Comparator Input Reversal in RC Oscillators for Clock Drift Stability

The patent applies input reversal to the comparator, where the inputs are periodically swapped every other clock cycle. This inversion technique causes the comparator offset error to manifest with opposite polarity in alternating cycles, enabling cancellation when averaged. The comparator receives inverted inputs during alternate cycles, transforming the systematic drift error into a canceling oscillating error, thus maintaining clock frequency stability while using simple on-chip RC components.

The patent implements a feedback mechanism where the comparator output feeds back to control the switching of capacitor charging/discharging, and simultaneously the inputs to the comparator are reversed based on the clock phase. This closed-loop operation with periodic input reversal creates a self-correcting system where offset drift effects are automatically compensated over cycles, maintaining stable frequency without external trimming while keeping the circuit simple and manufacturable.

Rather than attempting to trim or compensate for offset through complex manufacturing processes, the patent applies input reversal to the comparator where the same offset error that causes drift is systematically inverted every other cycle. This transforms the problematic drift into a canceling pattern, eliminating long-term instability without requiring complex trimming procedures or increasing manufacturing complexity.

The patent converts the harmful comparator offset drift into a beneficial canceling effect by periodically reversing the comparator inputs. The same offset error that would normally cause frequency drift is now caused to produce equal and opposite errors in alternating cycles, which cancel out over time. This transforms the harmful drift mechanism into a self-correcting feature, achieving long-term stability without additional trimming complexity.

The patent eliminates the need for external crystal oscillators by applying input reversal to the on-chip comparator. This inversion technique causes offset errors to cancel out over alternating cycles, achieving the same frequency stability that would otherwise require external crystals. The solution maintains simplicity by keeping all components on-chip while achieving the reliability normally requiring external oscillators.

The patent makes the on-chip RC oscillator self-correcting through periodic input reversal to the comparator. The circuit automatically compensates for its own offset drift errors without requiring external components or complex trimming. This self-service mechanism enables the simple on-chip oscillator to achieve the frequency stability previously only attainable with external crystal oscillators, eliminating the need for additional complexity.