Digital FSK transmitter receiver and method of operating same
AssigneeElsag International N.V.
InventorWilliam E. Baker
Life of this patent
Estimating the term…
Abstract
A digital FSK receiver includes a zero-crossing detector which detects the zero crossings in an FSK signal having at least two signal frequencies. The time interval between zero crossings is then measured with a first interval value corresponding to one of the signal frequencies and a second interval value corresponding to the other signal frequency. An accumulator outputs a digital signal which depends on whether the interval is at the first value or the second value, the digital signal including logical zeros and ones.
Claims5
A digital FSK receiver for receiving an FSK signal containing at least two different signal frequencies, comprising:
- a zero crossing detector for detecting zero crossings of the FSK signal;
- interval measuring means connected to the zero crossing detector for measuring the intervals between the zero crossings, the intervals having a first value when the FSK signal is at one of the at least two signal frequencies, a second value when the FSK signal is at the other of the at least two signal frequencies, and a plurality of intermediate values which are between the first and second values when the FSK signal switches between the frequencies;
- binary output means connected to the interval measuring means for receiving the interval values and or outputting a binary signal which switches between logical zero and logical one states when the binary output means receives one of the intermediate values;
- wherein the interval measuring means comprises a zero crossing counter connected to the zero crossing detector, a clock connected to the zero crossing counter for pulsing the zero crossing counter a plurality of times between each zero crossing, the zero crossing counter counting the number of clock pulses between intervals, and a zero crossing register connected to the zero crossing counter for storing the number of clock pulses counted during each interval which corresponds to one of the values for the interval;
- and
- a first in-first out buffer for receiving the contents of the zero crossing register and for applying the contents of the zero crossing register to the binary output means.
A method of recovering baseband and signal from a FSK signal having at least two different signal frequencies, comprising:
- detecting the zero crossings in the FSK signal;
- measuring the intervals between the zero crossings of the FSK signal by counting clock pulses between zero crossings and storing the counted clock pulses in a register, the intervals having a first value when the FSK signal is at one of the two signal frequencies, a second value when the FSK signal is at the other of the two signal frequencies and a plurality of intermediate values which are between the first and second values when the FSK signal switches between the frequencies;
- generating a binary signal which switches between logical zero and logical one states when the interval is at one of the intermediate values;
- and
- applying the stored counted pulses to a first in-first out buffer and outputting a signal from the first in-first out buffer to a binary adder and converting the counted pulses to the logical zeros and ones.
Dependencies are inferred from the claim text.