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Phase Detecting Voltage Controlled Oscillator

IP.com Disclosure Number: IPCOM000085341D
Original Publication Date: 1976-Mar-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 28K

Publishing Venue

IBM

Related People

Elliott, WY: AUTHOR

Abstract

Described is a phase detecting voltage-controlled oscillator that functions as a complete first order phase-locked loop. Except for the inversion of the input signal to current source 10, by a 180 degree phase shifter 12, the circuit is exactly like that of a conventional balanced voltage-controlled oscillator. Thus, it is this inversion of the input signal that enables the system to perform the phase detecting function and operate as a complete first order phase-locked loop. Current sources 10 and 14 can either be linear current sources or current switches depending on whether or not linear operation is desired. As depicted in the figure, switched operation is assumed.

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Phase Detecting Voltage Controlled Oscillator

Described is a phase detecting voltage-controlled oscillator that functions as a complete first order phase-locked loop. Except for the inversion of the input signal to current source 10, by a 180 degree phase shifter 12, the circuit is exactly like that of a conventional balanced voltage-controlled oscillator. Thus, it is this inversion of the input signal that enables the system to perform the phase detecting function and operate as a complete first order phase-locked loop. Current sources 10 and 14 can either be linear current sources or current switches depending on whether or not linear operation is desired. As depicted in the figure, switched operation is assumed.

The input signal, as shown, represents a binary-coded logic signal. Because of the signal inversion to current source 10, the current sources are alternately on. Assuming that current source 10 is on, I+i is approximately equal to 2I, and I- i is approximately equal to zero (I represents static current and i represents AC current).

Thus, as depicted, the upper input of relaxation oscillator 16 is on allowing a current of 2I to flow therefrom. Consequently, the lower input of relaxation oscillator 16 is open circuited since current source 10 is off. Accordingly, as aforementioned, the current I-i, through timing capacitor CT, is zero. VT is the threshold voltage of relaxation oscillator 16, and, as depicted, has a polarity of minus/plus with respect to...