Active Pull-Up Circuit for USB Devices Using Op-Amp Feedback
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Solution Overview
Problem
Battery-powered portable USB devices face challenges in pulling USB bus lines to the required voltage due to low voltage power supplies, and OTG devices must consider powering both as hosts and peripherals, with existing solutions limited by resistor tolerances and voltage constraints.
Innovation Solution
A pull-up circuit utilizing an operational amplifier feedback loop that generates a reference voltage from either the supply voltage or bus voltage, ensuring the D+ or D− line is maintained within the 2.7V-3.6V range, using a combination of transistors and resistors to adjust voltage levels based on supply voltage conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If battery-powered portable USB devices use low voltage power supplies, then power consumption is reduced and portability is improved, but the ability to pull USB bus lines to the required voltage is compromised
Solution Approach 1:
The patent introduces an operational amplifier as an intermediary active pull-up circuit to bridge the gap between the low battery voltage and the required USB bus line voltage (2.7V-3.6V). The op-amp receives the low voltage from the battery and amplifies it to the appropriate level for USB communication, enabling both low power consumption and reliable voltage levels on the bus lines.
Solution Approach 2:
The patent changes the voltage parameter through active amplification rather than passive resistance. By using an operational amplifier, the circuit dynamically adjusts and boosts the voltage from the low-voltage battery supply to the required USB voltage range, overcoming the limitation of low voltage power supplies while maintaining portability.
2Adaptability or versatility
If USB OTG devices act as hosts, then device functionality is improved, but the ability to provide bus voltage is compromised when battery voltage is low
Solution Approach 1:
The patent implements a dynamic voltage switching mechanism that automatically adapts the pull-up circuit operation based on the detected voltage level. When the battery voltage is sufficient, the circuit operates in one mode; when voltage drops below the threshold, it switches to active pull-up mode using the operational amplifier, ensuring continuous host functionality regardless of battery state.
Solution Approach 2:
The patent incorporates a feedback mechanism through a comparator that continuously monitors the voltage level and controls the enable signal to the operational amplifier. When the voltage on the bus line falls below the required threshold, the comparator detects this and activates the active pull-up circuit, providing feedback-based voltage regulation to maintain host capability.
3Device complexity
If pull-up circuits are integrated into USB Devices, then device complexity is reduced, but resistor tolerance requirements become more stringent
Solution Approach 1:
The patent replaces the passive mechanical/resistive pull-up mechanism with an active electronic system using an operational amplifier. This substitution eliminates the need for high-precision resistors, as the voltage control is achieved through active amplification rather than passive resistance, thereby maintaining low device complexity while relaxing manufacturing precision requirements.
Data Source
AI summary
A pull-up circuit comprises an operational amplifier which forms part of a feedback circuit, acting to bring a pull-up circuit output equal to a reference voltage input. The pull-up circuit may form part of a USB transceiver for incorporation in a USB Device. When the supply voltage of the USB Device is sufficiently high, it is used to provide the required pull-up voltage, with the feedback circuit including the operational amplifier the USB Device is not high enough to provide the required pull-up voltage. In that case, the USB bus voltage is used to generate the reference voltage which is used as an input to the feedback circuit.