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Introduction to MicroElectronics K.El-Ayat , Ch : 1.1 – 1.5

This text covers the basics of signal sources, including Thévenin and Norton forms, as well as frequency spectra and analog-to-digital conversion. It also explores CMOS logic gates and amplifier circuits.

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Introduction to MicroElectronics K.El-Ayat , Ch : 1.1 – 1.5

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  1. Introduction to MicroElectronics K.El-Ayat, Ch: 1.1 – 1.5 1

  2. Signal sources (a) Thévenin form, (b) the Norton form. Figure 1.1

  3. EX: 1 Sine-wave signal amplitude Va, frequency f = 1/T Hz. Figure 1.3 Sine-wave voltage signal of amplitude Va and frequency f = 1/T Hz. The angular frequency v = 2pf rad/s.

  4. EX 2: A symmetrical square-wave signal of amplitude V. Figure 1.4 A symmetrical square-wave signal of amplitude V.

  5. The frequency spectrum of periodic square wave in EX 2 Useful for signal analysis Figure 1.5 The frequency spectrum (also known as the line spectrum) of the periodic square wave of Fig. 1.4.

  6. Figure 1.2 An arbitrary voltage signal vs(t).

  7. Frequency spectrum of arbitrary waveform Figure 1.6 The frequency spectrum of an arbitrary waveform such as that in Fig. 1.2.

  8. Sampling continuous-time analog signal Figure 1.7 Sampling the continuous-time analog signal in (a) results in the discrete-time signal in (b).

  9. Binary Digital Signals: variations with time. Figure 1.8 Variation of a particular binary digital signal with time.

  10. Analog-to-digital conversion (ADC) or A/D. Most signals in real world Analog Need A/D to process in digital domain Figure 1.9 Block-diagram representation of the analog-to-digital converter (ADC).

  11. NMOS transistor structure Source (S), Drain (D), Gate (G) L channel length, W width of transistor NMOS transistor cross-section Figure 4.1 Physical structure of the enhancement-type NMOS transistor: (a) perspective view; (b) cross-section. Typically L = 0.1 to 3 mm, W = 0.2 to 100 mm, and the thickness of the oxide layer (tox) is in the range of 2 to 50 nm. 11

  12. CMOS structure, today’s ICs both NMOS & PMOS transistors PMOS formed in an n-well Figure 4.9 Cross-section of a CMOS integrated circuit. Note that the PMOS transistor is formed in a separate n-type region, known as an n well. Another arrangement is also possible in which an n-type body is used and the n device is formed in a p well. Not shown are the connections made to the p-type body and to the n well; the latter functions as the body terminal for the p-channel device. 12

  13. CMOS Logic gate Example 1 ? Figure 10.12 A two-input CMOS ……. gate.

  14. Digital Logic inverter Figure 1.28 A logic inverter operating from a dc supply VDD.

  15. Inverter Transfer Characteristic VTC = voltage transfer characteristic Ideal inverter Typical inverter Vol = output low; Voh = output high; Vil = max input interpreted as “0”; Vih = min input interpreted as “1”; Figure 1.29 The VTC is approximated by three straight line segments. Note the four parameters of the VTC (VOH, VOL, VIL, and VIH) and their use in determining the noise margins (NMH and NML).

  16. Inverter Circuit Implementation Figure 1.31 (a) The simplest implementation of a logic inverter using a voltage-controlled switch; (b) equivalent circuit when vIis low; and (c) equivalent circuit when vIis high. Note that the switch is assumed to close when vIis high.

  17. CMOS inverter implementation The most common inverter Figure 1.32 A more elaborate implementation of the logic inverter utilizing two complementary switches. This is the basis of the CMOS inverter studied in Section 4.10.

  18. Inverter Operation Figure 1.34 Example 1.6: (a) The inverter circuit after the switch opens (i.e., for t  0). (b) Waveforms of vI and vO. Observe that the switch is assumed to operate instantaneously. vO rises exponentially, starting at VOL and heading toward VOH .

  19. Inverter Propagation delays 10/90 rule Figure 1.35 Definitions of propagation delays and transition times of the logic inverter.

  20. Amplifier: Circuit symbol Figure 1.10 (a) Circuit symbol for amplifier. (b) An amplifier with a common terminal (ground) between the input and output ports.

