Detailed Notes on NMOS, CMOS & BiCMOS Circuits Lecture 9

Lecture 9: NMOS, CMOS, & BiCMOS Circuits

Instructor: Dr. Manuel Jiménez
Course: INEL-4207 Digital Electronics

Lecture Objectives

• Understanding of basic NMOS circuits
• NMOS inverter analysis
• NMOS logic gates
• Overview of CMOS circuits
• CMOS inverter analysis
• CMOS logic gates
• Introduction to BiCMOS circuits

NMOS Inverter with Resistive Load

Circuit Operation

• When input voltage (v_i) is LOW:
  • Transistor (Q) is OFF.
  • Drain current (i_D) = 0.
  • Output voltage (v_o) = V_DD.
• When input voltage (v_i) is HIGH:
  • Transistor (Q) is ON.
  • Drain current (i_D) ≠ 0.
  • Output voltage (v_o) = V_DD - i_DR_D.

Voltage Transfer Characteristics (VTC)

• Important thresholds:
  • V_OO, V_IL, V_IH.
• Equations:
  • d(v_o)/d(v_i) = -1 (for linear region).

Refreshing MOS Transistor Theory

NMOS Regions

• Cut-off:
  • V_GS ≤ V_t
  • i_D = 0, Output Resistance (r_o) = ∞.
• Linear Region:
  • V_DS < (V_GS - V_t)
  • Use relationship for i_D.
• Saturation Region:
  • V_DS ≥ (V_GS - V_t).

NMOS Inverter VTC

Finding V_OO

• Assume low input (v_i < V_t): Q is OFF,
  • V_OO = V_DD.

Finding V_II

• Assume Q is saturated; using equations for current relationships.

Finding V_M

• Set input and output voltages equal: v_G = v_D = V_M.

Static Power Dissipation

Analysis

• Average power dissipation can be found as follows:
  • P_sta = V_DD * i_D.
• Observations:
  • Static power varies with signal inputs.
  • Dynamic behavior also impacts power.

Dynamic Power Dissipation

Calculation

• Energy delivered during transitions:
  • E_d = C_L * V_DD² / 2.
• Total dynamic dissipation: P_d = f * C_L * V_DD².

Propagation Delay

• Time taken for output state to respond to input changes.
• Average propagation delay (t_p):
  • t_p = (t_P + t_P) / 2.

Logic Design with MOSFETs

Basic Principles

• Pull-up network (PUN): uses PMOS.
• Pull-down network (PDN): uses NMOS.
• Relationships:
  • AND operations = series; OR operations = parallel.
• Analyze worst-case conditions for switching.

Examples

Example 1: Design CMOS Inverter

• Adjust widths for n-channel based on specifications.

Example 2: Propagation Delay Computation

• Determine delays for a CMOS inverter driving other gates.

Summary

• Important factors in digital circuit design include power dissipation, propagation delay, and transistor sizing.
• Understanding VTC and load capacitances is crucial in optimizing circuit performance.