USB Peripheral Impedance Detection Circuit
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Solution Overview
Problem
USB peripherals lack the ability to securely determine if they are connected to a master device via a serial link, as they cannot reliably detect the presence of a master device, leading to potential security breaches and issues with data transmission speed detection.
Innovation Solution
A detection circuit within the peripheral that uses a bias stage and comparators to generate and compare measure voltages on the serial port terminals, allowing it to detect the presence of a master device by identifying impedance values, such as pull-down resistors, and adjust its operating mode accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a peripheral uses USB pull-up resistors to indicate data transmission speed, then the master device can detect the transmission speed, but the peripheral cannot detect the presence of a master device
Solution Approach 1:
Instead of the master device detecting the peripheral's speed capability through pull-up resistors, the invention inverts the detection direction by having the peripheral detect the master device's presence through pull-down resistors. This inversion allows the peripheral to gain detection capability while maintaining USB protocol compatibility.
Solution Approach 2:
The invention introduces pull-down resistors as intermediary elements connected to data terminals that serve as detection indicators. These resistors act as mediators between the master device and peripheral, enabling the peripheral to indirectly detect the master device's presence through voltage level changes without direct communication.
2Reliability
If a peripheral connects to a master device with faulty transmission links, then the peripheral can be powered but cannot communicate securely, but fraudsters can access secret information
Solution Approach 1:
The peripheral performs preliminary detection of the master device's presence and communication capability before establishing secure communication. By detecting pull-down resistors and verifying proper connection early in the initialization process, the system can prevent unauthorized access to secret information stored on security devices.
3Measurement precision
If the detection circuit generates measure voltages on serial port terminals, then it can detect impedance values, but it must adhere to USB standard voltage constraints
Solution Approach 1:
The detection circuit dynamically adjusts voltage parameters by generating measure voltages only when needed for detection, then returning to standard USB voltage levels for normal operation. This parameter change approach allows precise impedance detection while maintaining compliance with USB voltage constraints during data transmission.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables secure communication by ensuring the peripheral can determine if it is connected to a master device, preventing unauthorized access and correctly selecting data transmission speeds, while adhering to USB standard voltage constraints.
Implementation Method 1
a detection stage comprising at least one comparator for comparing the measure voltage to a reference voltage
Data Source
AI summary
A device includes a serial port for connecting as a slave to a master device through a serial link. The device further includes a detection circuit for detecting the presence of an impedance of the master device, linked to a terminal of the serial port. The device can be used with microprocessor cards comprising a USB port.