Frequency locked loop
First Claim
1. An microcontroller integrated circuit, comprising:
- a terminal;
a crystal oscillator circuit coupled to the terminal, the crystal oscillator circuit outputting a first clock signal of a first frequency;
a real time clock that receives the first clock signal;
a processor having a clock input lead; and
a clock multiplier circuit having an input lead and an output lead, the clock multiplier circuit receiving the first clock signal from the crystal oscillator circuit and generating therefrom a second clock signal, the second clock signal having a second frequency that is a multiple of the first frequency, wherein the second clock signal is supplied to the clock input lead of the processor.
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Accused Products
Abstract
A frequency locked loop in a microcontroller integrated circuit has a precision digital feedback control loop. The frequency locked loop performs a clock multiplication function such that an inexpensive and low frequency external crystal is usable to both clock a processor of the microcontroller with a higher frequency and low-jitter clock signal and to clock a real time clock of the microcontroller with a low frequency time base that is a power of two multiple of one hertz. In one embodiment, the digital feedback control loop includes a ramp generator, a digital filter, and a loop divider. The ramp generator is controlled to output steeper and steeper ramps as the frequency locking process proceeds toward frequency lock. A preset value that presets the loop divider is changed to adjust the phase of a feedback signal with respect to a reference input signal.
34 Citations
15 Claims
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1. An microcontroller integrated circuit, comprising:
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a terminal;
a crystal oscillator circuit coupled to the terminal, the crystal oscillator circuit outputting a first clock signal of a first frequency;
a real time clock that receives the first clock signal;
a processor having a clock input lead; and
a clock multiplier circuit having an input lead and an output lead, the clock multiplier circuit receiving the first clock signal from the crystal oscillator circuit and generating therefrom a second clock signal, the second clock signal having a second frequency that is a multiple of the first frequency, wherein the second clock signal is supplied to the clock input lead of the processor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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Specification