How Xilinx Chips Quickly Check If Memory Is Completely Erased

A method for programmable chips to instantly verify that all memory cells are wiped clean using a simple, high-speed logic gate circuit.

What it covers

This patent describes a hardware circuit designed to verify if memory cells in a programmable logic device (PLD) are fully erased. It uses an n-input NOR gate formed by NMOS transistors connected to sense amplifiers. When a wordline is activated, the circuit checks all memory cells on that line simultaneously. If any single cell is not fully erased, its sense amplifier outputs a high signal, which turns on an NMOS transistor and pulls the common output node low, signaling that the device is not yet clean.

What it doesn't cover

• —Does not cover software-based verification methods that check memory cells one by one.
• —Does not cover memory architectures that do not use sense amplifiers as input sources for the gate.
• —Does not cover non-volatile memory technologies that do not utilize wordline-based addressing.

The clever bit

Instead of reading each cell individually, the circuit uses the physical properties of a NOR gate to perform a parallel 'all-or-nothing' check, where a single un-erased cell immediately forces the output to a 'not erased' state.

Why it matters

Before this, checking if a large programmable chip was fully erased could be a slow, iterative process. By implementing this logic gate directly into the hardware, Xilinx made the erasure verification process nearly instantaneous, which is critical for manufacturing efficiency and device reliability in field-programmable gate arrays (FPGAs).

Real-world examples

• 1.Xilinx FPGA configuration memory
• 2.Programmable logic device (PLD) erasure cycles
• 3.High-density memory array testing