Charge Pump Circuit Leakage Current Reduction
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Solution Overview
Problem
The phase-locked loop system experiences instability in control voltage due to leakage currents from the charge pump circuit, leading to output jitter, particularly due to subthreshold leakage current, which affects the ability to achieve phase and frequency lock states.
Innovation Solution
A charge pump circuit design that includes an upper current source, a lower current source, and switches configured to minimize leakage currents by controlling the drain-source voltage to near zero, using a unity gain amplifier and MOSFET switches to manage the control voltage, thereby reducing the influence of leakage currents on the control voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional charge pump circuit is used in phase-locked loop system, then the circuit can provide control voltage to VCO, but leakage current causes control voltage instability and output jitter
Solution Approach 1:
The patent extracts and eliminates the harmful leakage current paths from the charge pump circuit by carefully controlling the switching时序 of the five switches. The fifth switch is specifically designed to be turned off before the first and second switches are turned on, thereby isolating and removing the leakage current paths that would otherwise flow through the current sources and affect the control voltage stability.
Solution Approach 2:
The patent applies preliminary action by pre-configuring the switching sequence where the fifth switch is turned off before the first and second switches are turned on. This preliminary switching action prevents the formation of leakage current paths before they can occur, ensuring that the control voltage remains stable by eliminating the subthreshold leakage current that would otherwise degrade the voltage level.
2Measurement precision
If subthreshold leakage current is present in charge pump circuit, then transistor operates in weak inversion mode, but this causes significant control voltage drift and reduces phase lock accuracy
Solution Approach 1:
The patent converts the harmful subthreshold leakage current into a beneficial effect by utilizing the fifth switch to create a controlled discharge path. Instead of allowing uncontrolled leakage current to degrade the control voltage, the fifth switch is used to actively discharge the control voltage node in a controlled manner, and then is turned off before the charge pumps operate, thereby preventing the harmful leakage while maintaining the ability to reset or discharge the voltage when needed.
3Productivity
If gate oxide layer thickness is reduced to improve process technology, then transistor performance improves, but gate tunnel leakage current increases exponentially
Solution Approach 1:
The patent extracts and removes the gate tunnel leakage current paths by controlling the switching sequence of the fifth switch. The fifth switch is turned off before the first and second switches are turned on, which isolates the current sources from the control voltage node and prevents the gate tunnel leakage current from flowing through the thin oxide layer and affecting the control voltage stability.
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 minimizes the impact of leakage currents on the control voltage, reducing output jitter and enhancing the stability of the phase-locked loop system by ensuring the drain-source voltage is nearly zero, thus improving the system's ability to maintain a stable phase and frequency lock state.
Implementation Method 1
the unity gain amplifier is electrically connected between the third node and fourth node, and configured to transfer the voltage on the third node to the fourth node
Implementation Method 2
the first switch is turned on or off by the first signal, and the second switch is turned on or off by the second signal, and the third switch is turned on or off by a third signal inverse to the first signal, and the fourth switch is turned on or off by a fourth signal inverse to the second signal
Data Source
AI summary
A charge pump circuit and a phase-locked loop (PLL) system using the same are provided. The charge pump circuit includes an upper current source, a lower current source and a plurality of switches. The switches are turned on or off by an error signal to increase or decrease the control voltage of the voltage-controlled oscillator (VCO) and further control the frequency of the output signal of the VCO. When the reference frequency signal matches with the divided frequency signal from the VCO, the upper current source and the lower current source are bypassed to decrease the voltage across the MOSFET, thereby minimizes the influence of the leakage current on the control voltage of VCO. In this way, the output jitter can be reduced due to smaller magnitude of peak-to-peak voltage on the control voltage of VCO in the PLL system caused by the leakage current of the MOSFET.