Fuse-Initialized Multiplexer Routing to Cut Leakage and Dynamic Current
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional multiplexer techniques in programmable logic devices result in increased dynamic current, leakage current, and signal fanout issues due to unused multiplexers, and require additional transistors or fuses for control, which increase silicon area and capacitive loading.
Innovation Solution
The proposed solution involves programming fuses to control multiplexer input selection, where unused multiplexers are initialized to a default logic high state using a 'transmitter' multiplexer's output, minimizing additional transistors and fuses, and leveraging the routing fabric to reduce leakage and dynamic current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If every multiplexer has a multiplexer input selected (with supply voltage input signal for unused multiplexers), then the multiplexer is held in proper off state, but dynamic Icc is significantly increased and signal loading, fanout, and leakage current issues occur
Solution Approach 1:
The patent applies preliminary action by initializing the routing multiplexer to a known state (selecting a default input terminal) before the device is programmed or configured. This default selection ensures that unused multiplexers are in a controlled state from power-up, preventing leakage current and dynamic power consumption issues that would occur with floating inputs. The initialization happens automatically during device startup, before any user configuration is applied.
2Reliability
If an additional multiplexer input tied to supply voltage or ground is provided, then leakage paths and fanout issues are reduced, but extra fuse and additional circuitry are required
Solution Approach 1:
The patent makes the existing default input terminal serve multiple functions: it acts as both a functional input for used multiplexers and as a leakage-prevention path for unused multiplexers. By routing the default input terminal to a controlled voltage level (through the inverter stage), the same circuit structure handles both active and inactive multiplexer states, eliminating the need for separate leakage-prevention circuitry.
Solution Approach 2:
The multiplexer's own default input terminal and inverter stage are used to provide the leakage-prevention function. The inverter stage naturally drives the default input terminal to a controlled state, making the multiplexer self-sufficient for leakage control without requiring external additional circuitry or fuses.
3Reliability
If an additional transistor is provided to tie off multiplexer inverter stage input, then leakage current and fanout issues are eliminated, but transistor requirement and silicon area increase
Solution Approach 1:
The existing inverter stage transistors are used to provide the leakage-prevention function. The inverter's pull-up and pull-down networks naturally drive the default input terminal to a controlled state, eliminating the need for additional dedicated transistors. The same transistors that perform the inversion function also provide the leakage control, making the circuit self-sufficient.
Solution Approach 2:
The inverter stage serves dual purposes: it inverts the select signal for active multiplexers and simultaneously provides leakage prevention for unused multiplexers by driving the default input terminal. This multi-functionality eliminates the need for separate leakage-control transistors, reducing silicon area.
4Reliability
If pulsed control signal is provided to control additional transistor, then multiplexer can be tied off, but buffering network and metal track width are required
Solution Approach 1:
The inverter stage automatically provides the control function without requiring external pulsed control signals. The inverter's inherent switching behavior, driven by the select signal, is sufficient to drive the default input terminal to the appropriate state, eliminating the need for buffering networks and complex control signal routing.
Data Source
AI summary
A programmable logic device, in accordance with an embodiment of the present invention, includes a plurality of multiplexers, having fuse input terminals and input signal terminals, and a plurality of associated fuses providing fuse signals to the fuse input terminals to control selection of the input signal terminals. The fuses in a first state select a first input signal terminal of the input signal terminals, with a first multiplexer from the plurality of multiplexers receiving a first logic level signal at the first input signal terminal and providing the first logic level signal to the first input signal terminal of a first set of the plurality of multiplexers. The fuses associated with the first set are adapted to be programmed before the fuses associated with the first multiplexer.