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Voltage controlled oscillator including voltage controlled delay circuit with power supply noise isolation
| Details |
Inventors: Zhang, Zhongxuan; Du, He;
Assignee: Cirrus Logic, Inc. (Fremont, CA)
Primary Examiner: Grimm; Siegfried H.
Assistant Examiner:
Attorney, Agent or Firm: Majestic, Parsons, Siebert & Hsue
A VCO includes a ring oscillator formed by connecting a plurality of voltage controlled inverting delay cells together, and a plurality of transistors for providing control voltages to the plurality of voltage controlled inverting delay cells. Preferably, each transistor has a drain connected to a reference voltage, and a source connected to a voltage controlled inverting delay cell paired to that transistor. Consequently, each transistor acts as a source-follower so that it provides a control voltage to its corresponding voltage controlled inverting delay cell which follows a control voltage driving its gate, thereby isolating the control voltage provided to its corresponding voltage controlled inverting delay cell from power supply noise. |
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DETAILED DESCRIPTION Accordingly, one object of the present invention is a VCO which is less sensitive than prior art VCOs to power supply noise.
Another object of the present invention is a delay circuit useful in a VCO which provides good power supply noise isolation.
Still another object of the present invention is a VCO which is of simple construction and easily manufacturable.
These and additional objects are accomplished by the various aspects of the present invention, wherein briefly stated, one aspect of the present invention is a voltage controlled delay circuit with power supply noise isolation, comprising: delay means responsive to an input voltage for varying the delay of a signal propagating through the delay means; and a transistor having a drain connected to a power supply, a gate connected to a control voltage, and a source providing the input voltage to the delay means such that the input voltage follows the control voltage and is isolated from noise on the power supply connection to the transistor.
Another aspect of the present invention is a voltage controlled delay circuit included in a voltage controlled oscillator, wherein the voltage controlled delay circuit comprises: delay means responsive to an input voltage for varying the delay of a pair of signals propagating through the delay means; and a transistor having a drain connected to a power supply, a gate connected to a control voltage, and a source providing the input voltage to the delay means such that the input voltage follows the control voltage and is isolated from noise on the power supply connection to the transistor.
Still another aspect of the present invention is a voltage controlled oscillator with power supply noise isolation comprising a plurality of transistor and voltage controlled delay cell pairs, wherein individual ones of the transistors have a gate connected to a control voltage, a drain connected to a power supply, and a source connected to a voltage controlled delay cell paired to the individual one transistor for providing an input voltage to the voltage controlled delay cell such that the input voltage follows the control voltage and is isolated from noise on the power supply connection to the individual one transistor
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