PLL filter having a capacitive voltage divider

Patent metadata

Field	Value
Publication number	US-10693474-B1
Application number	US-201916276329-A
Country	US
Kind code	B1
Filing date	Feb 14, 2019
Priority date	Feb 14, 2019
Publication date	Jun 23, 2020
Grant date	Jun 23, 2020

Abstract

A phase-locked loop (PLL) includes a detector configured to generate an error signal based on a difference between a reference signal and an output signal, a charge pump configured to generate current pulses based on the error signal, a loop filter configured to generate a control voltage based on the current pulses, and a voltage-controlled oscillator (VCO) configured to generate the output signal at a frequency which is a function of the control voltage. The loop filter includes a capacitive voltage divider configured to reduce the control voltage from a range that falls within a voltage domain of the charge pump to a range that falls within a voltage domain of the VCO, the voltage domain of the charge pump being greater than the voltage domain of the VCO.

First claim

What is claimed is:

1. A phase-locked loop (PLL), comprising:
a detector configured to generate an error signal based on a difference between a reference signal and an output signal;
a charge pump configured to generate current pulses based on the error signal;
a loop filter configured to generate a control voltage based on the current pulses; and
a voltage-controlled oscillator (VCO) configured to generate the output signal at a frequency which is a function of the control voltage,
wherein the loop filter comprises a capacitive voltage divider configured to reduce the control voltage from a range that falls within a voltage domain of the charge pump to a range that falls within a voltage domain of the VCO,
wherein the voltage domain of the charge pump is greater than the voltage domain of the VCO.

2. The PLL of claim 1 , wherein the capacitive voltage divider comprises a first capacitor connected to a second capacitor at a voltage division node of the capacitive voltage divider, and wherein the VCO is coupled to the voltage division node of the capacitive voltage divider.

3. The PLL of claim 2 , wherein the loop filter further comprises a resistive voltage divider in parallel with the capacitive voltage divider, and wherein the resistive voltage divider comprises a first resistor in parallel with the first capacitor of the capacitive voltage divider and a second resistor in parallel with the second capacitor of the capacitive voltage divider.

4. The PLL of claim 3 , wherein the resistive voltage divider is connected in parallel with the capacitive voltage divider in a fixed frequency mode of the PLL and disconnected from the capacitive voltage divider in a frequency ramp mode of the PLL.

5. The PLL of claim 2 , wherein the loop filter is a 2 nd or higher order filter, and wherein the capacitive voltage divider is coupled between a largest capacitor of the loop filter and an output of the loop filter.

6. The PLL of claim 5 , wherein the loop filter is a passive filter.

7. The PLL of claim 2 , wherein the loop filter is an active filter, wherein a feedback path of the active filter comprises a largest capacitor of the loop filter and a resistor, and wherein the capacitive voltage divider is coupled between the largest capacitor of the loop filter and an output of the loop filter.

8. The PLL of claim 2 , wherein values of the first and the second capacitors of the capacitive voltage divider are chosen so as to reduce the control voltage by a 3-to-1 or 2-to-1 ratio.

9. The PLL of claim 2 , wherein values of the first and the second capacitors of the capacitive voltage divider are chosen so as to reduce the control voltage from a range of 0V to 1.8V to a range of 0V to 0.9V.

10. The PLL of claim 2 , wherein a division ratio of the capacitive voltage divider is configurable by switching between different values for at least one of the first and the second capacitors of the capacitive voltage divider.

11. The PLL of claim 10 , wherein at least one of the first and the second capacitors of the capacitive voltage divider comprises two capacitors connected in series, and wherein one of the two capacitors connected in series is configured to be shorted so as to change the division ratio of the capacitive voltage divider.

12. The PLL of claim 11 , wherein the loop filter further comprises a resistive voltage divider in parallel with the capacitive voltage divider, and wherein the resistive voltage divider comprises a separate resistor in parallel with each capacitor of the capacitive voltage divider.

13. The PLL of claim 10 , wherein at least one of the first and the second capacitors of the capacitive voltage divider comprises two capacitors connected in parallel with one of the two capacitors connected in parallel being configured to be disconnected so as to change the division ratio of the capacitive voltage divider.

14. The PLL of claim 1 , wherein a division ratio of the capacitive voltage divider is configurable to accommodate different modes of the PLL and/or different Radar frequency ramp bandwidths.

15. The PLL of claim 1 , wherein the loop filter further comprises a resistive voltage divider in parallel with the capacitive voltage divider.

16. The PLL of claim 15 , wherein a division ratio of the capacitive voltage divider and a division ratio of the resistive voltage divider are configured to be switched simultaneously.

17. The PLL of claim 15 , wherein the resistive voltage divider is connected in parallel with the capacitive voltage divider in a fixed frequency mode of the PLL and disconnected from the capacitive voltage divider in a frequency ramp mode of the PLL.

18. The PLL of claim 1 , wherein a division ratio of the capacitive voltage divider is selected to optimize a total capacitance area of the loop filter for a specified noise performance, or to optimize noise performance for a specified capacitance area of the multi-order loop filter.

19. A phase-locked loop (PLL), comprising:
a detector configured to generate an error signal based on a difference between a reference signal and an output signal;
a charge pump configured to generate current pulses based on the error signal;
a loop filter configured to generate a control voltage based on the current pulses; and
a voltage-controlled oscillator (VCO) configured to generate the output signal at a frequency which is a function of the control voltage,
wherein the loop filter comprises a first capacitor connected with a second capacitor to form a capacitive voltage divider,
wherein the second capacitor of the capacitive voltage divider isolates a DC voltage level between first and second parts of the loop filter, to reduce the control voltage from a range that falls within a voltage domain of the charge pump to a range that falls within a voltage domain of the VCO,
wherein the charge pump is configured to operate within the first voltage domain,
wherein the VCO is configured to operate within the second voltage domain,
wherein the second voltage domain is lower than the first voltage domain supply.

20. A method of operating a phase-locked loop (PLL), the method comprising:
generating an error signal, by a detector of the PLL, based on a difference between a reference signal and an output signal;
generating current pulses, by a charge pump of the PLL, based on the error signal;
generating a control voltage, by a loop filter of the PLL, based on the current pulses;
generating the output signal, by a voltage-controlled oscillator (VCO) of the PLL, at a frequency which is a function of the control voltage;
operating the VCO within a first voltage domain and the charge pump within a second voltage domain greater than the first voltage domain; and
reducing the control voltage from a range that falls within the second voltage domain to a range that falls within the first voltage domain by a capacitive voltage divider of the loop filter.

Assignees

• Infineon Technologies Ag

Inventors

• Efthivoulidis George
• Thurner Peter

Classifications

• H03L7/093 Primary

  using special filtering or amplification characteristics in the loop (H03L7/087 - H03L7/091 take precedence) · CPC title

• H02M3/07

  using capacitors charged and discharged alternately by semiconductor devices with control electrode {, e.g. charge pumps} · CPC title

• H03H7/06

  including resistors (H03H7/075, H03H7/09, H03H7/12, H03H7/13 take precedence) · CPC title