Power converter having switching frequency phase locked to system clock
First Claim
1. An apparatus for synchronizing a periodic ramp signal with a periodic clock signal comprising:
- a. a voltage controlled oscillator for forming the periodic ramp signal; and
b. a waveform shaping circuit for forming a periodic rectangular signal having a same frequency as the periodic ramp signal; and
c. a phase comparator for comparing a phase of the periodic rectangular signal to a phase of the periodic clock signal and for controlling the voltage controlled oscillator.
1 Assignment
0 Petitions
Accused Products
Abstract
A circuit for synchronizing a periodic ramp signal utilized in a switching mode power converter to system clock signal. A capacitor is charged through a resistor. When a voltage across the capacitor reaches a predetermined level, the capacitor is discharged and the charging cycle is repeated, thereby generating the periodic ramp signal across the capacitor. A waveform shaping circuit shapes the ramp signal into a rectangular wave signal having a same frequency and phase as the ramp signal. A phase comparator compares a phase of the rectangular wave signal to a phase of the system clock signal for forming a phase error signal. The phase error signal controls a level of current supplied to the timing capacitor by a voltage controlled current source. When the frequency of the system clock signal is higher than the frequency of the ramp signal, the phase comparator causes the voltage controlled current source to supply additional current to the capacitor, increasing the frequency of the ramp signal. When the frequency of the system clock signal is lower than the frequency of the ramp signal, the phase comparator causes the voltage controlled current to supply less current to the capacitor, decreasing the frequency of the ramp signal. Therefore, the frequency of the ramp signal is controlled in phase locked loop to synchronize the ramp signal with the system clock signal. The synchronized ramp signal can then be utilized for controlling switching in the switching mode power converter, reducing the effects of switching noise.
62 Citations
25 Claims
-
1. An apparatus for synchronizing a periodic ramp signal with a periodic clock signal comprising:
-
a. a voltage controlled oscillator for forming the periodic ramp signal; and b. a waveform shaping circuit for forming a periodic rectangular signal having a same frequency as the periodic ramp signal; and c. a phase comparator for comparing a phase of the periodic rectangular signal to a phase of the periodic clock signal and for controlling the voltage controlled oscillator. - View Dependent Claims (2, 3, 4, 5, 6, 7)
-
-
8. An apparatus for synchronizing a periodic ramp signal with a periodic clock signal comprising:
-
a. a phase comparator having a first input, a second input and an output, wherein the first input is coupled to receive the periodic clock signal and the second input is coupled to receive a signal representative of the periodic ramp signal; b. a current source coupled to be controlled by the output of the phase comparator; and c. a timing capacitor coupled to be charged by a current supplied by the current source wherein the periodic ramp signal is formed across the capacitor and a frequency of the ramp signal is dependent upon a level of current supplied by the voltage controlled current source. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
-
-
19. A method of synchronizing a periodic ramp signal with a periodic clock signal comprising the step of:
-
a. forming a current signal wherein a level of the current signal is representative of a difference in phase between the periodic ramp signal and the periodic clock signal; and b. charging a charge storage device with the current signal and periodically discharging the charge storage device thereby forming the periodic ramp signal across the charge storage device. - View Dependent Claims (20, 21, 22, 23, 24, 25)
-
Specification