Chapter 7
TEMPORAL RESPONSE OF
DIODES AND BIPOLAR
TRANSISTORS
7.1 INTRODUCTION .................................
In chapters 4-6, we studied the dc properties of diodes and bipolar transistors. In practice,
these devices are used in circuits for both digital and analog applications, such as the circuit
pictured in figure 7.1. In digital circuits, the devices will constantly be switched from the “on”
(conducting) state to the “off” (non-conducting) state and back. The speed at which the circuit
can process bits of data is largely determined by the switching speed of the devices.
In analog applications, the circuit is biased at some dc value, and then a small ac signalvinis
applied at the input. The input signal is amplified by the circuit, resulting in a signalvoutat the
output. The gain of the devices in the circuit is frequency dependent and compresses at higher
frequencies. Therefore, in order to design high frequency circuits, it is important to understand
the frequency response of the devices.
In this chapter, we derive the frequency response of diodes and bipolar transistors. We address
issues for both large-signal switching applications and small-signal high frequency applications.
We will see that in many cases, there are trade-offs between achieving superior dc performance
and being able to operate at higher frequencies.
7.2 MODULATION AND SWITCHING OF AP-NDIODE: AC RESPONSE
In chapter 5, we discussed the dc characteristics of thep-ndiode. However, many applications
of diodes will involve transient or ac properties of the diode. The transient properties of the diode