Variable-Gain Clock Buffer for Sine-Wave Amplitude Control
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Solution Overview
Problem
Crystal oscillator output signals in integrated circuits often introduce harmonic frequency components due to non-linear buffer operation when amplitude deviates from nominal ranges, posing challenges in filtering, especially at higher frequencies like 50 MHz, where lower frequency harmonics are difficult to filter on-chip.
Innovation Solution
A clock signal generator with a variable gain buffer, peak detector, and control logic that adjusts the gain based on detected amplitude levels to maintain the output signal within a predefined range, preventing non-linear behavior and harmonic generation by incrementing, decrementing, or maintaining the counter count accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a buffer amplifier is used to provide drive capability for crystal oscillator output, then the output signal can drive required loads, but the buffer may operate in non-linear region and introduce harmonic frequency components
Solution Approach 1:
The patent implements a feedback control system where the amplitude of the buffer output signal is continuously monitored and fed back to adjust the buffer gain. The control logic compares the detected amplitude with target ranges and dynamically adjusts the gain control signal to maintain the buffer in linear operation region, thereby eliminating harmonic distortion while preserving drive capability.
Solution Approach 2:
The patent employs dynamic gain adjustment by making the buffer gain variable rather than fixed. The gain control signal is continuously modified based on real-time amplitude detection and control logic decisions, allowing the buffer to adapt its operating point and maintain linear operation across varying load conditions and input signal levels.
2Object-generated harmful factors
If filter is used to attenuate harmonics produced by buffer, then harmonic content can be reduced, but filtering becomes challenging at higher frequencies like 50 MHz where lower frequency harmonics are difficult to filter on-chip
Solution Approach 1:
The patent applies preliminary action by preventing harmonic generation at the source through proactive amplitude control. Instead of filtering harmonics after they are generated, the system continuously monitors the buffer output amplitude and adjusts the gain beforehand to keep the buffer operating in its linear region, thereby preventing non-linear distortion and harmonic production in the first place.
Solution Approach 2:
The patent converts the potentially harmful effect of buffer non-linearity into a beneficial control mechanism. By detecting amplitude deviations and using them as feedback signals to adjust gain, the system transforms what would be harmful distortion into useful information for maintaining optimal operation, eliminating the need for complex filtering.
3Adaptability or versatility
If crystal oscillator output amplitude varies due to environmental conditions and power supply voltages, then the oscillator can adapt to different operating conditions, but the buffer may operate non-linearly when amplitude deviates from nominal input range
Solution Approach 1:
The patent implements self-service through an automatic amplitude control system that monitors and adjusts the buffer operation without external intervention. The control logic continuously detects the output signal amplitude, compares it with target ranges, and autonomously adjusts the gain control signal to maintain linear operation, allowing the system to self-correct for environmental variations and power supply fluctuations.
Solution Approach 2:
The patent utilizes parameter changes by dynamically modifying the buffer gain parameter in response to amplitude variations. The gain control signal is adjusted as a variable parameter to compensate for changes in input amplitude caused by environmental conditions, ensuring the buffer remains in its linear operating region across different operating conditions.
Data Source
AI summary
A clock generator includes, in part, a buffer, a peak detector and a control logic. The buffer generates a clock output signal in response to receiving a clock signal and a feedback signal that controls the gain of the buffer. If the peak detector detects that the amplitude of the output signal is higher than the upper bound of the predefined range, the gain value applied to the variable buffer is decreased. If the peak detector detects that the amplitude of the output signal is lower than the lower bound of the predefined range, the gain value applied to the variable buffer to increased. If the peak detector detects that the amplitude of the output signal is within the predefined range, no change is made to the gain value applied to the variable buffer. The control logic generates the feedback signal in response to the peak detector's output signal.