PHYSICS 123 Lecture 18: Lecture 18
27 Oct 2016
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Phys 123 class notes: analog {::::=:}digital, pll (lab ds/18) Topics: what we"re after today: mostly , to link analog and digital domains. Incidentall y, we" ll slight man y of the topics li sted here , in order to get to the juiciest: adc methods, sampling and phase-locked loop: gate-to-gate inte1facin g (mixing logic families) five-volt logic. * only voltages (not currents) present a problem, these days. * in 5-volt logic, it"s ttl to cmos that presents the difficulty : voh for ttl is only 2. 4v (guaranteed) not high enough for cmos" v1 hof about 2/3 x vsupply. * strange to tell , some devices made of cmos show ttl levels: cmos pals and ouyr 8051 processor are important examples. * remedies? either 74hct (ttl input levels, cmos outputs) or pull up resistors. Mixing logic families powered by more than one power-supply voltage. * our pals can be rigged to mix 5v and 3. 3v logic on its inputs and outputs:
