Bidirectional Repeater Switching Without Passgate Bus Slowdown
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Solution Overview
Problem
Bidirectional serial data buses face challenges with increased parasitic capacitance and voltage drops due to the use of passgates, which slow down data transitions and reduce noise margins, and there is a need for a solution that isolates capacitance between sections of the bus and eliminates the need for passgates.
Innovation Solution
A bidirectional repeater design that includes inverting comparators and active pull-down transistors with adjustable pull-down and threshold voltages, allowing for optimized data transmission and reception while maintaining full noise margins, and an N:1 multiplexing mechanism that eliminates the need for passgates by using a bidirectional control circuit to manage data flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If passgates are used to multiplex data signals on a bidirectional bus, then data routing between multiple devices is enabled, but the non-zero on resistance of passgates slows down data transitions and reduces noise margins
Solution Approach 1:
The patent removes passgates from the bidirectional bus system entirely. Instead of using passgates for multiplexing, the invention employs separate dedicated data lines for each device connection, eliminating the source of resistance-induced slowdowns while maintaining the ability to route data between multiple devices through controlled line activation.
Solution Approach 2:
The bus system is segmented into separate dedicated data lines for each device connection rather than using a shared multiplexed line. Each device has its own direct connection path, which isolates the capacitance of each segment and prevents the cumulative capacitance effect that would slow transitions in a multiplexed system.
2Adaptability or versatility
If passgates are used for multiplexing, then multiple devices can share the bus, but the parasitic capacitance at I/O terminals and bus itself is not isolated, further slowing transitions
Solution Approach 1:
The bus system is divided into separate dedicated lines for each device, creating isolated segments. Each segment's parasitic capacitance is confined to its own line and does not accumulate with other devices, thereby maintaining fast transition times while still allowing multiple devices to share the overall bus system through controlled line selection.
3Adaptability or versatility
If the bus length increases or more devices are added, then the bus can cover more ground and connect more devices, but cumulative parasitic capacitance increases, further slowing transitions
Solution Approach 1:
The system uses separate dedicated lines for each device connection, creating isolated capacitance segments. When the bus is expanded to connect more devices, each new device adds capacitance only to its own dedicated line rather than to the entire bus, preventing cumulative capacitance effects and maintaining consistent transition speeds regardless of bus size.
4Productivity
If active pull-down transistors are used with standard threshold voltages, then data transmission is enabled, but voltage drops occur that lower input high voltage and raise input low voltage, decreasing noise margin
Solution Approach 1:
The patent modifies the threshold voltage parameter of the active pull-down transistors to be lower than standard values. This parameter change allows the transistors to maintain proper data transmission functionality while reducing voltage drops across the bus, thereby preserving higher input high voltages and lower input low voltages at receiving devices, which increases the noise margin and improves reliability.
Data Source
AI summary
A bidirectional repeater and data multiplexer for serial data has A-side 12C port devices A1-A4 coupled to comparators 302-308 and pull-downs to ground 316-322. Comparator outputs are coupled responsive to select lines S1-S4 of N:1 Select 310 to terminal A1 of bidirectional control 210 to control pull-down to non-zero low voltage Vp 206 at B-side device B. An inverting comparator 208 coupled to terminal B1 of bidirectional control 210 responds to input threshold voltage Vt less than low voltage Vp, to prevent data lockup due to data flowback to devices A1-A4. Output data from comparator 208 is coupled responsive to select lines S1-S4 of 1:N Select 312 to control pull-downs 316-322. This selectively repeats routing of device A1-A4 data to device B. Data from device B is selectively routed to pull-downs of devices A1-A4.