ESE 372 / Spring 2013 / Lecture 23
Last time: MOSFET differential pair
Common input
Output is taken differentially:
Differential input
Output is taken differentially:
perfectly matched
Output is taken single endedly:
Output is taken single endedly:
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ESE 372 / Spring 2013 / Lecture 23
Allowed range of input voltage
Common input
Differential input
Virtual ground
To keep MOSFETS is saturation
To keep both MOSFETS in on state
To keep MOSFETS in on state
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ESE 372 / Spring 2013 / Lecture 23
MOSFET differential pair
Single ended output needs only one RD
Single-ended
This configuration suffers from the same fg
ff f
problem as CS amplifier with resistive load – limited voltage swing for high gain.
AND
Limited CMRR:
What could be done?
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ESE 372 / Spring 2013 / Lecture 23
Why resistive load is not good?
Voltage gain is limited
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ESE 372 / Spring 2013 / Lecture 23
Why resistive load is not good?
O t t V lt
Output Voltage swing is limited
i i li it d
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ESE 372 / Spring 2013 / Lecture 23
Why resistive load is not good?
It i i
It is impossible to get high gain and maintain large voltage swing at the same time
ibl t
t hi h i
d
i t i l
lt
i
t th
ti
What could be done?
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ESE 372 / Spring 2013 / Lecture 23
Concept of active load.
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ESE 372 / Spring 2013 / Lecture 23
Basic p-MOS current mirror as a load.
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ESE 372 / Spring 2013 / Lecture 23
Basic p-MOS current mirror as a load.
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ESE 372 / Spring 2013 / Lecture 23
MOSFET differential pair
Differential stage with active load and balanced inputs
How?
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ESE 372 / Spring 2013 / Lecture 23
Cascode current mirror
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ESE 372 / Spring 2013 / Lecture 23
Cascode current mirror
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ESE 372 / Spring 2013 / Lecture 23
Cascode current mirrors for both current source bias and active load.
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ESE 372 / Spring 2013 / Lecture 23
Topics for final exam.
(next week we will be doing review and solving some problems no new material)
(next week we will be doing review and solving some problems, no new material)
MOSFET structure and operation: enhancement and depletion mode devices.
MOSFET structure and operation: enhancement and depletion mode devices.
MOSFET DC circuits and bias circuits (basic current mirror).
MOSFET
MOSFET small signal parameters.
ll i
l
MOSFET‐based single transistor amplifiers: CS, CG, CD.
MOSFET internal capacitances and frequency limitations.
Frequency response of CS amplifier
MOSFET differential stage with resistive load
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