Clock Buffer Bias Control for Duty Cycle Correction
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Solution Overview
Problem
Existing clock distribution circuitry faces challenges in accurately controlling the duty cycle of clock signals, especially in high-speed and low-power semiconductor devices, where precise duty cycle control is crucial for accurate operation and reduced energy consumption.
Innovation Solution
The proposed clock distribution circuitry employs low-pass filter and differential amplifier configurations to adjust DC bias signals across multiple buffers, ensuring that the duty cycles of complementary clock signals are synchronized and accurate, using cross-coupled inverter pairs and CMOS buffers with increasing transistor sizes along each clock path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If clock distribution circuitry is used in high-speed semiconductor devices, then operating speed is improved, but duty cycle accuracy deteriorates
Solution Approach 1:
The patent implements feedback circuitry that monitors the duty cycle of clock signals and dynamically adjusts DC bias voltages to correct duty cycle deviations. The feedback mechanism compares the actual duty cycle with a target value and generates correction signals that are applied to buffer stages, ensuring duty cycle accuracy is maintained even at high operating speeds where traditional fixed-bias approaches fail.
Solution Approach 2:
The patent changes the DC bias parameters of buffer stages dynamically based on detected duty cycle errors. By adjusting the DC bias voltage levels in response to measured duty cycle deviations, the circuit adapts its operating parameters to maintain accuracy. This parameter adjustment allows the circuit to compensate for speed-related distortions without sacrificing performance.
2Measurement precision
If DC bias signals are adjusted to correct duty cycle, then duty cycle accuracy is improved, but signal variation and instability worsen
Solution Approach 1:
The feedback circuitry continuously monitors clock signal characteristics and makes incremental DC bias adjustments only when duty cycle deviations are detected. This closed-loop approach ensures that DC bias signals remain stable during normal operation while providing corrective adjustments only when needed, thus maintaining both accuracy and stability.
Solution Approach 2:
The patent applies DC bias adjustments selectively and partially - only to the extent necessary to correct measured duty cycle errors. Rather than continuously varying DC bias signals or applying excessive correction, the circuit makes minimal necessary adjustments, preserving signal stability while achieving the required duty cycle accuracy.
3Measurement precision
If duty cycle correction is implemented, then duty cycle control accuracy is improved, but device complexity increases
Solution Approach 1:
The patent integrates duty cycle correction functionality into existing clock distribution buffer stages, allowing these multi-functional elements to both transmit clock signals and perform duty cycle adjustment. The same buffer circuitry that distributes clocks also receives DC bias control signals for duty cycle correction, eliminating the need for separate correction circuits and reducing overall system complexity.
Solution Approach 2:
The patent merges the duty cycle correction mechanism with the clock distribution network by integrating DC bias control circuitry directly into the buffer stages. The control circuitry is combined with the clock path, allowing duty cycle adjustment to occur within the existing distribution infrastructure rather than requiring additional standalone correction modules.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables precise control of duty cycles, achieving a large duty cycle correction range with minimal DC bias signal variation, thereby enhancing the accuracy and power efficiency of clock signals in high-speed semiconductor devices.
Implementation Method 1
The control circuitry may comprise low-pass filter circuitry configured to: receive the first output clock signal or another clock signal from along the first clock path and output the first measurement signal, the first measurement signal being indicative of a DC-level of the first output clock signal
Implementation Method 2
The control circuitry may comprise differential amplifier circuitry configured to: receive the first measurement signal and a second measurement signal and generate first and second DC bias signals based on a difference between the first measurement signal and the second measurement signal
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
Clock distribution circuitry (10) configured for duty cycle control, the circuitry comprising: a plurality of buffers (20, 40) connected in series along a clock path having an input node (CLKIN) and an output node (CLKOUT), each of the buffers having an input terminal and an output terminal, the input terminal being connected to the clock path via a corresponding AC coupling capacitor, and the clock path configured to receive an input clock signal at the input node and output an output clock signal at the output node, the output clock signal having an output duty cycle; and control circuitry (200) connected to apply a DC bias signal to the input terminal of each of the plurality of buffers, wherein the control circuitry is configured to: obtain a measurement signal indicative of the output duty cycle; and control the DC bias signals, based on a difference between the measurement signal and a reference signal, so as to control the output duty cycle.