252330 BJT Amplifier Lab

How it works

Every experiment follows the same pipeline: design and simulate the circuit in LTspice, parse the raw waveform data in Python, then compute and plot the results.

LTspice schematic (.asc)→ simulation output (.raw)→ Python (ltspice parser)→ NumPy analysis→ Matplotlib figure

Lab 1 · BJT Characterization

A DC sweep of the transistor: V_CE from 0 to 3 V, with the base current stepped from 0 to 10 µA in 2 µA steps. A second script fits the active region of each curve (V_CE > 0.4 V) and extends it back to the V_CE axis, which it crosses at −98.65 V.

Early voltage: 98.65 V

Ic vs Vce characteristic curves for six base currents — **I_C–V_CE characteristics** Six curves, I_B = 0 to 10 µA. The dashed line marks V_CE = 0.3 V.

Lab 1 · Single-Stage Amplifiers

The same transistor built into the three classic single-stage topologies — Common Emitter, Common Collector, and Common Base. Each one is run twice: a transient sweep driven by a 10 mV, 1 kHz sine (V_in vs V_out), and an AC sweep plotted as output magnitude in dB for a 1 V AC source, with the −3 dB cursors drawn on the plot.

Configuration	Midband	Lower −3 dB	Upper −3 dB	Output phase
Common Emitter	≈41 dB	≈60 Hz	≈20 MHz	inverted
Common Collector	≈0 dB (0.97 V/V)	1.8 Hz	21 GHz	in phase
Common Base	41.4 dB	500 Hz	18.8 MHz	in phase

The AC sweeps do not all cover the same span: CE and CB run 10 Hz–100 MHz, CC runs 1 mHz–100 GHz. All three drive R_L = 100 MΩ from a source with no series resistance.

Common Emitter Vin-Vout waveform — **Common Emitter · V_in–V_out** 10 mV in; the output swings about +1.0 V / −1.3 V, inverted.

Common Emitter frequency response — **Common Emitter · Frequency response** Flat at roughly 41 dB, with the −3 dB cursors near 60 Hz and 20 MHz.

Common Collector Vin-Vout waveform — **Common Collector · V_in–V_out** The output tracks the 10 mV input at almost the same amplitude and in phase.

Common Collector frequency response — **Common Collector · Frequency response** Flat just under 0 dB (0.97 V/V at 1 kHz) between 1.8 Hz and 21 GHz.

Common Base Vin-Vout waveform — **Common Base · V_in–V_out** 10 mV in; the output swings about +0.95 V / −1.2 V, in phase.

Common Base frequency response — **Common Base · Frequency response** 41.4 dB midband, with −3 dB points at 500 Hz and 18.8 MHz.

Lab 2 · Coupling Comparison

Two two-stage amplifiers, built with different inter-stage connections and swept with .ac over 10 Hz–100 MHz (capacitor) and 10 mHz–100 MHz (direct). Both keep 10 µF input and output coupling capacitors and an emitter bypass capacitor, so both roll off at the low end.

Build	Stages	Inter-stage link	Measured
Capacitor coupling	2SC458 → 2SC458, both common emitter	0.1 µF series capacitor	41.0 dB midband; −3 dB at 416 Hz and 599 kHz
Direct coupling	2SC458 (NPN) → 2SA1015 (PNP)	collector wired straight to the next base	37.7 dB midband; −3 dB at 10.5 Hz and 438 kHz

Capacitor coupling frequency response — **Capacitor coupling** 41.0 dB midband, 416 Hz to 599 kHz between the −3 dB cursors.

Direct coupling frequency response — **Direct coupling** 37.7 dB midband, 10.5 Hz to 438 kHz between the −3 dB cursors.