PROBLEM 011 · Easy · The common-gate stage
Gate Keeper
Common-gate amplifier
The problem
Build a common-gate amplifier: the input drives the transistor’s source, the gate is held at a fixed DC bias voltage, and the drain, loaded by a resistor from VDD, is the output.
You will need two voltage sources: the input source named “in”, connected to the source terminal, and a bias source of your own (name it anything except “in”) on the gate. Unlike the common-source stage, the output is in phase with the input, and the input sees a low resistance of about 1/gm.
The test bench
- Supply: VDD = 1.8 V.
- The test bench hangs a 200 fF load capacitor on the net named “out”.
- It applies the AC stimulus to the source named “in” only; your gate-bias source is held quiet.
Numbers to hit
- Voltage gain at least 14 dB
- Bandwidth (−3 dB) at least 30 MHz
- Output DC level between 0.6 V and 1.4 V
- Power at most 150 µW
- Every transistor in saturation
Design it yourself
Draw the circuit on a schematic canvas, size every transistor, and see it simulated in your browser with ngspice and the SkyWater SKY130 models. Every transistor lights up green, gold or red by operating region as you move the sliders.
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