintained, even though only one is used to generate the modulated carrier signal at any given time.
Hekimian (U.S. Pat. No. 3,222,619) teaches a frequency shift keying generator comprising a resonant circuit coupled to a capacitor through the parallel combination of a switch and an amplifier. When the switch is open, the capacitance C of the capacitor appears to the resonant circuit as C/B, B being the gain of the amplifier. When the switch is closed, the capacitance C appears to the resonant circuit as C. Distortion introduced when the capacitor is switched is minimized by selecting an amplifier having unity voltage gain. However, as voltage gain can fluctuate with temperature and frequency, in practice distortion may be introduced nevertheless.
Kageyama (U.S. Pat. No. 3,363,204) teaches a frequency shift oscillator having a switch which selectively connects an inductor and a capacitor to a resonant circuit. Distortion introduced when the inductor and capacitor are switched is minimized by selecting the values of the components such that the characteristic impedance of the circuit in both modes is identical. However, as the reactance of the components can vary with temperature and the age of the components, in practice the characteristic impedance may not always be identical.
Accordingly, there remains a need for a frequency shift keying signal transmitter which allows for frequency shifts to occur in the carrier signal without inducing transients from the switching action, and which also utilizes a highly efficient energy transfer between the power source and the modulated magnetic fields.
SUMMARY OF THE INVENTION
The present invention provides a frequency shift keying signal transmitter which allows for frequency shifts to occur in the carrier signal without inducing voltage transients in the carrier signal from the switching action. The frequency shift keying transmitter also features a highly efficient energy transfer between the power source and the modulated magnetic fields.
In a first aspect the present invention provides a frequency shift keying generator comprising: (a) a resonant circuit; (b) a reactive element; (c) a switch for coupling and decoupling said reactive element to and from said resonant circuit, said resonant circuit oscillating at a first frequency when said reactive element is coupled and said resonant circuit oscillating at a second frequency when said reactive element is uncoupled; (d) a power supply having an output port coupled to said resonant circuit, said power supply including means responsive to a control signal for enabling said output port for energizing said resonant circuit; (e) a detector coupled to said resonant circuit for detecting an energy level for said reactive element and producing an output signal indicative of said energy level; and (f) a controller for controlling said switch, said controller including an output port for actuating said switch and an input port coupled to said detector for receiving said energy level output signal, said controller also having a data input for receiving a data signal and means for selectively actuating said switch to shift the oscillation of said resonant circuit between said first and second frequencies in response to a change of state in the data signal, and said controller including means responsive to said energy level for synchronizing the actuation of said switch with the energy level in said reactive element.
In a second aspect, the present invention provides a method for producing frequency shift keying in an oscillating carrier signal, the oscillating carrier signal being generated by a resonant circuit having a modulating capacitor and a switch for selectively coupling and decoupling the capacitor to the resonant circuit, said method comprising the steps of: (a) generating the oscillating carrier signal at a given frequency; (b) receiving a binary data signal comprising a sequence of binary states; (c) monitoring the energy level in the modulating capacitor; (d) introducing a shift in the frequency of said oscillating carrier signal when there is a change in the binary state of the data signal; (e) wherein said step of introducing a frequency shift comprises selectively coupling the modulating capacitor to the resonant circuit and wherein said step of coupling is synchronized to the monitored energy level in the modulating capacitor.
In another aspect, the present invention provides a frequency shift keying generator comprising: (a) a resonant circuit; (b) a reactive element; (c) a switch for coupling and decoupling said reactive element to and from said resonant circuit, said resonant circuit oscillating at a first frequency when said reactive element is coupled and said resonant circuit oscillating at a second frequency when said reactive element is uncoupled; (d) a power supply having an output port coupled to said resonant circuit, said power supply including means responsive to a control signal for enabling said output port for energizing said resonant circuit; (e) a sensor coupled to said resonant circuit, said sensor including means for sensing current flow in said resonant circuit and means for generating an output signal indicative of the current flow; (
Chin Stephen
McKiernan Thomas E
Ridout & Maybee
LandOfFree
Apparatus and method for frequency shift keying does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus and method for frequency shift keying, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus and method for frequency shift keying will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2563036