| 摘要 |
The VCO circuit comprises a resonant circuit with two inductors (L1,L2) and a variable capacitive element (Cv), a pair of cross-coupled n-MOS transistors (N1,N2) connected between output terminals of the resonant circuit, two n-MOS transistors (N3,N4) connected as diodes each in parallel with a transistor of the pair so to form a current-mirror, and a loop for controlling the amplitude of oscillations by controlling the currents in each transistor connected as a diode. The voltage of common mode is extracted by two resistors (R1,R2) branched in series between the gates of the transistors of the pair (N1,N2), and is stored in a filter capacitor (Cm) in order to polarize a reference transistor (N5) connected in series with a reference resistor (R3). The value of current delivered to the transistors (N3,N4) connected as diodes depends on the value of the resistance and the detected voltage of the common-mode. The common-mode voltage decreases with increasing amplitude of oscillations, and vice versa. The average current in the transistors (N3,N4) connected as diodes is controlled so to obtain the maximum amplitude depending on the dimensioning of certain elements of the circuit. The control loop comprises three p-MOS transistors (P1,P2,P3), where the first transistor (P1) is connected as a diode, and the other two transistors (P2,P3) of a current-mirror are connected in parallel with the first transistor (P1) so to duplicate the reference current delivered to each n-MOS transistor (N3,N4) connected as a diode. The gate of each transistor of the pair (N1,N2) is connected by a coupling capacitor (C1,C3) to the drain of the other transistor of the pair, and the coupling capacitors with the capacitors (C2,C4) connected between the gates of the transistors and the lower voltage terminal, that is the ground, form two capacitive voltage dividers. In the second embodiment, the circuit comprises another pair of p-MOS transistors with coupling capacitors and branched resistors also connected to the output terminals of the resonant circuit, two n-MOS reference transistors connected in parallel, two p-MOS transistors connected as diodes, a p-MOS return transistor and an n-MOS return transistor connected as a diode. |
