1 / 19

Ch 11 Bipolar Transistors and Digital Circuits

Ch 11 Bipolar Transistors and Digital Circuits. Examine bipolar junction transistor (BJT) use in inverters for logic circuits. Basic Inverter (RTL) One npn transistor and a load resistor BJT Inverters Transistor-Transistor Logic (TTL) Emitter-Coupled Logic (ECL)

annberry
Télécharger la présentation

Ch 11 Bipolar Transistors and Digital Circuits

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Ch 11 Bipolar Transistors and Digital Circuits • Examine bipolar junction transistor (BJT) use in inverters for logic circuits. • Basic Inverter (RTL) • One npn transistor and a load resistor • BJT Inverters • Transistor-Transistor Logic (TTL) • Emitter-Coupled Logic (ECL) • Analyze to understand inverter performance: • voltage transfer characteristic, • noise margins, • fan-in and fan-out limits, • power dissipation and • switching speed. 2-input ECL OR / NOR Gate Y = A+B A B VR Y = A+B Ch 11 Bipolar Digital Pt. 1

  2. Bipolar Transistor Operation • Transistor regions of operation • Forward Active • VBE > 0 E jnc forward • VBC< 0 C jnc reverse • Cutoff • VBE < 0 E jnc reverse • VBC < 0 C jnc reverse • Saturation • VBE > 0 E jnc forward • VBC > 0 C jnc forward C _ VBC n Collector + + B VCE p Base + _ _ VBE n Emitter E IC Active Ic= βIb Saturation IC< β IB Note: VCE= VBE+VCB = VBE - VBC VCE Cutoff IC ≈ 0 Ch 11 Bipolar Digital Pt. 1

  3. Bipolar Transistor Operation Transistor regions of operation • Forward Active • Electron injection at emitter and collection at collector • VBE > 0 E jnc forward • VBC< 0 C jnc reverse • Ic = β Ib • * Cutoff • * No electron injection at Emitter • VBE < 0 E jnc reverse • VBC < 0 C jnc reverse • IC ≈ 0 • * Saturation • * Electron injection from both E & C • VBE > 0 E jnc forward • VBC > 0 C jnc forward • IC < β IB IC Saturation IC< β IB Active Ic= βIb VCE Cutoff IC≈0 Ch 11 Bipolar Digital Pt. 1

  4. Bipolar Transistor Operation - DC • Base bias VBE determines IB • VCC with RC determine output load line. • Base IB with output load line determines Quiescent Point (VCE , IC ) IC Output Load Line VCE IB VBE IC IB DC Base Current Quiescent Point Base Load Line VCE VBE Ch 11 Bipolar Digital Pt. 1

  5. Bipolar Transistor Operation – Small Signal AC • In small signal amplifiers, • AC signal at input is small –> base current variation is small. • Device moves around DC quiescent point • Device stays in the active region • Amplifier produces current and voltage gain depending upon the configuration, e.g. common emitter (above). iB iC vBE vCE VBB+vi Ch 11 Bipolar Digital Pt. 1

  6. Bipolar Transistor Operation – Digital Circuits • Input signal vi is large. • VBE and IB changes are large. • Important applications digital circuits and power amplifiers • Device can be in active, saturation or cutoff depending on VBE and IB. • Transistor still operates on the load line. • Moves from cutoff thru active to saturation or vice versa as the input signal changes. IC Saturation IC< β IB Active Ic=βIb VCE Cutoff IC≈ 0 Ch 11 Bipolar Digital Pt. 1

  7. Bipolar Transistor Operation - Characteristics • Each region of device operation has its own unique characteristics • Active • Current gain Ic= β Ib • VBE = VBE,active ≈0.7 V (typical value) • VCE,active ≈ ?,NOtypical value! • Saturation • Reduced current gain IC< β IB • VBE = VBE, sat ≈0.8 V(typical value) • VCE = VCE, sat ≈0.2V(typical value) • Cutoff • No current gain IC ≈ 0, IB ≈ 0 • VBE < O • VCE,cutoff ≈ ?,NOtypical value! IC Active Ic= βIb Saturation IC< β IB ~ 0.2 V VCE IB Cutoff IC 0 0.7 V 0.8V VBE Ch 11 Bipolar Digital Pt. 1

  8. Resistor Transistor Logic (RTL) • RTL Logic • Earliest and simplest logic • “0” = low voltage • “1” = high voltage • Inverter is the basic building bock • Combine two inputs in parallel to implement NOR • Combine two inputs in series to implement NAND • Transistors operate in cutoff for low “0”input (base) voltage, so IC ≈ 0 and output is high “1”. • Transistors operate in saturation for high“1” input (base) voltage, so IC ~ mA’s and the output is low “0” due to IR drop across RC. vo vo vi vi Ch 11 Bipolar Digital Pt. 1

  9. Basic Bipolar Transistor Inverter (RTL) • Resistor Transistor Logic (RTL) • For low vi input, output vo is high • Transistor is off (cutoff) since iB ≈ 0 because base-emitter junction is not biased sufficiently (VBE is too small). • Since iB ≈ 0, then iC ≈ 0 because iC ≈βiB. • So vo = VCC - iC RC≈VCC • For high vi input, output vo is low • Transistor is on since iB > 0 because base-emitter junction is biased sufficiently (VBE is large). • Since VBE is large (~0.8 V), iB >> 0, then iC >> 0 since iC ≈βiB. • So vo = VCC - iC RCis very small. • Transistor driven into saturation region so . vo = VCE,sat≈0.2V IB IC n p + n VBE 0.7 V 0.8V VBE IC Active Ic=βIb Saturation IC< β IB VCE ~ 0.2 V Cutoff IC≈ 0 Ch 11 Bipolar Digital Pt. 1

