CSCE 3303 - FUNDAMENTAL
MICROELECTRONICS
MOSFET DC CIRCUITS - PROBLEMS
DR. DALIA SELIM
ADJUNCT FACULTY (ASSISTANT PROFESSOR)
1. REVIEW
The relative levels of the terminal voltages of the enhancement NMOS transistor for
operation in the triode region and in the saturation region.
CSCE 3303 – FUNDAMENTAL MICROELECTRONICS MOSFET DC CIRCUITS - PROBLEMS 2
1. REVIEW
1 𝑊 𝑊 𝑊 21
𝑖𝐷 =𝑖𝑖𝐷
𝐷𝜇
=
=𝑛 𝐶 𝜇
𝑜𝑥𝜇𝑛𝑛𝐶𝐶𝑜𝑥
𝑜𝑥 𝑣𝑂𝑉𝑣𝑣
−𝑂𝑉 in
𝑂𝑉 𝑣𝐷𝑆𝐴 in𝑣𝐴
𝐷𝑆 in 𝐴
2 𝐿 𝐿 𝐿 2
CSCE 3303 – FUNDAMENTAL MICROELECTRONICS MOSFET DC CIRCUITS - PROBLEMS 3
1. REVIEW
The iD – vDS characteristics for an enhancement-type NMOS transistor
CSCE 3303 – FUNDAMENTAL MICROELECTRONICS MOSFET DC CIRCUITS - PROBLEMS 4
1. REVIEW
The iD-vGS characteristic of an NMOS transistor operating in the saturation region. The iD-vOV characteristic can be obtained by simply re-
labeling the horizontal axis, that is, shifting the origin to the point vGS = Vtn.
CSCE 3303 – FUNDAMENTAL MICROELECTRONICS MOSFET DC CIRCUITS - PROBLEMS 5
1. REVIEW
CSCE 3303 – FUNDAMENTAL MICROELECTRONICS MOSFET DC CIRCUITS - PROBLEMS 6
1. REVIEW
Effect of vDS on iD in the saturation region. The MOSFET
parameter VA depends on the process technology and, for a
given process, is proportional to the channel length L.
CSCE 3303 – FUNDAMENTAL MICROELECTRONICS MOSFET DC CIRCUITS - PROBLEMS 7
QUICK RECAP!
• The equation used to
define iD depends on 𝑖𝐷 = 𝜇𝑛 𝐶𝑜𝑥
𝑊
𝑣 𝑣 in 𝐴
relationship btw vDS 𝐿 𝑂𝑉 𝐷𝑆
and vOV.
• vDS << vOV 𝑊 1
• vDS < vOV 𝑖𝐷 = 𝜇𝑛 𝐶𝑜𝑥
𝐿
𝑣𝑂𝑉 − 𝑣𝐷𝑆 𝑣𝐷𝑆 in 𝐴
2
• vDS => vOV
• vDS >> vOV 1 𝑊 2
𝑖𝐷 = 𝜇𝑛 𝐶𝑜𝑥 𝑣𝑂𝑉 in 𝐴
2 𝐿
1 𝑊 2
𝑖𝐷 = 𝜇𝑛 𝐶𝑜𝑥 𝑣𝑂𝑉 1 + 𝜆𝑣𝐷𝑆 in 𝐴
2 𝐿
CSCE 3303 – FUNDAMENTAL MICROELECTRONICS MOSFET DC CIRCUITS - PROBLEMS 8
2. MOSFET CIRCUITS AT DC
• We move on to discuss how MOSFET’s
behave in dc circuits.
• We will neglect the effects of channel
length modulation (assuming l = 0).
• We will work in terms of overdrive
voltage (vOV), which reduces need to
DC
distinguish between PMOS and
NMOS.
CSCE 3303 – FUNDAMENTAL MICROELECTRONICS MOSFET DC CIRCUITS - PROBLEMS 9
EXAMPLE 1: NMOS TRANSISTOR
• Problem Statement: Design the circuit of the
figure, that is, determine the values of RD and
RS – so that the transistor operates at ID =
0.4mA and VD = +0.5V. The NMOS
transistor has Vt = 0.7V, mnCox = 100mA/V2,
L = 1mm, and W = 32mm. Neglect the
channel-length modulation effect (i. e. assume
that l = 0).
CSCE 3303 – FUNDAMENTAL MICROELECTRONICS MOSFET DC CIRCUITS - PROBLEMS 10
EXAMPLE 2:
• Problem Statement: The figure shows an NMOS
transistor with its drain and gate terminals connected
together.
• Find the 𝑖 − 𝑣relationship of the resulting two-terminal
device in terms of the MOSFET parameters 𝑘𝑛 and 𝑉𝑡𝑛 .
Neglect channel-length modulation (i.e., λ = 0). Note
that this two-terminal device is known as a diode-
connected transistor.
CSCE 3303 – FUNDAMENTAL MICROELECTRONICS MOSFET DC CIRCUITS - PROBLEMS 11
EXAMPLE 3: MOSFET
• Problem Statement: Design the circuit in
Figure 5.23 to establish a drain voltage
of 0.1V. What is the effective resistance
between drain and source at this
operating point? Let Vtn = 1V and
k’n(W/L) = 1mA/V2.
Figure 5.23: Circuit for Example
5.5.
CSCE 3303 – FUNDAMENTAL MICROELECTRONICS MOSFET DC CIRCUITS - PROBLEMS 12
EXAMPLE 4: MOSFET
• Problem Statement: Analyze the circuit shown in the figure to
determine the voltages at all nodes and the current through all
branches. Let Vtn = 1V and k’n(W/L) = 1mA/V2. Neglect the channel-
length modulation effect (i.e. assume l = 0).
CSCE 3303 – FUNDAMENTAL MICROELECTRONICS MOSFET DC CIRCUITS - PROBLEMS 13
EXAMPLE 5: PMOS TRANSISTOR
• Problem Statement: Design the circuit of Figure 5.25
so that transistor operates in saturation with ID =
0.5mA and VD = +3V. Let the enhancement-type
PMOS transistor have Vtp = -1V and k’p(W/L) =
1mA/V2. Assume l = 0.
• Q: What is the largest value that RD can have while
maintaining saturation-region operation?
Figure 5.25: Circuit for
Example 5.7.
CSCE 3303 – FUNDAMENTAL MICROELECTRONICS MOSFET DC CIRCUITS - PROBLEMS 14
EXAMPLE 6: CMOS TRANSISTOR
• Problem Statement: The NMOS and PMOS
transistors in the circuit shown in the are
matched, with k’n(Wn/Ln) = k’p(Wp/Lp) =
1mA/V2 and Vtn = -Vtp = 1V. Assuming l = 0
for both devices.
• Q: Find the drain currents iDN and iDP, as well as
voltage vO for vI = 0V, +2.5V, and -2.5V.
Figure 5.26: Circuits for Example
CSCE 3303 – FUNDAMENTAL MICROELECTRONICS
5.8.
MOSFET DC CIRCUITS - PROBLEMS 15
Copyright notice: most of these slides and figures are either reproduced or
adopted either from the required textbook and its official slides
CSCE 3303 – FUNDAMENTAL MICROELECTRONICS MOSFET DC CIRCUITS - PROBLEMS 16
