Symmetrical PHY Activity Detector for Common-Mode Rejection
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Solution Overview
Problem
Existing detector circuits for Media Oriented Systems Transport (MOST) networks struggle to reject large common mode signals while detecting small differential signals, consuming excessive current in the process, making them unsuitable for efficient operation in environments like car audio systems.
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 current consumption and effectively detecting differential signal activity on twisted wire buses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a diode, filter and comparator configuration is used to detect differential signals, then detection capability is provided, but common mode signal rejection is insufficient and current consumption is excessive
Solution Approach 1:
The patent converts the harmful common mode signals into a useful function by using them to control the switching of current sources. The common mode voltage directly controls the gate voltages of the MOSFETs, causing the current sources to switch in a way that generates a detection signal proportional to the common mode level, thereby transforming the interference into a useful detection mechanism
Solution Approach 2:
The patent changes the operating parameters of the detector by using variable current sources whose magnitude is controlled by the common mode signal level. This dynamic parameter adjustment allows the detector to adapt to different signal conditions and achieve both common mode rejection and differential signal detection
2Measurement precision
If a diode, filter and comparator configuration is used to detect differential signals, then detection capability is provided, but current consumption is excessive
Solution Approach 1:
The patent implements periodic switching action through the MOSFETs controlled by the common mode signal. The current sources are switched on and off periodically based on the common mode voltage level, creating a pulsed detection signal that reduces average current consumption compared to continuous operation of traditional comparator circuits
Solution Approach 2:
The detector circuit uses the common mode signal itself to control the switching of the current sources, eliminating the need for external control signals or additional active components. The circuit serves itself by using the interference signal to drive its own operation, reducing the need for additional power-consuming control logic
3Use of energy by moving object
If low current consumption is achieved through simplified circuitry, then power efficiency is improved, but common mode signal rejection capability deteriorates
Solution Approach 1:
The patent dynamically changes the current level parameter based on the common mode signal voltage. The current sources are controlled to provide different current magnitudes depending on the common mode level, allowing the simplified circuit to adapt its behavior to reject common mode signals effectively without requiring complex additional circuitry
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.