Sense amplifiers for reading FGFETs #1130
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I'm trying to make a custom non-volatile memory element and have sorted out the erase/write operations, but am having trouble with reading the high z state of a programmed floating gate FET as logical 0. I know real world devices use sense amplifiers and comparators to measure the current, but every design I try to implement gives me errors. Is there a workaround for this (other than using a pull down resistor) or are analog circuits not possible (I mean it is Digital after all:) |
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Replies: 2 comments 2 replies
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It is possible to sense high-z:
In reality this would not work, because the circuit relies on the fact that a transistor, which has a floating input, does not conduct. In reality, a floating input would drift, and possibly one of the transistors or even both would become conductive. |
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Wow you're fast at replying. Thanks! Maybe I should have included the above image for clarity. But yeah, your reply is exactly my issue. I want to read the FGFET as 1 when its not programmed and 0 when it is programmed. The high-z state gives floating inputs (like in image A) for Bus0 and Bus2. The pull down resistors (image B) solve the problem (in Digital) but I understand a real circuit would have issues with that which is why they typically employ sense amplifiers. I'm trying to be as realistic as possible (which is why I switched from logisim to Digital) but when I try to use a sense amplifier (based on the differential sense amplifier wikipedia page with current mirror, below image) I get oscillations. I'm guessing this is either the improper use/design of a sense amplifier or Digital has issues with this circuit.
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This circuit contains a current mirror with a differential amplifier. Something like this can only be simulated with an analog simulator. |
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Ok well at least I know now. Thanks! |
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It is possible to sense high-z:
In reality this would not work, because the circuit relies on the fact that a transistor, which has a floating input, does not conduct. In reality, a floating input would drift, and possibly one of the transistors or even both would become conductive.