Digital Phase Mixer With Break-Before-Make Clock Switching
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Solution Overview
Problem
Conventional phase locked loops (PLLs) and delay locked loops (DLLs) with digital phase mixers face issues of 'fighting' conditions due to timing gaps between early and late input signals, leading to short circuit currents and reduced reliability, power dissipation, and limited frequency range.
Innovation Solution
The implementation of a one-bit digital phase mixer with distributed break-before-make drivers, feedback loops, and early turn-off, along with separate pull-up and pull-down paths, controls the slew rates and duty cycle of clock signals to prevent 'fighting' conditions and enhance frequency performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional digital phase mixers are used, then the circuit structure is simple, but fighting conditions occur due to timing gaps between early and late input signals, leading to short circuit currents and reduced reliability
Solution Approach 1:
The phase mixer is divided into multiple independent one-bit phase mixers, each handling a specific weight. This segmentation eliminates fighting conditions by ensuring that only one phase mixer is active at a time through the enable signal mechanism, thereby improving reliability without significantly increasing overall circuit complexity.
Solution Approach 2:
The enable signal is generated in advance based on the thermometer code before the clock signals are processed. This preliminary action ensures that the appropriate phase mixer is already enabled and ready to receive clock signals, preventing timing gaps and fighting conditions that would otherwise reduce reliability.
2Productivity
If conventional phase mixers operate at high frequencies, then productivity is improved, but fighting conditions increase short circuit currents and power dissipation
Solution Approach 1:
The phase mixer dynamically adjusts which phase mixer is active based on the thermometer code, allowing operation across a wide frequency range. The dynamic enabling mechanism ensures that only the necessary phase mixer is active at any given time, reducing power dissipation even at high frequencies where productivity is improved.
Solution Approach 2:
The invention changes the operational parameters by using separate enable signals for each phase mixer based on thermometer codes. This parameter change allows the system to operate efficiently across a wide frequency range while minimizing power dissipation by ensuring that only one phase mixer is actively processing signals at any moment.
3Reliability
If conventional phase mixers are used, then the circuit structure is simple, but timing gaps between early and late input signals cause fighting conditions
Solution Approach 1:
The enable signal mechanism serves multiple functions: it selects which phase mixer is active, prevents timing gaps between early and late signals, and eliminates fighting conditions. This multi-functionality improves reliability without requiring separate control circuits for each problem, thereby limiting the increase in device complexity.
4Adaptability or versatility
If the number of phase mixers is increased to cover more frequencies, then frequency range is expanded, but device complexity increases
Solution Approach 1:
The phase mixer is segmented into multiple one-bit phase mixers, each handling a specific weight. This segmentation allows the system to cover a wide frequency range by selectively enabling different segments based on the thermometer code, without requiring a fully complex multi-phase-mixer design for all frequencies simultaneously.
Solution Approach 2:
Instead of designing a complex phase mixer that handles all frequencies simultaneously, the invention uses partial action by enabling only the necessary one-bit phase mixers based on the thermometer code. This approach expands the frequency range while keeping the active circuit complexity low at any given moment.
Data Source
AI summary
The present disclosure is directed to a unit phase mixer in combination with an input buffer. The unit phase mixer has a pull-up path for pulling an output terminal up to a first voltage. The pull-up path has a first transistor responsive to a first enable signal and a series connected second transistor responsive to a first clock signal. The unit phase mixer has a pull-down path for pulling the output terminal down to a second voltage. The pull-down path has a third transistor responsive to a second clock signal and a series connected fourth transistor responsive to a second enable signal. The input buffer skews the first and second clock signals by different amounts to enable a break-before-make method of operation so that the first voltage is not connected to the second voltage. The unit phase mixer can be used as a building block in more complex mixers which may include the ability to weight the input clocks as well as providing feed-forward paths for certain of the signals. Because of the rules governing abstract, this abstract should not be used to construe the claims.