Compact voltage controlled ring oscillator with quadrature outputs

A compact voltage controlled ring oscillator comprising:

• a first variable delay gate and a second variable delay gate, each of the variable delay gates comprising:
• an input port to receive a differential input signal;
• an output port to transmit a differential output signal;
• a fixed bias differential transconductance gain stage (GM1) coupled to the input port to receive the differential input signal and generate correspondingly a differential output current;
• a variable bias differential transconductance hysteresis feedback stage (GM2) having a pair of differential input terminals coupled to a first and a second voltage follower amplifier (G3 and G4) to provide a local positive feedback loop, where a differential output current of GM2 is coupled to the differential output current of GM1 to form a summation of differential currents;
• a pair of load elements which are connected to both a differential output port of GM1 and GM2 to convert the summation of currents to a differential output voltage;
• a voltage follower stage, where a pair of voltage follower stage inputs are coupled to the pair of load elements and a pair of voltage follower stage outputs are coupled to the input port of the other variable delay gate;
• wherein a variable bias current in the voltage follower stage is controlled to vary directly proportionately to a control voltage VX, and a bias current in the transconductance stage GM2 is controlled to vary inversely proportionately to the control voltage VX, and wherein the input port of one variable delay gate is connected to the output port of the other variable delay gate;
• and
• a control interface (CI) circuit, the control interface circuit receives a VCO input control voltage signal (VCON) and generates correspondingly an output control voltage signal (VX), wherein the control interface circuit is coupled to provide control signal VX to each of the variable delay gates to thereby vary the value of a pair of current sources in the voltage follower stage in opposing direction to the value of a current source in the GM2 stage.