Virtual Ground Bias Circuit With Charge Pump Voltage Stabilization
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Solution Overview
Problem
In devices with advanced process nodes, generating a virtual earth reference voltage is challenging due to the difference between supply voltages, which can lead to voltage bouncing and inadequate protection for transistors, especially when high-side PMOS devices switch between supply and supply-voltage differences, requiring complex circuitry and significant power consumption.
Innovation Solution
A bias circuit comprising a bias stage, voltage follower, charge pumps, and a switchable buffer is used to generate a virtual reference voltage, with charge pumps maintaining the voltage and the switchable buffer actively correcting deviations, reducing power consumption and enabling efficient switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If complex circuitry such as cascoded switching stages and LDMOS-based switching stages is used to handle voltage differences, then the device can operate under higher supply voltages, but the device complexity increases significantly
Solution Approach 1:
The patent introduces a virtual ground node as an intermediary reference voltage between the first supply voltage (VDD1) and second supply voltage (VDD2). This virtual ground serves as a mediator that allows baseline components operating at lower voltages to interface with higher voltage domains without requiring complex isolation circuitry. The virtual ground is generated by a dedicated circuit that balances current flows between the two supply domains, enabling simple baseline components to achieve voltage compatibility through this intermediate reference point.
2Adaptability or versatility
If rail to rail stages such as CMOS drivers supplied by higher voltages are used, then the device can communicate with other ICs at higher voltages, but the device complexity increases and power consumption rises
Solution Approach 1:
The virtual ground node acts as an intermediary that enables baseline components to interface with higher voltage domains. By referencing signals to this virtual ground rather than requiring full rail-to-rail operation, the driver circuit complexity is reduced while maintaining the ability to communicate at higher voltages through the switching device.
3Stability of the object's composition
If the bias circuit uses active correction with charge pumps and switchable buffers, then the virtual ground voltage stability improves, but the power consumption increases
Solution Approach 1:
The patent employs charge pumps that operate in periodic cycles to maintain the virtual ground voltage. Instead of continuous active correction, the charge pumps transfer charge in discrete periodic steps, reducing average power consumption while maintaining voltage stability. The switchable buffer further optimizes power usage by activating correction only when voltage deviations occur, rather than continuous operation.
Solution Approach 2:
The bias circuit incorporates feedback mechanisms where the virtual ground voltage is monitored and compared against reference levels. When deviations are detected, the charge pumps and switchable buffer activate to correct the voltage, creating a closed-loop control system that maintains stability while minimizing power consumption by acting only when necessary.
Data Source
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AI summary
A bias circuit for generating a virtual reference voltage is described. The bias circuit may bias a switching device configured to switch a switching device output between a first and second supply voltage. The bias circuit includes a bias stage coupled between the first supply voltage rail and the second supply voltage rail. The bias stage has a bias stage output configured to output a virtual reference voltage value having a value between the first and second supply voltage. The bias circuit further includes a voltage follower coupled to the bias stage. The voltage follower is configured to output the virtual reference voltage. The bias circuit further includes a first charge pump coupled to the voltage follower output; and at least one of a second charge pump coupled to the bias stage voltage output, and a switchable buffer coupled to the bias stage voltage output and the voltage follower output.