Low-Voltage Current Sense Amplifier for Flash Memory
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Solution Overview
Problem
Conventional current sense amplifiers for non-volatile memory devices require substantial power supply voltage headroom and are not suitable for operation at low voltage levels, making it difficult to configure programmable devices quickly at startup, especially in flash memory technologies.
Innovation Solution
A current sense amplifier design that operates at power supply voltage levels below 1V, featuring a trans-impedance amplifier with regenerative feedback and native NMOS transistors, which maintains excellent characteristics in size, power, speed, and noise immunity, and includes a bias reference generator for generating DC reference voltages and control signals to support an array of memory cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional current sense amplifier configurations (reference-biased or inverter-biased trans-impedance amplifiers) are used, then the amplifier can maintain stable operation and provide sufficient gain, but the power supply voltage headroom requirement becomes substantial (greater than 1.8V), making it unsuitable for low-voltage operation
Solution Approach 1:
The patent inverts the conventional approach by using a current-referenced biasing scheme instead of voltage-referenced biasing. The bias reference generator produces current references that are mirrored to set amplifier operating points, allowing the amplifier to operate stably at low voltage levels without requiring substantial voltage headroom, thus resolving the contradiction between reliability and power supply voltage headroom
Solution Approach 2:
The patent changes the biasing parameter from voltage-based to current-based. By using current mirrors to establish operating points and by implementing regenerative feedback that operates on current signals, the amplifier can maintain stable operation at low supply voltages, effectively changing the fundamental parameter used for biasing and feedback control
2Loss of time
If the power supply voltage is reduced to enable quick configuration of programmable devices at startup, then the configuration time is reduced, but conventional flash memory technology and amplifier designs cannot operate properly at these low voltage levels
Solution Approach 1:
The patent enables the amplifier to operate at low voltage levels during the supply ramp-up phase, allowing configuration to begin before the power supply reaches its normal operating level. This preliminary operation at reduced voltage accelerates the configuration process without compromising reliability, as the amplifier is specifically designed to function correctly in this low-voltage window
Solution Approach 2:
The patent implements dynamic voltage scaling capability by designing the amplifier to operate across a wide voltage range. The circuit parameters and biasing schemes are optimized to adapt to changing supply voltages, allowing the system to operate reliably from low voltage during startup up to the full operating voltage, thus reducing configuration time while maintaining reliability
3Reliability
If higher power supply voltage is used to ensure proper amplifier operation, then the amplifier can provide sufficient voltage swing for dependable digital conversion, but power consumption increases and low-voltage operation is compromised
Solution Approach 1:
The patent replaces voltage-swing-based operation with current-mode operation. By using current mirrors and trans-impedance amplification, the circuit achieves the necessary signal levels for digital conversion through current amplification rather than voltage amplification, allowing reliable operation at low supply voltages with reduced power consumption
Solution Approach 2:
The patent changes the operating parameter from voltage to current by implementing current-mode logic and current mirrors throughout the amplifier circuit. This parameter change allows the amplifier to achieve the required gain and output swing through current amplification, enabling reliable digital conversion at low voltage and power levels
Data Source
AI summary
In one embodiment, an integrated programmable device has a plurality of current sense amplifiers for reading data from non-volatile memory and a reference generator that provides common bias reference voltages to the sense amplifiers. The sense amplifiers can read data from the non-volatile memory at low power supply voltage levels (e.g., 750 mV) relative to the nominal supply level (e.g., 1.2V). Each sense amplifier has a trans-impedance amplifier that converts a memory bit-line current into a voltage level indicative of whether a selected memory cell is programmed or erased. The trans-impedance amplifier has a current mirror with a high-threshold regeneration device that lowers the sense amplifier's range of operating voltages. Each sense amplifier also has a level-shifted inverter that further lowers the sense amplifier's operating voltage range. The reference generator generates a ground-referenced bias voltage that each sense amplifier or group of sense amplifiers converts into a local, supply-referenced bias voltage.