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  • 12-Bit Level Translator for Digital Circuitry

  • Created: Feb 27, 2014

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This design circuit features GTL to LVTTL sampling receiver that is known to drive electronic backplane buses. It has series termination on the LVTTL outputs of 30 Ω. In digital circuits, a logic level is one of a finite number of states that a signal can have. Logic levels are usually represented by the voltage difference between the signal and ground (or some other common reference point), although other standards exist. The range of voltage levels that represents each state depends on the logic family being used. These logic levels have multiple categories that include GTL and TTL (specifically LVTTL).

Transistor–transistor logic (TTL) is a class of digital circuits built from bipolar junction transistors (BJT) and resistors. It is called transistor–transistor logic because both the logic gating function (e.g., AND) and the amplification is performed by the transistors. Successive generations of this technology produced compatible parts with improved power consumption or switching speed, or both. Although vendors uniformly marketed these various product lines as TTL with Schottky diodes, some of the underlying circuits, such as used in the LS family, could rather be considered DTL. Variations of and successors to the basic TTL family, which has a typical gate propagation delay of 10ns and a power dissipation of 10 mW per gate, for a power–delay product (PDP) or switching energy of about 100 pJ includes Low-voltage TTL (LVTTL) for 3.3-volt power supplies and memory interfacing. Meanwhile, Gunning transceiver logic or GTL is a type of logic signaling used to drive electronic backplane buses. It has a voltage swing between 0.4 volts and 1.2 volts—much lower than that used in TTL and CMOS logic—and symmetrical parallel resistive termination. The maximum signaling frequency is specified to be 100 MHz, although some applications use higher frequencies.

The growth of digital ICs that feature incompatible voltage rails, lower VDD rails, or dual rails for VCORE and VI/O have made the translation of logic levels necessary. The use of mixed-signal ICs with lower supply voltages that have not kept pace with those of their digital counterparts also creates the need for logic-level translation. These level translators provide an interface between components that operate at different voltage levels.



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