Lattice Semiconductor Corporation

Tawei David Li

Barry Britton

Richard Booth

Yang Xu

Phillip Johnson

A phase locked loop (PLL) circuit is provided with selectable feedback paths. In one example, a method of operating a device includes passing a clock signal provided by a PLL circuit of the device through an internal feedback path of the PLL circuit to provide a first input signal to the PLL circuit while at least one external circuit of an external feedback path of the device is disabled during a low power operation mode of the device. The method also includes detecting a lock between the first input signal and a reference signal during the low power operation mode. The lock indicates that the clock signal is operating at a frequency used during a normal operation mode of the device. The method also includes passing the clock signal through the external feedback path to provide a second input signal to the PLL circuit. The method also includes switching from detecting a lock between the first input signal and the reference signal to detecting a lock between the second input signal and the reference signal if the external circuit is enabled for the normal operation mode.

Phase locked loop circuit with selectable feedback paths

Techniques are provided to reduce glitches at an output signal node when a device is switched to and from a low power operation mode. In one example, a method of operating a device includes providing power to operate a signal source of the device during a normal operation mode of the device. The method also includes passing an output signal from the signal source through a signal path to an output node during the normal operation mode. The method also includes receiving an operation mode signal to switch the device from the normal operation mode to a low power operation mode. The method also includes disabling the signal path to prevent glitches from appearing at the output node during the switch from the normal operation mode to the low power operation mode. The method also includes continuing providing power to the signal source until after the signal path is disabled.

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Tawei David Li