Quadrature output ring oscillator and method thereof
Various circuits are described, which sustain an oscillation using a combination of four primary inverters, four feedforward inverters, and four coupling resistors for outputting a quadrature output signal while avoiding contention between a primary inverter and a feedforward inverter. In one configuration, a circuit includes four primary inverters configured in a ring topology, four coupling resistors uniformly interposed in the ring among the four primary inverters, and four feedforward inverters forming four sub-feedback loops, respectively, each sub-feedback loop comprising two primary inverters, one coupling resistor, and one feedforward inverter. In a further embodiment, the circuit further comprises a voltage-to-current converter is for receiving a control voltage and outputting a supply current to the four primary inverters and the four feedforward inverters. A corresponding method is also provided.
1. A circuit comprising:
four primary inverters configured in a ring topology;
four coupling resistors uniformly disposed in the ring among the four primary inverters, wherein a coupling resistor is interposed between each successive primary inverter; and
four feedforward inverters forming four sub-feedback loops, respectively, each comprising two primary inverters, one coupling resistor, and one feedforward inverter, wherein each end of each of the four coupling resistors shares a connection with one of the four primary inverters and one of the four feedforward inverters.
2. The circuit of claim 1 further comprising a voltage-to-current converter receiving a control voltage and outputting a supply current to the four primary inverters and the four feedforward inverters.
3. A method comprising:
cascading four primary inverters in a ring topology;
evenly inserting four coupling resistors among the four primary inverters in the ring; and
inserting four feedforward inverters to the ring to form four three-inverter sub-feedback loops, each comprising two primary inverters, one coupling resistor, and one feedforward inverter, wherein each end of each of the four coupling resistors shares a connection with one of the four primary inverters and one of the four feedforward inverters.
4. The method of claim 3 further comprising: using a voltage-to-current converter receiving a control voltage and outputting a supply current to the four primary inverters and the four feedforward inverters.
5. A circuit comprising:
four primary inverters, including a first primary inverter outputting a zero-degree phase of an output signal, a second primary inverter outputting a ninety-degree phase of the output signal, a third primary inverter outputting a one-hundred-eighty-degree phase of the output signal, and a fourth primary inverter outputting a two-hundred-seventy-degree phase of the output signal;
four resistors comprising a first resistor coupling the zero-degree phase of the output signal to an input of the second primary inverter, a second resistor coupling the ninety-degree phase of the output signal to an input of the third primary inverter, a third resistor coupling the one-hundred-eighty-degree phase of the output signal to an input of the fourth primary inverter, and a fourth resistor coupling the two-hundred-seventy-degree phase of the output signal to an input of the first primary inverter; and
four feedforward inverters comprising a first feedforward inverter receiving the one-hundred-eighty-degree phase of the output signal and providing an output to the input of the second primary inverter, a second feedforward inverter receiving the zero-degree phase of the output signal and providing an output to the input of the fourth primary inverter, a third feedforward inverter receiving the two-hundred-seventy-degree phase of the output signal and providing an output to the input of the third primary inverter, and a fourth feedforward inverter receiving the ninety-degree phase of the output signal and providing an output to the input of the first primary inverter, wherein each end of each of the four coupling resistors shares a connection with one of the four primary inverters and one of the four feedforward inverters.
6. The circuit of claim 5 , further comprising a voltage-to-current converter receiving a control voltage and outputting a supply current to the four primary inverters and the four feedforward inverters.