Folded Cascode Charge Pump for Wide Output Range and Low Ripple
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Solution Overview
Problem
Conventional charge pumps face limitations in generating a wide range of output voltages without increasing ripple in the output current and struggle to directly accept low-voltage input signals, leading to errors due to noise in control signals.
Innovation Solution
The implementation of a charge pump with a folded cascode structure using cascode transistors and current mirror circuitry, which allows for a wider output voltage range and direct acceptance of low-voltage control signals, reducing noise-related errors through the use of thin-oxide switching transistors and differential amplifier adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If larger switching transistors are used to generate a wider range of output voltages, then the output voltage range is improved, but the ripple in the output current increases
Solution Approach 1:
The charge pump circuit is divided into multiple independent charge pump stages, each with its own switching transistors and current sources. By segmenting the overall current delivery function across multiple stages with smaller transistors, the ripple generated by each stage is reduced while the cumulative output voltage range remains wide. Each stage operates with optimized transistor sizes that minimize ripple, and the stages are combined to achieve the desired total voltage range.
2Object-generated harmful factors
If smaller switching transistors are used to reduce ripple in output current, then the ripple is reduced, but the output voltage range becomes limited
Solution Approach 1:
Multiple charge pump stages with smaller switching transistors are merged in parallel to achieve the desired output voltage range. Each stage contributes a portion of the total current capability, and their combined effect provides both the wide voltage range and low ripple characteristics. The current sources from multiple stages are summed at the output node, creating a composite current signal with reduced ripple content while maintaining high current capability for wide voltage swing.
3Reliability
If conventional charge pumps operate at higher supply voltage to accept control signals, then the charge pump operation is improved, but the ability to directly accept low-voltage signals from phase detector is lost
Solution Approach 1:
Level shifting circuitry is introduced as an intermediary between the low-voltage phase detector and the high-voltage charge pump. The level shifter translates the low-voltage control signals from the phase detector into the appropriate high-voltage control signals required by the charge pump switches. This intermediary component enables direct interfacing between devices operating at different voltage levels without compromising the reliability of either the low-voltage digital section or the high-voltage analog section.
4Adaptability or versatility
If a converter circuit is added to convert low-voltage signals to high-voltage signals for charge pump input, then the signal compatibility is improved, but the device complexity increases
Solution Approach 1:
The charge pump circuit is designed with multi-functional control input stages that can directly accept control signals at the operating voltage of the switching transistors. By making the control input stage universal and compatible with the internal operating voltage, the need for separate converter circuitry is eliminated. The same control inputs that drive the switches also serve as the interface from the phase detector, reducing overall circuit complexity while maintaining signal compatibility.
Data Source
AI summary
A charge pump that includes cascode transistors and current mirror circuitry to form a folded cascode structure that isolates the control inputs from the charge pump output and also increases the range of the output. The charge pump includes inputs to receive UP and DN (down) control signals and provides an output current that is based on the control signals. The charge pump may be configured as either a differential or non-differential device. The switching transistors that receive the control signals may use a lower voltage than the current source transistors in the charge pump In differential-type embodiments of the present charge pump, an amplifier can be used to control current source transistors based on differences between the output voltages of the charge pump, thereby adjusting the current flowing through the current source transistors and driving the average of the output voltages to a desired common mode voltage.