MOSFETs Circuits
EEG 331: ELECTRONIC CIRCUITS I
Learning Outcomes
- To describe the MOSFET non – linear static iv characteristics and the equations for
each region of operations
- To analyze the MOSFET circuit at DC, as a switch and as amplifier.
- To analyze MOSFET amplifier circuit by small signal model and describe the need
for biasing
- To analyze MOSFET Active Load circuit
- To analyze MOSFET amplifier configurations such as common source, common
drain and common gate.
- To analyze the MOSFET differential amplifier and Opamp circuit by small signal
model
- To identify MOSFET multi-stage configuration in cascade and cascode
- To compare MOSFETs with BJTs in terms of structure, operation, iv characteristics,
application (amplifier and switch), and small signal analysis.
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
Learning Outcome
• DC analysis of circuits with
MOSFET and resistors
EEG 331: ELECTRONIC CIRCUITS I
Analysis of MOSFET circuits with DC
sources: Examples
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
Introduction
• In DC analysis of MOSFET, the
ideal current – voltage equations
are used.
• For n-channel MOSFET
EEG 331: ELECTRONIC CIRCUITS I
+VDD
Common Source Circuits
N – MOSFET
Id
Input: Gate-source
Output: Drain-source
RD
N – channel MOSFET R1
VDS
R2
VGS
V1
EEG 331: ELECTRONIC CIRCUITS I
Example
Refer to the circuit in previous slide, suppose R1 = 30 kΩ,
R2 = 20 kΩ and RD = 20 kΩ, VDD = 5 V, VT = 1 V and K = 0.2 mA / V2 .
Determine the drain current, Id and drain to source voltage VDS.
Assume that the transistor is biased in the saturation region.
𝑅2
By voltage divider: 𝑉𝐺𝑠 = 𝑉 =2𝑉
𝑅1 +𝑅2 𝐷𝐷
By KVL: 𝑉𝐷𝑆 = 𝑉𝐷𝐷 − 𝐼𝑑 𝑅𝐷
𝐾
At saturation 𝐼𝑑 = 𝑉𝐺𝑆 − 𝑉𝑇 2 = 0.1 𝑚𝐴
2
Hence, 𝑉𝐷𝑆 = 𝑉𝐷𝐷 − 𝐼𝑑 𝑅𝐷 = 3 𝑉
Remember 𝑉𝐷𝑆 > 𝑉𝐷𝑆(𝑠𝑎𝑡) = 𝑉𝐺𝑆 − 𝑉𝑇
Which confirms that the transistor was indeed in saturation
EEG 331: ELECTRONIC CIRCUITS I
Common Source Circuit +VDD
P-MOSFET
Input: Source-Gate
Output: Source-Drain
Id
P – channel MOSFET VSG
R1
VG
VSD
R2
RD
EEG 331: ELECTRONIC CIRCUITS I
For P-MOSFET
0 𝑖𝑓 𝑣𝑆𝐺 < 𝑉𝑡𝑝 𝑜𝑟 𝑣𝐺𝑆 > 𝑉𝑡𝑝 𝑐𝑢𝑡𝑜𝑓𝑓
𝐾 2
𝑖𝑑 = 𝑣 + 𝑉𝑡𝑝 𝑖𝑓 𝑣𝑆𝐺 > 𝑉𝑡𝑝 𝑜𝑟 𝑣𝐺𝑆 < 𝑉𝑡𝑝 𝑎𝑛𝑑 𝑣𝑆𝐷 ≥ 𝑣𝑆𝐺 + 𝑉𝑡𝑝 𝑠𝑎𝑡𝑢𝑟𝑎𝑡𝑖𝑜𝑛
2 𝑆𝐺
𝑣𝑆𝐷
𝐾 𝑣𝑆𝐺 + 𝑉𝑡𝑝 − 𝑣𝑆𝐷 𝑖𝑓 𝑣𝑆𝐺 > 𝑉𝑡𝑝 𝑜𝑟 𝑣𝐺𝑆 < 𝑉𝑡𝑝 𝑎𝑛𝑑 𝑣𝑆𝐷 < 𝑣𝑆𝐺 + 𝑉𝑡𝑝 𝑙𝑖𝑛𝑒𝑎𝑟
2
For N-MOSFET
EEG 331: ELECTRONIC CIRCUITS I
Example
Refer to the previous circuit for common source configuration
for P-MOSFET, suppose R1=R2= 50kΩ, VDD = 5V, RD = 7.5 kΩ,
Vtp = - 0.8 V and K = 0.4 mA / V2 . Determine the drain current
and source-to-drain voltage.
