# Transistor bypass capacitor for specific frequency

1. Mar 10, 2014

### oddjobmj

1. The problem statement, all variables and given/known data

To circumvent the negative feedback needed for thermal stability and to avoid the accompanying reduction of gain, a bypass capacitor CE needs to be placed in parallel with an emitter resistor RE, such as in Fig. 4.14a, cf. Fig. 18a. Determine what capacitor needs to be used for the amplifier in Fig. 4.14a if the amplifier is to amplify signals down to 30 Hz.

Fig 4.14a:

2. Relevant equations

fl=$\frac{1}{2πC(r_i+R_L)}$ (?)

3. The attempt at a solution

The equation above is the only seemingly relevant equation I can find in the book. The main issue I have with it is that it is used with a two-stage amplifier whereas the question is asking about a single stage. Can this work for both? If so, I'm not sure what my equivalent ri and RL are.

Am I even on the right track? We haven't covered this in class, I can't find it in the book, and my google searches aren't yielding anything.