US 12,418,262 B2
Low noise crystal oscillator
Chia-Liang (Leon) Lin, Fremont, CA (US)
Assigned to REALTEK SEMICONDUCTOR CORP., Hsinchu (TW)
Filed by Realtek Semiconductor Corp., Hsinchu (TW)
Filed on Feb. 16, 2024, as Appl. No. 18/443,607.
Prior Publication US 2025/0266792 A1, Aug. 21, 2025
Int. Cl. H03B 5/12 (2006.01); H03B 1/04 (2006.01)
CPC H03B 5/1228 (2013.01) [H03B 1/04 (2013.01); H03B 2200/0088 (2013.01)] 8 Claims
OG exemplary drawing
 
1. A crystal oscillator comprising:
a voltage regulator configured to receive a first power supply voltage and output a second power supply voltage;
a source follower configured to receive the second power supply voltage and output a third power supply voltage in accordance with a control voltage;
a first inverter operating under the third power supply voltage and configured to receive a first oscillatory signal at a first node and output a second oscillatory signal at a second node;
a second inverter operating under the third power supply voltage and configured to receive the second oscillatory signal and output a third oscillatory signal;
a crystal placed across the first node and the second node;
a first shunt capacitor configured to shunt the first node to ground;
a second shunt capacitor configured to shunt the second node to the ground; and
a clocked lowpass filter configured to receive a reference voltage and output the control voltage in accordance with a pulsed signal, which is synchronous with the third oscillatory signal;
wherein a first edge of the pulsed signal approximately aligns with a first edge of the third oscillatory signal, and a pulse width of the pulsed signal is substantially smaller than a period of the third oscillatory signal.