Duty cycle integrator with tracking common mode feedback control

A duty cycle integrator comprising:

• a differential component that is responsive to complementary clock inputs to produce a differential output signal;
• capacitance that integrates the differential output signal to produce an integrated differential output signal representing the duty cycle of the complementary clock inputs, the integrated differential output signal having a common mode output voltage;
• and
• common mode feedback circuitry associated with the differential component to control the common mode output voltage in response to a received reference voltage, wherein the differential component comprises a differential pair of transistors, the duty cycle integrator further comprising:
• a current source that establishes a reference current;
• a pair of mirrored transistors connected respectively in series with the transistors of the differential pair to mirror the reference current;
• and
• the common mode feedback circuitry comprising a pair of parallel transistors connected in series with the differential component, wherein the parallel transistors are controlled by the differential output signal.

A duty cycle integrator comprising:

• a differential component that is responsive to complementary clock inputs to produce a differential output signal;
• capacitance that integrates the differential output signal to produce an integrated differential output signal representing the duty cycle of the complementary clock inputs, the integrated differential output signal having a common mode output voltage;
• and
• common mode feedback circuitry associated with the differential component to control the common mode output voltage in response to a received reference voltage, wherein the differential component comprises a differential pair of transistors, the duty cycle integrator further comprising:
• a reference transistor that is controlled by the received reference voltage;
• a current source that establishes a reference current through the reference transistor;
• a pair of mirrored transistors connected respectively in series with the transistors of the differential pair to mirror the reference current;
• and
• the common mode feedback circuitry comprising a pair of parallel transistors connected in series with the differential component, wherein the parallel transistors are controlled by the differential output signal to establish the common mode output voltage in accordance with the received reference voltage.

A duty cycle integrator comprising:

• a differential component that is responsive to complementary clock inputs to produce a differential output signal;
• capacitance that integrates the differential output signal to produce an integrated differential output signal representing the duty cycle of the complementary clock inputs, the integrated differential output signal having a common mode output voltage;
• and
• common mode feedback circuitry associated with the differential component to control the common mode output voltage in response to a received reference voltage, wherein the differential component comprises a differential pair of transistors, the duty cycle integrator further comprising:
• a reference transistor that is controlled by the received reference voltage;
• a current mirror transistor connected in series with the reference transistor, the current mirror transistor having a source connected to a supply voltage, the current mirror transistor having a gate and a drain that are connected to each other;
• a current source that establishes a reference current through the reference transistor and through the current mirror transistor;
• a pair of mirrored transistors having gates that are connected to the gate of the current mirror transistor to mirror the reference current, the mirrored transistors being connected respectively between the supply voltage and the transistors of the differential pair;
• and
• the common mode feedback circuitry comprising a pair of parallel transistors connected in series with the differential component, wherein the parallel transistors are controlled by the differential output signal to establish the common mode output voltage in accordance with the received reference voltage.

A duty cycle integrator comprising:

• a differential pair of transistors that is responsive to complementary clock inputs to produce a differential output signal;
• capacitance that integrates the differential output signal to produce an integrated differential output signal representing the duty cycle of the complementary clock inputs, the integrated differential output signal having a common mode output voltage;
• a reference transistor that is controlled by a received reference voltage;
• a current source that establishes a reference current through the reference transistor;
• a pair of mirrored transistors connected respectively in series with the transistors of the differential pair to mirror the reference current;
• and
• a pair of parallel transistors connected in series with the differential transistor pair, wherein the parallel transistors are controlled by the differential output signal to establish the common mode output voltage in accordance with the received reference voltage.

An electrical circuit comprising:

• a differential component that is responsive to a differential input signal to produce a differential output signal, the input signal having a common mode input voltage and the output signal having a common mode output voltage;
• common mode feedback circuitry associated with the differential component to control the common mode output voltage;
• wherein the common mode feedback circuitry varies the common mode output voltage in accordance with a transistor voltage threshold;
• an input buffer that controls the common mode input voltage;
• and
• wherein the input buffer varies the common mode input voltage as a function of said transistor voltage threshold.

An electrical circuit comprising:

• a differential component that produces a differential output signal having a common mode output voltage;
• a reference generator that generates a reference voltage and that varies the reference voltage as a function of a transistor voltage threshold;
• and
• common mode feedback circuitry associated with the differential component to control the common mode output voltage in accordance with the reference voltage.

An electrical circuit comprising:

• a differential component that is responsive to a differential input signal to produce a differential output signal, the input signal having a common mode input voltage and the output signal having a common mode output voltage;
• common mode feedback circuitry associated with the differential component to control the common mode output voltage;
• an input buffer that controls the common mode input voltage;
• and
• wherein the input buffer varies the common mode input voltage as a function of a transistor voltage threshold.

In an electrical circuit that produces a differential output voltage having a common mode output voltage, a method comprising;

• generating a reference voltage;
• varying the reference voltage in accordance with a transistor voltage threshold;
• and
• controlling the common mode output voltage in accordance with the reference voltage.

A method to produce an output signal representing a duty cycle of two complementary clock inputs comprising:

• receiving the two complementary clock inputs;
• producing a differential output signal based on the two complementary clock inputs;
• integrating the differential output signal to an output signal having a common mode output voltage;
• and
• controlling the common mode output voltage in response to a received reference voltage.