Translinear Differential Activity Detection With Common-Mode Rejection
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Solution Overview
Problem
Existing Media Oriented Systems Transport (MOST) detector circuits struggle to reject large common mode signals while detecting small differential signals, often consuming excessive current and failing to accurately detect activity on twisted wire buses.
Innovation Solution
A low-current detector circuit utilizing a translinear buffer configuration with NMOS and PMOS devices, which half-wave rectifies differential input signals and filters them to reject common mode signals, maintaining low impedance and reducing current consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a diode, filter and comparator configuration is used for detection, then the detection capability is provided, but common mode signals cannot be rejected and current consumption increases
Solution Approach 1:
The patent replaces the mechanical/electronic diode-filter-comparator system with a translinear buffer circuit that uses nonlinear transistor characteristics to achieve both detection and common mode rejection. The translinear loop formed by NMOS and PMOS devices creates a natural rejection mechanism for common mode signals while maintaining differential signal detection capability.
Solution Approach 2:
The patent changes the operating parameters of the detector by using a translinear buffer configuration that operates in a specific current mode. The buffer is designed to operate with specific bias currents and voltage levels that enable it to reject common mode signals while detecting differential signals, fundamentally changing how the detection is performed compared to traditional voltage-mode approaches.
2Measurement precision
If a diode, filter and comparator configuration is used for detection, then the detection function is achieved, but current consumption exceeds ideal levels
Solution Approach 1:
The patent substitutes the high-current-consuming diode-filter-comparator architecture with a translinear buffer that operates efficiently in current mode. The translinear loop structure inherently provides the detection function with much lower current consumption by utilizing the exponential current-voltage characteristics of MOS transistors rather than requiring large bias currents in traditional components.
3Object-affected harmful factors
If the detector circuit is designed to reject common mode signals, then common mode rejection is improved, but the ability to detect small differential signals may be compromised
Solution Approach 1:
The patent segments the detection function into two distinct paths within the translinear buffer: one path handles common mode rejection through the balanced translinear loop structure, while another path detects small differential signals through the nonlinear output devices. This segmentation allows both functions to operate simultaneously without interfering with each other.
Solution Approach 2:
The patent introduces asymmetry in the output stage of the translinear buffer where the half-wave rectification is performed. The output devices are configured to provide asymmetric current flow that selectively responds to differential signals while the overall translinear loop maintains symmetry for common mode rejection. This controlled asymmetry enables the detector to distinguish between common mode and differential components.
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
The circuit effectively detects small differential signals while rejecting common mode signals up to 400 MHz and 1V peak-to-peak, with low current consumption, enhancing the detection of activity on MOST ePHY lines without introducing errors in data transmission.
Implementation Method 1
The differential input signal may be half-wave rectified through the buffer output devices
Implementation Method 2
and may be filtered to provide the detected output
Implementation Method 3
When applying a common mode signal, the buffer's input and output may track each other, and no current may be rectified in the output devices, thus providing excellent common mode rejection
Data Source
AI summary
A low-current differential signal activity detector circuit may be configured to reject large common mode signals on differential input lines, while still detecting smaller differential signals applied to the same set of differential input lines. The detector circuit may comprise a translinear buffer that is driven at the buffer input and at the buffer output by the differential input signals. The differential signal thereby driving the inputs of the detector circuit may be half-wave rectified through the buffer output devices and may be filtered to provide the detected output. When applying a common mode signal, the buffer's input and output may track each other, and no current may be rectified in the output devices, thus providing common-mode signal rejection. The detector circuit may also be configured with two buffers having their outputs coupled to a common node, each buffer input driven by a respective one of the differential input signals. The differential signal thereby driving the inputs of the detector circuit may be fully rectified through the output devices of the two buffers, and may be filtered to provide the detected output. The two buffers may be configured in a symmetrical structure that allows for the rejection of common-mode signals when the outputs of the buffers are coupled to a common node.