Frequency-Dependent Delay Cell for Wide DLL Clock Range
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Solution Overview
Problem
Conventional delay cells do not provide a wide enough delay range to support more than 10 times variation in clock frequencies, limiting their application in delay locked loops and duty cycle corrector circuits.
Innovation Solution
A current starved delay cell design incorporating variable current sources and a control circuit with NMOS transistors, coupled with a capacitor, allows for frequency-dependent current scaling and control voltage variation to achieve a wider delay range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional delay cells are used, then the circuit is simple, but the delay range is limited and cannot support more than 10x variation in clock frequencies
Solution Approach 1:
The delay cell employs dynamic current sources that automatically adjust their output current based on the input clock frequency. The current sources are designed to provide frequency-dependent current scaling, where the current magnitude varies proportionally with the input frequency, enabling the delay range to adapt dynamically across more than 10x frequency variations without manual intervention
Solution Approach 2:
The invention changes the operating parameters of the delay cell by introducing frequency-dependent current scaling. The current sources modify their output current parameter in response to frequency changes, and the control circuit adjusts the delay parameter through control voltage swings. This parameter adaptation enables the delay range to expand beyond conventional limits while managing circuit complexity through systematic design
2Adaptability or versatility
If conventional delay cells are used, then the control voltage swing is limited, but the delay range is insufficient for wide frequency variations
Solution Approach 1:
The delay cell incorporates frequency-dependent current scaling that provides automatic feedback adjustment. The current sources monitor the input frequency and adjust their output current accordingly, creating a feedback mechanism that enables larger control voltage swings to be effectively utilized across different frequency ranges, thereby expanding the delay range without proportionally increasing energy consumption
Solution Approach 2:
The control circuit parameters are designed to change in response to frequency variations. The control voltage swing parameter is optimized to work effectively with the frequency-dependent current scaling, allowing larger voltage swings at lower frequencies and smaller swings at higher frequencies, which expands the overall delay range while managing energy consumption across the frequency spectrum
Data Source
AI summary
A delay cell with a wider delay range is provided. The delay cell employs frequency dependent current source to generate the majority of the delay of the cell, while a control circuit (which is generally a current source that is controlled by a control voltage) provides additional delay. Thus, the delay cell provided here can be used to improve the performance of delay locked loops (DLLs) and other circuits.