Locking multiple voltage-controlled oscillators with a single phase-locked loop

1. A system including a phase-locked loop (PLL) circuit configured to lock multiple voltage-controlled oscillators (VCOs) for generating a plurality of local oscillator (LO) frequencies, the system comprising:

a plurality of VCOs, each VCO generating an output signal of a particular frequency;

a plurality of dividers, each divider configured to divide the output signal of a corresponding VCO, the plurality of dividers generating a plurality of divided VCO feedback signals;

a phase-to-digital converter (PDC) configured to receive the plurality of divided VCO feedback signals from the plurality of dividers and a reference signal multiplied by a predetermined number indicating a number of the plurality of VCOs, and to generate the predetermined number of phase differences between the multiplied reference signal and the plurality of divided VCO feedback signals;

a digital loop filter configured to receive and process the phase differences and generate a filter output,

wherein the digital loop filter includes a plurality of delay cells equal to the predetermined number; and

a digital-to-analog converter (DAC) configured to output control voltages for the plurality of VCOs based on the filter output.

2. The system of claim 1 , wherein the digital loop filter comprises:

a filter gain unit to multiply a serialized signal of the predetermined number of phase differences with a filter gain and output a first value;

the predetermined number of a plurality of delay cells;

a loop gain unit in the loop to multiply a delayed version of the filter output with a loop gain and output a second value; and

a summing unit to add the first value and the second value to produce the filter output.

3. A method to lock multiple VCOs to generate a plurality of LO frequencies, the method comprising:

receiving a plurality of divided VCO feedback signals from a plurality of VCOs;

receiving a reference signal multiplied by a predetermined number of the plurality of VCOs;

generating and processing the predetermined number of phase differences between the multiplied reference signal and the plurality of divided VCO feedback signals in a single PLL circuit including a digital loop filter to receive and process the phase differences and generate a filter output,

wherein the digital loop filter includes a plurality of delay cells equal to the predetermined number; and

generating and outputting control voltages for the plurality of VCOs based on the filter output.

4. The method of claim 3 , wherein the digital loop filter is configured to add one delay cell for each additional VCO to lock.

5. The method of claim 3 , wherein processing the predetermined number of phase differences comprises:

multiplying a serialized signal of the predetermined number of phase differences with a filter gain and outputting a first value;

multiplying a delayed version of the filter output with a loop gain and outputting a second value; and

summing the first value and the second value to produce the filter output.

6. An apparatus to lock multiple VCOs for generating a plurality of LO frequencies, the apparatus comprising:

means for receiving a plurality of divided VCO feedback signals from a plurality of VCOs;

mean for receiving a reference signal multiplied by a predetermined number of the plurality of VCOs;

mean for generating and processing the predetermined number of phase differences between the multiplied reference signal and the plurality of divided VCO feedback signals in a single PLL circuit including a digital loop filter to receive and process the phase differences and generate a filter output,

wherein the digital loop filter includes a plurality of delay cells equal to the predetermined number; and

means for generating and outputting control voltages for the plurality of VCOs based on the filter output.

7. The apparatus of claim 6 , wherein the digital loop filter is configured to add one delay cell for each additional VCO to lock.

8. The apparatus of claim 6 , wherein the means for generating and for processing the predetermined number of phase differences comprises:

means for multiplying a serialized signal of the predetermined number of phase differences with a filter gain and outputting a first value;

means for multiplying a delayed version of the filter output with a loop gain and outputting a second value; and

means for summing the first value and the second value to produce the filter output.

9. A non-transitory computer-readable storage medium storing a computer program to lock multiple VCOs for generating a plurality of LO frequencies, the computer program comprising executable instructions that cause a computer to:

receive a plurality of divided VCO feedback signals from a plurality of VCOs; receive a reference signal multiplied by a predetermined number of the plurality of VCOs;

generate and process the predetermined number of phase differences between the multiplied reference signal and the plurality of divided VCO feedback signals in a single PLL circuit including a digital loop filter to receive and process the phase differences and generate a filter output,

wherein the digital loop filter includes a plurality of delay cells equal to the predetermined number; and

generate and output control voltages for the plurality of VCOs based on the filter output.

10. The non-transitory computer-readable storage medium of claim 9 , wherein executable instructions that cause the computer to process the predetermined number of phase differences comprise executable instructions that cause the computer to:

multiply a serialized signal of the predetermined number of phase differences with a filter gain and outputting a first value;

multiply a delayed version of the filter output with a loop gain and outputting a second value; and

sum the first value and the second value to produce the filter output.

11. The non-transitory computer-readable storage medium of claim 9 , wherein executable instructions that cause the computer to process the predetermined number of phase differences comprise executable instructions that cause the computer to:

perform an initial phase adjustment in which each of the plurality of divided VCO feedback signals is adjusted to be confined within one distinct period of the multiplied reference signal.

12. The non-transitory computer-readable storage medium of claim 11 , wherein the initial phase adjustment comprises executable instruction that cause the computer to:

measure time differences between a rising edge of the reference signal and rising edges of the plurality of divided VCO feedback signals; and

adjust the rising edges of the plurality of divided VCO feedback signals using the time differences.