𝑅1
By voltage divider: 𝑉𝑆𝐺 = 𝑉 = 2.5 𝑉
𝑅1 +𝑅2 𝐷𝐷
By KVL: 𝑉𝑆𝐷 = 𝑉𝐷𝐷 − 𝐼𝑑 𝑅𝐷
𝐾 2
At saturation 𝐼𝑑 = 𝑉𝑆𝐺 + 𝑉𝑇𝑝 = 0.578 𝑚𝐴
2
Hence, 𝑉𝑆𝐷 = 𝑉𝐷𝐷 − 𝐼𝑑 𝑅𝐷 = 0.665 𝑉
But the condition for saturation𝑉𝑆𝐷 > 𝑉𝑆𝐷(𝑠𝑎𝑡) = 𝑉𝑆𝐺 + 𝑉𝑇
If we check we see that this solution is incorrect (1.7 V is more
than 0.665 V
Hence the transistor is not in saturation
EEG 331: ELECTRONIC CIRCUITS I
Continued…
Hence, we use the drain equation for the linear region
𝑣𝑆𝐷
𝐼𝑑 = 𝐾 𝑣𝑆𝐺 + 𝑉𝑡𝑝 − 𝑣𝑆𝐷 , and 𝑉𝑆𝐷 = 𝑉𝐷𝐷 − 𝐼𝑑 𝑅𝐷
2
Combining these, we obtain
𝑉𝐷𝐷 − 𝐼𝑑 𝑅𝐷
𝐼𝑑 = 𝐾 𝑣𝑆𝐺 + 𝑉𝑡𝑝 − 𝑉𝐷𝐷 − 𝐼𝑑 𝑅𝐷
2
Plugging in some values
5 − 7.5𝐼𝑑
𝐼𝑑 = 0.4 2.5 − 0.8 − 5 − 7.5𝐼𝑑
2
𝐼𝑑 = 0.4 1.7 − 2.5 + 3.75𝐼𝑑 5 − 7.5𝐼𝑑
We obtain a quadratic equation
11.25𝐼𝑑2 − 8.9𝐼𝑑 + 1.6 = 0
We take the positive value of the solution, hence 𝐼𝑑 = 0.515 mA
EEG 331: ELECTRONIC CIRCUITS I
Continued..
In this case, 𝑉𝑆𝐷 = 𝑉𝐷𝐷 − 𝐼𝑑 𝑅𝐷 = 5 − 7.5𝐼𝑑 = 1.1375 𝑉
But for linear region 𝑉𝑆𝐷 < 𝑉𝑆𝐷(𝑠𝑎𝑡) = 𝑉𝑆𝐺 + 𝑉𝑇
If we check we see that this solution is verified
Hence the transistor is operating in the linear region.
EEG 331: ELECTRONIC CIRCUITS I
Why do we need transistor bias?
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
Graphical Method – Load Line
• MOSFET has three region of operation: linear, saturation and cutoff
• Choosing a region of operation is called biasing
• Loadline can be used to visualize and determine the transistor
operating point
For N-MOSFET circuit, we can write
𝑉𝐷𝑆 = 𝑉𝐷𝐷 − 𝐼𝑑 𝑅𝐷
We plot two point on the : when 𝐼𝑑 = 0, 𝑉𝐷𝑆 = 𝑉𝐷𝐷
𝑉𝐷𝐷
And when 𝑉𝐷𝑆 = 0, 𝐼𝑑 =
𝑅𝐷
We draw a straight line connecting the two points, this line is called
the loadline
The intersection of the of the loadline on the IV characteristics gives
the Q-points
EEG 331: ELECTRONIC CIRCUITS I
Loadline and Modes of Operation
EEG 331: ELECTRONIC CIRCUITS I
Design example +VDD
𝑊
Given that parameter 𝐾 = 𝑘𝑛 , where
𝐿
𝐴 𝑊
𝑉𝐷𝐷 = 5𝑉 𝑘𝑛 = 80µ 2 , = 4, 𝑉𝑡𝑛 = 2𝑉,
𝑉 𝐿
𝑅𝑆 = 2 𝑘Ω, 𝑅𝐷 = 10 𝑘Ω R1
RD
Design the circuit such that the drain
current 𝐼𝑑 = 0.5 𝑚𝐴 and the current in the
bias resistor is approximately one tenth of
VG
the drain current.
