Abstract: A circuit provides an output signal for modulating the oscillation frequency of a voltage-controlled oscillator (VCO) in response to a control signal where the VCO includes a first voltage-controlled variable capacitance device for varying the oscillation frequency of the VCO according to the output signal. The circuit includes a charge pump providing a charge current to a first node, a first capacitor having a fixed capacitance and a second capacitor both coupled to the first node, and an amplifier providing the output signal. The second capacitor includes a second voltage-controlled variable capacitance device having the same device structure as the first voltage-controlled variable capacitance device of the VCO. In operation, a voltage change at the first node is generated in response to the charge current and the output signal causes the same voltage change to be applied across the first voltage-controlled variable capacitance device of the VCO.

Abstract: A circuit provides an output signal for modulating the oscillation frequency of a voltage-controlled oscillator (VCO) in response to a control signal where the VCO includes a first voltage-controlled variable capacitance device for varying the oscillation frequency of the VCO according to the output signal. The circuit includes a charge pump providing a charge current to a first node, a first capacitor having a fixed capacitance and a second capacitor both coupled to the first node, and an amplifier providing the output signal. The second capacitor includes a second voltage-controlled variable capacitance device having the same device structure as the first voltage-controlled variable capacitance device of the VCO. In operation, a voltage change at the first node is generated in response to the charge current and the output signal causes the same voltage change to be applied across the first voltage-controlled variable capacitance device of the VCO.