Frequency synthesizer having a plurality of cascaded phase locked loops

Claim 2

A digital frequency synthesizer, comprising: means providing a signal having a reference frequency; a first phase locked loop which includes a first controlled oscillator, said loop being responsive to the application thereto of a signal having a frequency dependent upon said reference frequency in such a manner that said first oscillator provides a signal having a frequency equal to a first predetermined frequency plus said frequency dependent upon said reference frequency; a second phase locked loop which includes a second controlled oscillator, said second loop being responsive to the application thereto of a signal having a frequency which is dependent upon the frequency of said first oscillator such that said second oscillator provides a signal having a frequency equal to a second predetermined frequency plus said frequency dependent upon the frequency of said first oscillator; and said first and second phase locked loops further including; a. a frequency dividing network having a divisor associated therewith and being responsive to the application thereto of a signal dependent upon the signal provided by the oscillator in that loop, said network providing a signal at an output thereof having a frequency which is a submultiple of said signal applied thereto, and b. a comparator circuit, responsive to the application thereto of said dividing network output signal and a signal having a frequency in fixed relationship with said reference frequency, for providing at an output thereof a signal dependent upon the phase changes between said signals applied thereto, said comparator circuit output signal being applied to said oscillator to control the frequency of the signal provided by said oscillator.

Claim 3

The invention according to claim 1: wherein said first predetermined frequency is the product of the divisor of said dividing network in said first loop times the frequency of the signal applied to said comparator circuit which is in fixed relationship to said reference frequency; and wherein said second predetermined frequency is the product of the divisor of said dividing network in said second loop times the frequency of the signal applied inputs and an output, means for connecting said comparator circuit which is in fixed relationship with said reference frequency.

Claim 4

The invention according to claim 1: wherein each of said loops further includes a mixer circuit having a first input to which the signal provided by said oscillator in that loop is applied, a second input to which a signal having a certain frequency is applied, and an output at which appears a signal having a frequency equal to the frequency difference between the signals applied to said first and second inputs thereof, said output being connected to said input of said dividing network in that loop; and wherein said signal having a frequency dependent upon reference frequency is applied to said second input of said mixer circuit included in said first loop and said signal having a frequency which is dependent upon the frequency of said first loop oscillator signal is applied to said second input of said mixer circuit included in said second loop.

Claim 5

The invention according to claim 1, wherein said synthesizer includes a third phased locked loop, which includes a third controlled oscillator, said third loop being responsive to the application thereto of a signal having a frequency dependent upon the frequency of said first oscillator output signal in such a manner that said third oscillator provides a signal having a frequency equal to a predetermined frequency associated with that loop plus a frequency dependent upon the frequency of said first oscillator output signal, the frequency of said second oscillator output signal being dependent upon said frequency of said third oscillator.

Claim 6

The invention according to claim 1 wherein said synthesizer further includes at least one mixer circuit having two inputs and an output, means for coupling said output of said second loop oscillator to the first input of said mixer, means for applying a signal having a frequency in fixed relationship with said reference frequency to the second input of said mixer, said mixer circuit providing a signal at said output thereof equal to the difference in the frequencies of the signals applied to said inputs thereof.

Claim 7

A frequency synthesizer for providing a signal having a desired frequency at an output thereof, said synthesizer comprising: a signal source having a reference frequency; first and second phase locked loops each of which includes at least, a controlled oscillator having an input and an output, said oscillator providing at said output signal having a frequency dependent upon a signal applied to said input thereof, a mixer circuit responsive to the application to a first input thereof of said oscillator output signal and to a second input thereof of a signal having a certain frequency to provide at an output thereof a signal having a frequency equal to the difference between the frequencies of the signals applied thereto, a frequency dividing network responsive to said mixer circuit output signal for providing to an output thereof a signal having a frequency which is a submultiple of said mixer circuit output signal frequency, a comparator circuit responsive to the application thereto of said dividing network output signal and a signal having a frequency in fixed relationship with said reference frequency, said comparator circuit providing at an output thereof a signal dependent upon the phase changes between said signals applied thereto; means for applying the output of said comparative circuit to said input of said oscillator; means coupled between said source and said second input of said mixer circuit in said first loop for applying to said first loop mixer circuit a signal having a frequency in fixed relationship to said reference frequency; means coupled between the output of said oscillator in said first loop and said second input of said mixer circuit in said second loop for applying to said second loop mixer circuit a signal having a frequency in fixed relationship with said first loop oscillator output frequency; and means connecting said output of said oscillator in said second loop to said synthesizer ouTput.

Claim 8

A frequency synthesizer for providing a signal having a desired frequency at an output thereof, said synthesizer comprising: a signal source having a reference frequency; first and second phase locked loops each of which includes at least, a controlled oscillator having an input and an output, said oscillator providing at said output signal having a frequency dependent upon a signal applied to said input thereof, a mixer circuit responsive to the application to a first input thereof of said oscillator output signal and to a second input thereof of a signal having a certain frequency to provide at an output thereof a signal having a frequency equal to the difference between the frequencies of the signals applied thereto, a frequency dividing network responsive to said mixer circuit output signal for providing to an output thereof a signal having a frequency which is a submultiple of said mixer circuit output signal frequency, a comparator circuit responsive to the application thereto of said dividing network output signal and a signal having a frequency in fixed relationship with said reference frequency, said comparator circuit providing at an output thereof a signal dependent upon the phase changes between said signals applied thereto; means for applying the output of said comparative circuit to said input of said oscillator; means coupled between said source and said second input of said mixer circuit in said first loop for applying to said first loop mixer circuit a signal having a frequency in fixed relationship to said reference frequency; means coupled between the output of said oscillator in said first loop and said second input of said mixer circuit in said second loop for applying to said second loop mixer circuit a signal having a frequency in fixed relationship with said first loop oscillator output frequency; and means connecting said output of said oscillator in said second loop to said synthesizer ouTput.

Claim 9

The invention according to claim 6, wherein said frequency dividing network can divide the frequency of the signal applied thereto by one of a plurality of preselected divisor values.

Claim 10

The invention according to claim 6 wherein said means connecting said oscillator in said second loop to said synthesizer output includes at least a further mixer circuit having two inputs and an output means for connecting said output of said oscillator in said second loop to the first input of said further mixer circuit, means for applying a signal having a frequency in fixed relationship with said reference frequency to the second input of said further mixer circuit, and means for connecting said output of said further mixer circuit to said synthesizer output, said further mixer circuit providing a signal at said output thereof having a frequency equal to the difference in the frequencies of the signals applied to said inputs thereof.

Claim 11

The invention according to claim 6 wherein said controlled oscillator is a voltage controlled oscillator and said comparator circuit provides a signal at its output having a certain voltage which changes whenever the phases of the signals applied to the inputs thereof change.