Bipolar Differential Output Circuit for Low-Voltage LVDS
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing LVDS bipolar output stages face challenges with power supply voltage reduction from 3.3V to 2.5V, leading to transistor saturation and suboptimal performance for data and RF applications, especially with PNP transistors, and differential multiplexer configurations suffer from output signal corruption due to select signal coupling.
Innovation Solution
A bipolar differential output circuit with an input differential stage and an output differential pair of bipolar transistors without a tail current source, utilizing current mirror circuits and inductive peaking resistors to maintain a keep-alive current and reduce power supply voltage requirements, while a differential multiplexer circuit separates select and input stages with additional current mirrors to improve isolation and speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If power supply voltage is reduced from 3.3V to 2.5V in bipolar LVDS output stages, then power consumption is reduced, but transistor saturation occurs and performance deteriorates
Solution Approach 1:
The patent introduces a current mirror circuit as an intermediary between the input differential stage and output stage. This current mirror actively regulates the tail current to prevent transistor saturation while enabling lower power supply voltage operation, thus resolving the contradiction between reduced power consumption and maintained transistor reliability
Solution Approach 2:
The patent changes the operating parameters of the bipolar transistors by implementing a specific current mirror configuration that adjusts tail current based on power supply voltage. This allows the circuit to maintain proper transistor operation at 2.5V by dynamically adjusting current parameters, preventing saturation while achieving lower power consumption
2Ease of manufacture
If PNP bipolar transistors are used in LVDS output stages, then circuit functionality is achieved, but operating speed becomes suboptimal for data and RF applications
Solution Approach 1:
The patent implements dynamic current control through the current mirror circuit, which actively adjusts tail current based on operating conditions. This dynamic adjustment optimizes the switching speed of PNP transistors by ensuring they operate in the most efficient region, thereby improving circuit speed while maintaining manufacturability
Solution Approach 2:
The current mirror circuit performs preliminary current regulation before signals pass through the PNP differential pair. By pre-establishing optimal current levels and preventing saturation, the transistors are prepared for faster switching operation, improving overall circuit speed without changing the PNP transistor configuration
3Adaptability or versatility
If select and input stages are stacked in differential multiplexer configuration, then multiplexing functionality is achieved, but select signal couples to output through junction capacitance causing signal corruption
Solution Approach 1:
The patent introduces an intermediate current mirror stage between the select differential pair and input differential pairs. This intermediate stage acts as a buffer that prevents direct capacitive coupling of the select signal to the output, thereby eliminating signal corruption while maintaining multiplexing functionality
Solution Approach 2:
The patent segments the differential multiplexer into distinct functional stages: select stage, current mirror stage, and input stage. This segmentation physically separates the select signal path from the output path, preventing harmful capacitive coupling while maintaining the ability to switch between multiple inputs
4Reliability
If sufficient high power supply voltage is used in differential multiplexer to avoid device saturation, then transistor operation is maintained, but implementation with 2.5V power supply becomes difficult
Solution Approach 1:
The current mirror circuit serves as an intermediary that actively regulates tail current to prevent transistor saturation. This allows the use of lower 2.5V power supply voltage while maintaining reliable transistor operation, as the current mirror ensures proper biasing without requiring high voltage headroom
Data Source
AI summary
A bipolar differential output circuit includes an input differential bipolar stage for receiving an input signal and generating a differential output current. An output differential pair of bipolar transistors without a bipolar tail current source responds to the input signal by providing a representative output signal. And a current mirror circuit passes current from the input differential pair to the output differential pair.