Body effect and substrate, live
11 parts
Four-terminal transistors expose the pin the three-pin models hide. Two identical M4 followers share one 6±2 V input: A's body is strapped to its source — the discrete-part default — and follows at ×0.96, while B's body is grounded, the IC reality, so its threshold climbs with its own source voltage: B's output rides a measured 0.55 V lower on average (0.32 V at the bottom of the swing, 0.76 V at the top) with its gain compressed to 0.85. Beside them an NPN Q4 amplifier has its substrate pin deliberately parked at +7 V: every downswing forward-biases the real collector–substrate junction, and the sine's bottom clips flat at 6.35 V. Body effect and the body/substrate diodes are genuine solved physics — the γ/φ threshold law plus Shockley junction companions — and MP4/QP4 are the same models mirrored.
- V1 2V·500Hz
- M41 Vt 2V
- R1 1kΩ
- M42 Vt 2V
- R2 1kΩ
- V2 800mV·500Hz
- Q41
- R3 1.5kΩ
- R4 470Ω
- V3 7V
- V4 12V
