Differential Divide-by-3 Prescaler for High-Frequency Clock Division
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Solution Overview
Problem
Existing prescalers face challenges in operating at high frequencies due to limitations in setup times and parasitic loading, which affect the generation of accurate divide by 3 clock signals.
Innovation Solution
A prescaler design utilizing differential clock inputs with separate logic blocks operating on inverse clock signals to generate a divide by 3 output, balancing parasitic elements and reducing setup time constraints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a conventional prescaler design is used, then the circuit structure is simple, but the operation frequency is limited due to setup time constraints and parasitic loading
Solution Approach 1:
The prescaler circuit is divided into multiple separate logic blocks (first logic block, second logic block, third logic block) that operate independently on different clock phases. This segmentation allows each block to be optimized for high-speed operation with reduced setup time requirements, enabling the overall circuit to operate at higher frequencies while maintaining functional simplicity through modular design.
Solution Approach 2:
The circuit utilizes differential clock inputs with inverse clock signals (CLK and CLK_bar) that operate in complementary phases. By distributing logic blocks across different clock phases and using periodic sampling at specific clock edges, the design achieves high-frequency operation by effectively multiplying the operating bandwidth while keeping each individual logic block's timing requirements manageable.
2Measurement precision
If a conventional prescaler design is used, then the setup time requirements are relaxed, but the duty cycle accuracy deteriorates at high frequencies
Solution Approach 1:
The circuit employs asymmetric logic block configurations where the first logic block generates a pulse at the rising edge and the second logic block generates a pulse at the falling edge of subsequent clock cycles. This asymmetric timing arrangement, combined with the third logic block's OR operation, ensures that the output pulse width accurately represents one complete clock cycle regardless of the high operating frequency, maintaining precise 50% duty cycle accuracy even at elevated speeds.
Solution Approach 2:
The first and second logic blocks are configured to generate their respective input pulses in advance at specific clock edges (rising edge and subsequent falling edge) before the final OR operation in the third logic block. This preliminary generation of precisely-timed pulses ensures that the duty cycle accuracy is established before the high-frequency operation amplifies timing errors, allowing accurate clock division at high speeds.
3Object-affected harmful factors
If a conventional prescaler design is used, then the parasitic loading is high, but the circuit implementation is simpler
Solution Approach 1:
By segmenting the prescaler into separate logic blocks that operate on different clock phases, the parasitic loading on any single logic block is reduced compared to a monolithic design operating at the same frequency. Each block sees lower effective loading because it processes signals at different times, allowing the use of smaller, lower-parasitic components while achieving the required overall functionality through the coordinated operation of multiple blocks.
Data Source
AI summary
Aspects relate to a divide by 3 prescaler for an integrated circuit. An apparatus includes a first logic block configured to generate a first input pulse at a rising edge of a clock signal, and a second logic block configured to generate a second input pulse after the first input pulse that ends at a falling edge of the clock signal. The falling edge is for a clock cycle subsequent to the rising edge. A third logic block is coupled to the first input pulse and the second input pulse and configured to generate a divide by 3 clock output.