Bootstrapped Pass Gate Transistor for Low-Impedance Column Multiplexer
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Column multiplexers in non-volatile memories face challenges in passing read bias voltages onto bitlines due to high voltage devices with high threshold voltages and limited power supply headroom, leading to degraded speed and increased chip area requirements.
Innovation Solution
A bootstrapped high voltage pass gate transistor couples the low voltage sense amplifier to the bitlines, allowing low impedance signal passing and overdriving the pass gate transistor, which results in fast read speeds and a smaller footprint by utilizing the bootstrapping effect with minimum-sized devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If thick oxide high voltage devices are used to withstand high voltages, then voltage withstanding capability is improved, but threshold voltage increases and area increases
Solution Approach 1:
The patent changes the gate voltage parameter dynamically through bootstrapping. The gate voltage is boosted above the source voltage during read operations, allowing the thick oxide device to operate with lower effective Vgs while still passing sufficient current, thereby reducing the required device area
Solution Approach 2:
The bootstrapping circuit pre-charges the gate of the pass transistor to a voltage higher than the source before the read operation begins. This preliminary voltage boosting ensures the transistor is properly overdriven before data is passed, eliminating the need for larger area devices
2Strength
If thick oxide high voltage devices are used to withstand high voltages, then voltage withstanding capability is improved, but read speed degrades
Solution Approach 1:
The patent dynamically changes the gate voltage parameter through bootstrapping, boosting it above the source voltage during read operations. This parameter change overdrives the pass transistor, reducing its on-resistance and improving read speed while maintaining voltage withstanding capability
Solution Approach 2:
The gate voltage of the pass transistor is made dynamic rather than static. The bootstrapping circuit actively adjusts the gate voltage during operation, allowing the transistor to transition from a high-impedance state during write operations to a low-impedance state during read operations, thereby improving speed
3Quantity of substance
If larger area pass devices are used to increase read currents, then read current is improved, but chip area increases
Solution Approach 1:
Instead of increasing device area to increase current, the patent changes the voltage parameter through bootstrapping. The boosted gate voltage increases the drive current capability of the same physical device, achieving higher read current without increasing area
Solution Approach 2:
The patent uses minimum-sized devices to create the bootstrapping effect rather than using large area pass devices. The bootstrapping circuitry (capacitors and switches) copies the voltage function, providing the necessary overdrive without requiring large transistor areas
4Speed
If bootstrapping is used to overdrive pass gate transistor, then read speed is improved, but circuit complexity increases
Solution Approach 1:
The bootstrapped pass gate transistor serves multiple functions: it acts as the column select transistor, the data pass transistor, and the voltage isolation element. The same transistor structure is used for both write isolation (when off) and read data passing (when overdriven), reducing the need for separate dedicated circuits
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves good sense differential margins and fast read speeds while reducing chip area usage by addressing voltage drop and headroom issues through the bootstrapping effect, enabling efficient read operations and isolating low voltage circuits from high voltage circuits during write operations.
Implementation Method 1
Since the pass gate transistor is bootstrapped its gate floats to the high voltage of the power supply (VCC) plus a delta voltage. This overdrives the pass gate transistor and allows it to pass signals between the sense amplifier and the bitlines with low impedance.
Data Source
AI summary
The invention has a bootstrapped high voltage pass gate transistor that couples the low voltage sense amplifier to the bitlines. Since the pass gate transistor is bootstrapped its gate floats to the high voltage of the power supply (VCC) plus a delta voltage. This overdrives the pass gate transistor and allows it to pass signals between the sense amplifier and the bitlines with low impedance. This results in good sense differential margins and fast read speeds. The circuit has a pass gate control circuit that places a negative high voltage signal on the gate of the pass gate during non-volatile write operations. This causes the pass gate to isolate the low voltage circuit from the high voltage circuits during this operation. Finally, the circuit is smaller than earlier column multiplexer circuits.