Charge Pump Drain-Node Tracking for Low-Voltage PLL Stability
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Solution Overview
Problem
The reduced transistor headroom in charge pumps of phase-locked loops (PLLs) due to lower supply voltages leads to significant voltage changes during current path switching, causing charge sharing and injection issues that increase mismatch current, affecting the PLL's performance and power consumption.
Innovation Solution
A tracking circuit is used to stabilize the drain node voltages of the charge pump by selectively modifying the voltage levels in response to the tuning voltage, employing NMOS and PMOS transistors to maintain the voltage at the drain nodes equivalent to the tuning voltage, thereby reducing charge sharing and injection effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If supply voltage is reduced to increase battery life, then power consumption is reduced, but transistor headroom is insufficient causing charge pump mismatch
Solution Approach 1:
The tracking circuits proactively adjust the drain node voltages in response to tuning voltage changes before charge sharing and injection effects can occur. By monitoring the tuning voltage and preemptively modifying drain node voltages through NMOS and PMOS tracking circuits, the system prevents mismatch conditions rather than reacting to them after they arise.
Solution Approach 2:
The charge pump circuit employs feedback mechanisms where the tuning voltage is continuously monitored and used to control the tracking circuits. This feedback loop ensures that drain node voltages are dynamically adjusted to maintain proper transistor saturation conditions, thereby preventing mismatch current while operating at reduced supply voltages for lower power consumption.
2Reliability
If current is increased to the charge pump to compensate for mismatch, then charge pump performance is improved, but power consumption increases
Solution Approach 1:
Instead of increasing current magnitude, the invention changes the voltage parameters at the drain nodes through tracking circuits. By adjusting drain node voltages to maintain proper transistor saturation, the system achieves improved charge pump performance without the penalty of increased power consumption that would result from higher current levels.
3Loss of energy
If transistor headroom is reduced due to lower supply voltage, then power consumption is reduced, but voltage changes during switching cause charge sharing and injection effects
Solution Approach 1:
The tracking circuits act as intermediary elements between the tuning voltage and the drain nodes of the charge pump. These intermediary circuits translate tuning voltage changes into appropriate drain node voltage adjustments, thereby mediating the effect of low supply voltage and preventing harmful charge sharing and injection effects while maintaining low power operation.
Data Source
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AI summary
A method includes tracking a tuning voltage at a first circuit coupled to a first drain node of a first supply of a charge pump. The method also includes tracking the tuning voltage at a second circuit coupled to a second drain node of a second supply of the charge pump. The method further includes stabilizing a first voltage of the first drain node and a second voltage of the second drain node responsive to the tuning voltage.