Infrared Receiver Input Stage Using MOSFET Ground Noise Isolation
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Solution Overview
Problem
Receiver circuits for infrared signals face challenges with ground noise injection, which can lead to incorrect signal decoding and reduced communication quality, especially in high-speed current mode communication systems where the receiver input stage has low impedance.
Innovation Solution
Incorporating a MOSFET with a gate terminal voltage-controlled by an amplifier, along with a reference voltage source and current sources, to create a low impedance node connected to the sensor output, referenced to a noise-free ground, while maintaining the receiver ground connected to a noisy communication ground, thereby isolating the receiver from ground noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the receiver input stage has low impedance for high-speed current mode communication, then communication speed is improved, but ground noise injection increases causing incorrect signal decoding
Solution Approach 1:
The patent segments the ground reference system into two distinct grounds: a noisy communication ground for the input stage and a clean reference ground for the detection circuitry. This segmentation allows the low-impedance input stage to operate on the noisy ground while the detection occurs on the clean ground, preventing noise injection into the detection path while maintaining high-speed communication capability
Solution Approach 2:
The patent introduces an intermediary voltage-controlled switch (MOSFET) that is controlled by an amplifier to dynamically isolate or connect the input node to the detection circuitry. This intermediary element acts as a gatekeeper, allowing the low-impedance input stage to receive high-speed signals while preventing ground noise from reaching the detection stage, thus resolving the contradiction between speed and reliability
2Ease of operation
If the receiver is directly connected to the communication ground, then ease of operation is improved, but immunity to ground noise deteriorates
Solution Approach 1:
The voltage-controlled switch serves as an intermediary between the communication ground and the detection circuitry. It maintains ease of operation by allowing direct connection during signal reception while providing ground noise immunity by isolating the detection path when the switch is open, thus resolving the contradiction between connectivity and noise immunity
Solution Approach 2:
The patent employs dynamic control of the voltage-controlled switch based on the received signal characteristics. The amplifier continuously monitors the input node voltage and adjusts the switch state accordingly, creating a dynamic system that adapts to maintain both ease of operation and ground noise immunity under different operating conditions
Data Source
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AI summary
A receiver circuit comprising: an input-pin; a receiver-input-node; a ground-pin; an internal-node that is connected to the input-pin; and a MOSFET. The MOSFET has a conduction channel connected in series between the internal-node and the receiver-input-terminal; and a gate terminal, the voltage at which sets the conductivity of the conduction channel. The receiver circuit also includes an amplifier that: has an input terminal that is connected to the internal-node; and provides a voltage control signal to the gate terminal of the MOSFET such that the voltage at the internal-node with respect to the ground-pin is constant.