I cannot afford a function generator and oscope right now, so I'm trying to learn analog electronics with Spice (MacSpice, to be specific). Below is the Spice model for a simple emitter-follower circuit. Vcc is 15V, and the input at the base is a 5V 60Hz sine wave with a 0V DC offset. R1 sits between the transistor base and the sine input, and R2 sits between the transistor emitter and ground.
The output at the emitter has me a bit puzzled and I would appreciate it if anyone has an explanation for the behavior.
* Simple Emitter Follower Vcc 3 0 DC 15 Vin 1 0 SIN(0 5 60) dc 0 R1 1 2 270 R2 4 0 3.3k Q1 3 2 4 generic .model generic npn .control tran 1ms 60ms plot v(1) v(4) .endc .end
The output of the transient analysis plot command is below.
I was surprised by this output. As expected, there is a slight voltage drop in the amplitude due to the base-emitter junction of the NPN. However, the output is clipped and does not swing below zero. What would I need to do to catch the negative part of the sine wave?