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Can you help identify this symbol?

opalko

As part of an encoder chip for the keyboard on an Apple II Plus I came across this symbol in the schematic that I can't identify. Any idea what this is?

Thanks

Robert Opalko

image

Here is where I clipped it from (also note the one on the other side denoted "ØP"??)

image

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  • 0

    It might just be a FET of different construction/dimensions, perhaps used in place of a resistor (normal resistors take up a lot of real-estate on a chip), so perhaps they invented that symbol. Although they violate that concept by using the device as a FET when they connected the phiP and phiIP (on mobile, don't know how to draw the Phi symbol) as inputs to a couple of the gates. Anyway, perhaps they are lower-performance FETs basically. 

    All my comment above is pure speculation however..

  • 0 in reply to shabaz

    Having both a weak pull-up and a stronger one that gets enabled when it's needed (by a clock phase) was probably a way to get the chip power consumption down a bit.

    I've seen the symbol elsewhere in material about chip design, so I don't think it's unique to Apple.

  • 0 in reply to jc2048

    Here's another example of the symbol's use. This is the internal schematic of a Signetics 2501 SRAM from a 1975 datasheet. They've drawn it a bit more like the usual MFET symbol.

    image

    Intel preferred this, where they've simply shown where the implanted channel for the depletion device sits. This is from an application note explaining how the SRAM cells worked.

    image

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  • 0 in reply to jc2048

    Here's another example of the symbol's use. This is the internal schematic of a Signetics 2501 SRAM from a 1975 datasheet. They've drawn it a bit more like the usual MFET symbol.

    image

    Intel preferred this, where they've simply shown where the implanted channel for the depletion device sits. This is from an application note explaining how the SRAM cells worked.

    image

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