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Unity Gain Dc Amplifier for Integrated, Phase-Locked Loop Circuits

IP.com Disclosure Number: IPCOM000034798D
Original Publication Date: 1989-Apr-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Ewen, JF: AUTHOR [+3]

Abstract

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.

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Unity Gain Dc Amplifier for Integrated, Phase-Locked Loop Circuits

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. Since the input and output voltages of the VCO generator must always be the same, the transistor pair T2 and T3 operate in the common mode. Resistors R2 and R3 are made equal, each having twice the value of resistor R4, so that a common-mode voltage applied to the bases of T2 and T3 will result in approximately unity voltage gain at node 3. If a voltage dV appears at input 1 and output 2, node 4 moves by the same amount since R2 and R3 resistors each contribute half of the resulting change in current through R4; i.e., half the current through twice the resistance causes node 3 to move by the amount -dV. Transistor...