Simple Push-Pull Follower, with Distortion

Complementary emitter followers reproduce both signal polarities but leave a crossover dead zone.

Circuit operation

An NPN transistor supplies positive load current and a PNP transistor supplies negative load current from ±6 V rails. Their bases share a 3 V peak sine input; their emitters share the output and a 1 kΩ load.

Expected behavior

$$V_o\approx\begin{cases}V_i-V_{BE},&V_i>V_{BE}\\0,&|V_i|<V_{BE}\\V_i+V_{BE},&V_i<-V_{BE}\end{cases}$$ $$I_L=V_o/R_L$$

Around zero input, neither transistor conducts appreciably and the output has a flattened crossover region. Away from crossover the output follows the input with the appropriate base-emitter offset.

Reading the results

The first voltage probe is green and the second is red. Additional voltage traces use distinct colors. Current probes, when present, start with blue and then purple. The chart opens with separate traces on a fixed time window; the table retains the same probe order. Zoom to extents includes the complete schematic.

The saved transient runs for 4.0 ms with a maximum step of 1.00 µs. Compare settled cycles after startup and use time-axis cursors to measure delays or periods.

Try a change

Set V1 peak amplitude to 1 V; compare the fraction of each cycle affected by crossover. Restore the saved values after comparing the result.

Model limits

These are generic transistor models, not a specific manufactured part. The bipolar models use nominal forward current gain 100 with illustrative junction capacitances and transit times. Device mismatch, temperature drift, layout parasitics, breakdown and detailed noise are not represented. The schematic and component properties expose the values used.