Unity Gain Dc Amplifier for Integrated, Phase-Locked Loop Circuits
Original Publication Date: 1989-Apr-01
Included in the Prior Art Database: 2005-Jan-27
The circuit described in this article matches the impedance between the output of a low-pass loop filter and the input of a voltage-controlled oscillator (VCO) while maintaining unity gain over the operating range of the VCO. The voltage-controlled oscillator (VCO) generator shown the in figure is used in a phase-locked loop circuit to match impedances between the output of the low-pass loop filter and the input of the voltage-controlled oscillator. It is required that the voltage at the input node 1 be equal to the voltage at the output node 2 over the operating range of the VCO, e.g., unity gain. The loop filter cannot drive the VCO directly because it cannot supply sufficient current, but the VCO generator meets this current requirement through the use of an emitter-follower output.