ChapterVII-MOSLogicCircuits-EE477-Nazarian-Spring09

ChapterVII-MOSLogicCircuits-EE477-Nazarian-Spring09 -...

Info iconThis preview shows pages 1–9. Sign up to view the full content.

View Full Document Right Arrow Icon
University of Southern California Combinational MOS Logic Circuits Nazarian EE477L – Spring 2009 Nazarian/EE477L/Spring 2009
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Combinational MOS Logic Circuits Combinational logic circuits, which perform Boolean operations on multiple input variables and etermine the determine the outputs as Boolean functions of the inputs, are the basic building blocks of all A multiple-input, single-output mbinational logic circuit Nazarian/EE477L/Spring 2009 2 digital system combinational logic circuit
Background image of page 2
MOS Logic Circuits with Depletion Loads Two-Input Depletion-Load NOR Gate (NOR2) =A+B A Z = A + B B low V A V B V out low high low high low high low low igh igh w Nazarian/EE477L/Spring 2009 3 high high low
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
NOR2: Calculation of V OH alculation f H Calculation of V OH – The load device, which operates in the linear region, should have zero drain current. In particular, its linear region current equation becomes , 2 ,, [2 | () | ] 0 n load D l o a d T l o a d O H D DO H D H k IV V V V V V =⋅ = 2 • The solution of this equation yields: OH DD VV = Nazarian/EE477L/Spring 2009 4
Background image of page 4
NOR2: Calculation of V OL • Calculation of V OL o calculate the output low voltage VOL, we must To calculate the output low voltage VOL, we must consider three different cases as follows: (i) V A =V OH , V B =V OL (ii) V A =V OL , V B =V OH (iii) V A =V OH , V B =V OH Nazarian/EE477L/Spring 2009 5
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
V OL Calculation: Single-Input Switch • Assuming that the threshold voltages of the two enhancement- type driver transistors are identical, the driver-to-load ratio of the corresponding inverter can be found as follows case (i) case (ii) In case (i) ' , , n driver driver A A W k k L ⎛⎞ ⎜⎟ ⎝⎠ == In case (ii) ' , , n driver driver B B W k k L = ' , R load n load load k W k k L ' , R load n load load k W k k L The output low voltage level V OL in SIS cases is found as: 22 0 () | ( ) | load L OH T OH T T load OL k VVV VV V V =− Nazarian/EE477L/Spring 2009 6 00 , OL driver k
Background image of page 6
V OL Calculation: Multiple-Input Switch • In case (iii), the saturated load current is the sum of the two linear-mode driver currents ,, , D load D driverA D driverB II I =+ 22 2 ,0 0 |( ) | [ 2 ( ) ] [ 2 ( ) ] 2 driver A driver B load T l o a d O L A TO L O L B L O L kk k V V VV V V V V =− +− • Since the gate voltages of both driver transistors are equal we can devise equivalent driver-to-load ratio for the NOR structure. , ' ndr iver driver A driver B AB R WW k LL k ⎡⎤ ⎛⎞ + ⎜⎟ ⎢⎥ + ⎝⎠ ⎣⎦ == Nazarian/EE477L/Spring 2009 7 , ' load nload load W k k L
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Output Voltage for MIS Case • In the MIS case (i.e., case iii), the output voltage level is 22 00 , ,, () | ( ) | load OL OH T OH T T load OL driver A driver B k VVV VV V V kk ⎛⎞ =− ⎜⎟ + ⎝⎠ • This result suggests a simple design strategy for designing NOR2 gates – achieve a certain max V OL for case i and ii: driver A driver B R load k k = = • This design choice yields two identical driver transistors, ote at e L r e IS se wer an at btained which guarantee the required value of V OL in the worst case Nazarian/EE477L/Spring 2009 8 Note that the V OL
Background image of page 8
Image of page 9
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 79

ChapterVII-MOSLogicCircuits-EE477-Nazarian-Spring09 -...

This preview shows document pages 1 - 9. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online