PE2-1.2 Single Stage Amplifiers & Current Mirrors
You can analyse common source stages with resistive, current source and diode loads and with source degeneration, plus source follower, common gate, cascode and folded cascode, and design basic and cascode current mirrors.
Every analog IC is assembled from these few stages, so learn each by its gain, its impedances and what it is for rather than as a circuit to recognise. The cascode is the key structure: stacking devices raises output resistance and therefore gain, at the cost of voltage headroom, and the folded version exists to buy that headroom back. Current mirrors replace resistors on chip because matched transistors are easy to fabricate and accurate resistors are not.
Work through these
Basic concepts of single stage amplifiers
The frame for the topic: gain, bandwidth, swing, noise and power all pull against each other. Naming the trade-offs first stops the eight stages below being a catalogue.
Common source stage with resistive load and current source load
The workhorse stage, with two load choices. The current source load gives far more gain and less swing, which is the first real design decision.
Common source with diode load and with source degeneration
Two more load and degeneration choices, trading gain for linearity and predictability. Diode loads set gain by a device ratio, which is robust against process variation.
Source follower
The buffer stage, with gain near one and low output impedance. Body effect degrades it, which is a good example of a second order effect mattering.
Common gate stage
The stage with low input impedance and no Miller effect. It is the reason cascode structures work, which the next item builds on.
Cascode stage and folded cascode
Stacking to raise output impedance and so raise gain. The folded version buys headroom back, which matters as supply voltages fall.
Basic current mirrors
Copying a current accurately, which is how bias is distributed across a chip. Matching is the whole game, and it is a layout problem as much as a circuit one.
Cascode current mirrors
The higher-accuracy version, using the stacking idea above. It costs headroom, which is the recurring trade of this topic.
Frequency response of single stage CS amplifiers; the Miller effect
How the stage behaves with frequency, and the capacitance that appears multiplied at the input. The Miller effect explains why the simple stage is slower than its device capacitances suggest.
Sign in to keep your progress.
Free resources
We haven't checked most of these for screen reader use yet.
Links last checked 30 Aug 2026.
Stuck here?
Ask a mentor. A real person answers, and they can see exactly which topic you're on. Usually within a couple of working days.
Checking your session…
Topics shown in module order.