PLL Charge Pump Tracking Circuit for Low Phase Noise
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Solution Overview
Problem
Prior charge pumps face limitations due to having almost the full supply voltage across output transistors, which restricts their use with smaller geometry semiconductor devices, leading to increased phase noise and decreased VCO performance.
Innovation Solution
A charge pump design incorporating a first and second pass transistor, coupled with controlled current sources and a tracking circuit that regulates voltages across these transistors, ensuring the potential between well voltages is substantially the same as the charge pump output, allowing for efficient voltage control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If smaller geometry semiconductor devices are used in charge pump circuits, then device integration and VCO frequency range are improved, but phase noise increases and VCO performance decreases
Solution Approach 1:
The patent changes the voltage parameters across the pass transistors by introducing a tracking circuit that dynamically adjusts well voltages. This allows smaller geometry devices to operate with controlled voltage drops, maintaining low phase noise while achieving extended frequency range through improved device matching and reduced stress effects.
2Power
If full supply voltage is applied across output transistors, then charge pump output voltage range is achieved, but transistor voltage stress increases limiting supply voltage design
Solution Approach 1:
The tracking circuit acts as an intermediary that dynamically adjusts the well voltages of the pass transistors. This mediator ensures that the voltage difference across each transistor remains within safe operating limits while still allowing the charge pump to achieve its full output voltage range, effectively decoupling the output swing from the transistor stress.
3Device complexity
If voltage across pass transistors is not regulated, then circuit complexity is reduced, but device matching and phase noise performance deteriorate
Solution Approach 1:
The tracking circuit implements a feedback mechanism that continuously monitors the charge pump output voltage and dynamically adjusts the well voltages of the pass transistors accordingly. This feedback ensures that the voltage across each transistor remains balanced and within optimal ranges, improving device matching and reducing phase noise while adding controlled complexity to the circuit.
Data Source
AI summary
Disclosed is an apparatus and method for controlling the voltage drop across output transistors in a charge pump.