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1、Goals for LectureDiodeBipolar transistorsTTL gatesFor ideal diodeThe diode acts as a one-way conductoranodecathodeis the current exists due to the minority carrier drift across the junctionUnder reverse-bias conditions, only small reverse- bias leakage current go through the diode.thresholdI-V chara
2、cteristic of the diodeForward biased regionReverse biased regionBreakdown voltageAvalanche breakdownPN+-the minimum voltage required to obtain noticeable current is 0.7V for silicon semiconductor, and 0.2V for germanium semiconductorPN+-Dynamic characteristic of DiodeRVDOnOffIs there any limit to th
3、e frequency of the signal?VittUnder ideal conditons tIn practice Working state of Bipolar TransistorSaturated:Off:0V0VAND gate using Diode.+VCCRD1D2ABF00 0101110100ABFInputOutputFunction tableF=A B.F&A B0V5V5V5VOR gate using Diode0V0V00 01110110V5V5V5V 1 1 0Truth tableABFInputOutputF=A+BF+A BRABFTTL
4、 NOT Gate (74x)=5VVIH=3.4V VIL=0.2VTTL NOT Gate (74x)=5V0.9VLoad CurrentTTL NOT Gate (74x)=5V4.1V2.1VTransmission characteristicVOHTypical value=3.4V，Usually 2.4V is OKVOLTypically 0.3V， 0.8V is OKTTL NOT Gate (74x)Output Characteristic (TTL NOT Gate)source currentOutput Characteristic (TTL NOT Gate
5、)sink currentInput characteristic of TTL NOT GateInput CurrentInput characteristic of TTL gateVi2RiVCCVO2RiVO1Vi2Propagation Delay (TTL NOT Gate)The tpd of TTL gate is about 10ns 40nsPropagation DelayAC Noise Margin (TTL NOT Gate)Positive pulseNegative pulseBook Page 70ICCL and ICCHICCL , ICCH and I
6、CCMCalculation of ICCMICCL ,ICCH and ICCMApproximate waveform of power-supply currentTTL NAND GateHow to calculate the input current under the following three conditions? (1) A=B=VIL (2) A=B=VIH (3)A=VIL B=VIH TTL NAND Gate(1) (3) 0.9V3.4V(2) TTL NOR GateTTL AND-OR-NOT GateTTL XOR GateF1F2Unused inp
7、uts for TTL GateRRFor OR gateFor AND gateOC (open collect) gateCan the two outputs be wired directly? NOOC gateOC gateOC gate (continue)When all the OC gates are offOC gateWhen only one of the OC gates is onExample on page 81Three state gatesApplication of three state gateApplication of three state
8、gateTTL families74S (Schottky TTL):74LS (Low-power Schottky TTL)74AS (Advanced Schottky TTL)74ALS (Advanced Low-power Schottky TTL)74F (Fast TTL)7400-series74H (High speed TTL)74L(Low-power consumption TTL)74H- Series NAND GatePower consumptionPropagation DelaySchottky TransistorsWhy longer propagat
9、ion delay in TTL?+-+-+- +-+-+-Schottky Diode is on, it will shunt current from the base to the collector before the transistor goes into deep saturation74S-Series NAND GatePower consumption74x NOT Gate74LS-Series NAND GateTTL families (continue)Characteristics of gates in TTL families-0.6Family74S74
10、LS74AS74ALS74FDescriptionSymbolMaximum propagation delay (ns)391.743Power consumption per gate (mW)19281.24 Low-level input voltage(V)VILmax0.80.80.80.80.8Low-level output voltage(V)VOLmax0.50.50.50.50.5High-level input voltage(V)VIHmin2.02.02.02.02.0High-level output voltage(V)VOHmin2.72.72.72.72.7Low-level input current(mA)IILmax-2.0-0.4-0.5-0.2Low-level output current(mA)IOLmax20820820High-level input current( )IIHmax202020205High-level output current( )IOHmax-1000-400-2000-400-1000
