🚀 go-pugleaf

In article <1990Nov08.222823.1925@hoss.unl.edu> 252u3130@fergvax.unl.edu (Phil Dietz) writes:
>
>I'm not too sure that TRUE statis rams are faster.  In my book Computer
>Organization (Hamacher Vranesic Zaky ver 3 pg 322) it quotes
>
>"MOS transistors are higher-impedence devices; they yield circuits that
>have lower power dissipation.	Their disadvantage is their slower speed
>of operation."
>

    This is true.  But you can also run CMOS and HCMOS at higher voltages.
    The higher the voltage, the faster it goes.  Normal CMOS can be run
    from 3V to 15V.  Even at 15V normal CMOS is quite slow though.

    HCMOS, however, runs at the same order of magnitude as TTL with a much
    greater supply voltage range.  You can run HCMOS from 2 to 6V.  Power
    dissipation is directly proportional to the frequency at which you run
    the device AND ALSO THE VOLTAGE.  This means you can *run* HCMOS at 2V
    and low frequency and get less than a micro-watt power dissipation *in
    active mode*.  At 2V an idle HCMOS device pulls only leakage current
    which is on the order of picoamps (all the spec sheets say the
    leakage is in microamps but if you measure it, it's actually much,
    much, much less than a microamps).

    You can run HCMOS at up to 6V.  At 6V HCMOS is *faster* than normal
    TTL.

    In comparison, TTL MUST be run between 4.5V and 5.5V, NO EXCEPTIONS.
    There is NO low power mode for TTL, it draws lots of current at
    any frequency, even at DC (no inputs changing).

    AS and ALS TTL is faster than HCMOS but, like TTL, also pull 3 orders
    of magnitude more power... that's from 100x to 1000x more power, even
    when running at high frequencies.  Even ALS pulls a lot of power
    compared to CMOS/HCMOS.

    You also have to take fan-in and fan-out into consideration.  HCMOS has
    much greater DRIVE capabilities (both to BAR and to GND) than TTL.

>Phil Dietz

					-Matt

--


    Matthew Dillon	    dillon@Overload.Berkeley.CA.US
    891 Regal Rd.	    uunet.uu.net!overload!dillon
    Berkeley, Ca. 94708
    USA