Charge Pump Feedthrough Suppression via Gate Coupling
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Solution Overview
Problem
Conventional charge pumps in phase-locked loops (PLLs) suffer from feedthrough effects, leading to mismatched charging and discharging currents, increased output spurs, and reduced output voltage range, which complicates signal synchronization and frequency generation.
Innovation Solution
A capacitor is introduced between the gate terminals of the switch transistor and the current source transistor to create a feedback path that opposes existing feedback, reducing feedthrough and allowing for decreased decoupling capacitance, thereby reducing die area and improving charge pump performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional charge pump design is used, then the circuit structure is simple, but feedthrough effect causes current mismatch and increased spurs
Solution Approach 1:
A feedthrough suppression capacitor is introduced as an intermediary component between the switch transistor gate and current source transistor gate. This capacitor mediates the voltage transmission, blocking the direct feedthrough path while allowing controlled charge transfer, thereby suppressing the harmful feedthrough effect without compromising current matching accuracy
Solution Approach 2:
The feedthrough suppression capacitor creates a feedback mechanism where voltage changes at the switch transistor gate are coupled back to the current source transistor gate. This feedback path compensates for voltage variations and maintains accurate current matching by dynamically adjusting the current source transistor gate voltage in response to switch transistor gate voltage changes
2Object-generated harmful factors
If decoupling capacitance is increased to reduce feedthrough, then feedthrough suppression improves, but die area increases
Solution Approach 1:
The feedthrough suppression capacitor serves as a compact intermediary that provides effective feedthrough suppression without requiring large decoupling capacitance. By placing this capacitor strategically between gate terminals, the design achieves feedthrough suppression with minimal area overhead, avoiding the need for large decoupling capacitors that would increase die area
Solution Approach 2:
The invention changes the capacitance parameter distribution by introducing a small feedthrough suppression capacitor rather than relying on large decoupling capacitance. This parameter change allows effective feedthrough suppression while maintaining compact die area, as the suppression capacitor requires significantly less area than traditional large decoupling capacitors would require
3Adaptability or versatility
If current source transistor operates in saturation region, then charge pump output voltage range increases, but feedthrough effect becomes more pronounced
Solution Approach 1:
The feedthrough suppression capacitor establishes a feedback path that dynamically compensates for feedthrough effects even when the current source transistor operates in the saturation region. The capacitor couples voltage changes from the switch transistor gate to the current source transistor gate, creating a negative feedback effect that counteracts the enhanced feedthrough that occurs in saturation operation, thereby maintaining accurate current control across the extended output voltage range
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design effectively suppresses feedthrough, increases the charge pump output voltage range, and reduces spurs in the PLL, enhancing the overall performance and reducing circuit area.
Implementation Method 1
a feedthrough suppression capacitor coupled between a gate terminal of a gate terminal of the switch transistor and a gate terminal of the current source transistor
Data Source
AI summary
A charge pump circuit includes a capacitor, a current source circuit coupled to the capacitor for providing a charging current and a discharging current to the capacitor. The current source circuit includes a switch transistor with a gate terminal for receiving a control signal, a current source transistor having a source terminal coupled to a drain of the switch transistor, and a feedthrough suppression capacitor coupled between a gate terminal of a gate terminal of the switch transistor and a gate terminal of the current source transistor. The feedthrough suppression capacitor is configured to lower a feedthrough effect.