Caller-ID demodulation apparatus and method using multiple thresholds

A method for demodulating caller identification (ID) information modulated in a continuous phase frequency shift keying (CPFSK) format, the method comprising the steps of:

• receiving the CPFSK-modulated caller ID information and generating a zero crossing signal, wherein the zero crossing signal comprises pulses produced at points where the modulated caller ID information crosses zero;
• calculating a zero crossing interval between pulses of the zero crossing signal;
• comparing the zero crossing interval with a plurality of thresholds to generate extract data;
• and
• generating a data recovery clock signal for recovering the extracted data, wherein the data recovery clock signal is enabled at the middle point of the unit data length of the extracted data.

An apparatus for generating a data recovery clock signal that is used for recovering data extracted from a demodulator, the apparatus comprising:

• an edge detector for detecting a rising or falling edge of the extracted data and outputting the detected edge as an edge detection signal;
• a clock counter for counting the number of cycles of a system clock signal, wherein the clock counter is reset in response to the edge detection signal or when the number of the cycles is n+1 (where n>1);
• a clock generator for generating a data recovery clock signal for recovering the extracted data, wherein the data recovery clock signal is enabled when the number of the cycles is n/2 and is disabled in response to a reset signal;
• and
• a reset signal generator for generating the reset signal.

A method for generating a data recovery clock signal that is used for recovering data extracted from a demodulator, the method comprising the steps of:

• initializing the number of cycles of a system clock signal;
• counting the number of cycles of the system clock signal until n/2 (where n>1) and generating a data recovery clock signal when the number of the cycles is n/2;
• determining whether a rising or falling edge of the extracted data is detected while the number of the cycles is greater than n/2 and less than n;
• and
• disabling the data recovery clock signal when the edge of the extracted data is detected or the number of the cycles is n.