Browse Prior Art Database

Detection and Correction of Phase Lock Failure in PLOs

IP.com Disclosure Number: IPCOM000075062D
Original Publication Date: 1971-Jul-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Johnson, HW: AUTHOR

Abstract

Many phase-locked VCO's (Voltage Controlled Oscillators) are susceptible to an off-frequency error condition from which they cannot recover under normal operating conditions without external intervention. The block diagram provides for detecting the error condition and effecting automatic recovery without external intervention.

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Detection and Correction of Phase Lock Failure in PLOs

Many phase-locked VCO's (Voltage Controlled Oscillators) are susceptible to an off-frequency error condition from which they cannot recover under normal operating conditions without external intervention. The block diagram provides for detecting the error condition and effecting automatic recovery without external intervention.

Control and reference signals on lines 10 and 11, respectively, out of phase detector 12 are trains of pulses. The reference pulse width is fixed and the control pulse width is identical to that of the reference under steady state phase-locked conditions. Hence, no net charge per cycle will be deposited on capacitive integrator, C14.

The DC charge on C14 will be that required to hold VCO 16 at the input frequency. In the event of an off-frequency condition, the charge on C14 and the corresponding error voltage will change by a significant amount. If the reference voltage applied to Schmitt triggers 17 and 18 is set at the nominal value of the error signal under locked conditions, the unlocked state may be detected. The Schmitt trigger output is then fed back to degate the appropriate current source 19 and 20 in the phase integrator, and thus to force the error voltage and consequently the VCO frequency back within lock-in range.

Note that hysteresis in the detector is necessary in order to restore the VCO within the lock-in range. The hysteresis ranges of the two Schmitt triggers overl...