Frequency synthesizer with improved priority channel switching

• US 4,559,505 A
• Filed: 01/04/1983
• Issued: 12/17/1985
• Est. Priority Date: 01/04/1983
• Status: Expired due to Term

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Suarez, Jose I., Irwin, James S., Shepherd, Wayne P.
• Primary Examiner(s): LaRoche, Eugene R.
• Assistant Examiner(s): Pascal, Robert J.
• Application Number:
  US06/455,454
• Time in Patent Office: 1,078 Days
• Field of Search: 331/1 A, 331/14, 331/17, 331/25, 332/19
• US Class Current: 331/1.00A
• CPC Class Codes: H03L 7/093 using special filtering or amplification characteristics in the loop H03L7/087 - H03L7/091 take precedence
• CPC Class Codes: H03L 7/1075 by changing characteristics of the loop filter, e.g. changing the gain, changing the bandwidth H03L7/1072 takes precedence
• CPC Class Codes: H03L 7/18 using a frequency divider or counter in the loop H03L7/20, H03L7/22 take precedence

Abstract

A frequency synthesizer is provided including a reference frequency generator coupled to one input of a phase detector. The output of the phase detector is coupled via a pair of alternatingly connected filters through a voltage controlled oscillator and a divider circuit to the remaining input of the phase detector to form a phase locked loop. The first filter of the pair is designated for operation on a main channel frequency while the remaining filter is designated for operation on a priority channel frequency. The capacitive elements of each respective filter remain fully charged up for operation on their respective frequencies and thus when such filters are alternately switched between to change frequency from the main channel to the priority channel, the capacitive elements need not be charged to new levels to accommodate such frequency change. Thus, switching between a main channel and a priority channel is accomplished in a minimal amount of time with a significant reduction in frequency synthesizer energy requirements.

Claims

1. A frequency synthesizer comprising:

reference frequency generating means for generating a reference signal exhibiting a predetermined frequency F_R ;

phase detector means, having first and second inputs, said first input being coupled to the output of said frequency generating means, for generating a signal exhibiting indicia of the difference in frequency and phase between signals applied to said first and second input thereof;

a first low pass filter switchably coupled to the output of said phase detector means;

a second low pass filter switchably coupled to the output of said phase detector means;

voltage controlled oscillator means, switchably coupled to the respective outputs of said first and second low pass filters, for generating a radio frequency signal at the output thereof which exhibits a frequency which is a function of the voltage applied at the input thereof;

frequency divider means, having an input coupled to the output of said oscillator means, for dividing the signal generated at the output of said oscillator means by a predetermined quality to generate a divided down signal F_V which is provided to the second input of said phase detector means;

switching means, responsive to a timing signal and coupled to said first and second filters, said switching means being operative in a first mode to switchably couple said first filter between the output of said phase detector means and the input of said oscillator means for providing a first output frequency from the voltage controlled oscillator means, said switching means being operative in a second mode to switchably couple said second filter between the input of said phase detector means and the input of said oscillator means for providing a second output frequency from the voltage controlled oscillator means, and

timing signal generating means, coupled to said switching means, for generating a timing signal which instructs said switching means to switch back and forth between said first and second modes at predetermined points in time,

said switching means comprising first and second transmission gates operatively coupled to the input and the output, respectively, of said first low pass filter and further comprising third and fourth transmission gates operatively coupled to the input and the output, respectively, of said second low pass filter,

said timing signal generating means, generating a timing signal to actuate said second gate prior to actuating said first gate when switching to said first low pass filter, and generating a timing signal to actuate said fourth gate prior to actuating said third gate when switching to said second low pass filter, whereby the output of the selectively coupled low pass filter is first selectively coupled to the voltage controlled oscillator means prior to selectively coupling the low pass filter to the phase detector means.