  21. Voltage Amplifier & Transfer characteristic Figure 1.11 (a) A voltage amplifier fed with a signal vI(t) and connected to a load resistance RL. (b) Transfer characteristic of a linear voltage amplifier with voltage gain Av.

  22. Some Amplifiers Require 2 supplies Eg 2 supply +ve & -ve swings Figure 1.12 An amplifier that requires two dc supplies (shown as batteries) for operation.

  23. output Amplifier transfer characteristics Amps have limitations .. may saturate ..signal (2) L+ >= A*vi Amp linearity desired Vout(t) = A * Vin(t) input Figure 1.13 An amplifier transfer characteristic that is linear except for output saturation. How many power supplies ?

  24. Amplifier Biasing – ensures linearity Nonlinear response Figure 1.14 (a) An amplifier transfer characteristic that shows considerable nonlinearity. (b) To obtain linear operation the amplifier is biased as shown, and the signal amplitude is kept small. Observe that this amplifier is operated from a single power supply, VDD. 24

  25. Inverting Amplifier Example Top limit = 10v, lower limit = 0.3v Output 180 degrees out of phase with input L+ =~ 10v @ Vt = 0 Vo = 10 - 10EXP(-11) * eEXP(40Vt) For 5 V bias @ Vo = 5v Vt = 0.673 L- = 0.3v Vt = 0.690 Figure 1.15 A sketch of the transfer characteristic of the amplifier of Example 1.2. Note that this amplifier is inverting (i.e., with a gain that is negative).

  26. Voltage Amplifier Circuit Model used for simulation, circuit analysis Gain = Aw; input resistance = Ri, Output resistance = Ro vo = Aw * vi * RL/(RL + Ro) ; effect of output resistance Ro vo / vi = Aw * RL/(RL + Ro) ; voltage gain vi = vs * Ri / (Ri+ Rs) ; effect of Ri vo / vs = Aw * Ri / (Ri + Rs) * RL/(RL + Ro); overall voltage gain accounting for input / output impedances Figure 1.17 (a) Circuit model for the voltage amplifier. (b) The voltage amplifier with input signal source and load.

  27. More Gain ? Use Cascaded stages Ex 1.3 Input stage needs high input impedance Output stage needs low output impedance Input resistance of a stage = load resistance of previous stage Vi1 / Vs = 1 M / ( 1M + 100k) = 0.909 ; effect of 1st Rin Av1 = Vi2 / Vi1 = 10 * 100k / (100k + 1k) = 9.9 ; gain 1st stage, A = 10 Av2 = Vi3 / Vi2 = 100 * 10k / (10k + 1k) = 90.9 ; gain 2nd stage, A = 100 Av3 = VL / Vi3 = 1 * 100 / ( 100 + 10) = 0.909 ; gain 3rd stage, A = 1 Av = VL / Vi1 = 9.9 * 90.9 * 0.909 = 818 ; 3 stage gain VL / Vs = 818 * 0.909 = 743.6 ; from source to load Ideal Gain = 10 * 100 = 1000 Figure 1.18 Three-stage amplifier for Example 1.3.

  28. Amplifiers have limited bandwidth  frequency response of Amplifiers Constant gain between w1 & w2 (Bandwidth) ; otherwise lower gain. Amp chosen so its BW coincides with required spectrum to be amplified … otherwise signals distorted Figure 1.21 Typical magnitude response of an amplifier. |T(v)| is the magnitude of the amplifier transfer function—that is, the ratio of the output Vo(v) to the input Vi(v).

  29. Frequency Response Amplifier output coupling DC (direct ) coupled Gain at low freq & DC Used in IC a.k.a low-pass amp. Capacitively coupled Amp ..Eg audio Band pass Amp Bandpass Filter Tuned Amps. TV, signal processing.. Figure 1.26 Frequency response for (a) a capacitively coupled amplifier, (b) a direct-coupled amplifier, and (c) a tuned or bandpass amplifier.

  30. Capacitively Coupled Amplifier Stages Figure 1.27 Use of a capacitor to couple amplifier stages.

  31. An NMOS Common Source Amplifier Amp. Circuit Xfer Characteristic Figure 4.26(a) Basic structure of the common-source amplifier. (b) Graphical construction to determine the transfer characteristic of the amplifier in (a). 31

  32. NMOS common source Amp. Cont’d Xfer Characteristic Biased at point Q Figure 4.26(Continued)(c) Transfer characteristic showing operation as an amplifier biased at point Q. 32

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