Ring Oscillator Ramp Modulation for Lower EMI Clocking
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Solution Overview
Problem
Charge pump circuits generate undesirable electro-magnetic emissions due to switching currents, and existing solutions like closed-loop phase-locked loop architectures are not feasible in all applications due to the need for a reference clock.
Innovation Solution
An open-loop frequency modulation oscillator circuit using a ring oscillator and a ramp generator to control the clock frequency, eliminating the need for a reference clock and reducing emissions by spreading noise across a wide band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a closed-loop phase-locked loop architecture is used to reduce electromagnetic emissions, then emissions are reduced, but the device complexity increases due to the need for a reference clock
Solution Approach 1:
The patent extracts and removes the reference clock component from the phase-locked loop architecture, converting it to an open-loop frequency modulation system. This eliminates the need for a reference clock while maintaining the frequency modulation capability that spreads spectral energy and reduces electromagnetic emissions at specific frequencies.
Solution Approach 2:
The patent inverts the conventional closed-loop PLL approach by using an open-loop frequency modulation architecture. Instead of using feedback control with a reference clock, it directly modulates the oscillator frequency using a ramp signal, achieving emission reduction through spectral spreading without the complexity of closed-loop control.
2Object-affected harmful factors
If a ring oscillator with ramp generator is used to reduce emissions, then electromagnetic emissions are reduced by spreading noise, but the clock timing precision deteriorates
Solution Approach 1:
The patent changes the timing parameters dynamically by applying frequency modulation through a ramp generator. The oscillator frequency is varied over time according to a ramp signal, which spreads the spectral energy of the clock signal. This parameter variation reduces peak emissions while the modulation is designed to maintain acceptable timing precision for applications with lax specifications.
3Object-affected harmful factors
If frequency modulation is applied to the oscillator circuit, then electromagnetic emissions are reduced, but the device complexity increases due to additional circuit components
Solution Approach 1:
The patent merges the frequency modulation function directly into the oscillator circuit by coupling the ramp generator output to the power terminal of the ring oscillator. This integration achieves frequency modulation using minimal additional components, combining the oscillator and modulation functions in a compact configuration that reduces emissions without significant complexity increase.
Data Source
AI summary
An oscillator circuit includes a ring oscillator and a ramp generator. The ring oscillator includes a first inverter and a second inverter. The first inverter has and a first inverter input, a first inverter output, and a first power terminal. The second inverter has a second inverter input, a second inverter output, and a second power terminal. The second inverter input is coupled to the first inverter output and the second inverter output is coupled to the first inverter input. The ramp generator circuit has a ramp output coupled to the first power terminal and the second power terminal.