Apparatus and method for automatically controlling a reference frequency in a dual mode receiver

In a receiver for receiving either an analog information signal or a digital information signal modulated on a carrier signal at a carrier frequency subsequent to transmission thereof by a transmitter, wherein the receiver includes a frequency translator for translating the carrier frequency to an intermediate frequency and maintaining the intermediate frequency at a desired value responsive to a reference frequency, a method for automatically controlling the reference frequency when the receiver receives either the analog information signal or the digital information signal, comprising the steps of:

• detecting a first measure of frequency error between the reference frequency and the intermediate frequency when the receiver receives the analog information signal;
• determining a second measure of frequency error between the reference frequency and the intermediate frequency when receiver receives the digital information signal;
• producing a current signal, wherein the current signal is responsive to the first measure of frequency error when the receiver receives the analog information signal, and wherein the current signal is further responsive to the second measure of frequency error when receiver receives the digital information signal;
• and
• producing a frequency control signal responsive to the current signal to automatically control thereby the reference frequency when the receiver receives either the analog information signal or the digital information signal.

A communication unit comprising:

• a receiver for receiving either an analog information signal or a digital information signal modulated on a carrier signal at a carrier frequency subsequent to transmission thereof by a transmitter, the receiver including:
• a frequency translator for translating the carrier frequency to an intermediate frequency and maintaining the intermediate frequency at a desired value responsive to a reference frequency;
• a phase detector coupled to receive the reference frequency and the intermediate frequency and operative to detect a first measure of frequency error between the reference frequency and the intermediate frequency;
• a processor coupled to receive the reference frequency and the intermediate frequency and operative to determine a second measure of frequency error between the reference frequency and the intermediate frequency;
• a current device coupled to receive the first measure of frequency error when the receiver receives the analog information signal and coupled to receive the second measure of frequency error when receiver receives the digital information signal, and operative to produce a current signal responsive to either the first or the second measure of frequency error;
• and
• a capacitive device coupled to receive the current signal and operative to produce a frequency control signal responsive to the current signal to automatically control thereby the reference frequency when the receiver receives either the analog information signal or the digital information signal.

A method of operating a communication unit comprising the step of:

• receiving either an analog information signal or a digital information signal modulated on a carrier signal at a carrier frequency subsequent to transmission thereof by a transmitter, the step of receiving further including the steps of:
• translating the carrier frequency to an intermediate frequency and maintaining the intermediate frequency at a desired value responsive to a reference frequency;
• detecting a first measure of frequency error between the reference frequency and the intermediate frequency when the receiver receives the analog information signal;
• determining a second measure of frequency error between the reference frequency and the intermediate frequency when receiver receives the digital information signal;
• producing a current signal, wherein the current signal is responsive to the first measure of frequency error when the receiver receives the analog information signal, and wherein the current signal is further responsive to the second measure of frequency error when receiver receives the digital information signal;
• and
• producing a frequency control signal responsive to the current signal to automatically control thereby the reference frequency when the receiver receives either the analog information signal or the digital information signal.