Charge Pump Drain Voltage Tracking for Low-Headroom PLLs
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Solution Overview
Problem
The performance and reliability of phase-locked loops (PLLs) in mobile devices are affected by mismatch currents in charge pumps due to reduced transistor headroom caused by lower supply voltages, leading to increased charge sharing and injection effects on the tuning voltage supplied to voltage-controlled oscillators (VCOs).
Innovation Solution
The implementation of tracking circuits that stabilize the drain node voltages of charge pumps by selectively modifying the voltage levels in response to the tuning voltage, using n-type and p-type metal oxide semiconductor transistors to maintain voltage stability during switching, thereby reducing charge sharing and injection issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If supply voltage is reduced to increase battery life, then power consumption decreases, but transistor headroom is insufficient causing charge pump mismatch current
Solution Approach 1:
The patent introduces an intermediary circuit between the charge pump and the VCO that includes tracking circuits and voltage stabilization circuits. This intermediary circuit compensates for the mismatch current by dynamically adjusting the charging and discharging paths to maintain equal voltage levels at the drain nodes, thereby eliminating charge sharing and injection effects while operating at reduced supply voltages.
Solution Approach 2:
The patent changes the voltage parameters dynamically by using tracking circuits that monitor the tuning voltage and adjust the drain node voltages accordingly. The voltage stabilization circuit modifies the charging and discharging voltage levels based on the instantaneous operating conditions, ensuring that the charge pump maintains balanced operation across the entire tuning range despite reduced supply voltage headroom.
2Reliability
If current to charge pump is increased to reduce mismatch, then charge pump performance improves, but power consumption increases
Solution Approach 1:
Instead of increasing current, the patent changes the voltage parameters by dynamically adjusting the drain node voltages through tracking circuits. This parameter change approach maintains proper transistor saturation and reduces mismatch current without increasing power consumption, as the adjustment is achieved through voltage level modulation rather than current scaling.
Solution Approach 2:
The patent replaces the conventional approach of increasing current (analogous to increasing mechanical force) with a voltage-based control mechanism. The tracking circuits use voltage feedback to dynamically balance the charge pump operation, substituting a more efficient electrical control mechanism for the brute-force current increase approach.
3Use of energy by moving object
If transistor headroom is reduced for lower supply voltage, then power efficiency improves, but charge sharing and injection effects increase
Solution Approach 1:
The patent introduces an intermediary voltage stabilization circuit that acts as a buffer between the reduced-headroom transistors and the charge pump output. This intermediary circuit actively compensates for charge sharing and injection effects by dynamically adjusting the drain node voltages to maintain balanced charging and discharging paths, thereby eliminating harmful effects while operating at efficient low voltages.
Solution Approach 2:
The tracking circuits perform preliminary anti-action by anticipating and counteracting charge sharing and injection effects before they manifest as errors. The circuits continuously monitor the tuning voltage and preemptively adjust the drain node levels to prevent mismatch current generation, thereby neutralizing harmful effects before they can degrade PLL performance.
Data Source
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.