In TTL with totem-pole output T3 is on when the output is low and T4 is on when the output is high. the tri-state TTL has three output states, high low and high-impedance. if the output is not in low state, it should definitely in the high state. the output is either in high state or low state. figure shows the circuit of a TTL NAND gate with open collector output.Ī normal digital circuit has two output states, low and high. this problem of TTL with totem-pole output is overcome in TTL with open collector output. TTL with totem-pole output has a major problem that the two outputs of the two gates cannot be connected together. Here, the outputs of two NAND gates are connected together.
using a wired-AND connection, the fan-in of the circuit is increased. In terms of 0 and 1, table (a) can be written as in table (b).Ī wired-AND connection has two or more than two gates connected together.
The operation of the circuit is summarized in table (a) TTL with active pull-up is known as TTL with totem-pole output. Thus, Vgs(on) for the output, is defined by input Vg(on) and the resistor ratio.What is ttl circuit with totem-pole output stage minimize gate and advantages disadvantages or ttl with totem pole output ?įigure shows the circuit of a two-input TTL NAND gate with totem-pole output. Anyway, once the current is fixed, simply apply that current to a specific value pullup, and the pullup drops a voltage V = Id * Rpu. Note that the drain/collector won't saturate to a voltage lower than Vs, so there is some tradeoff. Vgs(th) is pretty sloppy, so this isn't great with MOS it's perfectly serviceable with BJTs, with the tighter spread in Vbe (say 0.5~0.8V over commercial temperature range). The source voltage Vs rises to a bit below Vg(on) - Vgs(th), and the drain current is set by the resistor value, Id = Vs / Rs. An alternate option: use a fixed current from the common-source transistor, by driving it with a known Vg(on) input level, and adding source degeneration (a resistor between source and GND).
Simple limit is just a series resistor from the first (level shifting / common source) transistor, then a zener from gate to VDD. Vgs(max) might be rated 20V or whatever, but that doesn't mean you want to hang at that forever, you're left with no headroom for supply transients, and the excessive gate swing costs a huge amount of drive power and switching time. For higher supply voltage (over 10-15V), I strongly recommend adding a voltage limiter, to avoid applying excessive gate voltage. And by 39 and friends, I mean 2N- for classic TO-92, MMBT for SOT-23, or various other manufacturer-specific designations, alternate packages, etc. 4401/3 or PBSS303NX/PX or the types shown, will do fine for faster speed while using a corresponding lower pullup value, or some other means of drive (a 74HC or CD4000 family logic gate can do well here, translating level from the 3.3V input to up to 6V or 15V respectively). The pullup merely sips current, maybe not something you'd want for battery operation but easy to ignore elsewhere. This is already in the 100s of ns range, good for certain PWM applications. If you're just turning stuff on and off, a 10k pullup and optional 3904/6 follower (i.e., capable of 100-200mA) will do. There's really no penalty to using BJTs, so it might be that a pair of 3904/6 or 4401/3 are used to drive the MOSFETs, which drive the final big gate, or yet more BJTs for an even bigger gate (5-10A BJTs are commonly used in this way, for large industrial IGBT modules with 100s of nC gate charge and +/-15V swings).
Which for most parts is maybe a volt away from the supply so the 1.4V range will draw more or less the full current those transistors are capable of (which is at least as much as peak gate current will be). The discrete inverter (doing it with MOSFETs) is not a bad way to do it, but it does suffer from shoot-through during the period when the gate voltage is above (N-ch Vgs(th)) and below VDD + (P-ch Vgs(th)). 120R is a quite strong pullup, consuming 42mA continuously while on (and more at higher supply voltage). Just how fast do you need this poor thing to go? 3A bipolars at full poop will do it in about 18ns.