VS
Choose the appropriate value of R1 and R2 R2
to the nearest standard resistor values. RS
Id
- VDD
EEG 331: ELECTRONIC CIRCUITS I
Solution
𝑊 𝐴
𝐾 = 𝑘𝑛 𝐿
= 320 µ 𝑉 2 = 0.32 𝑚𝐴/𝑉 2
𝐾 2
Assume the transistor is at saturation 𝐼𝑑 = 𝑉𝐺𝑆 − 𝑉𝑇
2
0.32𝑚𝐴/𝑉 2
0.5 𝑚𝐴 = 𝑉𝐺𝑆 − 𝑉𝑇 2
2
𝑉𝐺𝑆 − 𝑉𝑇 = 1.768, 𝑉𝐺𝑆 = 3.768 𝑉
1
Current through the biasing resistor is allowed to be maximum 10 𝐼𝑑 = 0.05 mA
Potential across R1 and R2 is 10 V
𝑉 10
R1+R2 = 𝐼 = 0.05 𝑚𝐴 = 200 𝑘Ω
𝑅2
𝑉𝐺𝑆 = 𝑉𝐺 − 𝑉𝑆 = 10 − 5 − 𝐼𝑑𝑅𝑠 − 5
𝑅1 + 𝑅2
𝑅2
3.768 𝑉 = 10 − 5 − 0.5𝑚𝐴 × 2𝑘Ω − 5
𝑅1 + 𝑅2
𝑅2
3.768 𝑉 = 10 − 5 + 4
𝑅1 + 𝑅2
−0.232 + 5 𝑅2
=
10 𝑅1 + 𝑅2
EEG 331: ELECTRONIC CIRCUITS I
Continued
𝑅2
0.4768 = 𝑅1+𝑅2 But, R1+R2 = 200 kΩ R1 = 95 k R2 = 105 k
To the nearest standard resistor values R1 = 100 k R2 = 110 k
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
Non-linear resistor / Active Load
• In this circuit, one can easily see that 𝑉𝐺𝑆 = 𝑉𝐷𝑆
• Remember, in saturation, 𝑉𝐷𝑆 > 𝑉𝐷𝑆(𝑠𝑎𝑡) = 𝑉𝐺𝑆 − 𝑉𝑇
• Thus, 𝑉𝐺𝑆 = 𝑉𝐷𝑆 > 𝑉𝐷𝑆(𝑠𝑎𝑡) = 𝑉𝐺𝑆 − 𝑉𝑇
• Hence, this circuit will always be in saturation
𝐾 2 𝐾 2
• Which means, 𝐼𝑑 = 𝑉𝐺𝑆 − 𝑉𝑇 = 𝑉𝐷𝑆 − 𝑉𝑇
2 2
• Hencce, current is always proportional to square of voltage
• This is just a non-linear resistor
• Often times, we use this in CMOS IC effectively as
load resistors
EEG 331: ELECTRONIC CIRCUITS I
Non-linear resistor- IV Curve
EEG 331: ELECTRONIC CIRCUITS I
Application of non-linear load resistor
EEG 331: ELECTRONIC CIRCUITS I
Constant-current source biasing
EEG 331: ELECTRONIC CIRCUITS I
MOSFET Applications
• Amplifier: Stay in saturation regime
• Switch: Operate between cutoff and linear regime
• Digital Logic Gate: Operate between cutoff and linear regime
EEG 331: ELECTRONIC CIRCUITS I
MOSFET Applications: Amplifier circuit
EEG 331: ELECTRONIC CIRCUITS I
MOSFET Small Signal Analysis
EEG 331: ELECTRONIC CIRCUITS I
Outline
• Loadline and Small Signal
Parameters
• Small Signal Equivalent Circuits
• Problem-Solving Technique for
MOSFET AC Analysis
EEG 331: ELECTRONIC CIRCUITS I
Introduction
➢ To determine suitable transistor bias
i.e linear, cutoff, or saturation
DC analysis
➢ Analyze the circuit with dc inputs
➢ Use the equations for drain currents
➢ Determine the bias and load
resistance
➢ First use DC analysis to set the
AC analysis Q-point and determine the small
