DAC High Voltage Generator Sub-Band Gap Regulation
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Solution Overview
Problem
DAC-controlled high voltage generators struggle to regulate output voltage effectively when it falls below the band gap voltage, particularly in new generation non-volatile memory devices with reduced linear sizes and low driving voltages, leading to limitations in staircase voltage operations for cell writing and erasing.
Innovation Solution
Incorporating an additional current regulation portion supplied by a second voltage reference, which enables the pull-up resistor to act as a pull-down resistor, extending the regulation range below the band gap voltage through a current generator and switch or a pair of transistors, allowing the high voltage generator to operate correctly even when the output voltage is lower than the band gap voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional voltage control circuit with band-gap reference is used, then the output voltage can be regulated above the band-gap voltage, but the regulation fails when the output voltage falls below the band-gap voltage
Solution Approach 1:
A current generator is introduced as an intermediary component between the voltage control circuit and ground. This current generator produces a compensation current that flows through the pull-up resistor, creating an additional voltage drop that allows the output voltage to be regulated below the band-gap reference voltage. The current generator acts as a mediator that enables the regulation function to extend into the sub-band-gap voltage range without requiring changes to the core voltage control circuitry.
Solution Approach 2:
The invention changes the operating parameters by introducing a controllable current through the pull-up resistor. By varying the current generated by the current generator, the voltage drop across the pull-up resistor changes, which directly affects the output voltage level. This parameter change approach allows the output voltage to be independently controlled below the band-gap reference voltage while maintaining stable regulation.
2Productivity
If the linear size of memory devices is reduced, then the integration density is improved, but the driving voltage requirements become more stringent and regulation below band-gap voltage becomes necessary
Solution Approach 1:
The voltage regulation function is segmented into two independent parts: the existing voltage control circuit that handles regulation above band-gap voltage, and the newly added current generator that handles regulation below band-gap voltage. This segmentation allows each part to operate independently within its optimal range, enabling the system to accommodate reduced linear sizes and lower driving voltages in memory devices without compromising regulation capability.
3Measurement precision
If a DAC-controlled architecture is used, then the voltage regulation precision is improved, but the control range is limited to above band-gap voltage
Solution Approach 1:
The invention merges the DAC-controlled voltage regulation function with the current generator control. The digital control signal that originally only adjusted the pull-down resistor now also controls the current generator through the DAC. This combination allows the precise digital control mechanism to extend its effective range below the band-gap voltage, maintaining regulation precision while expanding the controllable voltage range.
Data Source
AI summary
A high voltage generator of the DAC-controlled type, has an input terminal connected to a first voltage reference and an output terminal providing an output voltage and comprises at least a voltage control circuit and a charge pump circuit inserted, in series to each other, between the input and output terminals of the high voltage generator, and an output regulator connected to the output terminal of the high voltage generator and comprising at least a digital-to-analog converter or DAC. The output regulator further comprises at least an additional current regulation portion connected to the output terminal of the high voltage generator through a first resistive element of the output regulator as well to an enabling terminal which provides an enabling signal, the additional current regulation portion being supplied by a second voltage reference having a voltage level higher than a voltage level of the first voltage reference.