Programmable Frequency Divider With 50% Duty Cycle at Multi-GHz Speeds
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Solution Overview
Problem
Designing a programmable frequency divider that operates at multi-GHZ clock frequencies with a 50% duty cycle is challenging due to the complexity and increased power requirements associated with counting in half-cycles, especially when the division ratio is odd.
Innovation Solution
A frequency divider architecture that includes a multiplexer, a multi-modulus divider, and a divide-by-two counter with duty cycle correction logic, alternately generating output pulses at M and M+LSB clock cycles to achieve a 50% duty cycle without requiring complex half-cycle counting, using a simplified architecture and reduced power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a frequency divider counts in half-cycles to achieve 50% duty cycle, then the output duty cycle is 50%, but the device complexity increases and power consumption increases
Solution Approach 1:
The frequency division function is segmented into two independent parts: a multi-modulus divider that handles the integer division by M, and a separate duty cycle correction module that adjusts the output pulse width. This segmentation allows the main division logic to operate simply while the duty cycle is corrected independently, reducing overall complexity.
Solution Approach 2:
An intermediary duty cycle correction circuit is introduced between the multi-modulus divider and the final output. This intermediary component receives the divided clock signal and actively adjusts its pulse width to ensure 50% duty cycle, isolating the complex duty cycle control from the main frequency division logic.
2Manufacturing precision
If a frequency divider counts in half-cycles to achieve 50% duty cycle, then the output duty cycle is 50%, but the power consumption increases
Solution Approach 1:
The power-consuming duty cycle adjustment function is segmented from the main frequency division operation. The multi-modulus divider operates with simple integer division requiring minimal power, while the duty cycle correction module handles only the pulse width adjustment, separating the power-intensive operations from the core division function.
Solution Approach 2:
The duty cycle correction is implemented using periodic toggling of the output signal based on a predetermined number of clock cycles. Instead of continuous complex counting, the system uses periodic action to extend or truncate output pulses, reducing the continuous power consumption associated with half-cycle counting mechanisms.
3Speed
If a frequency divider operates at high input frequencies, then the clock speed is high, but achieving 50% duty cycle becomes difficult
Solution Approach 1:
The system performs preliminary frequency division by the integer value M in the multi-modulus divider before the final duty cycle adjustment stage. This preliminary action reduces the input frequency to a manageable level where precise duty cycle control can be easily implemented, avoiding the difficulty of achieving 50% duty cycle directly at high input frequencies.
Solution Approach 2:
An intermediary duty cycle correction stage is introduced after the high-speed multi-modulus division. This intermediary component receives the high-frequency divided signal and applies precise pulse width control to ensure 50% duty cycle, separating the high-speed division function from the precision duty cycle adjustment function.
4Device complexity
If a frequency divider uses simplified architecture without half-cycle counting, then the device complexity is reduced, but the output duty cycle may not be 50%
Solution Approach 1:
A dedicated duty cycle correction intermediary is placed in the signal path to ensure 50% duty cycle output. This intermediary component actively monitors and adjusts the output pulse width based on the divided clock signal, guaranteeing precise duty cycle control without requiring the main frequency division logic to be complex.
Solution Approach 2:
The system changes the parameter being controlled from the division ratio to the output pulse width. Instead of using complex half-cycle counting to achieve 50% duty cycle, the system maintains simple division logic and adjusts only the pulse width parameter of the output signal, achieving the same effect with simpler architecture.
Data Source
AI summary
A frequency divider includes a multiplexer having a first input terminal coupled to receive a first value M and a second input terminal for receiving a second value that is M+LSB, the multiplexer is configured to alternately output the first value M and the second value. The frequency divider includes a multi-modulus divider coupled to the multiplexer for receiving the output of the multiplexer, the multi-modulus divider operable to alternately generate an output pulse at M input clock cycles and at M+LSB clock cycles. A divide-by-two counter having an input coupled to the output of the multi-modulus divider, is operable to divide the output of the multi-modulus divider to generate a divided clock signal having a frequency of N, where N is equal to 2M+LSB. Duty cycle correction logic is coupled to the output of the divide-by-two counter and is configured to correct the duty cycle of the divided clock signal to a fifty percent duty cycle when N is odd.