Source-injection parallel coupled LC-quadrature voltage controlled oscillator

1. A quadrature VCO (voltage controlled oscillator) comprising a first delay cell for outputting a first in-phase signal and a second in-phase signal with different phases, and a second delay cell for outputting a first quadrature-phase signal and a second quadrature-phase signal with different phases,

wherein the first delay cell comprises:

a first differential VCO coupled between a power supply and a first current source, the first differential VCO comprising a LC resonance circuit;

a first coupling transistor including a first terminal, a second terminal directly coupled to the power supply, and a third terminal coupled to the first current source, the first coupling transistor varying a magnitude and a direction of a current which flows from the second terminal to the third terminal according to a magnitude of the first quadrature-phase signal applied to the first terminal; and

a second coupling transistor including a first terminal, a second terminal directly coupled to the power supply, and a third terminal coupled to the first current source, the second coupling transistor varying a magnitude and a direction of a current which flows from the second terminal to the third terminal according to a magnitude of the second quadrature-phase signal applied to the first terminal, and

wherein the LC resonance circuit of the first differential VCO comprises;

a first inductor coupled between the power and the first in-phase signal;

a second inductor coupled between the power and the second in-phase signal;

a first varactor having a first terminal coupled to the first in-phase signal and a second terminal for receiving a first control voltage for controlling frequencies of the first in-phase signal and the second in-phase signal; and

a second varactor having a first terminal coupled to the second in-phase signal and a second terminal for receiving the first control voltage, and

wherein the second delay cell comprises:

a second differential VCO coupled between a power supply and a second current source, the second differential VCO comprising a LC resonance circuit;

a third coupling transistor including a first terminal, a second terminal directly coupled to the power supply, and a third terminal coupled to the second current source, the third coupling transistor varying a magnitude and a direction of a current which flows from the second terminal to the third terminal according to a magnitude of the second in-phase signal applied to the first terminal; and

a fourth coupling transistor including a first terminal, a second terminal directly coupled to the power supply, and a third terminal coupled to the second current source, the third coupling transistor varying a magnitude and a direction of a current which flows from the second terminal to the third terminal according to a magnitude of the first in-phase signals applied to the first terminal, and

wherein the LC resonance circuit of the second differential VCO comprises:

a third inductor coupled between the power and the first quadrature-phase signal;

a fourth inductor coupled between the power and the second quadrature-phase signal;

a third varactor having a first terminal coupled to the first quadrature-phase signal and a second terminal receiving a second control voltage for controlling frequencies of the first quadrature-phase signal and the second quadrature-phase signal; and

a fourth varactor having a first terminal coupled to the second quadrature-phase signal and a second terminal receiving the second control voltage.

2. The quadrature VCO of claim 1 , wherein the first differential VCO comprises:

a first transistor including a first terminal, a second terminal for outputting the first in-phase signal, and a third terminal coupled to the first current source, the first transistor varying a magnitude and a direction of a current which flows from the second terminal to the third terminal according to a voltage applied to the first terminal;

a second transistor including a first terminal coupled to the second terminal of the first transistor, a second terminal being coupled to the first terminal of the first transistor and outputting the second in-phase signal, and a third terminal coupled to the first current source, the second transistor varying a magnitude and a direction of a current which flows from the second terminal to the third terminal according to a voltage applied to the first terminal; and

the second differential VCO comprises:

a third transistor including a first terminal, a second terminal for outputting the first quadrature-phase signal, and a third terminal coupled to the second current source, the third transistor varying a magnitude and a direction of a current which flows from the second terminal to the third terminal according to a voltage applied to the first terminal;

a fourth transistor including a first terminal coupled to the second terminal of the third transistor, a second terminal being coupled to the first terminal of the third transistor and outputting the second quadrature-phase signal, and a third terminal coupled to the second current source, the fourth transistor varying a magnitude and a direction of a current which flows from the second terminal to the third terminal according to a voltage applied to the first terminal.

3. The quadrature VCO of claim 2 , wherein the first to fourth transistors and the first to fourth coupling transistors include NMOS transistors, the first terminal is a gate, the second terminal is a drain, and the third terminal is a source.

4. The quadrature VCO of claim 2 , wherein the first to fourth transistors and the first to fourth coupling transistors include PMOS transistors, the first terminal is a gate, the second terminal is a source, and the third terminal is a drain.