and small signal parameters
signal analysis ➢ Assume dc are short circuited, only
ac signals are used
➢ Mainly desired to obtain
EEG 331: ELECTRONIC CIRCUITS I amplification parameters
Loadline and Small Signal Parameters Vdd
• N-channel MOSFET connected in CS configuration Id
• DC input VGSQ is used to set the Q-point, ac input Vac is also applied
• The loadline with ac input is shown below RD
• Q-point depends on vGS, RD, Vdd and transistor parameters
vo
vi vGS
VGSQ
EEG 331: ELECTRONIC CIRCUITS I
Transistor Parameters
DC components of AC components of
Instantaneous gate
gate to source gate to source volt
to source voltage
voltage age
𝑣𝐺𝑆 = 𝑉𝐺𝑆𝑄 + 𝑣𝑖 =𝑉𝐺𝑆𝑄 + 𝑣𝑔𝑠
where 𝑣𝐺𝑆 = instantaneous gate to source voltage,
𝑉𝐺𝑆𝑄 = dc input bias at Q point which is also the dc component of the gate to source voltage,
𝑣𝑔𝑠 = ac component of the gate to source voltage
Instantaneous drain current is given as:
𝐾 2
𝐾 2 𝐾 2
𝑖𝐷 = 𝑣 − 𝑉𝑇 = 𝑉 + 𝑣𝑔𝑠 − 𝑉𝑇 = 𝑉 − 𝑉𝑇 + 𝑣𝑔𝑠 =
2 𝐺𝑆 2 𝐺𝑆𝑄 2 𝐺𝑆𝑄
𝐾 2 𝐾 2
𝑉𝐺𝑆𝑄 − 𝑉𝑇 + 𝑣𝑔𝑠 + 𝐾𝑣𝑔𝑠 𝑉𝐺𝑆𝑄 − 𝑉𝑇
2 2
𝐼𝐷𝑄 (dc drain current at Q-point)
𝑐𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡 𝑜𝑓 𝑖𝐷 𝑙𝑖𝑛𝑒𝑎𝑟𝑙𝑦 𝑝𝑟𝑜𝑝𝑜𝑟𝑡𝑖𝑜𝑛𝑎𝑙 𝑡𝑜 𝑣𝑔𝑠
𝑈𝑛𝑑𝑒𝑠𝑖𝑟𝑒𝑑 ℎ𝑎𝑟𝑚𝑜𝑛𝑖𝑐𝑠
EEG 331: ELECTRONIC CIRCUITS I
Transistor Parameters
We always want to minimize harmonics in amplifiers ! Hence we require that:
𝐾 2
𝑣𝑔𝑠 ≪ 𝐾𝑣𝑔𝑠 𝑉𝐺𝑆𝑄 − 𝑉𝑇 OR 𝑣𝑔𝑠 ≪ 2 𝑉𝐺𝑆𝑄 − 𝑉𝑇
2
We may achieve this condition, if we make 𝑣𝑔𝑠 small enough, compare to 2 𝑉𝐺𝑆𝑄 − 𝑉𝑇
Hence we require this small signal condition in linear amplifiers
(for output to be linear combination of the input).
Assuming this condition is satisfied, we may neglect the harmonics and obtain:
𝐾 2
𝑖𝐷 = 𝑉 − 𝑉𝑇 + 𝐾𝑣𝑔𝑠 𝑉𝐺𝑆𝑄 − 𝑉𝑇 = 𝐼𝐷𝑄 + 𝑖𝑑
2 𝐺𝑆𝑄
𝐾 2
𝐼𝐷𝑄 = 𝑉𝐺𝑆𝑄 − 𝑉𝑇 is the dc component of the drain current at Q-point
2
𝑖𝑑 = 𝐾𝑣𝑔𝑠 𝑉𝐺𝑆𝑄 − 𝑉𝑇 is the ac component of the drain current or the linearized
component
𝑖𝐷 is the instantaneous drain current
EEG 331: ELECTRONIC CIRCUITS I
Transistor Parameters
Hence, we may write:
𝑖𝑑 = 𝑔𝑚 𝑣𝑔𝑠 𝑔𝑚 = 𝐾 𝑉𝐺𝑆𝑄 − 𝑉𝑇
𝒈𝒎 is called transconductance, which linearly relates the ac components of the
drain current (output) with the ac component of the gate to source voltage (input)
𝑊
Also parameter: 𝐾 = µ𝑛 𝑐𝑜𝑥 where, µ𝑛 is the electron mobility
𝐿
𝑐𝑜𝑥 is the oxide capacitance per unit area, W is the transistor width,
L is the gate length.
