Cadence Ams Design India Private Limited

Rishi Mathur

Prasenjit Bhowmik

Sriram Ganesan

Sunil Rajan

Jyoti Arya

The main feedback loop of a PLL/DLL receives a reference clock and an output clock as inputs, and operates to achieve one or both of a phase and a frequency lock of the output clock with respect to the reference clock. The PLL/DLL includes an RS-latch connected to receive the output clock and the reference clock. The RS-Latch generates a digital output representing a phase difference between the reference clock and the output clock. A correction block in the PLL/DLL receives the digital output and adjusts an electrical characteristic of the main feedback loop by a value that is based on a polarity of the digital output. Effects of offset-errors in the PLL/DLL are thereby minimized or corrected for.

Correcting for offset-errors in a PLL/DLL

A relaxation oscillator circuit with reduced sensitivity of oscillation frequency to comparator delay variation includes a first current source that generates charging current, a second current source coupled to the first current source to generate reference voltage, a resistor coupled to the second current source to enable generation of the reference voltage, a capacitor coupled to the first current source that is charged based on the charging current, a comparator responsive to voltage corresponding to the capacitor and the reference voltage to generate output voltage, a peak detector coupled to the capacitor to generate peak voltage, an error detector coupled to the peak detector and the second current source to generate an error based on the peak voltage and the reference voltage, and a controller coupled to the error detector to control one of the charging current, offset voltage input to the comparator, and capacitance of the capacitor.

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Delhi, India

Rishi Mathur