A
variable frequency oscillator comprising a first
transistor (10) and a second
transistor (20); wherein the first
transistor (10) has a first terminal—collector—which is connected to a reference
voltage, and a second terminal—emitter—which is connected to a first terminal of a first
current source (13), which second terminal is connected to ground, and a third terminal—base—connected to a first terminal of a first
inductor (14) and to a top terminal of a first
capacitor (11), wherein the first
capacitor (11) has a bottom terminal which is connected to the second terminal—emitter—of the first transistor (10) but also to a top terminal of a second
capacitor (12) having a bottom terminal being connected to ground;wherein the second transistor (20) has a first terminal—collector—which is connected to a reference
voltage, and a second terminal—emitter—which is connected to a first terminal of a second
current source (23), which second terminal is connected to ground, and a third terminal—base—connected to a first terminal of a second
inductor (14) and to a top terminal of a third capacitor (21), wherein the third capacitor (21) has a bottom terminal which is connected to the second terminal—emitter—of the second transistor (20) and also to a top terminal of a fourth capacitor (22) having a bottom terminal connected to ground;wherein the first and second inductors (14, 24) have a second terminal which are connected via a circuit (100) achieving variable
capacitance, so as to form a circuit connecting in series all passive components composing the LC tank, so as to achieve a variable
capacitance which can be used for performing a tuning of the oscillator, andwherein the second capacitor (12) and the fourth capacitor (22) are both connected to the physical ground thereby avoiding a 2nd
harmonic common mode oscillation that might dominate over the differential fundamental one and might destroy the first and the second transistors (10, 20).