Clock signal conversion circuit for high-speed serial data controllers

A Universal Serial Bus (USB) integrated circuit (IC) controller, the USB IC controller comprising:

• a clock generation circuit configured to generate a differential clock signal;
• and
• a physical layer circuit comprising:
• an amplification circuit configured to amplify the differential clock signal that has sub rail-to-rail voltage swings relative to a supply voltage for the amplification circuit, such that an amplified differential clock signal output by the amplification circuit has complementary positive and negative signal components with full rail-to-rail voltage swings relative to the supply voltage;
• and
• a duty cycle distortion correction circuit comprising:
• a filter having a cutoff frequency below the frequency of the differential clock signal and configured to output a differential voltage that is proportional to a difference in duty cycle between the positive and negative signal components of the amplified differential clock signal;
• a transconductance amplifier configured to convert the differential voltage to a differential current that is provided to the amplification circuit as feedback for reducing the duty cycle difference between the positive and negative signal components of the amplified differential clock signal;
• and
• a common-mode loop comprising a PMOS transistor having a gate driven by a mid-rail voltage reference, wherein the common-mode loop is configured to force the average of a positive side of the differential voltage and a negative side of the differential voltage to half the mid-rail voltage reference.

A clock signal conversion circuit, comprising:

• an amplification circuit configured to amplify a differential clock signal that has sub rail-to-rail voltage swings relative to a supply voltage for the amplification circuit, such that an amplified differential clock signal output by the amplification circuit has complementary positive and negative signal components with full rail-to-rail voltage swings relative to the supply voltage;
• and
• a duty cycle distortion correction circuit comprising:
• a filter having a cutoff frequency below the frequency of the differential clock signal and configured to output a differential voltage that is proportional to a difference in duty cycle between the positive and negative signal components of the amplified differential clock signal;
• a transconductance amplifier configured to convert the differential voltage to a differential current that is provided to the amplification circuit as feedback for reducing the duty cycle difference between the positive and negative signal components of the amplified differential clock signal;
• and
• a common-mode loop comprising a PMOS transistor having a gate driven by a mid-rail voltage reference, wherein the common-mode loop is configured to force the average of a positive side of the differential voltage and a negative side of the differential voltage to half a mid-rail voltage reference input to the common-mode loop.