Patent ID: 8830007
Filing Date: 2014-09-09
Classification: H03B

Abstract:
1. An ultra-low phase noise voltage controlled oscillator comprising: a resonant circuit; an active circuit electrically connected to said resonant circuit and including at least one transistor connected in a Colpitts oscillator configuration; said transistor having a transistor input node, a positive feedback node, and a negative feedback node; a negative feedback path including a first negative feedback element and a second negative feedback element electrically connected in series; an oscillator output having a circuit path connected to said negative feedback node; said first negative feedback element being electrically connected to said negative feedback node; said second negative feedback element being electrically connected to said transistor input node; at least one of said negative feedback elements being a capacitor; said resonant circuit and said active circuit in combination functioning as an oscillator circuit; said resonant circuit includes: a first resonant circuit capacitor connected to said transistor input node; a second resonant circuit capacitor connected to said first resonant circuit capacitor and to said positive feedback node; a resonant circuit portion connected to said first resonant circuit capacitor; said resonant circuit portion further includes a first varactor and a second varactor, said varactors providing voltage-controlled capacitance and thereby permitting control over the resonant frequency of said oscillator; an inductor is connected between cathodes of said first varactor and said second varactor, one side of said inductor is connected to said cathodes of said first varactor and another side of said inductor is connected to said cathodes of said second varactor; and a first control voltage is applied to said cathodes of said first varactor and said second varactor, thereby controlling the capacitances of said varactors; and a second control voltage is applied to the anode of said first varactor, thereby permitting modulation of the capacitance of said first varactor; whereby phase noise present at said negative feedback node is fed at opposite phase back to said transistor input node, providing high levels of phase noise cancellation at said oscillator output; wherein odd harmonics present at said negative feedback node are subtracted from said odd harmonics present at said transistor input node and thereby reduce the odd harmonic power level present in said oscillator output, adding to the high levels of phase noise cancellation at said oscillator output.