Two-State Unity Gain Buffer for Contention-Free Output Multiplexing
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Solution Overview
Problem
Conventional LIDAR receiver systems face challenges in reducing board area, power dissipation, and cost due to noise gain and bandwidth limitations caused by multiplexing TIAs, and existing unity gain buffers cannot be used to form a voltage-mode maximum follower circuit or output multiplexer without signal contention.
Innovation Solution
A 2-state unity gain buffer is developed, allowing input signals with higher voltages to drive an output node while isolating lower voltage inputs, using a differential amplifier, bipolar transistor, and diode matrix, enabling multiple buffers to share a common load and form a voltage-mode maximum follower or multiplexer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If multiplexing is achieved using additional analog switches and gain blocks in the signal paths, then board area and power dissipation are reduced, but noise gain increases and bandwidth is compromised
Solution Approach 1:
The patent extracts the multiplexing function from the traditional switch-based approach and relocates it to the output stage of the TIA. By placing the switch at the output terminal rather than in the signal path, the harmful effects of switch on-resistance and capacitance on noise gain are eliminated while maintaining the board area reduction benefit
Solution Approach 2:
The patent introduces an intermediate buffering stage between the TIA output and the multiplexer switch. This buffer acts as an intermediary that isolates the switch from the sensitive TIA input, allowing the switch to perform multiplexing without degrading the noise performance of the overall system
2Area of stationary object
If a voltage-mode switch is used to multiplex TIA outputs, then board area is reduced, but bandwidth is limited and transition time increases
Solution Approach 1:
The patent employs dynamic switching elements (such as MOSFETs or bipolar transistors) that can rapidly transition between on and off states. These dynamic switches are designed with optimized dimensions and biasing to achieve sub-nanosecond transition times, far exceeding the capability of static or mechanically-based switches
3Device complexity
If conventional unity gain buffers are used to share output terminals, then device complexity is reduced, but signal contention occurs and proper operation is compromised
Solution Approach 1:
The patent implements preliminary action by ensuring that only one buffer is enabled at a time through control logic that activates a single buffer based on the desired output channel. This pre-activation approach prevents signal contention before it can occur, as the inactive buffers are already in a high-impedance state and cannot interfere with the active buffer's output
Solution Approach 2:
The patent applies local quality by giving each buffer in the multi-buffer system distinct characteristics through individual enable/disable control. Each buffer can be independently activated or deactivated, allowing the system to present a high-impedance state at inactive buffer outputs while maintaining low-impedance drive capability at the active buffer output
Data Source
AI summary
A unity gain buffer provides an “ON” state in which the input signal is coupled to the output terminal and an “OFF” state in which the input signal is isolated from the output terminal. Multiple unity gain buffers may share the same load to form a voltage-mode maximum follower or a multiplexer.