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Single Stage Phase Corrections in a Multi-Stage Voltage Controlled Oscillator

IP.com Disclosure Number: IPCOM000116856D
Original Publication Date: 1995-Nov-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 4 page(s) / 67K

Publishing Venue

IBM

Related People

Greene, RA: AUTHOR

Abstract

In order to improve the rise time of small digital phase corrections in a differential stage ring Voltage Controlled Oscillator (VCO), the phase correction was applied only to some of the stages. The topology change results in higher performance without proportionately increasing the circuit power.

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Single Stage Phase Corrections in a Multi-Stage Voltage Controlled
Oscillator

      In order to improve the rise time of small digital phase
corrections in a differential stage ring Voltage Controlled
Oscillator (VCO), the phase correction was applied only to some of
the stages.  The topology change results in higher performance
without proportionately increasing the circuit power.

      The VCO is a differential ring oscillator composed of five
stages (Fig. 1), and the frequency is a function of the stage delay
which is controlled by the tail current: larger bias current means
shorter delay which translates to higher frequency, and smaller bias
current leads to longer stage delay which causes a lower frequency.
The frequency dependence on tail current is nearly linear; this
ensures the corrections are accurate and well-controlled over the
full range of center frequencies.

      In the past, we modulated the current on all of the delay
stages to alter the phase; this adds increased capacitance to the
correction path because the correction current must be divided by a
larger number and because the load due to the number of corrected
stages is increased.

      The phase corrections are generated in the small correction
block by sending pulses of current to temporarily increase or
decrease the frequency without altering the capacitor-controlled
center frequency.  The low-glitch switch shown in Fig. 2 is used to
provide the burst current; then, the small ph...