Utilizing the LC oscillator of a frequency synthesizer as an injection source for crystal oscillator startup

An apparatus comprising:

• a phase-locked loop (PLL);
• a controller responsive to a wakeup event from a sleep mode to configure the PLL based on stored parameters to generate an injection clock signal with a frequency that is substantially equal to a crystal oscillator frequency of a crystal oscillator signal;
• and
• a crystal oscillator circuit configured to generate the crystal oscillator signal, which is coupled to the PLL, the crystal oscillator circuit further configured to generate anti-phase signals using the injection clock signal and to inject the anti-phase signals into a crystal of the crystal oscillator circuit during startup of the crystal oscillator circuit;
• wherein the PLL supplies a clock signal for operations other than crystal startup after the crystal oscillator circuit reaches steady state following the startup of the crystal oscillator circuit.

An apparatus comprising:

• a crystal oscillator circuit;
• a storage;
• and
• a frequency synthesizer responsive to a first wakeup event to generate an injection clock signal for use in startup of the crystal oscillator circuit, the frequency synthesizer using parameters stored in the storage that cause a frequency of the injection clock signal to be substantially equal to a crystal oscillator frequency;
• wherein the crystal oscillator circuit generates injection signals from the injection clock signal and injects the injection signals into a crystal during the startup of the crystal oscillator circuit;
• wherein subsequent to the crystal oscillator circuit reaching a steady state, the frequency synthesizer is configured to generate an operational clock signal for use as a local oscillator signal for one or more radio frequency (RF) operations;
• wherein after completion of the one or more RF operations, an integrated circuit on which the frequency synthesizer is disposed enters a sleep mode;
• and
• wherein responsive to a second wakeup event the frequency synthesizer generates the injection clock signal for use in another startup of the crystal oscillator circuit.