Transconductance (𝒈𝒎) can also be obtained from:
𝑖𝑑 = 𝐾𝑣𝑔𝑠 𝑉𝐺𝑆𝑄 − 𝑉𝑇
𝜕𝑖
𝑔𝑚 = 𝜕𝑣 𝑑 ฬ = 𝐾 𝑉𝐺𝑆𝑄 − 𝑉𝑇 = 2𝐾𝐼𝐷𝑄
𝑔𝑠
𝑣𝑔𝑠 =𝑉𝐺𝑆𝑄 =𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡
𝐾 2
Remember, 𝐼𝐷𝑄 = 2 𝑉𝐺𝑆𝑄 − 𝑉𝑇
EEG 331: ELECTRONIC CIRCUITS I
AC equivalent Circuit Vdd
From this circuit shown we may write the output as: Id
RD
𝑣𝑜 = 𝑉𝑑𝑑 − 𝑖𝐷 𝑅𝐷 = 𝑉𝑑𝑑 − 𝐼𝐷𝑄 𝑅𝐷 − 𝑖𝑑 𝑅𝐷
AC component of output voltage vo
DC component of output voltage
Hence, we may write the ac component of the output voltage as:
𝑣𝑜 = 𝑣𝑑𝑠 = −𝑖𝑑 𝑅𝐷
Also, 𝑖𝑑 = 𝑔𝑚 𝑣𝑔𝑠
vi vGS
𝐼𝑑 = 𝑔𝑚 𝑉𝑔𝑠
𝑉𝑑𝑠 = −𝐼𝑑 𝑅𝐷
VGSQ
To obtain the ac equivalent circuit, we set all dc sources to
zero. This is because a time varying drain current produces
no voltage across 𝑉𝑑𝑑 , hence the impedance is zero at 𝑉𝑑𝑑 .
We therefore say the node connecting 𝑅𝐷 and 𝑉𝑑𝑑 is at
ground potential. This is shown in the next slide.
EEG 331: ELECTRONIC CIRCUITS I
MOSFET AC equivalent Circuit
vo
id
RD
vi vGS
EEG 331: ELECTRONIC CIRCUITS I
Small Signal Equivalent Circuit of CS-
NMOS
EEG 331: ELECTRONIC CIRCUITS I
𝜕𝑖𝑑
𝑟𝑜 = ቤ
𝜕𝑣𝑑𝑠 𝑣
𝑔𝑠 =𝑉𝐺𝑆𝑄 =𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡
λ is channel length modulation parameter
EEG 331: ELECTRONIC CIRCUITS I
Small Signal Models for MOSFETs
(Contd)
EEG 331: ELECTRONIC CIRCUITS I
Small Signal Models for MOSFETs
(Contd)
In the analysis of a MOSFET amplifier circuit, the transistor can be replaced by the
equivalent circuit models. The rest of the circuit remains unchanged except that ideal
constant dc voltage sources are replaced by short circuits.
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
The T Equivalent Circuit-model
Through a simple circuit
transformation it is
possible to develop an
alternative equivalent
circuit model for the
MOSFET. The development
of such a model, known as
the T model.
EEG 331: ELECTRONIC CIRCUITS I
Amplifier Configurations:
Common Source Amplifier without Rs
What is the purpose of Cc1,
Cc2 and Cs ?
EEG 331: ELECTRONIC CIRCUITS I
Common Source Amplifier without Rs
Small Signal Equivalent circuit of the amplifier circuit
What is a unilateral transistor ?
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
Common Source Amplifier without Rs
Small signal analysis can also be directly performed on the equivalent circuit with the MOSFET
model implicitly implied. This is as shown above.
