Current Driver Circuit With Integrated DAC and Slew Rate Control
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Solution Overview
Problem
Existing digitally controlled current driver circuits using MOS transistors suffer from increased circuit area and degraded slew rate of output current waveform due to the necessity of a current amplifier, especially when applied in high-speed communication standards like DSI3.
Innovation Solution
A current driver circuit integrating a current conversion unit with both digital-analog conversion and current amplifying functions, utilizing MOS transistors, and an adjustment unit to control the slew rate of output current, along with a delay unit to reduce harmonic components and electromagnetic interference, allowing for high slew rate output current with reduced circuit area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a current amplifier is added after the D/A converter to achieve current amplification, then the current amplifying function is improved, but the circuit area is increased
Solution Approach 1:
The patent merges the D/A converter and current amplifier into a single integrated circuit block. The D/A converter generates a current signal that directly controls the gate of the output MOS transistor, which acts as the current amplifier. This integration eliminates the need for separate amplifier circuits, thereby achieving current amplification while reducing overall circuit area.
Solution Approach 2:
The output MOS transistor serves multiple functions: it acts as the amplifying element, the output stage, and the current control device simultaneously. By making the transistor multi-functional, the patent eliminates the need for dedicated separate amplifier circuits, thus improving current amplification capability while minimizing circuit area occupation.
2Power
If a current amplifier is added after the D/A converter to achieve current amplification, then the current amplifying function is improved, but the device complexity is increased
Solution Approach 1:
The patent combines the D/A converter and current amplifier functions into a single integrated block where the D/A converter output directly drives the gate of the output MOS transistor. This merging reduces the number of discrete components and interconnections, thereby simplifying the overall device complexity while maintaining current amplification capability.
Solution Approach 2:
The output MOS transistor is designed to perform multiple roles including amplification, output buffering, and current control. This multi-functionality reduces the total component count and simplifies the circuit architecture, making the device less complex while achieving the required current amplification function.
3Area of stationary object
If a MOS transistor is used for current amplification, then the circuit area is reduced, but the slew rate of the output current waveform is degraded
Solution Approach 1:
The patent applies different quality characteristics to different parts of the circuit. The output MOS transistor is specifically designed with optimized dimensions and biasing conditions to achieve fast switching and high slew rate performance. By locally optimizing the transistor parameters rather than using a generic amplifier design, the patent maintains high speed performance while using area-efficient MOS transistors.
Solution Approach 2:
The patent employs dynamic biasing and switching techniques where the MOS transistor operates in different regions depending on the signal phase and amplitude requirements. During transitions, the transistor is biased to maximize slew rate, while during steady states, it operates in a more area-efficient mode. This dynamic operation allows the circuit to achieve high slew rate when needed without permanently requiring large transistor dimensions.
4Speed
If the output current changes rapidly to achieve high slew rate, then the speed is improved, but electromagnetic interference is increased
Solution Approach 1:
The patent acknowledges that rapid current changes produce electromagnetic interference but converts this potential harm into a benefit by carefully controlling the slew rate to meet communication protocol requirements. The controlled high slew rate enables fast data transmission while the interference is managed through proper timing and signaling protocols, turning what could be a harmful EMI issue into an advantage for high-speed communication performance.
Data Source
AI summary
A current driver circuit includes: a current conversion unit including an input side transistor, in which a reference current is input, and multiple output side transistors, which output an output current corresponding to the reference current, and having an digital-analog conversion function for converting a digital control signal to an analog signal and a current amplifying function for amplifying the reference current according to an amplification ratio corresponding to the digital control signal; and an adjustment unit adjusting the digital control signal to be input into the output side transistors. When the adjustment unit adjusts the digital control signal, the current conversion unit changes the amplification ratio to gradually increase or decrease the output current, and controls a slew rate of the output current within a predetermined range.