  10. Basic Bipolar Transistor Inverter (RTL) • Transistor operates along load line. • Transistor operates in cutoff when input is low since iB ≈ 0. • As input vi increases, iB increases and transistor moves into active region. • As input vi increases further, transistor moves into saturation region and VCE goes towards zero. + VCE + VBE IC IC Output Load Line active Input high vi large Saturation iC/iB < β Input low vi small 0 cutoff VCE VCE Ch 11 Bipolar Digital Pt. 1

  11. RTL Voltage Transfer Characteristic • Region I (A to B) • Transistor is in cutoff • VBE is small, iB ≈ 0, vo = VCC. • Region II (B to C) • Transistor is on in the active mode (iC = βiB). • iB and VBE are larger; VBE≈ 0.7V • iC andiB increase as vi and VBE increase. • vo and VCE falls as icRC increases. • Region III (C to D) • Transistor is in the saturation mode (iC <βiB). • iB and VBE are larger, VBE≈ 0.8 V • iC is larger • VCE is small, ≈VCE,sat ≈ 0.2V VCC = 5 V IB + VCE + VBE VBE 0.7 0.8 vo A B I II III C D vi Ch 11 Bipolar Digital Pt. 1

  12. Noise Margins • Noise margins are a measure of the reliability of the technology. • Measure of the sensitivity to noise. • Consider one inverter driving an identical inverter. • How large a noise spike can be tolerated before an error occurs? Drive Inverter Load Inverter v01 v02 vi1 vi2 • For output of driver high (v01=VOH), then input of load inverter is high (vi2=VOH ). • A negative noise spike on input of load inverter reduces input signal. • Trouble when net input signal is less than VIH so noise margin is NMH = VOH - VIH . • Similarly, for the low state NML = VIL - VOL . v02 v01 Load Inverter Drive Inverter NML NMH vi1 VOH VOL VIL VIH vi2 Ch 11 Bipolar Digital Pt. 1

  13. RTL Inverter Noise Margins • Noise Margin for Low State • NML = VIL - VOL • VIL = VBE,active= 0.7 V • VOL = VCE,sat = 0.2 V • NML = VIL - VOL = 0.7 V - 0.2 V = 0.5 V • Noise Margin for High State • NMH = VOH - VIH • VOH = VCC = 5 V • VIH= VBE,sat= 0.8 V • NMH = VOH - VIH = 5 V - 0.8 V = 4.2 V • Unequal noise margins for high and low states. VCC = 5 V IB + + VCE VBE VBE 0.7 0.8 vo A B VOH I II III C D NML NMH VOL vi VOH VOL VIL VIH Ch 11 Bipolar Digital Pt. 1

  14. RTL Power Dissipation • Output High State (Low input) • Transistor is in cutoff so iC 0. • No static power dissipation for high state, PH = 0. • Output Low State (High input) • Transistor is in saturation so v o = VCE,sat = 0.2 V. • iC = (VCC - VCE,sat )/RC = (5V - 0.2 V)/10K = 0.48 mA. • PL =VCC iC = (5 V)(0.48 mA) = 2.4 mW • Average P = 1/2(PH + PL) = 1.2 mW VCC = 5 V IB RC = 10K + VCE + VBE VBE 0.7 0.8 vo A B VOH I II III C D VOL vi VIL VIH Ch 11 Bipolar Digital Pt. 1

  15. RTL Propagation Delay • Output going high • Transistor turned off (cutoff) • Charging current flows through RC • tPLH is time it takes the output to rise from VOL = VCE,sat = 0.2 V to 1/2(VOH + VOL) = 2.6 V VCC = 5 V vo iR iCap VCC + vo + C VCE + VBE VCE,sat t tPLH vo A B VOH I II III Long charge – up time! C D VOL vi VIL VIH Ch 11 Bipolar Digital Pt. 1

  16. RTL Propagation Delay • Output going high • Transistor turned off (cutoff) (M  N) • Charging current flows through RC • tPLH is time it takes the output to rise from VOL = VCE,sat = 0.2 V to 1/2(VOH + VOL) = 2.6 V (N  O) VCC=5V vo iR iCap VCC + vo + C VCE + VCE,sat VBE t Transient Response M  N  O tPLH vo A B VOH IC I II M III C D P VOL vi N VCE VIL VIH O Ch 11 Bipolar Digital Pt. 1

  17. RTL Propagation Delay • Output going low • Transistor turned on (saturation) and providing discharge current (PR) • But current also flows through RC • tPHL is time it takes the output to fall from VOH = VCC = 5 V to 1/2(VOH + VOL) = 2.6 V(R  S) VCC = 5 V vo iR iCap VCC + vo + C + VCE VBE VCE,sat t tPHL vo Transient Response P  R  S A B VOH IC I II S R III C D VOL P vi VCE VIL VIH Ch 11 Bipolar Digital Pt. 1

  18. RTL Propagation Delay • Output going low VCC = 5 V iR iCap + vo + C + VCE VBE IC S R Short discharge time! P VCE Ch 11 Bipolar Digital Pt. 1

  19. Resistor Transistor Logic (RTL) * RTL provides simple, basic digital technology based on bipolar transistors and resistors. • Logic levels and noise margins • Noise Margin for Low State • NML = VIL – VO = 0.7 V - 0.2 V = 0.5 V • Noise Margin for High State • NMH = VOH - VIH = 5 V - 0.8 V = 4.2 V • Unequal noise margins for high and low states. • Propagation delays • Output going low • Output going high • Propagation delay • Power – Delay Product vo vo vi vi Ch 11 Bipolar Digital Pt. 1

More Related