Charge Pump Feedback Circuit for Duty Cycle Offset Reduction
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Solution Overview
Problem
Charge pumps experience systematic offset errors due to transistor mismatches, which affect the duty cycle and phase accuracy in applications like duty cycle correctors and phase locked loops.
Innovation Solution
A charge pump system with a feedback loop and bias circuit to equalize drain voltages of transistors, reducing systematic current mismatches and incorporating switches to minimize charge sharing errors, thereby stabilizing the control voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If transistor mismatches are present in the charge pump, then the device can be manufactured with standard processes, but systematic offset errors occur affecting duty cycle and phase accuracy
Solution Approach 1:
The patent implements a feedback mechanism where the control voltage generated by the charge pump is fed back to the gates of the transistors through amplifier circuits. This feedback loop continuously adjusts the transistor operating points to compensate for mismatches, thereby reducing systematic offset errors in duty cycle and phase measurements while maintaining standard manufacturing processes.
Solution Approach 2:
The patent dynamically adjusts the gate voltages of the transistors based on the control voltage output from the charge pump. By changing the electrical parameters (gate voltages) in response to detected errors, the system compensates for transistor mismatches and reduces systematic offsets without requiring higher precision manufacturing.
2Measurement precision
If a feedback loop is added to reduce systematic offset errors, then duty cycle and phase accuracy improve, but device complexity increases
Solution Approach 1:
The control voltage generated by the charge pump serves multiple functions: it corrects duty cycle errors, compensates for transistor mismatches, and adjusts the operating points of multiple transistors simultaneously. This multi-functionality reduces the need for separate correction circuits, thereby limiting the increase in device complexity while achieving improved accuracy.
Solution Approach 2:
The patent combines the error correction function with the existing charge pump operation. The same control voltage that regulates the charge pump current is also used to compensate for systematic offsets by adjusting transistor gate voltages. This merging of functions achieves accuracy improvement without adding entirely separate correction circuitry.
3Ease of operation
If charge sharing between transistors occurs, then the charge pump can operate with simpler switching, but systematic current mismatches are introduced
Solution Approach 1:
The feedback loop monitors the control voltage and adjusts transistor gate voltages to compensate for current mismatches caused by charge sharing. This continuous adjustment maintains current matching accuracy despite the simplified switching operation that allows charge sharing to occur.
Data Source
AI summary
A charge pump includes a first transistor, a first switch coupled between the first transistor and an output of the charge pump, a second transistor, and a second switch coupled between the output of the charge pump and the second transistor. The charge pump also includes a third transistor, wherein a gate of the third transistor is coupled to a gate of the first transistor, a fourth transistor, wherein a drain of the fourth transistor is coupled to a drain of the third transistor, and a bias circuit configured to bias a gate of the fourth transistor and a gate of the second transistor. The charge pump also includes an amplifier having a first input coupled to the output of the charge pump, a second input coupled to the drain of the third transistor, and the output coupled to the gate of the third transistor.