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Ace Virgil Villaruz
DCTL, I2L, D2L, TTL Logic Families: Principles & Applications
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Direct-Coupled Transistor Logic (DCTL) MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz Direct-Coupled Transistor Logic • Similar to RTL but the base of the transistors are connected directly to the input or to the collector output of the preceding transistor • Has fewer components, more economical, simpler to fabricate onto IC’s • Low power consumption • Since there is no input resistor, transistors are overdriven • Since there is no resistor at the input, logic 1 = 0.8 V, logic 0 = 0.2 V • Smaller noise margin • Disadvantage: Prone to phenomenon called “current hogging” MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz Direct-Coupled Transistor Logic VCC VCC VCC RC RC RC AB A+B A A A A B B NOR Gate NAND Gate MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY Inverter EEE134 Engr. Villaruz Direct-Coupled Transistor Logic 0.8 V 1 kΩ Vo1 0.8 V 0.8 V 1 kΩ 0.8 V 1 kΩ 0.8 V Vo2 0V 0V MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz DCTL Current Hogging Current Hogging - when two BJT’s are in parallel, the one with the lower VBE voltage turns ON, and takes up all the voltage drop resulting to overheating or breakdown. The other transistor does not turn ON. MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz Direct-Coupled Transistor Logic 0.8 V 1 kΩ Vo1 0.8 V 0.8 V 1 kΩ 0.8 V 1 kΩ 0.8 V Vo2 0V 0V MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz Integrated-Injection Logic 2 (I L) MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz Integrated-Injection Logic • • • • Similar to DCTL, uses very small silicon chip area Consumes very little power Easier to fabricate Used to MSI and LSI Example: Texas Instruments SBP 9900 16-bit microprocessor • Also called Merged-Transistor Logic MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz Integrated-Injection Logic • • • • Similar to DCTL, uses very small silicon chip area Consumes very little power Easier to fabricate Used to MSI and LSI Example: Texas Instruments SBP 9900 16-bit microprocessor • Also called Merged-Transistor Logic MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz I2L Inverter VCC I1 REXT A A A A MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz I2L NOR Gate VCC REXT VCC RC A VCC A+B RC B MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz I2L NAND Gate Consider the case: A = ‘1’, B = ‘0’ VCC REX T Q2 is off, Q1 is also off (no current path to GND) Q3 collector has higher potential than base EB - forward, BC - forward but overdriven current from input A will go up to the base of Q3 going to GND RC Q3 Q1 A Thus, this NAND implementation of I2L is not practiced. AB Q4 B Q2 How to implemend NAND? MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz I2L NAND Gate A AB B MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz Diode-Transistor Logic (D2L) MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz Diode-Transistor Logic • Inspiration: Diode AND Gate VCC A AB B A AB B MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz Diode-Transistor Logic VCC VCC RC REXT AB DA AB A D1 B DB D2 RB Level-shifting diodes Discharge path MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz Diode-Transistor Logic • Has greater fan-out • Main disadvantage is slower speed MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz DTL NAND Gate VCC VCC RC REXT AB DA A D1 B D2 RB DB MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz Modified DTL NAND Gate • Increased fan-out VCC VCC R1 RC R2 DA A T1 A T2 D2 B RB DB MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz High-Threshold Logic • Allows higher VCC for industrial applications VCC VCC R1 RC R2 DA A T1 A T2 Zener B RB DB MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz DTL Inverter VCC VCC RC REXT A A MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz DTL NOR Gate VCC RC RA A+B DA A B RB RB DB MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz DTL Sample Problem 1 • Calculate the fan-out of the DTL circuit below. 5V 2.2 kΩ 5 kΩ DA D1 D2 A A β = 30 B 5 kΩ DB MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz DTL Sample Problem 2 • Calculate the fan-out of the modified DTL circuit below. 5V 1.75 kΩ 2.2 kΩ 2 kΩ DA A T1 β = 30 A T2 β = 30 D2 B 5 kΩ DB MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz Transistor-Transistor Logic (TTL) MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz Transistor-Transistor Logic • Faster than DTL • Input diodes are replaced with E-B junction of a transistor • C-B junction of T1 acts as D1 • E-B junction of T2 acts as D2 VCC B B E1 C E1 E2 C E2 VCC VCC VCC VCC RB1 RC2 RC3 RC REXT AB DA A D1 B D2 A B RB AB T2 T1 T3 RE2 DB MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz TTL NAND GATE VCC RB1 A B VCC VCC RC2 RC3 AB T2 T1 T3 RE2 MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz TTL NAND GATE Active Pull-up Speeds up charging at the output VCC RB1 VCC VCC RC2 RC4 T4 A B AB T2 T1 T3 RE2 MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz Sample TTL Problem 1 Calculate the current through RC3 when output is on and off. 5V RB1 4 kΩ β = 30 A B RC2 1.4 kΩ RC3 4 kΩ AB T2 T1 T3 RE2 1kΩ MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz Sample TTL Problem 2 Calculate the current through RC4 when output is on and off. 5V RB1 4 kΩ RC2 1.4 kΩ RC4 100 Ω β = 30 A B AB T2 T1 T3 RE2 1 kΩ MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz TTL NAND GATE Clamping Diodes Suppress ringing caused from transitions of input voltage RB A B VCC VCC VCC RC1 T2 RC2 AB T1 RB MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY EEE134 Engr. Villaruz TTL NOR GATE VCC VCC VCC RC1 A RC2 B C MINDANAO STATE UNIVERSITY - ILIGAN INSTITUTE OF TECHNOLOGY A+B+C EEE134 Engr. Villaruz
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