The operation of the circuit is summarized in table (a) In terms of 0 and 1, table (a) can be written as in table (b). TTL with active pull-up is known as TTL with totem-pole output. For extra points, apply 10 millivolts to the input, and examine the slewrate on base of that transistor located between 1K and 1.6K. TTL with Totem-pole Outout Figure shows the circuit of a two-input TTL NAND gate with totem-pole output. And compute the output noise of this linear amplifier. That drive capability guarantees each TTL output the capability to drive 10 TTL inputs with a guaranteed noise margin of 400mV or greater. \\begingroup\ For a lotta fun, implement a 3rd case: tie the output back to input thru 4Kohm or 1Kohm resistor. TTL outputs will be 400mV or less when low (and sinking 16mA or less), and 2.4V or more when high (and sourcing 400uA or less). TTL inputs are defined as 'low' if they are less than or equal to 800mV and 'high' if they are greater than or equal to 2V. Without the collector resistor it would behave more like a few ohms (1.6K divided by the current gain of Qp). When Qs is 'off', the base of Qp is pulled to Vcc by Rc, so the effective pullup resistance is limited by the collector resistance Rcp - so it's about 120\$\Omega\$, meaning that for a 50pF load, the time constant is about 6ns. Totem pole outputs like this one use an active pullup, which is Qp, Rc and Rcp. It's a component part of the (active) pullup circuit, but it's not a 'pullup resistor'. The primary purpose of the 120\$\Omega\$ resistor is to reduce the current spikes when the output switches (when Qo and Qp are both on simultaneously for a brief moment).
0 kommentar(er)