2. The frequency synthesizer of claim 1 wherein the first low pass filter includes a first capacitor means and the switching means includes a transmission fifth gate for selectively coupling the capacitor means directly to the output of the first low pass filter,

the second low pass filter includes a second capacitor means and the switching means includes a transmission sixth gate for selectively coupling the second capacitor means directly to the output of the second low pass filter, and

the timing signal generating means providing signal to momentarily actuate the fifth gate on when the second gate is on but prior to actuating the first gate on, and providing a signal to momentarily actuate the sixth gate on when the fourth gate is on but prior to actuating the third gate on.

3. A frequency synthesizer comprising:

reference frequency generating means for generating a reference signal exhibiting a predetermined frequency F_R ;

phase detector means, having first and second inputs, said first input being coupled to the output of said frequency generating means, for generating a signal exhibiting indicia of the difference in frequency and phase between signals applied to said first and second input thereof;

a plurality of low pass filters switchably individually coupled to the output of said phase detector means;

voltage controlled oscillator means, switchably coupled to the respective outputs of said plurality of low pass filters, for generating a radio frequency signal at the output thereof which exhibits a frequency which is a function of the voltage applied at the input thereof;

frequency divider means, having an input coupled to the output of said oscillator means, for dividing the signal generated at the output of said oscillator means by a predetermined quality to generate a divided down signal F_V which is provided to the second input of said phase detector means;

switching means, responsive to a timing signal and coupled to said low pass filters, said switching means being operative in a first mode to switchably couple a first of said filter between the output of said phase detector means and the input of said oscillator means for providing a first output frequency from the voltage controlled oscillator means, said switching means being operative in a second mode to switchably couple a second of said filters between the input of said phase detector means and the input of said oscillator means for providing a second output frequency from the voltage controlled oscillator means, and

timing signal generating means, coupled to said switching means, for generating a timing signal which instructs said switching means to switch to said first and second modes at preselected points in time,

said timing signal generating means generating timing signals to actuate said switching means to connect the output of the selected low pass filter to the voltage controlled oscillator means prior to connecting the input of the selected low pass filter to the phase detector means.

4. The frequency synthesizer of claim 3 wherein each of the low pass filter includes a capacitor means, and

the timing signal generating means providing a signal to momentarily actuate the switching means when the output of the selectively coupled low pass filter is connected to the voltage controlled oscillator means to momentarily connect said capacitor means of the coupled low pass filter directly to the output of said filter.

5. A frequency synthesizer comprising:

reference frequency generating means for generating a reference signal exhibiting a predetermined frequency F_R ;

phase detector means, having first and second inputs, said first input being coupled to the output of said frequency generating means, for generating a signal exhibiting indicia of the difference in frequency and phase between signal applied to said first and second input thereof;

a plurality of low pass filters switchably coupled to the output of said phase detector means, each of said filters including a capacitor means;

voltage controlled oscillator means, switchably coupled to the respective outputs of said plurality of low pass filters, for generating a radio frequency signal at the output thereof which exhibits a frequency which is a function of the voltage applied at the input thereof;

frequency divider means, having an input coupled to the output of said oscillator means, for dividing the signal generated at the output of said oscillator means by a predetermined quality to generate a divided down signal F_V which is provided to the second input of said phase detector means;

switching means, responsive to a timing signal and coupled to said plurality of low pass filters, said switching means being operative in a first mode to switchably couple a first of said filters between the output of said phase detector means and the input of said oscillator means for providing a first output frequency from the voltage controlled oscillator means, said switching means being operative in a second mode to switchably couple a second of said filter between the input of said phase detector means and the input of said oscillator means for providing a second output frequency from the voltage controlled oscillator means, and

timing signal generating means, coupled to said switching means, for generating a timing signal which instructs said switching means to switch to said first and second modes at preselected points in time,

the timing signal generating means provides a signal to momentarily actuate the switching means when the output of the selectively coupled low pass filter is connected to the voltage controlled oscillator means to momentarily connect the capacitor means of the coupled low pass filter directly to the output of said filter.