EEG 331: ELECTRONIC CIRCUITS I
Common Source Amplifier with Rs
EEG 331: ELECTRONIC CIRCUITS I
Common Source Amplifier with Rs:
Small Signal Equivalent Circuit
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
Common Gate Amplifier
CG Amplifier Circuit
EEG 331: ELECTRONIC CIRCUITS I
Common Gate Amplifier:
Small Signal Equivalent Circuit
EEG 331: ELECTRONIC CIRCUITS I
Common Gate Amplifier with
current signal input
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
Application of CG Amplifier
EEG 331: ELECTRONIC CIRCUITS I
Common Drain Amplifier or Source
Follower
Circuit
EEG 331: ELECTRONIC CIRCUITS I
Common Drain Amplifier or Source
Follower
Small Signal Equivalent Circuit
EEG 331: ELECTRONIC CIRCUITS I
Common Drain Amplifier or Source
Follower
Small Signal Analysis by Inspection on the Circuit
EEG 331: ELECTRONIC CIRCUITS I
Common Drain Amplifier or Source
Follower
Fig 4.46 d
Circuit for determining the output resistance Rout of the source follower
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
Summary: MOSFET Amplifier
Configurations
EEG 331: ELECTRONIC CIRCUITS I
Summary: MOSFET Amplifier
Configurations
EEG 331: ELECTRONIC CIRCUITS I
Summary: MOSFET Amplifier
Configurations
EEG 331: ELECTRONIC CIRCUITS I
Summary: MOSFET Amplifier
Configurations
EEG 331: ELECTRONIC CIRCUITS I
Summary: MOSFET Amplifier
Configurations
EEG 331: ELECTRONIC CIRCUITS I
MOSFETS CURRENT MIRROR,
ACTIVE LOAD, CURRENT STEERING
EEG 331: ELECTRONIC CIRCUITS I
MOSFETS CURRENT MIRROR,
ACTIVE LOAD, CURRENT STEERING
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
Consider the circuit below
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
Differential Amplifier (DA) and
Operational Transconductance
Amplifier (OTA)
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
Remaining part of the course plan
to be covered is in red
- To describe the MOSFET non – linear static iv characteristics and the equations for
each region of operations
- To analyze the MOSFET circuit at DC, as a switch and as amplifier.
- To analyze MOSFET amplifier circuit by small signal model and describe the need
for biasing
- To analyze MOSFET Active Load circuit
- To analyze MOSFET amplifier configurations such as common source, common
drain and common gate.
- To analyze the MOSFET differential amplifier and Opamp circuit by small signal
model
- To identify MOSFET multi-stage configuration in cascade and cascode
- To compare MOSFETs with BJTs in terms of structure, operation, iv
characteristics, application (amplifier and switch), and small signal analysis.
EEG 331: ELECTRONIC CIRCUITS I
Comparison between MOSFET and
BJT: Structure
BJT
EEG 331: ELECTRONIC CIRCUITS I
Output IV Characteristics
MOSFET BJT
EEG 331: ELECTRONIC CIRCUITS I
Saturation region for MOSFET ≈ Forward active for BJT
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
MOSFET BJT
EEG 331: ELECTRONIC CIRCUITS I
EEG 331: ELECTRONIC CIRCUITS I
Multistage Amplifiers: Cascade
Practical transistor amplifiers usually consist of a number of stages connected in
cascade. In addition to providing gain, the first (or input) stage is usually required to
provide a high input resistance in order to avoid loss of signal level when the
amplifier is fed from a high resistance source.
A cascade amplifier is a two-port network comprised of a series of amplifiers in which
each amplifier connects (sends) its output to the input of the next amplifier in the chain.
EEG 331: ELECTRONIC CIRCUITS I
Multistage Amplifiers: Cascode
By placing a common-gate (common-base) amplifier stage in cascade with a common-
source (common-emitter) amplifier stage, a very useful and versatile amplifier circuit
results. It is known as the cascode configuration.
The basic idea behind the cascode amplifier is to combine the high input resistance and
large transconductance achieved in a common-source (common-emitter) amplifier with
the current-buffering property and the superior high-frequency response of the
common-gate (common-base) circuit.
EEG 331: ELECTRONIC CIRCUITS I
MOS Cascode
EEG 331: ELECTRONIC CIRCUITS I
MOS Cascode
EEG 331: ELECTRONIC CIRCUITS I
