Micro Linear Corporation

Robert Cox

Gwilym Francis Luff

Gwilyn Luff

A fuse-trimmed tank circuit for an integrated voltage-controlled oscillator (VCO). The tank circuit includes an L-C portion; a cross-coupled pair of transistors, whose collectors are coupled to the L-C portion; a capacitor coupled across the emitters of the cross-coupled pair of transistors; and a pair of resistors, where each resistor is coupled between a corresponding one of the emitters and a ground node. This oscillator circuit provides improved performance over prior oscillator circuits. A technique for trimming the VCO is utilized to adjust its center frequency. Capacitance for the L-C portion of the tank circuit is provided by one or more varactor diodes. When the VCO is operational, the varactors are reverse biased and, thus, act as capacitive elements. One or more of the varactors has an associated fuse coupled in series with the corresponding varactor. To trim the center frequency of the VCO, the capacitance of the L-C portion is adjusted by selectively blowing the fuses. To blow a fuse, a dc voltage is applied to forward bias the corresponding varactor such that the resulting current is sufficiently high to blow the fused. In the preferred embodiment, the varactors are arranged in pairs, where each varactor of the contributes to the capacitance of one or the other sides of the tank circuit for maintaining its symmetry. The two fuses associated with each varactor of the pair are preferably blown together. Preferably, the VCO is integrated into an integrated circuit.

Fuse-trimmed tank circuit for an integrated voltage-controlled oscillator

A method and apparatus for modulation of a voltage-controlled oscillator (VCO). The VCO receives a tuning control voltage for adjusting a center frequency of an output periodic signal formed by the VCO. In addition, the VCO receives a modulation control voltage for modulating the output periodic signal by a content-carrying signal according to frequency modulation techniques. A frequency deviation obtained in the output periodic signal in response to changes in the modulation control voltage is linearized by forming the modulation control voltage as the result of a linear correction polynomial. A linear correction circuit forms the modulation control voltage. More particularly, a first amplifier having a gain of K receives the tuning control voltage. A first summing block then receives the output of the first amplifier and adds the constant K . A second amplifier having a gain of m receives the content-carrying signal. An output of the second amplifier and an output of the first summing block are summed by a second summing block. An output of the second summing block forms the modulation control voltage. The present invention results in a more linear relationship between changes in a modulation control voltage applied to the VCO and frequency deviation in the VCO output signal in comparison to prior techniques.

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Little Abington, United Kingdom

Robert Cox