Introduction

In Lab 2 we only considered midband frequencies, which were high enough so that coupling capacitors could be treated as short circuits for AC, and low enough that the intrinsic capacitances of the transistor could be ignored. In this lab, we will remove this constraint and examine how frequency affects circuit performance.

In general, the frequency-dependent gain A(s) of amplifier circuits can usually be expressed as

A(s)=A_MF_L(s)F_H(s)

Where $s=j\omega$ is the complex frequency, A_M is the midband gain, F_L(s) describes the low frequency response, and F_H(s) describes the high frequency response. Ironically, F_L usually represents a high pass filter, and F_H usually represents a low pass filter. The general frequency response usually has the overall characteristics shown in Fig.4.1.

  

Figure 4.1: Typical Amplifier Frequency Response

In this lab, you will investigate how this response comes about. First, we will first examine the brute force direct approach for low frequency signals, then we will discuss the Miller effect, as well as single pole approximation approaches. For all experiments use general purpose BJT's such as the 2N3904.